Mechanical, Corrosion, and Wear Properties of TiZrTaNbSn Biomedical High-Entropy Alloys

Round 1

Reviewer 1 Report

The authors study two slightly modified compositions of HEA for biomedical use, elaborating them by conventional casting, before characterizing their microstructure, mechanical, tribological and physicochemical properties.

Although the difference in the chemical compositions of the two alloys concerns a pair of elements that are modified by compensation (Sn and Zr), the authors focus only on the influence of Sn.

However, it appears that these two elements are not fixed in the same constituent phases of the raw casting structure, phases that can be in the primary grains and/or in the eutectic precipitates, or even at the primary grain boundaries (not cited by the authors).

In addition to this first major observation, here are the other remarks that can be made about the manuscript.

On the organization, it does not respect the classical framework prescribed by the author. Indeed, apart from sections 1, 2 and 5, the other sections 3 and 4 are difficult to classify. Normally, it is expected that there will be a Results section, which can be followed by a Discussion section. Authors are encouraged to reorganize the section headings, putting all the results in one section, before opening the discussion in another section.

The following additional comments can be made, considering the markers in the text.

 

Lines 18 to19. « Furthermore… Sn35 BHEA ».

Please, also mention the friction coefficient of Sn35 within the abstract, as this corresponds to a relevant information. People should know how low this other friction coefficient is!

 

Line 20. … “the value of wear resistance is 0.78 (km/mm³).”

Usually, people talk about wear loss or wear rate. Please adapt.

Lines 21 to 24. “Moreover, …, respectively”.

It should be more relevant to mention which material has got a better corrosion resistance, instead of just mentioning specific parameters obtained from the corrosion tests, which do not help to catch the results.

 

Line 32. …”material. From”…

Please, withdraw the full stop and replace it by a comma!

Lines 32 to 33. …”Ti-6Al-4V [2,3]… alloys [4-7].”

Please, add within the text for which purpose such alloys were developed. In fact, adding other element to pure Titanium can help to achieve improved mechanical properties.

 

Line 34. …”human body. In 1970s”…

Please, withdraw the full stop!

Line 38. …”still contains Al element”…

Please, withdraw « element ».

Lines 39 to 40. … “above reasons, a news type of Ti alloy”…

Not a single alloy. Please change for "new types of alloys free of both V and Al, but with addition of Nb, Zr, Ta, Sn, etc..) have been developed”...

 

Line 48. [11-15]

Reference [10] and reference [11] are the same!

 

Line 50. …”the possibility OF application”…

Not capital letters for “Of”.

 

Line 60. … “[13, 28-34]”

This makes 7 references in a row, which is too many! See how to withdraw the less relevant!

For example, references dealing with HEA containing Al can be withdrawn, given the fact that Al is known to promote "organ damage and harmful. symptoms". Both references [32] and [33] can be withdrawn.

 

Line 61. [35-37]

Withdraw reference [37] because it is redundant with reference [35].

 

Line 62. [38-45]

8 references for this group is too many. Please make a selection to keep only half of them, which should represent the  most relevant ones, including those that are quoted elsewhere in the manuscript.

 

Lines 73 to 74. … “composition of Ti15Zr35Ta10Nb10Sn30 and Ti15Zr30Ta10Nb10Sn3”5…

The authors should explain how they manage to choose the make a balance between Zr and Sn to achieve both HEA compositions. What are the motivations to change Sn content in the expense of Zr content (Zr35-Sn30 for Sn30, and Zr30-Sn35 for Sn35)?

In what extend can the authors also talk about Zr variations to achieve both compositions instead of just focusing on Sn? What is the influence of Zr on the major properties that have been studied by the authors?

 

Line 74. “The master alloy ingot was”…

Please provide the sizes of the ingot and show where the various samples have been cut to carried out the different tests.

 

Line 83. “Vikers »

Change for « Vickers ».

Line 93. …“electrode, 1mm thick sample is embedded”…

Please provide the location/orientation of the corrosion test samples within the ingot.

Line 105. “The wear behaviors of the HEAs”…

Again, provide the sizes, the location/orientation of wear samples within the ingots. In addition, the final roughness and the related preparation of the samples prior to wear tests must be given.

 

Line 124. …”the thermodynamic parameter VEC,”…

Please give the full signification before using the abbreviation.

Lines 130 to 135. “Fig.2 shows the microstructure… of the atomic ratio”…

The authors should make a comment regarding the grain size. In fact, based on Fig2b and fig2c which consider the same scale, it can be assumed that together with the modification of the structure type which is eutectic-like for Sn35 and hypo-eutectic for Sn30, there are two other features than can be mentioned. The firt one is the grain refining in Sn35 compared to Sn30, and the second one is the solidification mode which looks more equiaxed for Sn35, while it seems to be more columnar dendritic for Sn30.

 

Lines 135 to 136.  …”the content and the morphology… changed significantly”.

Do the authors try with a quantitative analysis of the eutectic volume fraction?

Lines 136 to 137. In order to analyze… was carried out”.

The authors should specify if the so-called areas 1 to 3 were chosen while assuming them to be similar in both alloys!

 

Line 137.  Table 2

Please, add close to "area", columns where mentions related to the contrast of each phase (gray, light, etc.) are made. If possible, the shape or the morphology of phases can also be added to better distinguish them, according to Figure 2.

 

Figure 2.

Please, change the color of the labels (try with yellow, blue or green, that should be more easily distinguished than red)

 

Line 155. “(a5) Sn30 BHEA, (b)- (b5) Sn35 BHEA.”

The region of interest that has been chosen seems to be not relevant enough for the EDS mapping carried out on Sn35. In fact, according to Fig2d, a third feature that has not been considered buy the authors should be mentioned with a related EDS response. This feature is the grain boundary which seems to be characterized by a continuous network of grey precipitates, probably Ti-rich ones. Those precipitates are clearly visible within Fig2d, around the so-called area1. The authors should either show a region of interest that contains those precipitates for the EDS mapping or check for their composition to better discuss about the moment when they form, regarding either the solidification sequence or the thermodynamic considerations.

 

Line 159. …“in Figs. 4 and 5”…

Please add the standard deviation on histograms of both Fig4b and Fig5, while assuming several tests that help to achieve statistics on the results.

 

Lines 167 to 169.

Ok. The Standard deviation (STD) can be determined from the 5 hardness measurements and then after, be mentioned on Fig4b.

 

Lines 169 to 170. “Fig. 4c)  - f) shows… after compression testing.”

Both Fig5d and fig5f should be provided with higher magnification than can help to better observe the dimple zones. The proposed magnification is not high enough.

 

Lines 175 to 176. “In general, 175 the samples basically show brittle quasi cleavage fracture.”

What does it mean? Please give references in the literature that show such general trend.

 

Lines 176 to 180. “It can be detected … brittle cleavage fracture.”

Please provide fractographs with higher magnification that can help showing the dimples.

 

Figure 4 a).

There is a plateau that can be related to the so-called double-yielding behavior, which may occur on Sn30 during compression test. Can the authors discuss about that phenomenon that is ascribed to strain hardening behavior which in turn lowers the plasticity? See for example work from [Yunjong Jung et al., JAC 886 (2021)]. In the same work, it has been established that increased amount of Zr can promote stress-induced phase transformation.

 

Figure 5.

Again, STD for compressive strength is missing on the histograms. Else, a third axis should be added on the right side of the chart, that will be linked to maximum strain (%)

 

Figure 6 c) – d)

Missing scale and sizes (depth) for the wear profiles.

Figure 7.

In addition to the deeper wear track profile, it seems that both flake-like wear debris and peeling phenomenon are more often found on Sn35 wear track, the HEA that contains less Zr. Such phenomena can be ascribed to higher level of delamination that occurs within Sn35 while the same phenomena is less evident within Sn30. This seems to be in good agreement with the work of [Zening Wang et al., Mat Let 312 (2022)]. Considering a comment already made before that consider the work hardening phenomenon which may occurs on Sn30 due to its higher Zr content), can the authors discuss about that?

 

Figure 9.

Many comments can be drawn out from Fig9.

Firstly, the authors may suppress the gradient background color for none (white), to help better distinguishing the polarization curves for both alloys on the whole chart.

Secondly, the authors should consider conventional approaches for discussion, which means that the corrosion potential must be considered first (Ecorr), prior to the passivation range that ends up with the pitting potential.

 

With the above considerations, it seems that the HEA which exhibits the higher corrosion resistance is Sn35 (with the higher Ecorr of -0.67 V), and not Sn30 (Ecorr = -0.96 V). In fact, large dendritic Zr-rich zones within hypo-eutectic Sn30, which also represent the main phase, are prompt to undergo corrosion whereas the situation is less extended within the eutectic-like Sn35 HEA.

 

Author Response

Dear Dr. Editor and Reviewers,

Thank you very much for your comments and explanation. We have carefully read your comments on the manuscript, titled “Mechanical, corrosion, and wear properties of TiZrTaNbSn biomedical high entropy alloys” (Manuscript ID: coatings-2014293). We have revised the manuscript and responded point by point to the comments as listed below.

Response to Reviewer 1 Comments

Point 1: Extensive editing of English language and style required

Response 1: Thanks for your comments. The manuscript has been checked carefully, and the revised manuscript was edited for proper English language by means of “MDPI English Editing Services” before it is submitted to the journal this time. The “Certificate of MDPI English Editing Services” is shown in Fig. 1. The revised parts are highlighted in revised manuscript, we hope that can meet the reviewer’s and magazine’s standard.

Fig.1 Certificate of MDPI English Editing Services

Point 2: The authors study two slightly modified compositions of HEA for biomedical use, elaborating them by conventional casting, before characterizing their microstructure, mechanical, tribological and physicochemical properties. Although the difference in the chemical compositions of the two alloys concerns a pair of elements that are modified by compensation (Sn and Zr), the authors focus only on the influence of Sn. However, it appears that these two elements are not fixed in the same constituent phases of the raw casting structure, phases that can be in the primary grains and/or in the eutectic precipitates, or even at the primary grain boundaries (not cited by the authors).

Response 2: Thank you so much for your comments. And please forgive us if we misunderstood your question. As the BCC and FCC phase were the solid solution in high entropy alloy. Clearly, the Zr and Sn atoms distribute in whole sample. However, they are mainly distribute in the matrix.

