Simulation of Particle Interaction with Surface Microdefects during Cold Gas-Dynamic Spraying

Round 1

Reviewer 1 Report (New Reviewer)

Referee Comments

Manuscript ID: coatings-1859627-peer-review-v1

Title: Simulation of particle interaction with surface microdefects during cold gas-dynamic spraying

Authors: O. Aleksieieva, L. Dereviankina, P. Breuninger, M. Bozoglu, P. Tretiakov, A. Toporov, S. Antonyuk

 

Comments:

A-The manuscript is well written and organized. The references are updated.

B-The research is focused on the investigation of the impact behavior of cold sprayed particles with the wall surface having microdefects by modelling. It is important to understand the effect of fine particles impact on the component surface and the interaction between the particle and surface properties to use these coatings against corrosion or crack propagation. Furthermore, the cold gas-dynamic spraying (CGDS) process has been used to repair and coat the surface of substrates in different types of applications.

The subject is relevant and important for industrial applications. However, there are few points which should be clarified in the manuscript.

 

1-     The authors mention in several sections “smooth surface”. What is the surface roughness range which is used in the modelling? How can be related to the real applications for the selected material?

2-     In addition, Table 1 summarizes the parameters used in the modelling for the selected material. However, although the authors present temperature and its effects there is no quantitative data on this parameter, eg. Temperature is lower than melting temperature but what is its value?

3-     The research’s contribution to the literature should be emphasized further.

4-     The authors present at the end of the Conclusion section which is not clear:

“In this work the Johnson-Cook failure model was used for prediction of extremely high plastic deformation and stresses, which are a function of the strain rate at high-speed impact. Moreover, the dependence of the mechanical parameters on the temperature is well defined in this model and the effect of the temperature on the deformation can be described.

                                                                                                           Best Regards

Comments for author File: Comments.pdf

Author Response

1- The authors mention in several sections “smooth surface”. What is the surface roughness range which is used in the modelling? How can be related to the real applications for the selected material?
➔ The smooth surface we mention is a flat surface without any roughness. These is the general assumption in the modelling that is made for cold spraying on polished substrates. For better reading comprehension we added this information in the method section. “In the reference case (Figure 1a), the normal impact of a spherical particle on a smooth surface (without surface roughness) of the substrate without damages was simulated.”

2- In addition, Table 1 summarizes the parameters used in the modelling for the selected material. However, although the authors present temperature and its effects there is no quantitative data on this parameter, eg. Temperature is lower than melting temperature but what is its value?
➔ The melting temperature of the studied material is specified with 1460°C in Table 1 .

3- The research’s contribution to the literature should be emphasized further.
➔ We added this in our conclusion: “In future work, the simulation results can be validated with experimental tests to understand the influence of the deformation behavior during particle impact with defects on particle-substrate bonding”.

4- The authors present at the end of the Conclusion section which is not clear:
“In this work the Johnson-Cook failure model was used for prediction of extremely high plastic deformation and stresses, which are a function of the strain rate at high-speed impact. Moreover, the dependence of the mechanical parameters on the temperature is well defined in this model and the effect of the temperature on the deformation can be described.
➔ We changed this section to clarify our statement: The parameters used in this model were obtained from experimental studies in the literature and also take temperature dependence into account. Therefore, the effect of the temperature on the deformation can be described well.

Reviewer 2 Report (New Reviewer)

1. The article on CGDS has been very nicely structured. The concepts have been very crisply stated without any ambiguity.

2. Labelling of Figure no. 10 needs to be looked into. The subfigures mentioned in the text are not properly labelled in the figure.

3. The authors should provide the details of the procedures and working parameters used during modelling in ABACUS. This will help readers who are new to modelling to get an insight into the modelling method along with the results.

 

Author Response

1. The article on CGDS has been very nicely structured. The concepts have been very crisply stated without any ambiguity.

2. Labelling of Figure no. 10 needs to be looked into. The subfigures mentioned in the text are not properly labelled in the figure.

→ We changed the label.

3. The authors should provide the details of the procedures and working parameters used during modelling in ABACUS. This will help readers who are new to modelling to get an insight into the modelling method along with the results.
→ For a better understanding for the reader we have added more information to this section.

