Microstructure and Nanoindentation Evolution of (Ni,Pt)Al Coating on IC21 Substrate at 1100 °C

Round 1

Reviewer 1 Report

In this study, a ~20 μm (Ni,Pt)Al coating was applied on IC21 substrate via electroplating followed by aluminizing. A thermal exposure test at 1100 °C in air was used for investigating the microstructure evolution and nanoindetation behavior of samples with and without coating. The paper is well-written, well-structured and well-presented. There is enough experimental data and arguments are very well supported with results. I do recommend this paper for publication after following revisions:

• Discussions on the mechanisms of formation of Al2O3 layer is poor. Authors are recommended to explain how this layer forms in more details. I recommend authors use discussions in this manuscript: High temperature oxidation behavior of aluminide coatings applied on HP-MA heat resistant steel using a gas-phase aluminizing process, Surface and Coatings Technology 434, 128181, 2022
• Authors need to explain how inter-diffusion ends up in the formation of TCP phases. More explanations on the inter-diffusion mechanisms can be found in this paper: An investigation on anti-coking behavior of gas phase aluminide coatings applied on a high performance micro alloyed (HP-MA) steel, Surface and Coatings Technology 389, 125607, 2020.   
• What is the implications of NiAl and Ni3Al? Which one is more preferred? This needs to be further clarified. The following manuscript might be helpful: Towards a High Strength Ductile Ni/Ni3Al/Ni Multilayer Composite using Spark Plasma Sintering, Science of Sintering 51 (4), 2019
• Please re-write the conclusion, as current conclusion is very short and does not reflect all findings of your research.
• Authors need to provide more explanation on what exactly TCP phases are and how they implicate for the properties of the coating. The following manuscript gives an overview of TCP phases in superalloys: A new method in prediction of TCP phases formation in superalloys, Materials Science and Engineering: A 396 (1-2), 138-142, 2005

Author Response

Response to Reviewer 1 Comments

In this study, a ~20 μm (Ni,Pt)Al coating was applied on IC21 substrate via electroplating followed by aluminizing. A thermal exposure test at 1100 °C in air was used for investigating the microstructure evolution and nanoindetation behavior of samples with and without coating. The paper is well-written, well-structured and well-presented. There is enough experimental data and arguments are very well supported with results. I do recommend this paper for publication after following revisions:

Point 1: Discussions on the mechanisms of formation of Al2O3 layer is poor. Authors are recommended to explain how this layer forms in more details. I recommend authors use discussions in this manuscript: High temperature oxidation behavior of aluminide coatings applied on HP-MA heat resistant steel using a gas-phase aluminizing process, Surface and Coatings Technology 434, 128181, 2022

Response 1: Thanks for the reviewer’s suggestion. As shown in the manuscript, in aluminide coatings, the oxidation resistance is mainly provided by the β-NAli phase and deterioration of this phase would obviously decrease the substrate protection. The deterioration rate of β-NiAl phase is dependent on the initial Al content of the coating and the rate of Al consumption. The aluminum oxide formed during the initial stages of oxidation undergoes transformations through a series of transitional metastable alumina polymorphs such as γ-Al2O3 and θ-Al2O3 before transforming to the stable α-Al2O3 phase. The authors added descriptions of the formation of Al2O3 layer to the manuscript and cited the literature provided by the reviewer.

 

Point 2: Authors need to explain how inter-diffusion ends up in the formation of TCP phases. More explanations on the inter-diffusion mechanisms can be found in this paper: An investigation on anti-coking behavior of gas phase aluminide coatings applied on a high performance micro alloyed (HP-MA) steel, Surface and Coatings Technology 389, 125607, 2020.  

Response 2: Thanks for the reviewer’s suggestion. In order to reduce the free energy of nickel based single crystal superalloy at high temperature, refractory elements in solid solution substrate are easy to precipitate and TCP phase is formed in the γ/γ´ substrate due to the outward diffusion of Ni from the substrate and Al inward diffusion in the coating.

 

Point 3: What is the implications of NiAl and Ni3Al? Which one is more preferred? This needs to be further clarified. The following manuscript might be helpful: Towards a High Strength Ductile Ni/Ni3Al/Ni Multilayer Composite using Spark Plasma Sintering, Science of Sintering 51 (4), 2019

Response 3: Thanks for the reviewer’s suggestion. NiAl and Ni3Al are both high temperature structural materials with high melting point. Ni3Al is a face-centered cubic structure with melting point of about 1400 ℃,while NiAl is a body-centered cubic structure with melting point of about 1640℃. NiAl has a higher melting point and more advantages in high temperature oxidation resistance. The authors cited the literature provided by the reviewer.

 

Point 4: Please re-write the conclusion, as current conclusion is very short and does not reflect all findings of your research.

Response 4: Thanks for the reviewer’s suggestion. The authors rewrote the conclusion according to the requirements of reviewer.

 

Point 5: Authors need to provide more explanation on what exactly TCP phases are and how they implicate for the properties of the coating. The following manuscript gives an overview of TCP phases in superalloys: A new method in prediction of TCP phases formation in superalloys, Materials Science and Engineering: A 396 (1-2), 138-142, 2005

Response 5: Thanks for the reviewer’s suggestion. TCP phase is a topological close-packed phase with complex structure. It’s hard and brittle properties make it easy to form cracks at high temperature and accelerate the peeling of the coating. The authors cited the literature provided by the reviewer.