In order to analyze the element content of each phase in Fig. 2, EDS analysis was carried out on eutectic microstructure (area 1), gray phases (area 2), and bright white blocky phases (area 3). The results are shown in Table 2, We discovered a high content of Zr and Sn in the dark gray phase of both high-entropy alloys.

To further analyze the element distribution, the map scanning results of its element distribution are shown in Fig. 3. Fig. 3 shows the map scanning results of the element distribution. The Zr, Nb, and Sn elements are mainly distributed in the dark gray phase, while Ti tends to be uniformly distributed in the dark gray phase, and is eutectic in structure; however, Ti is segregated in the bulk phase close to the eutectic microstructure (Figs. 3 (a1)–(a5)). For Sn35 BHEA, the distribution of elements tends to be consistent with that of Sn30 BHEA. 

 

Point 3: On the organization, it does not respect the classical framework prescribed by the author. Indeed, apart from sections 1, 2 and 5, the other sections 3 and 4 are difficult to classify. Normally, it is expected that there will be a Results section, which can be followed by a Discussion section. Authors are encouraged to reorganize the section headings, putting all the results in one section, before opening the discussion in another section.

 Response 3: Thank you and we appreciate your comments very much. The whole work was reorganized and the section of discussion was added.

 

Point 4: Lines 18 to19. « Furthermore… Sn35 BHEA ».

Please, also mention the friction coefficient of Sn35 within the abstract, as this corresponds to a relevant information. People should know how low this other friction coefficient is!

 Response 4: We are very sorry for this mistake and thank you very much for reminding us. The changes are shown below and highlighted in the revised manuscript.

Moreover, the Sn30 and Sn 35 BHEA friction coefficients are 0.152 and 0.264, respectively. Sn30 BHEA has the smallest and shallowest furrow-groove width, and its wear rate is 0.86 (km/mm³); at the same time, we observed the delamination phenomenon. Sn35 BHEA has a wear rate value of 0.78 (km/mm³),

Point 5: Line 20. … “the value of wear resistance is 0.78 (km/mm³).”

Usually, people talk about wear loss or wear rate. Please adapt.

Response 5: Thank you so much for your suggestion. The revised content is highlighted in revised manuscript.

Point 6: Lines 21 to 24. “Moreover, …, respectively”.

It should be more relevant to mention which material has got a better corrosion resistance, instead of just mentioning specific parameters obtained from the corrosion tests, which do not help to catch the results.

 Response 6: We appreciate your suggestion very much. The revised content is listed and highlighted in revised manuscript.

Therefore, Sn30 BHEA preferentially produces passive film and has a small corrosion tendency, and its corrosion resistance is considerably better than that of the Sn35 BHEA alloy.

 

Point 7: Line 32. …” material. From” …

Please, withdraw the full stop and replace it by a comma!

Response 7: We are very sorry for this mistake and thank you very much for reminding us. The changes are shown below and highlighted in the revised manuscript.

In the 1960s, Ti alloys (first Ti-6A1-4V [2,3] and later Ti-5Al-2.5Fe and Ti-6A1-7Nb) began to be widely used in clinical practice as a human implant material [4-7]. In 1970s and 1980s, researchers began to prepare Ti alloys with V-free implants because of its toxic and potentially harmful effects on the human body; furthermore, in the mid-1980s, new types of α+β Ti alloys, namely Ti-5Al-2.5Fe and Ti-6Al-7Nb, were developed in Europe [3].

Point 8: Lines 32 to 33. …” Ti-6Al-4V [2,3]… alloys [4-7].”

Please, add within the text for which purpose such alloys were developed. In fact, adding other element to pure Titanium can help to achieve improved mechanical properties.

Response 8: Please forgive us if we misunderstood your question. Actually, we totally agree with you that adding other element to pure Titanium can help to achieve improved mechanical properties. However, in the field of biomedicine, mechanical properties are not the only issues that need to be considered. Elastic modulous and stress shielding should also be considerate. α+β Ti alloys (Al, Fe, Nb) and β Ti alloys (Zr, Ta, Sn) are currently the most suitable systems for human implantation.

In the 1960s, Ti alloys (first Ti-6A1-4V [2,3] and later Ti-5Al-2.5Fe and Ti-6A1-7Nb) began to be widely used in clinical practice as a human implant material [4-7]. In 1970s and 1980s, researchers began to prepare Ti alloys with V-free implants because of its toxic and potentially harmful effects on the human body; furthermore, in the mid-1980s, new types of α+β Ti alloys, namely Ti-5Al-2.5Fe and Ti-6Al-7Nb, were developed in Europe [3].

Point 9: Line 38. …” still contains Al element” …Please, withdraw « element ».

Response 9: Thank you very much for your suggestions. It has been revised and marked red in manuscript.

Point 10: Lines 39 to 40. … “above reasons, a news type of Ti alloy”…

Not a single alloy. Please change for "new types of alloys free of both V and Al, but with addition of Nb, Zr, Ta, Sn, etc..) have been developed”...

 Response 10: we totally agree with you and thank you very much. Revised part can be seen as follows:

Based on the above reasons, new types of alloys, which are free of both V and Al but with addition of Nb, Zr, Ta, Sn, (Ti-13Nb-13Zr, Ti-35Nb-5Ta7Zr, Ti-24Nb-4Zr-7.9Sn) has been developed in recent years [4-6], their elastic modulus are closer to that of natural human bone, and their strength is also higher than that of pure Ti.

Point 11: Line 48. [11-15] Reference [10] and reference [11] are the same!

 Response 11: We are very sorry for this mistake and thank you very much for reminding us. Relevant contents and references have been deleted, and replaced by the following contents.

Traditional alloys system usually consist of one or two main elements, and the content of the other elements is much lower. In 2004, Yeh et al. [8-10] first proposed high-entropy alloy, a class of materials containing five or more elements in relatively high concentrations (5–35 at.%) [11, 12]. Because of their unique high-entropy, sluggish diffusion, lattice distortion and cocktail effects [13-15], HEAs show excellent comprehensive properties compared with traditional alloys, such as high hardness [16], high strength [17], corrosion resistance and wear resistance [18, 19], etc. At the same time, high-entropy alloys break the traditional alloy design concept of using only one principal element. Despite this, researchers are actively exploring the possibility of applying high-entropy alloys in new products [20], such as biomedical, magnetic, and hydrogen storage materials, etc. [21-25].

Point 12: Line 50. …”the possibility OF application”…Not capital letters for “Of”.

 Response 12:We are very sorry for this mistake and thank you very much for reminding us. It has been revised and marked red in manuscript.

Point 13: Line 60. … “[13, 28-34]” This makes 7 references in a row, which is too many! See how to withdraw the less relevant!

For example, references dealing with HEA containing Al can be withdrawn, given the fact that Al is known to promote "organ damage and harmful. symptoms". Both references [32] and [33] can be withdrawn.

 Response 13: Thank you so much for your comments. It has been revised and highlighted in the revised manuscript.

Point 14: Line 61. [35-37] Withdraw reference [37] because it is redundant with reference [35].

 Response 14: Thank you very much for your suggestions. It has been revised in manuscript.

Point 15: Line 62. [38-45] 8 references for this group is too many. Please select to keep only half of them, which should represent the most relevant ones, including those that are quoted elsewhere in the manuscript.

 Response 15: We are very sorry for this mistake and thank you for your comments. Relevant contents and references have been deleted, and replaced by the following contents.

In the past decade, a series of Ti-Zr-Hf-Nb-Ta [21-25], Ti-Mo-Ta-Nb-Zr [26-29], and Ti-Nb-Hf-Ta-Zr-Mo [30, 31] HEAs with considerable mechanical and chemical properties suitable for biomedical applications have been designed. Researchers are also improving the performance of HEAs by alloying with O, Si, Al, and Cr [32-35]. However, we noticed that adding Sn to Fe-Co-Cu-Ni(-Mn) HEAs can improve elongation strain and tensile strength by 16.9% and 476.9MPa, respectively [36, 37]. In addition, Sn is non-cytotoxic and widely present in β-Ti alloys [38-41]. Previously, we studied the effects of atomic ratios on as-cast microstructural evolution, and the mechanical and electrochemical properties of TiZrTaNbSn high-entropy alloy [42]. While its elastic modulus is relatively high, with a value of 110GPa, it does not match the elastic modulus of human bones (30-50 GPa). Moreover, Zr-based TiZrTaNbSn high-entropy alloys display an elastic modulus value of about 40 GPa [43]. Therefore, in our study, we designed a new Zr-based high-entropy Ti-Zr-Ta-Nb-Sn alloy based on metastable β titanium alloy, which is based on the four elements of Ti-Zr-Ta-Nb. We prepared two kinds of biomedical-grade high-entropy alloys, namely Sn30 BHEA and Sn35 BHEA, by vacuum arc melting, and we systematically studied the feasibility of preparing biomedical-grade high-entropy alloy with five elements (Ti, Zr, Ta, Nb, and Sn), paying specific attention to morphology, compressive strength, electrochemical corrosion, and friction and wear properties. Our work will provide data for the future development of biomedical-grade high-entropy alloy, in addition to guidance for further scientific research on Ti alloys.

Point 16: Lines 73 to 74. … “composition of Ti15Zr35Ta10Nb10Sn30 and Ti15Zr30Ta10Nb10Sn3”5…The authors should explain how they manage to choose the make a balance between Zr and Sn to achieve both HEA compositions. What are the motivations to change Sn content in the expense of Zr content (Zr35-Sn30 for Sn30, and Zr30-Sn35 for Sn35)?

In what extend can the authors also talk about Zr variations to achieve both compositions instead of just focusing on Sn? What is the influence of Zr on the major properties that have been studied by the authors?

 Response 16: Thank you so much for your comments. Following contents have been added to explain your questions.