Reviewer 3 Report (New Reviewer)

1. It is better to tell for readers that defect is a kind of cavity.

2. The Fig. 2 shows simulation results. The color of the defect is blurr. Can you show more clearly?

3. The line 429: deepth is wrong. It is "depth".

4. The line 435: 0,9 is "0.9".

Author Response

Reviewer #3:
1. It is better to tell for readers that defect is a kind of cavity.
➔ We have three passages in the manuscript where we tell the reader that the microdefects are a kind of a cavity.:
• This work focuses on the investigation of the impact behavior of cold sprayed particles with the wall surface having microdefects in the form of cavities.
• Different rectangular microdefect slot geometries and contact scenarios were studied and analyzed.
• The other studied cases shown in Figure 1 (b-d) describe different scenarios of particle collisions on substrate with microdefects that are represented as a regular-shaped open cavity.

2. The Fig. 2 shows simulation results. The colour of the defect is blurr. Can you show more clearly?
→ We have changed this. In the figures (Figure 2, 6, 8, 9), the contours of the defects are highlighted in white.

3. The line 429: deepth is wrong. It is "depth".
→ Done.

4. The line 435: 0,9 is "0.9".
→ Done.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The article entitled "Simulation of particle interaction with surface microdefects during cold gas-dynamic spraying" presents a detailed work about simultation of cold gas-dynamic spraying of AISI 1045 steel. The article is well-written and adequately prepared. Only some questions that could be further clarified:

• What kind of repairs are admited by the parts? What level of damage? What is the maximum size of defects that can be repaired?
• Paragraph of lines 84-94: Please provide further (numerical) details of the conditions. Are conditions analogous for the different materials? Is there any methodology to determine the conditions (i. e. critical velocity) apart from simulations=
• Lines 140-141: Why these dimensions of defect? Where they determined by microscopy?
• Lines 162-166: What do you mean with "..." between the values?
• Lines 330-331: Is there good adherence of the particles to the substrate in this case?

Author Response

The article entitled "Simulation of particle interaction with surface microdefects during cold gas-dynamic spraying" presents a detailed work about simulation of cold gas-dynamic spraying of AISI 1045 steel. The article is well-written and adequately prepared. Only some questions that could be further clarified:

1. What kind of repairs are admitted by the parts? What level of damage? What is the maximum size of defects that can be repaired?

• We have added the part about the size of defects to the introduction. Dislocation or cracks in the size of a few micrometres to mm can be repaired by cold spray.

2. Paragraph of lines 84-94: Please provide further (numerical) details of the conditions. Are conditions analogous for the different materials? Is there any methodology to determine the conditions (e.g. critical velocity) apart from simulations?

• We added further details about the conditions. The critical velocity can be estimated by empirical model for example according to T. Schmidt et al. [17,18]. CFD simulations provide the temperatures of the particle and the component surface for this model. The critical velocity was determined in our previous works [21] that we now describe in the manuscript.

3. Lines 140-141: Why these dimensions of defect? Where they determined by microscopy?

• We added the information in the introduction. These are the general size ranges for defects that can be observed by SEM of damaged surfaces. We add literature data as well. We simulated additionally the smaller defects and particles in the size range of 1-2 µm and described the results in the new chapter 3.2.

4. Lines 162-166: What do you mean with "..." between the values?

• “….” means the range. We corrected it.

5. Lines 330-331: Is there good adherence of the particles to the substrate in this case?

• As stated in the revised manuscript we can assume that a good adherence of the particle to the substrate during the impact can be reached because the collision velocity exceeds the calculated critical velocity for these materials. We performed also cold spray experiments and compared the results with FEM simulations. This was described in the new section 3.3 of the revision. The experiments showed that the particles are deposited on the surfaces and have a strong bonding to the surface.

Reviewer 2 Report

Review of manuscript

Simulation of particle interaction with surface microdefects during cold gas-dynamic spraying

The paper topic is known and well described in the literature. It looks actual.  However, the task statement needs considerable corrections in accordance to comments below. Additionally, the models are discussible, and are far from real. English needs to be edited. So, unfortunately, I cannot recommend the manuscript for publication. The comments are below.