Reviewer 2 Report

Paper investigates the effect of elevated temperature exposure on the microstructure and mechanical properties of the intermetallic alloy. My comments on the paper.

• The introduction should be improved. The drawback in knowledge should be clarified. The scientific motivation of the study is not explained properly. There are many papers available that relate to the high-temperature evolution of intermetallics.
• In the introduction, please write instead of  "

IC21 is an intermetallic compound superalloys,

write "IC21 is an intermetallic compound superalloys (Ni₃Al-based)..." 

• improve the introduction by removing the unnecessary phrases "

introduction should briefly place the study in a broad context and	62
highlight why it is important. It should define the purpose of the work and its significance.	63
The current state of the research field should be carefully reviewed and key publications	64
cited. Please highlight controversial and diverging hypotheses when necessary. Finally,	65
briefly mention the main aim of the work and highlight the principal conclusions. As far	66
as possible, please keep the introduction comprehensible to scientists outside your partic-	67
ular field of research. References should be numbered in order of appearance and indi-	68
cated by a numeral or numerals in square brackets—e.g., [1] or [2,3], or [4–6]. See the end	69
of the document for further details on references.	7

•  

improve the typos likewise 

48

ent elements(such as Pt,Re,Zr.ect)

to remove H2 and dilute

The EDS results in Table1

area (By Image Pro) was about 20.8%

forming Al2O3 on the surface, resulting in the

165

188

α-Al2O3.The main phase were both AlNi3

255

elements (such as Mo, Ta, Re,etc.)

 formation of a Al2O3 273 

• In figure 4 - explain why at approx 35 degree you revealed different phases for coatings and substrate (marked as 1,3 and 1,2). Clarify it.
  The same, you have differences in peaks identification form 55 to approx 70. Clarify it.
• In my opinion, to state the evolution of the microstructure you should compare the XRD before and after high-temperature exposure.
• Clarify the novelty of your study in the conclusions section
• Finally, I think that paper includes to limited research material and discussion is also too scant. Moreover authors wrote that 

  For the nanoindentation, it can	206
  not only characterize the hardness at the nanoscale, but also characterize the elastic mod-	207
  ulus, fracture toughness, strain hardening effect, viscoelastic or creep behavior of materi-	208
  als, so it has been widely used in the field of materials science [19–22]

  and I think that all mentioned above items should be taken into account while discussing the evolution of tested alloy. You should reanalyse the nanoindentation results and use them to compare untreated and treated alloy. Probably then, much more scientific conclusions could have been drawn. 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

• Kindly include experimental results in the abstract.
• Detail literature survey and research gap is included.
• In line 152 by mistaken two “the” are there. Kindly remove.
• In 165 Al2O3 termed as Al₂O₃
• Kindly mark the attributes in fig. 1, 2 and 3
• In XRD kindly include the Miller Indices
• In load displacement curve kindly include the indendation photos in fig. 6.
• Conclusion is too generic. Revised the conclusion part.

Author Response

Response to Reviewer 3 Comments

 

Point 1: Kindly include experimental results in the abstract.

 

Response 1: Thanks for the reviewer’s suggestion. The authors have rewrote the experimental results in the abstract (highlighted in yellow)

 

Point 2: Detail literature survey and research gap is included.

 

Response 2: Thanks for the reviewer’s suggestion. The authors added the content of literature survey and research gap in the introduction section.

 

Point 3: In line 152 by mistaken two “the” are there. Kindly remove.

 

Response 3: Thanks very much for your careful patience. The mistake in the manuscript has been corrected. The authors have reviewed the full text of the manuscript and tried to avoid similar errors.

 

Point 4: In 165 Al2O3 termed as Al₂O₃

 

Response 4: Thanks very much for your careful patience. The mistake in the manuscript has been corrected. The authors have reviewed the full text of the manuscript and corrected similar errors.

 

Point 5: Kindly mark the attributes in fig. 1, 2 and 3

 

Response 5: Thanks for the reviewer’s suggestion. The red box in fig.1, 2 and 3 represents the EDS analysis sampling locations in Table 1 and a related description has been added to the manuscript.

 

Point 6: In XRD kindly include the Miller Indices

 

Response 6: Thanks for the reviewer’s suggestion. We added the Miller Indices in fig.4

 

Point 7: In load displacement curve kindly include the indendation photos in fig. 6.

 

Response 7: Thanks for the reviewer’s suggestion. A typical indendation photo has added in fig.6

 

Point 8: Conclusion is too generic. Revised the conclusion part.

 

Response 8: Thanks for the reviewer’s suggestion. The conclusion section has been rewrote according to the reviewer’s comment.

Round 2

Reviewer 1 Report

Thanks for taking my comments into consideartion. The paper can be published as is. 

Author Response

Thank you for your valuable comments on my manuscript.

Reviewer 2 Report

Thank you for your response. All blurred phrases are now explained, the required novelty is clarified, and overall sufficient improvements were made in the manuscript. I have no comments on the paper content. 

Author Response

Thank you for your valuable comments on my manuscript.