However, we noticed that adding Sn to Fe-Co-Cu-Ni(-Mn) HEAs can improve elongation strain and tensile strength by 16.9% and 476.9MPa, respectively [36, 37]. In addition, Sn is non-cytotoxic and widely present in β-Ti alloys [38-41]. Previously, we studied the effects of atomic ratios on as-cast microstructural evolution, and the mechanical and electrochemical properties of TiZrTaNbSn high-entropy alloy [42]. While its elastic modulus is relatively high, with a value of 110GPa, it does not match the elastic modulus of human bones (30-50 GPa). Moreover, Zr-based TiZrTaNbSn high-entropy alloys display an elastic modulus value of about 40 GPa [43]. Therefore, in our study, we designed a new Zr-based high-entropy Ti-Zr-Ta-Nb-Sn alloy based on metastable β titanium alloy, which is based on the four elements of Ti-Zr-Ta-Nb.

Point 17: Line 74. “The master alloy ingot was”…

Please provide the sizes of the ingot and show where the various samples have been cut to carried out the different tests.

 Response 17: we are really sorry that we did not express clearly in the paper. The following contents have been added and mark red in manuscript.

Wire cut electrical discharge machining (WEDM, DHL-500) was used to cut samples from the core region of the master alloy ingot (Buttonhole, maximum diameterφ32mm, maximum height 16mm).

Point 18: Line 83. “Vikers » Change for « Vickers ».

Response 18:

We are very sorry for this mistake and thank you very much for reminding us. The changes are shown below and highlighted in the revised manuscript.

Point 19: Line 93. …“electrode, 1mm thick sample is embedded”…

Please provide the location/orientation of the corrosion test samples within the ingot.

Response 19: we are really sorry that we did not express clearly in the paper. The following contents have been added and mark red in manuscript.

Wire cut electrical discharge machining (WEDM, DHL-500) was used to cut samples from the core region of the master alloy ingot (Buttonhole, maximum diameterφ32mm, maximum height 16mm).

Point 20: Line 105. “The wear behaviors of the HEAs”…

Again, provide the sizes, the location/orientation of wear samples within the ingots. In addition, the final roughness and the related preparation of the samples prior to wear tests must be given.

 Response 20: Thank you so much for your comments. The following contents have been added and mark red in manuscript.

Wire cut electrical discharge machining (WEDM, DHL-500) was used to cut samples from the core region of the master alloy ingot (Buttonhole, maximum diameterφ32mm, maximum height 16mm).

When performing the friction and wear test, we ensured each specimen of the two materials was wet-ground and polished using a polishing machine (UNIPOL-1502, Shenyang Kejing Auto-Instrument Co., LTD, China) with a series of silicon carbide papers of P320, P400, P800, P1200, P1500, P2000, and P3000 grits (Matador Starcke, Germany) under water cooling. Finally, after ultrasonically cleaning for 10 min in deionized water, we fine-polished all specimens with a diamond velour polishing pad under a flowing cerium oxide solution (particle size: 1.5 μm) (Shenyang Kejing Auto-Instrument Co., LTD, China) before finishing with a mirror-like surface. Then, we tested the wear behaviors of the HEAs by a VHX-2000 tribology tester using a Si₃N₄ ball (4 mm in diameter) as the couple-pair. In our study, the test parameters are as follows: load 10 N, time of 30 min, sliding velocity 600 r/min, and friction reciprocating motion amplitude 2 mm. We recorded the friction coefficient during the sliding process. After the wear test, we determined the wear volume (W_V) of the alloy samples by a MT-500 Probe-type material surface profile measuring instrument. We examined the morphologies and compositions of the HEAs’ wear scars by SEM and EDS, respectively.

Point 21: Line 124. …” the thermodynamic parameter VEC,” …

Please give the full signification before using the abbreviation.

Response 21: Thank you so much for your suggestion. They are defined and marked red in the manuscript.

Table 1 shows the calculated values of the entropy-enthalpy quotient parameter (Ω), the valence electron concentration (VEC) criterion, and the mean square deviation of the atomic radius of elements (δ).

Point 22: Lines 130 to 135. “Fig.2 shows the microstructure… of the atomic ratio” The authors should make a comment regarding the grain size. In fact, based on Fig2b and fig2c which consider the same scale, it can be assumed that together with the modification of the structure type which is eutectic-like for Sn35 and hypo-eutectic for Sn30, there are two other features than can be mentioned. The first one is the grain refining in Sn35 compared to Sn30, and the second one is the solidification mode which looks more equiaxed for Sn35, while it seems to be more columnar dendritic for Sn30.

Response 22: Thank you so much for your advice. Please forgive us if our answer focus on the wrong points. The relevant contents have been revised as follows:

Sn30 BHEA is a typical hypoeutectic structure composed of long-strip gray phases, a bright white small-block phase, and an interphase rod eutectic microstructure (Figs. 2 a and b). Moreover, the eutectic microstructure’s volume fraction is 33.8%. Sn35 BHEA is a typical eutectic microstructure with lamellar distribution; however, there are some bright white blocky phases distributed on the dark gray phase. Additionally, the solidification mode looks more equiaxed for Sn35 BHEAs, while it seems more columnar-dendritic for Sn30 BHEAs.

Point 23: Lines 135 to 136.  …”the content and the morphology… changed significantly”. Do the authors try with a quantitative analysis of the eutectic volume fraction?

Response 23: We apologize for the lack of quantitative analysis. Following contents has been added in manuscript.

Moreover, the eutectic microstructure’s volume fraction is 33.8%.

 

Fig. 2. Volume fraction of Zr-rich phase in Sn30 BHEA and Sn35 BHEA

Point 24: Lines 136 to 137. In order to analyze… was carried out”.

The authors should specify if the so-called areas 1 to 3 were chosen while assuming them to be similar in both alloys!

Response 24: Thank you so much for your suggestions. It has been revised and marked red in manuscript.

EDS analysis was carried out on eutectic microstructure (area 1), gray phases (area 2), and bright white blocky phases (area 3)

Point 25: Line 137.  Table 2 Please, add close to "area", columns where mentions related to the contrast of each phase (gray, light, etc.) are made. If possible, the shape or the morphology of phases can also be added to better distinguish them, according to Figure 2.

 Response 25: Thank you for your suggestions. The revised table are shown below and highlighted in the revised manuscript.

Composition	Place	Color	Ti/at%	Zr/at%	Ta/at%	Nb/at	Sn/at%
Sn30 BHEA	area 1 area 2 area 3	- gray Bright white	19.51 15.96 28.69	26.56 39.71 19.14	8.21 3.75 12.07	16.80 8.52 15.38	28.93 32.06 24.72
Sn35 BHEA	area 1 area 2 area 3	- gray Bright white	19.58 15.69 24.55	27.83 34.01 18.39	7.82 0.98 14.65	20.02 8.83 14.55	24.73 40.50 27.86

 

Point 26: Figure 2. Please, change the color of the labels (try with yellow, blue or green, that should be more easily distinguished than red)

 Response 26: Thank you so much for your suggestions. It has been revised as below:

 

Fig. 3. The microstructure of non-equiatomic TiZrTaNbSn BHEAs. (a)(b) Sn30 BHEA, (c)(d) Sn35BHEA.

Point 27: Line 155. “(a5) Sn30 BHEA, (b)- (b5) Sn35 BHEA.”

The region of interest that has been chosen seems to be not relevant enough for the EDS mapping carried out on Sn35. In fact, according to Fig2d, a third feature that has not been considered buy the authors should be mentioned with a related EDS response. This feature is the grain boundary which seems to be characterized by a continuous network of grey precipitates, probably Ti-rich ones. Those precipitates are clearly visible within Fig2d, around the so-called area1. The authors should either show a region of interest that contains those precipitates for the EDS mapping or check for their composition to better discuss about the moment when they form, regarding either the solidification sequence or the thermodynamic considerations.

 Response 27: Thank you very much for your suggestion. It has been revised as can be seen as follow:

 

Fig. 4. The map scanning of Sn30 BHEA and Sn35 BHEA (a)-(a5) Sn30 BHEA, (b)- (b5) Sn35 BHEA

Point 28: Line 159. …“in Figs. 4 and 5”…

Please add the standard deviation on histograms of both Fig4b and Fig5, while assuming several tests that help to achieve statistics on the results.

 Response 28: Thank you very much for your suggestion. It has been revised as can be seen as follow:

 

Fig. 5. Compressive stress–strain curves and corresponding fracture morphologies of Sn30 BHEA and Sn35 BHEA: (a) stress–strain curves, (b) HV of Sn30 BHEA and Sn35 BHEA, (c)(d) fracture morphology of Sn30 BHEA, (e)(f) fracture morphology of Sn35 BHEA.

Point 29: Lines 167 to 169. Ok. The Standard deviation (STD) can be determined from the 5 hardness measurements and then after, be mentioned on Fig4b.

Response 29: Thank you very much for your proposal, we have modified b) of Figure 4 and supplemented its standard deviation (STD).

 

Fig. 6. Compression properties of Sn30 BHEA and Sn35 BHEA

Point 30: Lines 169 to 170. “Fig. 4 c) -f) shows… after compression testing.” Both Fig5d and fig5f should be provided with higher magnification than can help to better observe the dimple zones. The proposed magnification is not high enough.

Response 30: Thank you very much for your comment, it is our mistake, we have replaced d) and f) in Figure 4.

 

Fig. 5. Compressive stress–strain curves and corresponding fracture morphologies of Sn30 BHEA and Sn35 BHEA: (a) stress–strain curves, (b) HV of Sn30 BHEA and Sn35 BHEA, (c)(d) fracture morphology of Sn30 BHEA, (e)(f) fracture morphology of Sn35 BHEA.

Point 31: Lines 175 to 176. “In general, 175 the samples basically show brittle quasi cleavage fracture.” What does it mean? Please give references in the literature that show such general trend.

 Response 31: The reference has been added and highlighted in the revised manuscript.

[45] S. Gurel, M.B. Yagci, D. Canadinc, G. Gerstein, B. Bal, H. J. Maier, Fracture behavior of novel biomedical Ti-based high entropy alloys under impact loading, Materials Science and Engineering: A, 1 (2021), PP 803

 

Point 32: Lines 176 to 180. “It can be detected … brittle cleavage fracture.”

Please provide fractography with higher magnification that can help showing the dimples.

 Response 32: Thank you so much for your suggestion. we have replaced d) and f) in Figure 4.

 

Fig. 5. Compressive stress–strain curves and corresponding fracture morphologies of Sn30 BHEA and Sn35 BHEA: (a) stress–strain curves, (b) HV of Sn30 BHEA and Sn35 BHEA, (c)(d) fracture morphology of Sn30 BHEA, (e)(f) fracture morphology of Sn35 BHEA.

Point 33: Figure 4 a). There is a plateau that can be related to the so-called double-yielding behavior, which may occur on Sn30 during compression test. Can the authors discuss about that phenomenon that is ascribed to strain hardening behavior which in turn lowers the plasticity? See for example work from [Yunjong Jung et al., JAC 886 (2021)]. In the same work, it has been established that increased amount of Zr can promote stress-induced phase transformation.

 Response 33: Thank you so much, and we appreciate your comments very much, the contents have been added and the manuscript has been revised, as can be seen as follows:

The mechanical properties of TiZrTaNbSn BHEAs are shown in Figs. 4 and 5. Fig. 4 (a) shows the compression stress–strain curves of TiZrTaNbSn BHEAs at room temperature. Compared with Sn35 HEAs, the Sn30 HEAs exhibit double-yielding behavior, which is often observed in shape memory alloys as a stress-induced phase transformation and has relatively lower plasticity [44]. Fig. 4 (b) displays the Vickers hardness results for both alloys. Hardness is one of their mechanical properties, and it has a considerable impact on the application of alloys.

[44] Y. Jung, K. Lee, S. J. Hong, J. K. Lee, J. Han, K. B. Kim, P. K. Liaw, C. O. L. Lee, G. Song, Investigation of phase-transformation path in TiZrHf(VNbTa)x refractory high-entropy alloys and its effect on mechanical property, Journal of alloys and compounds, 886  (2021), PP 161187

Point 34: Figure 5. Again, STD for compressive strength is missing on the histograms. Else, a third axis should be added on the right side of the chart, that will be linked to maximum strain (%)

 Response 34: Thank you so much for your suggestions. we have modified b) of Figure 4 and supplemented its standard deviation (STD).

 

Fig. 6. Compression properties of Sn30 BHEA and Sn35 BHEA

 

Point 35: Figure 6 c) – d)

Missing scale and sizes (depth) for the wear profiles.

Response 35: Thank you for your comments. The scale and sizes for the wear profiles were added in Figs. 6 (c) and (d).

 

Fig. 7. Friction and wear test results of non-equiatomic TiZrTaNbSn BHEAs (a)samples, (b) Friction coefficient curves, Profiles of the worn surfaces for sintered composites and corresponding 2D cross-section profiles of wear tracks: (c) Sn30 BHEA, (d) Sn35 BHEA.

 

Point 36: Figure 7. In addition to the deeper wear track profile, it seems that both flake-like wear debris and peeling phenomenon are more often found on Sn35 wear track, the HEA that contains less Zr. Such phenomena can be ascribed to higher level of delamination that occurs within Sn35 while the same phenomena are less evident within Sn30. This seems to be in good agreement with the work of [Zening Wang et al., Mat Let 312 (2022)]. Considering a comment already made before that consider the work hardening phenomenon which may occurs on Sn30 due to its higher Zr content), can the authors discuss about that?

 Response 36: Your suggestion is very useful to our work. We sincerely thank you. Following contents have been added.

Sn30 BHEA’s worn surfaces were smoother with less debris and smaller grooves compared with Sn30 BHEA, as shown in Fig. 8 (a–d). Moreover, Fig. 8 (a) shows that the surface morphology of the Sn30 BHEA alloy’s friction structure tends to form a regular pit structure, and the wear surface is almost free of wear debris. Fig. 8 (c) (d) show that there are wear debris generated on Sn35 BHEA’s surface morphology, resulting in poor surface quality and cracks. Furthermore, we found severe delamination in Sn35 BHEA. The subsurface generates work hardening owing to its dislocation motion, rearrangement, and grains refinement. However, once deformed, dislocation accumulation occurred to a certain extent, resulting in crack formation and, finally, delamination. The absence of obvious work hardening for Sn30 BHEA (Fig. 7) was due to its higher material loss rate. This consecutive deformation can be easily induced through delamination [50].

[50] Z. Wang, Y. Yan, Y. Wu, Y. Su, L. Qiao, Repassivation and dry sliding wear behavior of equiatomic medium entropy TiZr (Hf, Ta, Nb) alloys, Materials Letters, 312 (2022), PP 131643

Point 37: Figure 9. Many comments can be drawn out from Fig9.

Firstly, the authors may suppress the gradient background color for none (white), to help better distinguishing the polarization curves for both alloys on the whole chart.

Secondly, the authors should consider conventional approaches for discussion, which means that the corrosion potential must be considered first (Ecorr), prior to the passivation range that ends up with the pitting potential.

 Response 37: We appreciate your suggestions very much, the relevant content has been added and marked red in manuscript.

 

Fig. 8. Corrosion properties characterization for Sn30 BHEA and Sn35 BHEA: a) Potentiodynamic polarization curves, (b) (c) corrosion morphology of Sn30 BHEA, (d) (f) corrosion morphology of Sn35 BHEA.

The Potentiodynamic polarization curve and the corrosion morphology of TiZrTaNbSn BHEAs are shown in Fig.10. The key parameters derived by the Tafel method such as the corrosion current density (I_corr) and the corrosion potential (E_corr) are listed in Table 4. Clearly found that Sn30 BHEA exhibited an I_corr value smaller than of Sn35 BHEA. Moreover, for passivation current density I_pass, the smaller the value is, the easier it is to enter the passivation state. I_pass value of Sn30 BHEA is 4.44x10^-4 A/cm^-2, which is 88% lower than that of Sn35 BHEA-a significant improvement. Another noteworthy fact is that in the anode and cathode area, the value of β_a and β_b of Sn30 BHEA is lower than that of Sn35 BHEA, demonstrating that Sn35 BHEA has stronger corrosion resistance properties. The corrosion potential (E_corr) can determine the corrosion trend of the alloy. According to the thermodynamic principle, the smaller the E_corr, the greater the corrosion tendency. The E_corr of Sn30 HEAs is -0.96, which is about 43.3% smaller than Sn35 BHEAs. However, the data that most directly reflects the corrosion resistance of the alloy is the corrosion rate, which can be obtained by the following equation.

                                (1)

Where EW is the equivalent weight, and d is the density of the metal (g /cm³). The calculation results are shown in Table 4. The corrosion rate of Sn30 BHEA is 1.37×10^-4mm/a, The corrosion rate of Sn35 BHEA is 1.20×10^-3mm/a, which is nearly 88.6% greater than that of ambient pressure. Therefore, Sn30 BHEA has stronger corrosion resistance properties.

The corrosion surface morphology was observed by scanning electron microscopy (SEM) after the potentiodynamic polarization test, as shown in Figs. 10 b) - e). The surfaces of these two high-entropy alloys show certain levels of corrosion after electrochemical corrosion for 2400s. and the corrosion degree of (Zr, Sn) rich phase is high. Meanwhile, the corrosion of Sn35 BHEA also mainly occurs in the gray phase, which is accompanied by many irregular corrosion pits and some cracks. There are also some electrochemical corrosion products on the surface, as shown in Figs. 10 (d) and (e). The volume fractions of large dendritic Zr-rich zones within Sn30 BHEA and Sn35 BHEA are 77.7% and 90.8% (Fig. (11)), respectively. Then, from the corrosion morphology and analysis of the above two high-entropy alloys, it can be concluded that the corrosion resistance of Sn30 BHEA is better than that of Sn30 BHEA. However, both alloys exhibit high levels of corrosion resistance [51], indicating that TiZrTaNbSn alloys are a suitable alternative material considering corrosion resistance.

Point 38: With the above considerations, it seems that the HEAs which exhibits the higher corrosion resistance is Sn35 (with the higher Ecorr of -0.67 V), and not Sn30 (Ecorr = -0.96 V). In fact, large dendritic Zr-rich zones within hypo-eutectic Sn30, which also represent the main phase, are prompt to undergo corrosion whereas the situation is less extended within the eutectic-like Sn35 HEAs.

Response 38: Thank you so much for your comments. And we are really sorry for the mistakes. The content of Zr-rich zones of both alloys was calculated by using image-pro plus software. The results can be seen as follows:

 

 

 

 

 

Fig. 2. Volume fraction of Zr-rich phase in Sn30 BHEA and Sn35 BHEA

                 

 

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript discusses composition, phase formation, microstructure, and properties of bulk Ti-Zr-Ta-Nb-Sn so called high entropy alloys (HEA) with two specific Sn contents of 20 and 25 %. From the properties, the mechanical, corrosion, and wear properties are discussed and the values of the two alloys are compared to each other.

 

The manuscript contains results, which are worth to be published. However, the choice to published the results in Coating does not seem to be appropriate.

 

Hence, I would recommend resubmission to another journal, such as Condensed Matter.

 

The authors should address the following point prior to resubmission:

 

1) The authors state the composition of the prepared alloys in the abstract as well as on page 2, in the 2. Experimental section to be Ti15-Zr35-Ta10-Nb10-Sn30 (Sn30) and …Zr30-…-Sn35 (Sn35).

However, it is not clear whether the composition is stated in wt.% or at.%.

Please add the information.

 

2) In the introduction, the authors present historical trends in alloy in general, in high entropy, and biological alloy development. Then, they state the focus of the manuscript in Sn30 and Sn35 alloys.

However, the authors do not mention they former publications on Sn-containing alloys.

Li et al., Crystals 11 (2021) 1527.

Ma et al., China Foundry, 2022

 

Moreover, the properties of the alloys reported in the manuscript are not compared neither to the author’s previous results on the Sn-containing alloys nor another benchmark alloy.

 

Please present your former results on the Sn-containing alloys in the introduction.

Please whenever you present the properties of the Sn30 and Sn35 alloys, compare them to the properties of other already published Sn-containing alloys or any other benchmark alloy.

 

3) Page 2, line 48

“At the same time, the appearance of high-entropy alloy breaks the traditional alloy design concept.”

This statement is unclear.

What traditional concept of alloy design do you refer to? What is the role of appearance of the alloy in the discussion?

Please explain.

 

4) Page 2, line 50

“Researches actively explored the possibility OF application of high-entropy alloy in new fields.”

Please be specific. Please state the “new fields” for the reader.

 

5) Page 2, line 56, 60

“ …a series of Ti-Zr-Hf-Nb-Ta [17-21], Ti-Mo-Ta-Nb-Zr [22-25] and Ti-Nb-Hf-Ta-ZrMo [26,27] HEAs with good mechanical and chemical properties which suitable for biomedical applications have been designed in the past decade.”

 

“At the same time, we noticed that in Fe-Co-Cu-Ni(-Mn) HEAs, adding Sn can improve its tensile strength [35-37].”

 

Please consider to state a range of the mechanical properties and tensile strength of the alloys.

 

6) Page 3, line 99

“After the polarization experiment, TAFEL and IMP are used to measure the polarization curve and AC impedance of CoCrFeNiAl0.5Cu0.8 alloy, respectively.”

The properties of a reference alloy were measured, however, they were not presented.

Please present the properties of the reference alloy and compare them to the properties of the studied Sn30 and Sn35 alloys.

 

7) Fig. 1

The assignment of the peak in the figure do not seems to be correct.

The peak at 36.8 degree is assigned to be (111) Ta for Sn30, while the same peak is assigned to (110) Zr for Sn35.

Please check and correct.

 

8) Figs. 4 and 5

On page 5, section 4.1, Fig. 5 seems to be discussed prior to Fig. 4.

Please discuss the figures in the order they are presented. Alternatively, please swap the order of the figures.

 

Please consider splitting Fig. 4 into more figures, presenting the morphologies in a separate figure.

 

 

 

Technical comments:

 

1) Abstract

“…with body-centered-cubic (BCC) and Face-centered-cubic (FCC) solid solution phases.”

“body” is written with small “b”, while “Face” is written with capital “F”

Please keep the same writing style.

 

2) Abstract

The comparison of the film properties is somewhat incomplete.

a) The friction coefficient of Sn30 is presented, however, the friction coefficient of Sn35 not.

b) The wear resistance of Sn35 is presented, however, the wear resistance of Sn30 not.

c) The impedance vale of Sn30 is stated to be the highest, however, not value is state nor the value of Sn35 is presented.

d) The corrosion current density of Sn30 is presented and only a relative comparison to Sn35 is stated.

Please state the values of both alloys. Moreover, please compare the values of standard benchmark alloys for better comparison for the reader.

 

3) Page 1, line 33, 38

“…and Ti-6A1-7Nb alloys …”

“…still contain A1 element …”

It seems that aluminum is written as A1 (A and a number 1) not as Al (A and a letter l).

Please check.

 

4) Page 2, line 50

“Researches actively explored the possibility OF application of high-entropy alloy in new fields.”

Why is “OF” written in capital letters?

Please check.

 

5) Page 2, line 83

“Cylinder (phi 4 mm x 6 mm) shape samples …”

I suppose that 4 mm is the diameter of the cylinder. Please use a diameter sign instead of phi.

 

6) Page 2, line 84

“The microhardness test was carried out … using an applied load of 1000 gf and ….”

Please explain the load unit “gf”.

 

7) Page 2, line 95

“… and scanning range is -1.5 – 1.5 V.”

Please consider writing “scanning voltage range …”

 

8) Fig. 2

The red markers indicating different locations at the samples are not visible.

Please consider using a different color, for example white.

 

9) Fig. 3

The labels indicating the different elements in the figure are not visible.

Please consider using a white background for the label for better visibility.

 

10) Short names of the two investigates alloys Sn30 and Sn35 have been introduces. Nevertheless, the manuscript repeats stating the composition of the alloys throughout the manuscript.

For example

page 3, line 114 “non-equiatomic ratio TiZrTaNbSn BHEAs …”

page 4, line 130 “non-equiatomic ratio TiZrTaNbSn BHEAs …”

page 5, lines 159 and 160 “TiZrTaNbSn BHEAs”

Please use the shorter names of the investigated alloys or name the samples simply alloys when referring to both.

 

11) Fig. 6

It seems the Fig. 6(a) be omitted as it does not provide any addition value for the reader.

The color background in Fig. 6(b) also appears redundant.

 

12) Page 7, line 214

“Therefore, comprehensive analysis shown that the friction and wear morphology of Sn30 BHEA is the best.”

When comparing properties of only two materials, using “comparative degree”, i.e. it is better, that using “superlative degree”, i.e. is the best, appear more appropriate.

Please consider revision.

 

Author Response

Dear Dr. Editor and Reviewers,

Thank you very much for your comments and explanation. We have carefully read your comments on the manuscript, titled “Mechanical, corrosion, and wear properties of TiZrTaNbSn biomedical high entropy alloys” (Manuscript ID: coatings-2014293). We have revised the manuscript and responded point by point to the comments as listed below.

Response to Reviewer 2 Comments

Point 1: The authors state the composition of the prepared alloys in the abstract as well as on page 2, in the 2. Experimental section to be Ti15-Zr35-Ta10-Nb10-Sn30 (Sn30) and …Zr30-…-Sn35 (Sn35). However, it is not clear whether the composition is stated in wt.% or at.%.

Please add the information.

 Response 1: Thank you so much for your suggestion. They are defined and marked red in the manuscript.

The Ti, Zr, Ta, Nb, and Sn raw materials with a purity of more than 99.9wt.% were used to prepare BHEAs with the atom ratio of Sn30 BHEA and Sn35 BHEA.  

 

Point 2: In the introduction, the authors present historical trends in alloy in general, in high entropy, and biological alloy development. Then, they state the focus of the manuscript in Sn30 and Sn35 alloys. However, the authors do not mention they former publications on Sn-containing alloys. Li et al., Crystals 11 (2021) 1527. Ma et al., China Foundry, 2022.   Moreover, the properties of the alloys reported in the manuscript are not compared neither to the author’s previous results on the Sn-containing alloys nor another benchmark alloy. Please present your former results on the Sn-containing alloys in the introduction. Please whenever you present the properties of the Sn30 and Sn35 alloys, compare them to the properties of other already published Sn-containing alloys or any other benchmark alloy.

 Response 2: Thank you so much for your suggestion. The relevant contents have been added and marked red in manuscript.

In the past decade, a series of Ti-Zr-Hf-Nb-Ta [21-25], Ti-Mo-Ta-Nb-Zr [26-29], and Ti-Nb-Hf-Ta-Zr-Mo [30, 31] HEAs with considerable mechanical and chemical properties suitable for biomedical applications have been designed. Researchers are also improving the performance of HEAs by alloying with O, Si, Al, and Cr [32-35]. However, we noticed that adding Sn to Fe-Co-Cu-Ni(-Mn) HEAs can improve elongation strain and tensile strength by 16.9% and 476.9MPa, respectively [36, 37]. In addition, Sn is non-cytotoxic and widely present in β-Ti alloys [38-41]. Previously, we studied the effects of atomic ratios on as-cast microstructural evolution, and the mechanical and electrochemical properties of TiZrTaNbSn high-entropy alloy [42]. While its elastic modulus is relatively high, with a value of 110GPa, it does not match the elastic modulus of human bones (30-50 GPa). Moreover, Zr-based TiZrTaNbSn high-entropy alloys display an elastic modulus value of about 40 GPa [43]. Therefore, in our study, we designed a new Zr-based high-entropy Ti-Zr-Ta-Nb-Sn alloy based on metastable β titanium alloy, which is based on the four elements of Ti-Zr-Ta-Nb.

Point 3: Page 2, line 48“At the same time, the appearance of high-entropy alloy breaks the traditional alloy design concept.” This statement is unclear.

What traditional concept of alloy design do you refer to? What is the role of appearance of the alloy in the discussion?

Please explain.

 Response 3: Thank you so much for your comments. The following contents have been added and the manuscript has been revised.

Traditional alloys system usually consist of one or two main elements, and the content of the other elements is much lower. In 2004, Yeh et al. [8-10] first proposed high-entropy alloy, a class of materials containing five or more elements in relatively high concentrations (5–35 at.%) [11, 12]. Because of their unique high-entropy, sluggish diffusion, lattice distortion and cocktail effects [13-15], HEAs show excellent comprehensive properties compared with traditional alloys, such as high hardness [16], high strength [17], corrosion resistance and wear resistance [18, 19], etc. At the same time, high-entropy alloys break the traditional alloy design concept of using only one principal element. Despite this, researchers are actively exploring the possibility of applying high-entropy alloys in new products [20], such as biomedical, magnetic, and hydrogen storage materials, etc. [21-25].

Point 4: Page 2, line 50“Researches actively explored the possibility OF application of high-entropy alloy in new fields.” Please be specific. Please state the “new fields” for the reader.

Response 4: we appreciate you very much, and we are sorry for our mistakes. It has been revised in manuscript and marked in red.

Point 5: Page 2, line 56, 60 “a series of Ti-Zr-Hf-Nb-Ta [17-21], Ti-Mo-Ta-Nb-Zr [22-25] and Ti-Nb-Hf-Ta-Zr-Mo [26,27] HEAs with good mechanical and chemical properties which suitable for biomedical applications have been designed in the past decade”. “At the same time, we noticed that in Fe-Co-Cu-Ni(-Mn) HEAs, adding Sn can improve its tensile strength [35-37].” Please consider to state a range of the mechanical properties and tensile strength of the alloys.

 Response 5: Thank you very much for your comments. The contents are modified as follows:

In the past decade, a series of Ti-Zr-Hf-Nb-Ta [21-25], Ti-Mo-Ta-Nb-Zr [26-29], and Ti-Nb-Hf-Ta-Zr-Mo [30, 31] HEAs with considerable mechanical and chemical properties suitable for biomedical applications have been designed. Researchers are also improving the performance of HEAs by alloying with O, Si, Al, and Cr [32-35]. However, we noticed that adding Sn to Fe-Co-Cu-Ni(-Mn) HEAs can improve elongation strain and tensile strength by 16.9% and 476.9MPa, respectively [36, 37].

 

 

Point 6: Page 3, line 99

“After the polarization experiment, TAFEL and IMP are used to measure the polarization curve and AC impedance of CoCrFeNiAl0.5Cu0.8 alloy, respectively.” The properties of a reference alloy were measured, however, they were not presented. Please present the properties of the reference alloy and compare them to the properties of the studied Sn30 and Sn35 alloys.

 Response 6: We are ashamed of our mistakes. And sincerely thank you for your reminder. It has been revised and mark red in manuscript.

After the polarization experiment, TAFEL and IMP are used to measure the polarization curve and AC impedance of Sn30 and Sn35 BHEAa respectively. Then use Corrview software to analyze the Tafel curve and Zview software to analyze the impedance spectrum. The corroded morphologies on the sample surface were examined by SEM, and the composition of the corroded surface was determined by EDS.  

Point 7: Fig. 1 The assignment of the peak in the figure do not seems to be correct. The peak at 36.8 degree is assigned to be (111) Ta for Sn30, while the same peak is assigned to (110) Zr for Sn35. Please check and correct.

Response 7: Thank you so much for your comments. And Sorry we didn't make it clear. Find peaks function of Jade software is used to determine the 2 Theta degree of Sn30 BHEA and Sn35 BHEA. The results are list in Table 1. The corresponding diffraction peak has a certain degree of deviation.

Table 1 The 2 Theta degree of Sn30 BHEA and Sn35 BHEA

Alloys	2 Theta degree
Sn30 BHEA	35.377	36.858	38.399	41.856	64.806	75.885	80.171
Sn35 BHEA	36.624	37.433	38.539	-	64.411	75.431	79.159

Fig. 1 shows the XRD diffraction patterns of Sn30 BHEA and Sn35 BHEA. We found that there is an obvious peak correspondence relationship by comparing with the standard PDF database. The diffraction peaks of 35.4 °, 36.8 °, and 38.4 °correspond to BCC Zr, FCC Ta, and BCC Ti solid solutions, respectively. At the same time, 64.8 ° corresponds to the FCC Ti solid solution, while 75.9 ° and 80.2 ° correspond to the diffraction peaks of the BCC Zr and BCC Ti solid solutions, respectively. We also observed that 41.8 ° corresponds to the diffraction peak of the BCC Ti solid solution in Sn30 BHEA. Furthermore, the changes in Sn and Zr composition did not affect the phase composition, while the corresponding diffraction peaks displayed a certain degree of deviation

Point 8: Figs. 4 and 5 On page 5, section 4.1, Fig. 5 seems to be discussed prior to Fig. 4. Please discuss the figures in the order they are presented. Alternatively, please swap the order of the figures. Please consider splitting Fig. 4 into more figures, presenting the morphologies in a separate figure.

Technical comments:

 Response 8: Thank you so much for your advice. Your first suggestion was accepted, and then we adjusted the structure of the manuscript. The results are as follows:

The mechanical properties of TiZrTaNbSn BHEAs are shown in Figs. 4 and 5. Fig. 4 (a) shows the compression stress–strain curves of TiZrTaNbSn BHEAs at room temperature. Compared with Sn35 HEAs, the Sn30 HEAs exhibit double-yielding behavior, which is often observed in shape memory alloys as a stress-induced phase transformation and has relatively lower plasticity [44]. Fig. 4 (b) displays the Vickers hardness results for both alloys. Hardness is one of their mechanical properties, and it has a considerable impact on the application of alloys. At the same time, it is also one of the factors that affect alloys’ friction and wear properties. Sn30 HEA has the highest hardness level, and the average value of 5 times measurements is 501.2HV, while the hardness of alloy Sn35 HEAs is 488.72HV, which is slightly lower. Figs. 4 (c)–(f) show the fracture morphologies of these two high-entropy alloys after compression testing. Fig. 4 (c) and (d) show that Sn30 BHEA’s macrofracture morphology is relatively flat, while its micromorphology has river patterns, showing obvious shear failure characteristics. On the gray strip, it also shows typical brittle-fracture characteristics. Furthermore, after increasing the magnification, we observed tear edges and dimples on the eutectic structure, showing the mixed characteristics of quasi-cleavage and ductile fractures. Generally, the samples show brittle quasi-cleavage fractures [45]. Fig. 4 (e) and (f) show that the compression fracture surfaces of Sn35 HEAs are uneven and considerably fluctuate, and there are obvious signs of shear tear on the fractures. After increasing the magnification, we observed shallow and slender dimples on the relatively flat shear plane, and we determined that the compression fracture is generally a brittle cleavage fracture. Fig. 5 shows the maximum strain and compressive strength values corresponding to the two alloys. The maximum strain value and compressive strength of Sn30 HEAs are 46.6% and 684.5MPa, respectively, and the maximum strain value and compressive strength of Sn35 HEAs are 49.9% and 999.2MPa, respectively. Therefore, Sn35 HEAs exhibit better mechanical properties.

 

Point 9: Abstract “…with body-centered-cubic (BCC) and Face-centered-cubic (FCC) solid solution phases.” “body” is written with small “b”, while “Face” is written with capital “F” Please keep the same writing style.

 Response 9: Thank you so much for your kind suggestions, it has been revised and marked red in manuscript.

Point 10: Abstract

The comparison of the film properties is somewhat incomplete.

1. a) The friction coefficient of Sn30 is presented, however, the friction coefficient of Sn35 not.
2. b) The wear resistance of Sn35 is presented, however, the wear resistance of Sn30 not.
3. c) The impedance vale of Sn30 is stated to be the highest, however, not value is state nor the value of Sn35 is presented.
4. d) The corrosion current density of Sn30 is presented and only a relative comparison to Sn35 is stated.

Please state the values of both alloys. Moreover, please compare the values of standard benchmark alloys for better comparison for the reader.

Response 10: We appreciate your comments very much. The abstract has been revised as follows:

The phase composition, microstructure, mechanical, corrosion, and wear behaviors of the Sn30 BHEA  (Sn30) and Sn35 BHEA  (Sn35) biomedical high-entropy alloys (BHEAs) were studied. We found that the Ti–Zr–Ta–Nb–Sn BHEAs showed hyper-eutectic and eutectic structures with body-centered cubic (BCC) and face-centered cubic (FCC) solid-solution phases. The Sn30 BHEA exhibited a high Vickers hardness of approximately 501.2 HV, a compressive strength approaching 684.5 MPa, and plastic strain of over 46.6%. Furthermore, the Vickers hardness and compressive strength of Sn35 BHEA are 488.7 HV and 999.2 MPa, respectively, with a large plastic strain of over 49.9%. Moreover, the Sn30 and Sn 35 BHEA friction coefficients are 0.152 and 0.264, respectively. Sn30 BHEA has the smallest and shallowest furrow-groove width, and its wear rate is 0.86 (km/mm³); at the same time, we observed the delamination phenomenon. Sn35 BHEA has a wear rate value of 0.78 (km/mm³), and it displays wear debris and the largest–deepest furrow groove. Sn30 BHEA has the highest impedance value, and its corrosion current density I_corr is 1.261x10^-7(A /cm²), which is lower than that of Sn35 BHEA (1.265x10^-6(A /cm²)) by 88%, and the passivation current density I_pass of Sn30 BHEA and Sn35 BHEA is 4.44x10^-4(A /cm²) and 3.71x10^-3(A /cm²), respectively. Therefore, Sn30 BHEA preferentially produces passive film and has a small corrosion tendency, and its corrosion resistance is considerably better than that of the Sn35 BHEA alloy.

Point 11: Page 1, line 33, 38

“…and Ti-6A1-7Nb alloys …”

“…still contain A1 element …”

It seems that aluminum is written as A1 (A and a number 1) not as Al (A and a letter l). Please check.

 Response 11: Thank you so much, it has been revised.

Point 12: Page 2, line 50

“Researches actively explored the possibility OF application of high-entropy alloy in new fields.” Why is “OF” written in capital letters?Please check.

Response 12: We appreciate your comments, it has been revised.

Point 13: Page 2, line 83 “Cylinder (phi 4 mm x 6 mm) shape samples …”

I suppose that 4 mm is the diameter of the cylinder. Please use a diameter sign instead of phi.

 Response 13: Thank you so much, it has been revised.

Point 14: Page 2, line 84

“The microhardness test was carried out … using an applied load of 1000 gf and ….” Please explain the load unit “gf”.

Response 14: The meaning of gf is gram, and it has been added in manuscript.

Point 15: Page 2, line 95 “… and scanning range is -1.5 – 1.5 V.”

Please consider writing “scanning voltage range …”

 Response 15: Thank you so much for your comments, it has been revised and marked red in manuscript.

Point 16: Fig. 2 The red markers indicating different locations at the samples are not visible.

Please consider using a different color, for example white.

 Response 16: Thank you and it has been revised as follows:

Point 17: Fig. 3 The labels indicating the different elements in the figure are not visible. Please consider using a white background for the label for better visibility.

 Response 17: Thank you and it has been revised as follows:

Point 18: Short names of the two investigates alloys Sn30 and Sn35 have been introduces. Nevertheless, the manuscript repeats stating the composition of the alloys throughout the manuscript.

For example:

page 3, line 114 “non-equiatomic ratio TiZrTaNbSn BHEAs …”

page 4, line 130 “non-equiatomic ratio TiZrTaNbSn BHEAs …”

page 5, lines 159 and 160 “TiZrTaNbSn BHEAs”

Please use the shorter names of the investigated alloys or name the samples simply alloys when referring to both.

Response 18: We apologize for our mistakes. The entire manuscript has been thoroughly checked and revised.

Point 19: Fig. 6 It seems the Fig. 6(a) be omitted as it does not provide any addition value for the reader. The color background in Fig. 6(b) also appears redundant.

Response 19: Thank you very much for your advice. The color background has changed. However, we regret that we chose not to omit Figure 6 (a). As shown in Fig. 6 (a), we can observe the sample used in the friction and wear test, including its wear marks and approximate dimensions.

Point 20: Page 7, line 214 “Therefore, comprehensive analysis shown that the friction and wear morphology of Sn30 BHEA is the best.” When comparing properties of only two materials, using “comparative degree”, i.e. it is better, that using “superlative degree”, i.e. is the best, appear more appropriate. Please consider revision.

 Response 20: Thank you very much for your comments. However, we are sorry that the content of friction and wear analysis has been extensively revised. Therefore, the relevant content has been deleted.

We carried our SEM characterizations of the worn surfaces to explore the wear mechanisms of Sn30 BHEA and Sn35 BHEA, and the results are displayed in Fig. 8, the plastic deformation and delamination traces showed severe wear for both alloys. Furthermore, the wear surfaces of all Sn30 BHEA and Sn35 BHEA showed typical furrow characteristics, and there are grooves and wear debris along the sliding direction due to the micro cutting and furrow effects of the Si₃N₄ ball, which indicates that furrow wear is the main wear mechanism [47, 49].

Point 21: Extensive editing of English language and style required

Response 21: Thanks for your comments. The manuscript has been checked carefully, and the revised manuscript was edited for proper English language by means of “MDPI English Editing Services” before it is submitted to the journal this time. The “Certificate of MDPI English Editing Services” is shown in Fig. 1. The revised parts are highlighted in revised manuscript, we hope that can meet the reviewer’s and magazine’s standard.

Certificate of MDPI English Editing Services

 

Author Response File: Author Response.docx

Reviewer 3 Report

In this article the author reports ‘Mechanical, Corrosion, and Wear Properties of TiZrTaNbSn Biomedical High Entropy Alloys’. This topic could be interesting for the readers. However, the paper needs a minor revision before publication. I have listed a few comments that need to be addressed:

 

1.      The novelty of the present article should be discussed in the Introduction section.

2.      Introduction could be much better with more background about the work with up-to-date citations.

3.      Write the full form once at the first appearance.

4.      The author should write the purpose for each test in one/two sentences (in brief) before explaining the results of the characterization techniques. Therefore, the logic and organization of this part will be enhanced.

5.      Conclusion should be precise with key findings of the results.

6.      Carefully revise the typos and linguistic errors to make the manuscript error-free.

Author Response

Dear Dr. Theeranon Tankam and Reviewers,

Thank you very much for your comments and explanation. We have carefully read your comments on the manuscript, titled “Mechanical, corrosion, and wear properties of TiZrTaNbSn biomedical high entropy alloys” (Manuscript ID: coatings-2014293). We have revised the manuscript and responded point by point to the comments as listed below.

Response to Reviewer 3 Comments

Point 1: The novelty of the present article should be discussed in the Introduction section.

Response 1: Thank you so much for your comments. The introduction has been revised extensively.

Pure Ti has the advantages of non-toxicity, light weight, high strength and good biocompatibility, etc. Therefore, in the 1950s, the United States and the United Kingdom start to apply it for use with living organisms [1]. In the 1960s, Ti alloys (first Ti-6A1-4V [2,3] and later Ti-5Al-2.5Fe and Ti-6A1-7Nb) began to be widely used in clinical practice as a human implant material [4-7]. In 1970s and 1980s, researchers began to prepare Ti alloys with V-free implants because of its toxic and potentially harmful effects on the human body; furthermore, in the mid-1980s, new types of α+β Ti alloys, namely Ti-5Al-2.5Fe and Ti-6Al-7Nb, were developed in Europe [3]. The mechanical properties of these alloys are similar to Ti-6Al-4V [7], albeit with higher biocompatibility and corrosion resistance properties. However, these alloys still contain A1, which can cause organ damage and harmful symptoms, such as osteomalacia, anemia and neurotin disorder [4,5]. Based on the above reasons, new types of alloys, which are free of both V and Al but with addition of Nb, Zr, Ta, Sn, (Ti-13Nb-13Zr, Ti-35Nb-5Ta7Zr, Ti-24Nb-4Zr-7.9Sn) has been developed in recent years [4-6], their elastic modulus are closer to that of natural human bone, and their strength is also higher than that of pure Ti. Consequently, Ti alloys are being rapidly developed for human implant materials; however, their strength, friction and wear, and corrosion resistance need to be studied further.

.

Traditional alloys system usually consist of one or two main elements, and the content of the other elements is much lower. In 2004, Yeh et al. [8-10] first proposed high-entropy alloy, a class of materials containing five or more elements in relatively high concentrations (5–35 at.%) [11, 12]. Because of their unique high-entropy, sluggish diffusion, lattice distortion and cocktail effects [13-15], HEAs show excellent comprehensive properties compared with traditional alloys, such as high hardness [16], high strength [17], corrosion resistance and wear resistance [18, 19], etc. At the same time, high-entropy alloys break the traditional alloy design concept of using only one principal element. Despite this, researchers are actively exploring the possibility of applying high-entropy alloys in new products [20], such as biomedical, magnetic, and hydrogen storage materials, etc. [21-25]. At present, the comprehensive mechanical properties of medical alloys are still to be improved in clinical practice. Therefore, the design concept of high-entropy alloy can be used to prepare biomedical high entropy alloy materials with low modulus, high strength, corrosion resistance, and other excellent comprehensive properties to meet demand.

In the past decade, a series of Ti-Zr-Hf-Nb-Ta [21-25], Ti-Mo-Ta-Nb-Zr [26-29], and Ti-Nb-Hf-Ta-Zr-Mo [30, 31] HEAs with considerable mechanical and chemical properties suitable for biomedical applications have been designed. Researchers are also improving the performance of HEAs by alloying with O, Si, Al, and Cr [32-35]. However, we noticed that adding Sn to Fe-Co-Cu-Ni(-Mn) HEAs can improve elongation strain and tensile strength by 16.9% and 476.9MPa, respectively [36, 37]. In addition, Sn is non-cytotoxic and widely present in β-Ti alloys [38-41]. Previously, we studied the effects of atomic ratios on as-cast microstructural evolution, and the mechanical and electrochemical properties of TiZrTaNbSn high-entropy alloy [42]. While its elastic modulus is relatively high, with a value of 110GPa, it does not match the elastic modulus of human bones (30-50 GPa). Moreover, Zr-based TiZrTaNbSn high-entropy alloys display an elastic modulus value of about 40 GPa [43]. Therefore, in our study, we designed a new Zr-based high-entropy Ti-Zr-Ta-Nb-Sn alloy based on metastable β titanium alloy, which is based on the four elements of Ti-Zr-Ta-Nb. We prepared two kinds of biomedical-grade high-entropy alloys, namely Sn30 BHEA and Sn35 BHEA, by vacuum arc melting, and we systematically studied the feasibility of preparing biomedical-grade high-entropy alloy with five elements (Ti, Zr, Ta, Nb, and Sn), paying specific attention to morphology, compressive strength, electrochemical corrosion, and friction and wear properties. Our work will provide data for the future development of biomedical-grade high-entropy alloy, in addition to guidance for further scientific research on Ti alloys.

 

Point 2:  Introduction could be much better with more background about the work with up-to-date citations.

Response 2: We appreciate your comments and have added many new references. However, since the introduction is developed from the development of biomedical materials, the literature cited earlier is a long time ago. I hope we can get your understanding.

Point 3: Write the full form once at the first appearance.

Response 3: Thank you so much for your suggestion. The revised content is listed and highlighted in revised manuscript at the same time. They are defined and marked red in the manuscript.

Point 4: The author should write the purpose for each test in one/two sentences (in brief) before explaining the results of the characterization techniques. Therefore, the logic and organization of this part will be enhanced.

Response 4: We appreciate your comments and thank you very much. The contents have been added and marked red in manuscript.

Point 5: Conclusion should be precise with key findings of the results.

Response 5: Thank you so much for your suggestion. It has been revised as follows:

Taking β-type titanium alloy as the design conception, the comprehensive properties of biomedical high-entropy alloy based on Ti-Zr-Nb-Ta and Sn element were systematically discussed. The main conclusions are as follows:

1. Sn30 BHEA and Sn35 BHEA are typical hypo-eutectic and eutectic structures, respectively, and both alloys are composed of BCC and FCC phases;
2. The two high-entropy alloys have brittle fractures at room temperature. The maximum strain value and compressive strength of Sn30 BHEA are 46.6% and 684.5MPa respectively, while the maximum strain value and compressive strength of Sn35 BHEA are 49.9% and 999.2MPa, respectively. Sn30 HEA’s strength and yield strength are better than those of Sn35 HEA;
3. The friction coefficient of Sn30 BHEA is 0.152, the specific and linear wear rates (K_v and K₂, respectively) are 2.27×10^-4(mm³/nm) and 1.163 (mm³/km), respectively, while the width of the furrow groove is the smallest and shallowest, with almost no wear debris. Furthermore, the friction coefficient of Sn35 BHEA is 0.264, and the values of specific and linear wear (K_v and K₂, respectively), in addition to wear resistance E, are 2.49×10^-4(mm³/nm), 1.277 (mm³/km), and 0.78 (km/mm³), respectively. Furthermore, the width of the furrow groove is the largest and deepest, and there are wear debris. In conclusion, the Sn30 HEA has excellent wear resistance and rates compared with Sn35 HEA;
4. Sn30 BHEA has the highest impedance value. The corrosion current density I_corr is 1.261x10^-7(A /cm²), which is lower than that of Sn35 BHEA by about 88%. The capacitive arc curvature radius of Sn30 BHEA also considerably decreases. Therefore, Sn30 HEAs preferentially produce passivated film with a small corrosion tendency, indicating that its corrosion resistance is considerably better than that of Sn35 BHEA alloy.

Point 6: Carefully revise the typos and linguistic errors to make the manuscript error-free.

Response 6: Thanks for your comments. The manuscript has been checked carefully, and the revised manuscript was edited for proper English language by means of “MDPI English Editing Services” before it is submitted to the journal this time. The “Certificate of MDPI English Editing Services” is shown in Fig. 1. The revised parts are highlighted in revised manuscript, we hope that can meet the reviewer’s and magazine’s standard.

Fig.1 Certificate of MDPI English Editing Services

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have taken care to respond to each of the remarks made by the reviewer, providing any missing information.

Many thanks for the work achieved.

Author Response

Response to Reviewer 1 Comments

Point 1: The authors have taken care to respond to each of the remarks made by the reviewer, providing any missing information. Many thanks for the work achieved.

Response 1: Thanks for your comments and guidance on our writing. We realize our deficiency in writing scientific papers. Your comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript discusses the properties of bulk Ti-Zr-Ta-Nb-Sn alloys; not coatings.

Hence, I recommend the manuscript to consider for publication in other journals, such as Condensed Matter or Alloys.

 

The authors have tried to address most of the comments.

However, there are still some comments, which were not consequently addressed.

Moreover, some authors’ amendments need to be clarified.

 

to 2)

The authors have modified a paragraph in the introduction presenting the work on Sn-containing alloys.

Page 2, lines 71-76

“Previously, we studied the effects of atomic ratios on as-cast microstructural evolution, and the mechanical and electrochemical properties of Ti-Zr-Ta-Nb-Sn high-entropy alloy [42]. While its elastic modulus is relatively high, with a value of 110 GPa, it does not match the elastic modulus of human bones (30-50 GPa). Moreover, Zr-based Ti-Zr-Ta-Nb-Sn high-entropy alloys display an elastic modulus value of about 40 GPa [43].”

 

First, the authors write that the elastic modulus of their Ti-Zr-Ta-Nb-Sn is 110 GPa, which is much higher than the elastic modulus of human bones (30-50 GPa). Then, in the following sentence, the authors state that the elastic modulus of the Ti-Zr-Ta-Nb-Sn alloys is about 40 GPa.

 

This is confusing.

Why is the elastic modulus of the investigated Ti-Zr-Ta-Nb-Sn alloy of 110 GPa higher than the elastic modulus of the Ti-Zr-Ta-Nb-Sn alloys in general of about 40 GPa in ref. [43].

Please explain.

 

to 7)

The peak assignment to Zr bcc and Ta fcc in Fig. 1 does not seems to be correct.

While the (110) Zr peak is reported to shift towards higher 2theta angle from Sn30 to Sn35, this is not the case for the (220) Zr peak. Since the (220) peak is a multiple of the (110) peak, strictly, the same shift must be expected. Hence, the peak assignment is not correct.

Please revise.

 

to 13)

page 2, line 91 and 98

The authors still write “phi” to specify the diameter of their samples.

Please us the sign for a diameter.

 

to 11)

page 1, line 41

“However, these alloys still contain A1, which can cause …”

The authors still write “A1” (A one) rather than “Al” (A and l).

Please correct.

 

to 14)

page 2, line 101

The authors specify the load used in hardness measurements “1000 gram (gf)”.

 “g” in “gf” can be understood as gram. However, it is unclear what “f’ in “gf” stands for.

Please explain.

 

to 15)

Please consider writing “from -1.5 to +1.5 V” to avoid confusion between the minus sign and “-“-sign having the meaning of “to” of the investigated range. Please also consider writing a plus sign explicitly.

 

to 18)

The authors have replaced the long label of the alloy Ti-Zr-Ta-Nb-Sn with a shorter version Sn30 and Sn35. However, this has not been done throughout the whole manuscript.

For example, the old longer label of the alloy is still used in Figs. 4, 5, 6, and 10.

Please use the shorter and simpler version of referring to the alloys – Sn30 and Sn35.

 

to 19)

page 9, line 254

“Therefore, our comprehensive analysis shows that Sn30 BHEA has the best friction and wear morphologies.”

The authors still use the “superlative degree” rather than the “comparative degree”, which appears more appropriate in a comparison of the data of two samples.

 

Author Response

Dear Dr. Editor and Reviewers,

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Mechanical, corrosion, and wear properties of TiZrTaNbSn biomedical high entropy alloys” (Manuscript ID:  coatings-2014293). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked with purple in the revised manuscript. The main corrections in the paper and the responds to the reviewer’s comments are as following:

Response to Reviewer 2 Comments

Point 1: The authors have modified a paragraph in the introduction presenting the work on Sn-containing alloys (Page 2, lines 71-76).

“Previously, we studied the effects of atomic ratios on as-cast microstructural evolution, and the mechanical and electrochemical properties of Ti-Zr-Ta-Nb-Sn high-entropy alloy [42]. While its elastic modulus is relatively high, with a value of 110 GPa, it does not match the elastic modulus of human bones (30-50 GPa). Moreover, Zr-based Ti-Zr-Ta-Nb-Sn high-entropy alloys display an elastic modulus value of about 40 GPa [43].” First, the authors write that the elastic modulus of their Ti-Zr-Ta-Nb-Sn is 110 GPa, which is much higher than the elastic modulus of human bones (30-50 GPa). Then, in the following sentence, the authors state that the elastic modulus of the Ti-Zr-Ta-Nb-Sn alloys is about 40 GPa. This is confusing. Why is the elastic modulus of the investigated Ti-Zr-Ta-Nb-Sn alloy of 110 GPa higher than the elastic modulus of the Ti-Zr-Ta-Nb-Sn alloys in general of about 40 GPa in ref. [43]. Please explain.

Response 1: Thank you so much for your reminder. And we are really sorry for the inaccurate writing of TiZrTaNbSn composition. The contents have been revised and marked with purple in manuscript.

However, we noticed that adding Sn to Fe-Co-Cu-Ni(-Mn) HEAs can improve elongation strain and tensile strength by 16.9% and 476.9MPa, respectively [36, 37]. In addition, Sn is non-cytotoxic and widely present in β-Ti alloys [38-41]. Previously, we studied the effects of atomic ratios on as-cast microstructural evolution, and the mechanical and electrochemical properties of Ti30Zr20Ta20Nb20Sn10 high-entropy alloy [42]. While its elastic modulus is relatively high, with a value of 110GPa, it does not match the elastic modulus of human bones (30-50 GPa). Moreover, Zr-based Ti_0.5Zr_1.5Ta_0.5NbSn_0.2 (Ti13.5Zr40.5Ta13.5Nb27Sn5.5) high-entropy alloys display an elastic modulus value of about 40 GPa [43]. Therefore, in our study, we designed a new Zr-based high-entropy Ti-Zr-Ta-Nb-Sn alloy based on metastable β titanium alloy, which is based on the four elements of Ti-Zr-Ta-Nb.

Point 2: The peak assignment to Zr bcc and Ta fcc in Fig. 1 does not seems to be correct. While the (110) Zr peak is reported to shift towards higher 2theta angle from Sn30 to Sn35, this is not the case for the (220) Zr peak. Since the (220) peak is a multiple of the (110) peak, strictly, the same shift must be expected. Hence, the peak assignment is not correct. Please revise.

Response 2: Thanks for your comments and guidance on our writing. We realize our inadequacy in writing scientific papers. After consulting massive related references, we find that it was exactly the same as your comments. We sincerely thank you. The Fig. 1 has been modified and the relevant contents have been revised and marked with purple in manuscript.

 

Furthermore, the 37.6 ° (Sn35 BHEA) and 35.9 ° (Sn30 BHEA) diffraction peaks correspond to the HCP Zr₅Sn₃ phase.

Point 3: page 2, line 91 and 98. The authors still write “phi” to specify the diameter of their samples. Please us the sign for a diameter.

Response 3: Thank you so much for your suggestion. The revised content is listed and highlighted in revised manuscript at the same time.

Wire cut electrical discharge machining (WEDM, DHL-500) was used to cut samples from the core region of the master alloy ingot (Buttonhole, maximum diameter Φ32mm, maximum height 16mm).

Cylinder (Φ4mm×6mm)-shaped samples were cut via WEDM

Point 4: page 1, line 41. “However, these alloys still contain A1, which can cause …” The authors still write “A1” (A one) rather than “Al” (A and l). Please correct.

Response 4: We are really sorry for our mistakes. And thank you so much. The contents have been added and marked purple in manuscript.

However, these alloys still contain Al, which can cause organ damage and harmful symptoms

Point 5: page 2, line 101. The authors specify the load used in hardness measurements “1000 gram (gf)”. “g” in “gf” can be understood as gram. However, it is unclear what “f’ in “gf” stands for. Please explain.

Response 5: Thank you so much for your comments. It has been revised as follows:

The microhardness test was carried out on a HYHVS-1000T Vickers hardness tester using an applied load of 1000 gram force (gf) and a dwell time of 15 s.

Point 6: Please consider writing “from -1.5 to +1.5 V” to avoid confusion between the minus sign and “-“-sign having the meaning of “to” of the investigated range. Please also consider writing a plus sign explicitly.

Response 6: Thanks for your advice and we appreciate it very much. It has been revised as follow:

and scanning voltage range is from - 1.5 to +1.5V.

 

Point 7: The authors have replaced the long label of the alloy Ti-Zr-Ta-Nb-Sn with a shorter version Sn30 and Sn35. However, this has not been done throughout the whole manuscript. For example, the old longer label of the alloy is still used in Figs. 4, 5, 6, and 10. Please use the shorter and simpler version of referring to the alloys – Sn30 and Sn35.

Response 7: Thanks for your comments. They have been revised as follows:

 

Figure 4. Compressive stress–strain curves and corresponding fracture morphologies of Sn30 BHEA and Sn35 BHEA: (a) stress–strain curves, (b) HV of Sn30 BHEA and Sn35 BHEA, (c)(d) fracture morphology of Sn30 BHEA, (e)(f) fracture morphology of Sn35 BHEA.

 

Figure 5. Compression properties of Sn30 BHEA and Sn35 BHEA

 

Figure 6. Friction and wear test results of Sn30 BHEA and Sn35 BHEA (a)samples, (b) friction coefficient curves, and profiles of the worn surfaces for sintered composites and corresponding 2D cross-section profiles of wear tracks: (c) Sn30 BHEA, (d) Sn35 BHEA.

 

Figure 9. EIS of Sn30 BHEA and Sn35 BHEA (a) Nyquist plots, (b) Bode plots.

 

Figure 10. Corrosion properties characterization for Sn30 BHEA and Sn35 BHEA: a) Potentiodynamic polarization curves, (b) (c) corrosion morphology of Sn30 BHEA, (d) (f) corrosion morphology of Sn35 BHEA.

Point 8: page 9, line 254 “Therefore, our comprehensive analysis shows that Sn30 BHEA has the best friction and wear morphologies.”

The authors still use the “superlative degree” rather than the “comparative degree”, which appears more appropriate in a comparison of the data of two samples.

Response 8: We are really sorry that we misunderstood in our first response. Thank you so much for your kindhearted. It has been revised and marked in purple in manuscript.

Therefore, our comprehensive analysis shows that Sn30 BHEA has better friction and wear morphologies.

Author Response File: Author Response.docx