 

1. Line 20-21: The sentence “Compared to the particle impact on a smooth  surface, the simulation showed that the particle impact on a microdefect leads to similar temperatures in the contacts with the cavitiy.”  is not clear and contains error (cavitiy). Authors need to rewrite it
2. Line 22: How can “….the obtained results contribute to the improvement of the CS technology”?
3. Lines 37- 39: “… In this process, dispersed particles in a gas stream are heated up by an energy source (e.g. combustion or electric discharge). Through a nozzle the particles are accelerated and focused towards a solid substrate. The kinetic and thermal energy lead to high velocity  impacts on the solid surface of the substrate.” – English is not proper. How do kinetic and thermal energy leads to high velocity. The kinetic energy is a function of velocity.
4. Line 46: The authors statement “…binding energy is mainly achieved by the high kinetic energy of the particles during the impact.” is not correct because bonding process is the function of thermomechanical conditions which depends on the kinetic energy. Secondly, the parameter “binding energy” is not usually applied.
5. Lines 53-56: The information “….Alkhimov et al. investigated and described the cold spray phenomenon [4] and patented the experimental setup for CS protective coating [5], and in particular, the setup for internal anticorrosion coating of long pipes and the mobile setup for CS coating inside tanks [6]” is old and does not contain the real data of especially mobile unit for CS repair inside the tanks. This is only Russian patents description. There are a lot of new data in literature about repair issues which need to be described here
6. Lines 62-83: Authors only listed the papers [9-10]. The main principles of cold spray particles interaction with the substrate are well known. However, authors do not analyze these principles in detail (particle deformation and adiabatic shear band formation at critical velocity, effects of particle bonding to the substrate, effects of bow shock formation, etc.) from the viewpoint of the impact behavior of particles during impingement with the surface with microdefects. Author only listed their works [11-13] without any assessment from the viewpoint of tasks of this paper.
7. Lines 95-101: The authors’ description of the surface microdefects is far from real. First of all, grinding and grit blasting are performed to eliminate the microcracks and corrosion damage before cold spraying step. Secondly, the size of possible defects to be repaired is below 1-3μ It may be the pores and microcracks at the grain boundaries of the substrate materials. The stress corrosion crack defects mentioned by authors on the base of work [24] of 0.1 - 10 µm need to  be eliminated by grinding.  The possible slip bands marks on the substrate surface  have no size of 10 - 100 µm. The pipeline defects due to structure change (50 µm) after 30year exploitation [25-27] cannot be repaired in general by cold spraying of pipeline internal surface. So, these examples are not real, and definition of defect size in the range of 1-100µm  is not true.
8. Lines 134-141: The contact scenarios presented by authors are far from real (Fig.1) in all cased the defect sizes are similar to particle size 50 µm.  In this case the differences of deformation behavior and areas localization effects are known and described in a lot of papers of Assadi, Kreye, Gartner, Klassen and other authors. Authors did not compare these data with available in the literature.
9. Lines 144-146: Authors chose the erroneous “….impact scenarios: b) four lateral contacts with edges of the microdefect, c) two contacts with closer microdefect edges, and d) one contact with the edge of the defect”. It means the substrate has the surface cavities of size similar to particle size. However, such a surface defects do not occur in real material.
10. Line 205: Authors state “…The plastic deformation (Figure 4) starts at the contact surfaces and contact edges and spread out slightly during the penetration”. However, the real defects have the smaller sizes as compared to models chosen.
11. Lines 310-316: Authors state the defect filling mechanism of repair: “…During the collision the microdefect void volume is filled with the deformed particle that can close the cavity and repair the component surface. It was determined that for almost completely filling of the microdefect the volumes of the particle and the microdefect sizes should be comparable.”  Do you authors familiar with particle super deep penetration mechanism (Kosarev at al)? It might be discussed for real defect cold spray repair.
12. Lines 351-365; Authors did not analyze the effect of interlocking which is well described in the numerous papers.
13. Line 366: Conclusions: There is no validation of numerical simulation results. Conclusions need to be corrected

Author Response

Simulation of particle interaction with surface microdefects during cold gas-dynamic spraying

The paper topic is known and well described in the literature. It looks actual.  However, the task statement needs considerable corrections in accordance to comments below. Additionally, the models are discussible, and are far from real. English needs to be edited. So, unfortunately, I cannot recommend the manuscript for publication. The comments are below.

1. Line 20-21: The sentence “Compared to the particle impact on a smooth surface, the simulation showed that the particle impact on a microdefect leads to similar temperatures in the contacts with the cavity.”  is not clear and contains error (cavity). Authors need to rewrite it

• Thank you for your comment. The definition was wrong. We have modified this sentence and this section.

2. Line 22: How can “….the obtained results contribute to the improvement of the CS technology”?

• We have changed the last sentence in the abstract. We have added further information in the introduction and the conclusion section to make the results clear. The deposition conditions in well-known models consider the temperature and deformation only for the case of the single contact of particle with the surface. In this work, different collision scenarios on not smooth surfaces were studied to describe the deformation and temperature in the multiple contacts of particles with the diameters in the size range of defects. This is important for repair applications of cold spray. It was shown that maximum deformation in contacts with cavity edges is nearly the same and the maximum temperature are slightly higher compared to the impact on a smooth surface. Taking the size range of the defects into account, it is possible to enhance the bonding strength due to mechanical interlocking that takes place..

3. Lines 37- 39: “… In this process, dispersed particles in a gas stream are heated up by an energy source (e.g. combustion or electric discharge). Through a nozzle the particles are accelerated and focused towards a solid substrate. The kinetic and thermal energy lead to high velocity impacts on the solid surface of the substrate.” – English is not proper. How do kinetic and thermal energy leads to high velocity. The kinetic energy is a function of velocity.

• We have rewritten this paragraph. The kinetic energy of gas leads to the particle acceleration in the nozzle.

4. Line 46: The authors statement “…binding energy is mainly achieved by the high kinetic energy of the particles during the impact.” is not correct because bonding process is the function of thermomechanical conditions which depends on the kinetic energy. Secondly, the parameter “binding energy” is not usually applied.

àWe have rewritten this section.

 

5. Lines 53-56: The information “….Alkhimov et al. investigated and described the cold spray phenomenon [4] and patented the experimental setup for CS protective coating [5], and in particular, the setup for internal anticorrosion coating of long pipes and the mobile setup for CS coating inside tanks [6]” is old and does not contain the real data of especially mobile unit for CS repair inside the tanks. This is only Russian patents description. There are a lot of new data in literature about repair issues which need to be described here

àWe have edited this part and extended it with new literature data.

6. Lines 62-83: Authors only listed the papers [9-10]. The main principles of cold spray particles interaction with the substrate are well known. However, authors do not analyze these principles in detail (particle deformation and adiabatic shear band formation at critical velocity, effects of particle bonding to the substrate, effects of bow shock formation, etc.) from the viewpoint of the impact behavior of particles during impingement with the surface with microdefects. Author only listed their works [11-13] without any assessment from the viewpoint of tasks of this paper.

• We have added further sections where we mention the mechanisms (Line 67-75). The focus of this work was not to analyse the mechanisms of bonding to the substrate at critical velocity. The influence of the cavity geometry on the deformation, stresses and temperatures depending on the contact geometry comparing to the well-known case of the collision on the flat surfaces are our main interest.

7. Lines 95-101: The authors’ description of the surface microdefects is far from real. First of all, grinding and grit blasting are performed to eliminate the microcracks and corrosion damage before cold spraying step. Secondly, the size of possible defects to be repaired is below 1-3 μm It may be the pores and microcracks at the grain boundaries of the substrate materials. The stress corrosion crack defects mentioned by authors on the base of work [24] of 0.1 - 10 µm need to be eliminated by grinding.  The possible slip bands marks on the substrate surface have no size of 10 - 100 µm. The pipeline defects due to structure change (50 µm) after 30 years exploitation [25-27] cannot be repaired in general by cold spraying of pipeline internal surface. So, these examples are not real, and definition of defect size in the range of 1-100 µm is not true.

• The sizes of defects and damages of components and apparatus can be in a wide range. However, the idea was to study theoretically the case of the collision of a particle in the same size range as the cavity in the surface. According to your remark about the smaller defects, we performed the new simulations of cavities with a height of 1.7 µm. We reduced the particle size up to 2.1 µm and kept the ratio to the defect size constant. We compared the obtained results with experiments with the particles of the same size. These new results are described in new sections 3.2 and 3.3.

8. Lines 134-141: The contact scenarios presented by authors are far from real (Fig.1) in all cased the defect sizes are similar to particle size 50 µm.  In this case the differences of deformation behavior and areas localization effects are known and described in a lot of papers of Assadi, Kreye, Gartner, Klassen and other authors. Authors did not compare these data with available in the literature.

• We have added a simulation case with smaller defects and particles. That allows us to compare the scenarios with different defect sizes. The mentioned authors have performed experiments, where it can be seen that for steel particles defect sizes on the coating can be created with a size of 40 µm. We have also added further literature that shows that after grit blasting and cold spraying defect sizes of 1 to 100 µm can occur (Line 19-129).

9. Lines 144-146: Authors chose the erroneous “…impact scenarios: b) four lateral contacts with edges of the microdefect, c) two contacts with closer microdefect edges, and d) one contact with the edge of the defect”. It means the substrate has the surface cavities of size similar to particle size. However, such a surface defects do not occur in real material.

• As mentioned above. We assume an ideal case of a defect. Additionally, we performed further simulations with smaller particles and defects and described it in the sections 3.2 and 3.3.

10. Line 205: Authors state “…The plastic deformation (Figure 4) starts at the contact surfaces and contact edges and spread out slightly during the penetration”. However, the real defects have the smaller sizes as compared to models chosen.

• For this case we have done additional studies for smaller defects and described it in the sections 3.2, 3.3.

11. Lines 310-316: Authors state the defect filling mechanism of repair: “…During the collision the microdefect void volume is filled with the deformed particle that can close the cavity and repair the component surface. It was determined that for almost completely filling of the microdefect the volumes of the particle and the microdefect sizes should be comparable.”  Do you authors familiar with particle super deep penetration mechanism (Kosarev at al)? It might be discussed for real defect cold spray repair.

• Our simulation assumptions are based on cold sprayed experiments performed in our previous works where the impact velocity was under 1000 m/s (see Ref. [21]). Therefore, super-deep penetration would not arise here. The idea is to use particles with sizes in the defect size range to fill and close the cavities.

12. Lines 351-365; Authors did not analyse the effect of interlocking which is well described in the numerous papers.

• We have added further information on the mechanisms. The interlocking is described as well. We have added further literature data that surface roughness can enhance mechanical interlocking (see Ref. [36-38]).

13. Line 366: Conclusions: There is no validation of numerical simulation results. Conclusions need to be corrected

• We added a further part in our results section (section 3.3). We validated the model with fib-cut cross-sections on deposited steel particles. The simulation results showed a good agreement with experiment.

Reviewer 3 Report

 

Simulation of particle interaction with surface microdefects 2 during cold gas-dynamic spraying

The manuscript discusses how the particles used in cold gas-dynamic spraying (CS) interact with the surfaces having microdefects and how effectively aids against corrosion or repair the crack propagation. The abovementioned interaction is simulated with the FEM using the Johnson-Cook failure model. I have gone through the manuscript thoroughly and suggest the following comments to enhance the quality of the same.

• Cold gas-dynamic spray (CS); why do not authors use CGDS as acronym? It is used widely in literature.
• More physical explanation is required to understand the technical know-how of how the obtained results can contribute to the improvement of the CS technology.
• Cold gas dynamic spray technology and the associated deposition conditions have been developed through many years and are widely available in the literature. Authors claim that the obtained results can contribute to the improvement of the cold gas-dynamic spray technology. How is it improved? Please do reveal any innovative findings with regard to various deposition conditions.
• ?, ?, ?, ?, ? are indicated as material parameters. What type of material parameters and what are its significances? Consider including a nomenclature section to elaborate all the parameters discussed in section 2.
• What should be the sizes of particles in the cold gas-dynamic spraying technology for a moderate bonding strength with the substrates having
• Could you elaborate the process behavior associated with the thermal kinetics of the particles within the gas flow?
• What is the deposition efficiency? Whether the present simulation can optimize it?
• Elaborate on the structural changes during the deposit formation.
• Whether the cold gas-dynamic spray technology can be used for combinations other than metal/metal combination? For example, ceramic/metal combination, oxide/polymer, metal/polymer etc.
• Whether the cold gas-dynamic spray technology can be improved by using nanoparticles?
• Specify the boundary and initial conditions in flow domain and particle tracking.
• How did you validate the results?

**********************

Comments for author File: Comments.pdf

Author Response

The manuscript discusses how the particles used in cold gas-dynamic spraying (CS) interact with the surfaces having microdefects and how effectively aids against corrosion or repair the crack propagation. The abovementioned interaction is simulated with the FEM using the Johnson-Cook failure model. I have gone through the manuscript thoroughly and suggest the following comments to enhance the quality of the same.

1. Cold gas-dynamic spray (CS); why do not authors use CGDS as acronym? It is used widely in literature.

• We changed CS to CGDS.

2. More physical explanation is required to understand the technical know-how of how the obtained results can contribute to the improvement of the CS technology.

• We have extended the introduction part with the important mechanisms for cold spraying (Line 69-78). The abstract/conclusion was extended as well. The results improve the understanding of the collision and deformation behaviour of particles on the damaged surface that is important for the repair applications of the CGDS technology

3. Cold gas dynamic spray technology and the associated deposition conditions have been developed through many years and are widely available in the literature. Authors claim that the obtained results can contribute to the improvement of the cold gas-dynamic spray technology. How is it improved? Please do reveal any innovative findings with regard to various deposition conditions.

• We have added further information in introduction and the conclusion to make the results clear. The deposition conditions in well-known models consider the temperature and deformation only for the case of the single contact of particle with the surface. In this work, different collision scenarios on not smooth surfaces were studied to describe the deformation and temperature in the multiple contacts of particles with the diameters in the size range of defects. This is important for repair applications of cold spray. It was shown that maximum deformation in the contact of a microdefect is nearly the same and the maximum temperature are higher compared to the impact on a smooth surface. Taking the size range of the defects into account (see section 3.1 and 3.2) it is possible to enhance the bonding strength due to mechanical interlocking that takes place next to an adiabatic shear instability.

4. ?, ?, ?, ?, ? are indicated as material parameters. What type of material parameters and what are its significances? Consider including a nomenclature section to elaborate all the parameters discussed in section 2. The parameters can be estimated by nanoindentation or split-Hopkins pressure bar to find optimal parameter sets [44].

• We have added the type of the material parameters. A nomenclature section is not included but every quantity is mentioned when a new equation is described.

5. What should be the sizes of particles in the cold gas-dynamic spraying technology for a moderate bonding strength with the substrates having

• We added this in the introduction. From the semi-empirical equations the bonding can be estimated by the critical velocity. It depends on the material properties and impact temperature and velocity. From our previous work [21], we showed that fine steel particles particles can attach successful on the surface.

6. Could you elaborate the process behaviour associated with the thermal kinetics of the particles within the gas flow?

• In our previous works [19, 21] we did CFD simulations of the nozzle jet and particle movement and calculated the temperatures of particles and surface for collision. We described it shortly in the method section of the manuscript.

7. What is the deposition efficiency? Whether the present simulation can optimize it?

• We added the definition of deposition efficiency in our manuscript (Line 56-60).
• The main conclusion is that under the same process conditions the bonding strength could be enhanced due to the improved mechanical interlocking by a microdefect. However, the performed FEM simulations do not describe the bonding of the particle. For this, the cohesion models have to be implemented in the future works.

8. Elaborate on the structural changes during the deposit formation.

• The structural changes in the particle and substrate shape are shown on the timelines, and in the isometry cross-section at the moment the particle stop.

9. Whether the cold gas-dynamic spray technology can be used for combinations other than metal/metal combination? For example, ceramic/metal combination, oxide/polymer, metal/polymer etc.

• Yes it can be used for different material combinations [7]. In a previous work, we studied TiO2 particles cold sprayed on Ti surfaces [20] (Lines 47-48).

10. Whether the cold gas-dynamic spray technology can be improved by using nanoparticles?

• There are available literature data for nanoparticles that can be used for CGDS but in our case it is not relevant.

11. Specify the boundary and initial conditions in flow domain and particle tracking.

• In our FEM model a flow domain is not present. We have added a further part in the method section where we describe how to get the initial velocity for the impact.

12. How did you validate the results?

• We added a new section 3.3 in the chapter with results. In this, we validated the FEM model with fib-cut cross-sections on deposited steel particles deposited on the steel surface in cold spray experiments. The simulation showed a good agreement with experiment.

Round 2

Reviewer 2 Report

Review 2

of manuscript 1691654

 

A main manuscript drawbacks are absence of real validation results, some English and technical errors which are discussed in the some comments.  From my viewpoint, the significant errors of numerical simulation parameters choice and mistake of experimental validation of numerical results (experimental validation was made with AISI 316 steel) do not allow to recommend this paper for publication. Unfortunately,  the authors additions do not solve above problems. Moreover, these additions only enhance some misunderstandings and uncertainties. For this reason, there is no sense to analyse the authors additions in Discussion and Conclusion chapters. So, I cannot recommend the manuscript for publication.

 

Some comments are below:

i)                 Lines 17-18:  The sentence “…The impact phenomena of the particles with different microdefect geometries implemented in the FEM model were obtained and compared with the collision on the smooth surface” is not clear. How to understand it?

ii)                Line 19:  The statement ”….The size of the particles and defects were varied keeping the mass specific impact energy constant” is completely unclear. Bonding processes being recognized during cold spraying are of complex nature, and they do not depend on particle size only.

iii)              Lines 21-22:  There is a mistake in the sentence (underlined) “… The deformed particle shape obtained in the simulation showed good agreement with the focused ion beam measurements of particles deposited in cold spray experiments”. Focused ion beam technology is applied for processing foil for HRTEM examination. The particle size  measurements usually are being made during HRTEM examination.

iv)              Lines 56- 57: English mistake: ”…The depositon efficiency”.

v)                Lines 110-111: The authors statement “… that for smaller particle sizes (1 µm) the kinetic energy is not high enough to provide successful bonding” is not completely correct. The high pressure cold spray technology usually is applied for particle size of 12-13micron to achieve the high deposition efficiency and bonding. So, simulation of smaller particle behavior during impact seems to be not reasonable.

vi)              Lines 118-128: Description at lines 118-128 is completely unclear. Authors try to talk about surface defects types (not clearly defined), defects size (?) grit blasting topography and about “…the surface roughness of the  substrate which can enhance the mechanical interlocking of deposited particles”.  What is the purpose of this description?

vii)             Line 130: The choice of AISI 1045 steel is not reasonable because it is well known that cold gas dynamic spray technology is effective for stainless steels (not for carbon steels). The deposition efficiency of AISI1045 is low, and mechanisms of interface AISI 1045 structure formation differ considerably from those of stainless steels.

viii)           Lines 137-235: The numerical simulation parameters are chosen for AISI 1045 steel. It is not correct because the numerical results validation is made by comparison with results of work [23] which performed with austenitic stainless steel AISI 316.  Authors state that “… The particle properties at the moment of impact have a significant influence on the resulting coating” (line 99). The J-C constants for these steels differ considerably.  For example, the material parameters A, B and n determined from the experimentally obtained true stress versus true strain curves of AISI 304 are 554 MPa, 995 MPa and 0.64 respectively. The C-parameter at strain rates, 350s^-1, 750s^-1, 1050s^-1, 1300s^-1 and 1500s^-1are 0.035, 0.041, 0.046, 0.0484 and 0.0463 respectively.

ix)              Line 234: The choice of AISI 1045 simulation parameters (Table 1. Material data of AISI 1045 steel) is not real. The parameters at reference strain rate, ?_?=0.001s^-1 are not correct and are so far from those at the impact velocity of about ?_?=1500s^-1 (!).

x)                Lines 427-440: Comparison of the simulation with experiments is made based only for flattening ratio of the particles. First of all, it cannot be made based only on one image. Authors do not know the location of particle cross section made by FIB. Secondly, there is no seen any signs of adiabatic shear band formation at low magnification. However, it is well known the adiabatic shear band formation is on of the main bonding mechanisms responsible for bonding process. The similar pictures in the paper [23, Fig. 6] do not refer about some details of the interface structure formation. From the third side, the [23] experiments made with austenitic steel AISI 316 which has another J-C constants as compared to data of Table1.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf