Preparation of CrCoFeNiMn High-Entropy Alloy Coatings Using Gas Atomization and Laser Cladding: An Investigation of Microstructure, Mechanical Properties, and Wear Resistance

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

An interesting study. The results and methods are clear. However minor changes can be made to improve the paper. My comments are as below:

1- For Figure 3, please explain in more detail in the text about the changes between columnar and equiaxed grains. For example, why columnar? why equiaxed? any difference in location? 

2- Figure 7 is hard to understand even after reading the text explanation. Please check if some adjustments can be made to the figure to make it clearer. 

3- Subtopic 4 Discussion is Conclusion? Please change it to Conclusion. 

Author Response

Response to the Reviewer 1：

Thank you so much for reviewing the paper and giving some constructive and solid comments. Your thoughtful comments are very comprehensive and clear. They helped improve the manuscript by more clearly defining the observations and analysis the results. Based on the comments and advice, we have significantly revised the manuscript. The following is a point to point response to your comments.

Response:

（1） For Figure 3, please explain in more detail in the text about the changes between columnar and equiaxed grains. For example, why columnar? why equiaxed? any difference in location?

Thank you very much for your comments. Our explanation of equiaxed and columnar grains is not sufficiently clear, which is an oversight in our writing. According to literature, the grain structure within the coating is related to the ratio of the temperature gradient (G) to the solidification rate (R). In the lower part of the coating, the G/R ratio is higher, resulting in a microstructure primarily composed of columnar grains that grow in the direction of heat transfer. In the upper region of the coating, due to direct contact with air, the solidification rate (R) is higher, leading to the formation of numerous nuclei, which causes the columnar grain structure to transition to an equiaxed grain structure. The modified manuscript is as following:

 

Line 175-182

Detao Liu and his team have demonstrated that the transformation of the microstructure in the coating region is closely related to changes in the internal temperature gradient (G) and solidification rate (R) [30]. In the lower part of the coating, the G/R ratio is higher, resulting in a microstructure primarily composed of columnar grains that grow in the direc-tion of heat transfer. In the upper region of the coating, due to direct contact with air, the solidification rate (R) is higher, leading to the formation of numerous nuclei, which causes the columnar grain structure to transition to an equiaxed grain structure.

Line 516-517

30. Liu, D.; Kong, D. Effects of WC–10Co4Cr and TiC Additions on Microstructure and Tribological Properties of Laser Cladded FeMnCoCr HEA Coatings. Ceramics International 2024, 50, 12108–12120, doi:10.1016/j.ceramint.2024.01.115

 

（2）Figure 7 is hard to understand even after reading the text explanation. Please check if some adjustments can be made to the figure to make it clearer.

Thank you for your valuable suggestions. Our explanation of the mechanism in Figure 7 is not very clear. We have revised the annotations on the image and the textual explanations in the manuscript. The modified manuscript is as following:

Line 237-246

The transformation mechanism of the grain structure within the substrate and coating is illustrated in Fig. 7. Figures 7(a) and 7(b) depict the microstructure of the substrate region, characterized by predominant large-angle grain boundaries. Following laser intensification, the number of small-angle grain boundaries in the substrate region increases, gradually transforming the grains into a columnar crystal structure in the coating, facilitated by the subgrain boundary structure shown in Fig. 7(b1). As the cooling rate increases along with the number of small-angle grain boundaries, subgrain boundary structures emerge at the grain boundaries of the columnar crystals, as depicted in Fig. 7(c1). Simultaneously, grain refinement continues in the coating, eventually transforming into the equiaxed crystal structure shown in Fig. 7(d).

Line 275-278

Fig 7. Explanation of the microstructure transformation mechanism in the Laser cladding process (a) Substrate region, (b) Substrate region, (b1) Subgrain structure, (c) Columnar grain structure, (c1) Subgrain structure, (d) Equiaxed grain structure

（3）Subtopic 4 Discussion is Conclusion? Please change it to Conclusion.

We appreciate the reviewer’s careful review. This was an oversight in our manuscript writing. The modified manuscript is as following:

Line 393

 

4. Conclusion

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1.       The main idea of the study is unclear. Why form CrCoFeNiMn coating on 316 L steel? In what areas can such coatings be used?

2.       Why was 316 L steel chosen as the substrate? It is unclear how the substrate was prepared before coating? What was the surface roughness of the substrate?

3.       It is unclear when the CrCoFeNiMn powder was sprayed onto the substrate. During the powder making process? During the research, was laser processing of the powder already sprayed onto the substrate carried out, or was the powder sprayed directly during the laser cladding process? From what distance was the powder sprayed? What was the thickness of the CrCoFeNiMn powder layer before laser processing?

4.       How were the laser cladding/processing parameters selected? During the coating formation process, only one mode was used. How was it determined that these were the optimal laser processing parameters?

5.       It is unclear what indenter amplitude (or total way) was used in tribological testing? How were the samples prepared before tribological testing? What was the surface roughness of the samples before tribological studies?

6.       Please explain why particles with a size of 30-50 µm are visible in figure 2.a, but not in graph 2.b?

7.       There are grammatical errors in the text: 6 figure – misporientation→misorientation; lines 233 and 235 - m→µm; 7 figure lacks a legend; 13 figure b1 - mm→µm.

8.       Please explain why the results presented in Figure 6 c do not correspond to the microstructure images in Figure 5 a, b, c? The largest grain size of the substrate was about 22 µm (Figure 6), but from the microstructure images in Figure 5 it can be seen that the largest grain size was larger. Also, in the text it is written that the average grain size after laser cladding/processing decreased from 8.7 to 6.8 µm, but from the microstructure images in Figure 5 it is clear that the decrease in grain size was greater.

9.       In the article, it is difficult to understand what is included in the thermally affected zone (Figure 9)? Substrate? Coating?

10.   Please specify at what load the microhardness was measured? 1 gram (105 line) or 25 grams (107 line)? In Figure 9 it is necessary to indicate the load (HV0.025?).

11.   Please specify at what load the scratch test was carried out? Under constant load? This is not like a standard scratch test. Was the scratch test carried out from the coating to the substrate or vice versa? How were the samples prepared? There is no measurement scale in Figure 10a.

12.   The term composite processing (line 275) is incorrect.

13.   It is unclear how the average friction coefficient was calculated. What is the way of tribological tests (test time of 30 min does not give a complete picture)? Which section of the tribological test way was evaluated to calculate the average coefficient of friction?

14.   Please clarify why, when analyzing the wear of the coating (Figure 13 b and b1), the contour of the end of track was analyzed (not the central part of track)?

15.   In the text of the article, when analyzing the wear of the samples, the wear track depth for the substrate was about 167 µm (line 318) and for the coating about 66 µm (line 319), but when analyzing the profiles in Figure 13 a1 and b1, the track depth was about 75 µm and 27 µm, respectively .

16.   I believe that the statement “CrCoFeNiMn HEA coatings have high hardness” (line 321) is incorrect. The studied coatings after laser cladding had an average hardness of about 330 HV. This is not much.

17.   1 conclusion is incorrect. During the work, no studies were carried out on adhesion and the number of defects (cracks) of the coating, and porosity was assessed only qualitatively, but not quantitatively.

18.   Conclusions represent the formulation of the results obtained. More general conclusions or generalizations are needed to explain why these results were obtained.

Author Response

Response to the Reviewer 2：

Thank you so much for reviewing the paper and giving some constructive and solid comments. Your thoughtful comments are very comprehensive and clear. They helped improve the manuscript by more clearly defining the observations and analysis the results. Based on the comments and advice, we have significantly revised the manuscript. The following is a point-to-point response to your comments.

Response:

（1）The main idea of the study is unclear. Why form CrCoFeNiMn coating on 316 L steel? In what areas can such coatings be used?

Thank you for your valuable suggestions. This was an oversight in our manuscript writing. We have now supplemented the Introduction section of the manuscript to explain the practical significance of preparing CrCoFeNiMn HEA coatings on the surface of 316L stainless steel and have cited relevant references. The modified manuscript is as following:

Line 36-47

 

CrCoFeNiMn HEA has a typical face centered cubic (FCC) structure. CrCoFeNiMn HEA coatings have excellent plastic deformation properties and can be adapted to various surface shapes, while their stable solid solution structure gives them good abrasion resistance, making them valuable for use in aerospace, nuclear energy, and automotive fields [7–9]. Because of its low cost and ease of machining and molding, 316L stainless steel material is commonly used to manufacture important structural components in hydraulic and automotive transmission systems [10]. In the actual working environment, impurity particles such as dust and grit can contaminate transmission components, causing scratches, wear, and other forms of failure [11]. Combining the CrCoFeNiMn HEA coating, known for its good mechanical properties and process adaptability, with the low cost 316L stainless steel material can effectively extend the working life of 316L stainless steel parts and enhance the application potential of CrCoFeNiMn HEA.

 

Line 459-464

10. Ling, J.; Li, J.; Zhou, J.; Lin, M.; Huang, J.; Gao, P.; Xue, B. Evolution of the Interfacial Microstructure in 316L/AlxCoCrFeNi Composite Material Induced by High-Velocity Impact Welding. Materials Characterization 2024, 211, 113929, doi:10.1016/j.matchar.2024.113929.

 

11. Ren, X.; Sun, W.; Tian, S.; Zhu, C.; Qin, M.; Yang, Y.; Wu, W. Tribological and Electrochemical Behaviors of FeCoNiCrMox HEA Coatings Prepared by Internal Laser Cladding on 316L Steel Tube. Materials Characterization 2024, 211, 113906, doi:10.1016/j.matchar.2024.113906.

 

（2）Why was 316 L steel chosen as the substrate? It is unclear how the substrate was prepared before coating? What was the surface roughness of the substrate?

Thank you for your valuable suggestions. 316L stainless steel offers advantages such as low cost and ease of processing and molding, making it commonly used for manufacturing critical structural components in hydraulic and automotive transmission systems. However, in actual operating conditions, these transmission components are susceptible to contamination by impurity particles like dust, sand, and gravel, leading to scratches, wear, and other types of failures. Therefore, there is a need to enhance the surface of 316L stainless steel. The 316L stainless steel used in this study was sourced from Nanjing TengYao Stainless Steel Co., Ltd., with an initial surface roughness of Ra 0.3 μm. The modified manuscript is as following:

Line 40-47

 

Because of its low cost and ease of machining and molding, 316L stainless steel material is commonly used to manufacture important structural components in hydraulic and automotive transmission systems [10]. In the actual working environment, impurity particles such as dust and grit can contaminate transmission components, causing scratches, wear, and other forms of failure [11]. Combining the CrCoFeNiMn HEA coating, known for its good mechanical properties and process adaptability, with the low cost 316L stainless steel material can effectively extend the working life of 316L stainless steel parts and enhance the application potential of CrCoFeNiMn HEA.

 

Line 93-97

 

The 316L stainless steel sheets prepared via the casting process were provided by Nanjing Tengyao Stainless Steel Co., Ltd., with an initial surface roughness of Ra 0.3 μm. The surface of the 316L stainless steel substrate was cleaned with alcohol to remove oil and other contaminants. Sandpaper was used to remove the oxide layer and impurities from the substrate surface.

（3）It is unclear when the CrCoFeNiMn powder was sprayed onto the substrate. During the powder making process? During the research, was laser processing of the powder already sprayed onto the substrate carried out, or was the powder sprayed directly during the laser cladding process? From what distance was the powder sprayed? What was the thickness of the CrCoFeNiMn powder layer before laser processing?

Thank you for your valuable suggestions. Our description of the experimental method in the manuscript lacks clarity. In this experiment, CrCoFeNiMn HEA powder was initially prepared using gas atomization. Subsequently, the powder was uniformly applied to the surface of 316L stainless steel with a powder layer thickness of 2 mm. The final CrCoFeNiMn HEA coating was achieved through rapid laser scanning. The modified manuscript is as following:

Line 93-99

The 316L stainless steel sheets prepared via the casting process were provided by Nanjing Tengyao Stainless Steel Co., Ltd., with an initial surface roughness of Ra 0.3 μm. The surface of the 316L stainless steel substrate was cleaned with alcohol to remove oil and other contaminants. Sandpaper was used to remove the oxide layer and impurities from the substrate surface. Subsequently, a 2 mm layer of CrCoFeNiMn HEA powder prepared by gas atomization was uniformly spread onto the surface of the 316L stainless steel substrate.

（4）How were the laser cladding/processing parameters selected? During the coating formation process, only one mode was used. How was it determined that these were the optimal laser processing parameters?

The laser parameters used in this study were determined empirically based on previous orthogonal experiments performed in our laboratory. Relevant notes have been added to the Experimental Methods section. The modified manuscript is as following:

Line 101-103

 

Table 2 displays the laser parameters determined based on the experience gained from orthogonal experiments and preliminary experimental results.

Table 2 . Laser Processing Parameters

Process	Parameters	Values
	Spot size/mm	3
Laser Cladding	Scannig speed/(mm/s)	6
	Power/W	1300

（5）It is unclear what indenter amplitude (or total way) was used in tribological testing? How were the samples prepared before tribological testing? What was the surface roughness of the samples before tribological studies?

Thank you very much for your comments. Our description of the sample preparation for the wear test and the specific experimental parameters was not sufficiently clear. We have supplemented the corresponding content in the manuscript. The modified manuscript is as following:

Line 129-132

 

The coating and substrate specimens were cut into samples (20×10×4 mm) using wire cutting. The wear test sample surfaces were polished to an Ra of 0.1 μm using a polishing machine (METKON). Reciprocating wear tests were conducted at room temperature using a wear tester (RTEC-MFT5000) under a load of 10N, with a wear stroke of 10 mm.

（6）Please explain why particles with a size of 30-50 µm are visible in figure 2.a, but not in graph 2.b?

We appreciate the reviewer’s meaningful suggestions. This was an error in our image processing where we incorrectly labeled the scale in Figure 2(a). Thank you for bringing this to our attention. We have now corrected the labeling to ensure consistency between Figure 2(a) and Figure 2(b). The modified manuscript is as following:

Fig 2. (a) displays the SEM image of atomized CrCoFeNiMn HEA powder. (b) represents the particle size distribution of atomized CrCoFeNiMn HEA powder. (c) shows the TEM image of the powder interior, while (d) presents the elemental composition analysis of the powder in the region.

（7）There are grammatical errors in the text: 6 figure – misporientation→misorientation; lines 233 and 235 - m→µm; 7 figure lacks a legend; 13 figure b1 - mm→µm.

Thank you for your valuable suggestions. Due to editorial errors, there were issues with image labeling and spelling mistakes. After careful review, we have corrected these errors. The modified manuscript is as following:

Line 283-285

 

The microhardness test results are shown in Figure 9. In the substrate region (0-600 µm), the microhardness ranges from 174.76 to 231.89 Hv_0.1, with an average microhardness of 195.56 Hv_0.1.

 

Line 290-291

 

In the coating region (900-1500 µm), the microhardness ranges from 278.54 to  365.08 Hv_0.1, with an average recorded microhardness of 324.74 Hv_0.1.

 

Line 272-274

Fig 6. particle size and Orientation angle distribution: (a)(c) for substrate organization and (b)(d) for coating area

Line 275-278

Fig 7. Explanation of the microstructure transformation mechanism in the Laser cladding process (a) Substrate region, (b) Substrate region, (b1) Subgrain structure, (c) Columnar grain structure, (c1) Subgrain structure, (d) Equiaxed grain structure

 

Line 389-392

 

Fig. 13 3D morphology of wear areas. (a) localized area wear morphology of substrate, (a1) substrate wear depth and contour curve, (b) localized area wear morphology of coating, and (b1) coating wear depth and contour curve.

（8）Please explain why the results presented in Figure 6 c do not correspond to the microstructure images in Figure 5 a, b, c? The largest grain size of the substrate was about 22 µm (Figure 6), but from the microstructure images in Figure 5 it can be seen that the largest grain size was larger. Also, in the text it is written that the average grain size after laser cladding/processing decreased from 8.7 to 6.8 µm, but from the microstructure images in Figure 5 it is clear that the decrease in grain size was greater.

Thank you for your valuable suggestions. Due to our error, there were mistakes in the data when calculating and analyzing the grain size as well as in the EBSD scale labeling. We have reevaluated the grain size distribution in both the coating and substrate regions and corrected the statistical graph and EBSD images accordingly. The modified manuscript is as following:

 

Line 268-271

Fig 5. EBSD plots of the substrate and coating regions of CrCoFeNiMn HEA (a) (b) Microstructure of the substrate region(c) Heat affected zone organization (d) HEA coating region organization

 

Line 272-274

 

Fig 6. particle size and Orientation angle distribution: (a)(c) for substrate organization and (b)(d) for coating area

 

（9）In the article, it is difficult to understand what is included in the thermally affected zone (Figure 9)? Substrate? Coating?

Thank you for your valuable suggestions. This was an error in our labeling and description. In the analysis of the microhardness experiment results, we incorrectly included the HAZ (heat affected zone) within the coating region and failed to analyze the microhardness variations in the HAZ. The HAZ is a transition area between the coating and the substrate. Although this region does not completely melt when the substrate is heated, its microstructure changes, as shown in the SEM results in Figure 3. Consequently, the microhardness of the HAZ is higher compared to the substrate. The modified manuscript is as following:

 

Line 282-292

 

The microhardness test results are shown in Fig. 9. In the substrate region (0-600 µm), the microhardness ranges from 174.76 to 231.89 Hv_0.1, with an average microhardness of 195.56 Hv_0.1. In the HAZ region (600-900 µm), the microhardness ranges from 207.43 to 289.11 Hv_0.1, with an average microhardness of 241.35 Hv_0.1. The HAZ is a transition area between the coating and the substrate. Although this region does not completely melt when the substrate is heated, its microstructure changes, as shown in the SEM results in Fig. 3. Consequently, the microhardness of the HAZ is higher compared to the substrate. In the coating region (900-1500 µm), the microhardness ranges from 278.54 to 365.08 Hv_0.1, with an average recorded microhardness of 324.74 Hv_0.1. This can be attributed to the grain refinement shown in Fig. 6.

（10）Please specify at what load the microhardness was measured? 1 gram (105 line) or 25 grams (107 line)? In Figure 9 it is necessary to indicate the load (HV_0.025?).

Thank you very much for your comments. Our specific experimental parameters for the microhardness test were not clearly described, and the units for microhardness were not correctly labeled. The modified manuscript is as following:

 

Line 118-121

 

For microhardness testing, a digital micro Vickers hardness tester (HV-1000Z) was used. A 136° diamond indenter was selected, and measurements were taken at 100 μm intervals from the substrate to the center of the coating area. The load applied was 100 grams, with a dwell time of 10 seconds.

 

Line 311-312

 

Fig 9. Microhardness of substrate and coating

 

（11）Please specify at what load the scratch test was carried out? Under constant load? This is not like a standard scratch test. Was the scratch test carried out from the coating to the substrate or vice versa? How were the samples prepared? There is no measurement scale in Figure 10a.

Thank you very much for your comments. Our description of the experimental procedure and parameters of the micro-scratch test were not clear enough. The scratch test was conducted from the substrate towards the coating area under a linear normal load ranging from 0 to 300 mN. The experimental samples were prepared by wire cutting. Additionally, we have updated the scale in Fig.10(a). The modified manuscript is as following:

 

Line 122-126

 

Scratch testing was performed using a micro scratch tester (HM500), where coating specimens were prepared with cross sectional dimensions (20 x 10 x 4 mm) using wire cutting. Scratches were initiated from the substrate into the coating under a linear normal load ranging from 0 to 300 mN, with each scratch extending a length of 800 μm.

 

Line 313-316

Fig.10 (a) Scratch surface photomicrograph, (b) Three-dimensional morphology of micrometer scale scratches, (c) SEM image of micrometer scratches, (d) Enlarged view of scratches in the substrate

（12）The term composite processing (line 275) is incorrect.

Thank you for your valuable suggestions. In the article, we incorrectly used the term "composite processing," and we have now made the necessary correction. The modified manuscript is as following:

 

Line 332-334

 

The friction coefficient of the coating decreased by approximately 9.71%, indicating a sig-nificant improvement in wear resistance compared to the substrate.

（13）It is unclear how the average friction coefficient was calculated. What is the way of tribological tests (test time of 30 min does not give a complete picture)? Which section of the tribological test way was evaluated to calculate the average coefficient of friction?

Thank you for your valuable suggestions. We overlooked describing the specific measurement method and calculation formula for the friction coefficients in both the coating and substrate areas. The modified manuscript is as following:

 

Line 318-321

 

The friction test machine measures the frictional force and normal pressure in the coating and substrate regions during the wear process using pressure and displacement sensors. Instantaneous friction coefficients µ_i at each time point are calculated using Equation (3-3), as shown in Fig. 11.

Line 330-331

 

The average friction coefficients µ for the substrate and coating regions were calculated using Equation (3-4).

 

Line 335-338

 

                                                                                                                            （3-3）

Where F_fi is the friction force at the i-th measurement point, and Fn is the normal pressure.

                                                                                                                       （3-4）

Where n is the number of measurement points in the steady state stage.

（14）Please clarify why, when analyzing the wear of the coating (Figure 13 b and b1), the contour of the end of track was analyzed (not the central part of track)?

Thank you for your valuable suggestions. In analyzing the wear profiles of Fig. 13(b) and (b1), we mistakenly selected an image of the end of the coating wear track for depth testing. We have since remeasured the central region of the coating wear track and replaced the incorrect image. The modified manuscript is as following:

 

Line 389-392

Fig. 13 3D morphology of wear areas. (a) localized area wear morphology of substrate, (a1) substrate wear depth and contour curve, (b) localized area wear morphology of coating, and (b1) coating wear depth and contour curve.

（15）In the text of the article, when analyzing the wear of the samples, the wear track depth for the substrate was about 167 µm (line 318) and for the coating about 66 µm (line 319), but when analyzing the profiles in Figure 13 a1 and b1, the track depth was about 75 µm and 27 µm, respectively .

Thank you very much for your comments. Due to calculation and statistical errors, we inaccurately plotted the depth profiles of the substrate and coating regions. After remeasuring and replotting, we have revised the content and figures in the manuscript. The modified manuscript is as following:

 

Line 337-380

 

The data in the figure show that the maximum wear depth in the substrate region is 151.69 μm and the coating region is 52.19 μm. The coating wear depth is reduced by 65.59% as compared to the substrate.

 

Line 389-392

 

Fig. 13 3D morphology of wear areas. (a) localized area wear morphology of substrate, (a1) substrate wear depth and contour curve, (b) localized area wear morphology of coating, and (b1) coating wear depth and contour curve.

（16）I believe that the statement “CrCoFeNiMn HEA coatings have high hardness” (line 321) is incorrect. The studied coatings after laser cladding had an average hardness of about 330 HV. This is not much.

Thank you for your valuable suggestions. We made an error in stating in the manuscript that the laser cladding prepared coating has high hardness. The correct statement should indicate that the CrCoFeNiMn HEA coating prepared by laser cladding exhibits significantly increased hardness compared to the substrate. We have already made the necessary modifications to the relevant content. The modified manuscript is as following:

 

Line 379-383

 

The wear depth of the coating decreased by 65.59% compared to the substrate, and the microhardness in the coating area increased by 66.06% relative to the substrate. In summary, the CrCoFeNiMn HEA coating prepared using laser cladding technology exhibits significantly improved hardness and wear resistance compared to the 316L stainless steel substrate.

（17）1 conclusion is incorrect. During the work, no studies were carried out on adhesion and the number of defects (cracks) of the coating, and porosity was assessed only qualitatively, but not quantitatively.

Thank you for your valuable suggestions. This is a correction of our misstatement regarding the SEM experiment results. Upon SEM observation, the coating area initially showed coarse and uneven grain arrangement. However, the coating prepared by laser cladding exhibits a significantly optimized microstructure, with dense and uniform columnar and equiaxed crystals. The modified manuscript is as following:

 

Line 401-403

 

(1)  The CrCoFeNiMn HEA coating prepared by laser cladding shows significant microstructural optimization compared to the 316L stainless steel substrate. The coarse and uneven grain structure of the substrate is transformed into a dense and uniform columnar equiaxed structure.

（18）Conclusions represent the formulation of the results obtained. More general conclusions or generalizations are needed to explain why these results were obtained.

Thank you for your valuable suggestions. This issue pertains to an error in our experimental conclusion summary. We stated the research results without providing an explanation for the enhancement. The modified manuscript is as following:

 

Line 405-419

 

(2)  Under the influence of the subgrain boundary structure, the internal grain structure of the coating is refined by 74.15% when compared to the substrate. Simultaneously, a synergistic strengthening phenomenon involving twinning and dislocations was observed in the coating area. This indicates that the strengthening mechanisms of laser cladding technology include grain refinement and the synergistic effects of twinning and dislocations.

(3)  Due to the observed grain refinement in EBSD and TEM experiments, along with the synergistic strengthening effects of twinning and dislocations, the microhardness of the coating has increased by approximately 66.06% when compared to the substrate. Additionally, during microscratch tests, there were fewer cases of surface delamination and cracking in the coating.

(4)  The coating region exhibits a combination of abrasive and adhesive wear characteristics. Furthermore, the mechanical alloying structure enhances the wear resistance of the coating area. When compared to the substrate, the maximum wear depth in the coating region has decreased by 65.59%.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper has presented "Preparation of CrCoFeNiMn high-entropy alloy coatings using gas atomization and laser cladding: an investigation of microstructure, mechanical properties, and wear resistance." However, there are some issues that need to be addressed before the manuscript can be accepted by the journal:

1)      There are several grammatical errors throughout the text, including punctuation issues, sentence fragments, and awkward phrasing. It is essential to ensure that the text is grammatically correct to maintain clarity and professionalism.

2)      The FeMnCoCrNi high entropy alloy has a good property in bulk condition, but the corrosion and wear resistance of this alloy is not comparable with other common coating alloys, the authors should explain why choosed this alloy for coating on steel?

3)      Please explain how the samples were prepared for EBSD analysis.

4)      Since the surface chemical condition of powders effect on flowability, viscosity of melt and final microstructure evolution, please report the oxygen content of powders.

5)      In 3.1 section the authors stated that “It is evident that the prepared powder exhibits a uniform spherical structure with a smooth surface, with some fine particles adhering to the powder surface” but it seems that there are too many satellite particles on the surface of powders which can affect the final microstructure.

6)      Figure 2 (c) doesn’t provide useful information it was better to prepared the FIB TEM sample from one powder and present the distribution of element.

7)      Please calculate the lattice parameter of alloy in powder and as coated state and discuss about peak shift and lattice distortion. Below are some references to help this:

 

-           Effects of carbon and molybdenum on the nanostructural evolution and strength/ductility trade-off in Fe40Mn40Co10Cr10 high-entropy alloys, Journal of Alloys and Compounds Volume 911, 5 August 2022, 165108.

-          Significant strength enhancement of high-entropy alloy via phase engineering and lattice distortion, Journal of Alloys and Compounds Volume 976, 5 March 2024, 172963.

 

 

Comments on the Quality of English Language

 

Author Response

Response to the Reviewer 3：

Thank you so much for reviewing the paper and giving some constructive and solid comments. Your thoughtful comments are very comprehensive and clear. They helped improve the manuscript by more clearly defining the observations and analysis the results. Based on the comments and advice, we have significantly revised the manuscript. The following is a point-to-point response to your comments.

Response:

（1）There are several grammatical errors throughout the text, including punctuation issues, sentence fragments, and awkward phrasing. It is essential to ensure that the text is grammatically correct to maintain clarity and professionalism.

Thank you for your valuable suggestions. We apologize for any grammatical issues in the manuscript. We have enlisted the assistance of a native English speaker to meticulously revise the grammar, punctuation, and other aspects of the manuscript to ensure clarity and professionalism.

（2）The FeMnCoCrNi high entropy alloy has a good property in bulk condition, but the corrosion and wear resistance of this alloy is not comparable with other common coating alloys, the authors should explain why choosed this alloy for coating on steel?

Thank you very much for your comments. CrCoFeNiMn HEA features a homogeneous solid solution structure that minimizes internal stress concentrations during wear, resulting in excellent wear resistance. As a coating material, CrCoFeNiMn HEA coatings exhibit high adaptability to a wide range of surface shapes and processes. Compared to high performance coating materials such as ceramics or precious metals, CrCoFeNiMn HEA's well-balanced performance and relatively low raw material and manufacturing costs make it a more cost-effective solution.

Our studies have demonstrated a 66.06% increase in the hardness of CrCoFeNiMn HEA coatings compared to 316L stainless steel substrates, while reducing the maximum wear depth of the coating by 60.42% compared to the substrate. The stable solid solution structure, excellent mechanical properties, and versatile process adaptability of CrCoFeNiMn HEA coatings effectively extend the service life of 316L components and broaden the application potential of CrCoFeNiMn HEA. These findings have been incorporated into the introductory section of the manuscript.The modified manuscript is as following:

 

Line 36-47

 

CrCoFeNiMn HEA has a typical face centered cubic (FCC) structure. CrCoFeNiMn HEA coatings have excellent plastic deformation properties and can be adapted to various sur-face shapes, while their stable solid solution structure gives them good abrasion resistance, making them valuable for use in aerospace, nuclear energy, and automotive fields [7–9]. Because of its low cost and ease of machining and molding, 316L stainless steel material is commonly used to manufacture important structural components in hydraulic and automotive transmission systems [10]. In the actual working environment, impurity parti-cles such as dust and grit can contaminate transmission components, causing scratches, wear, and other forms of failure [11]. Combining the CrCoFeNiMn HEA coating, known for its good mechanical properties and process adaptability, with the low cost 316L stain-less steel material can effectively extend the working life of 316L stainless steel parts and enhance the application potential of CrCoFeNiMn HEA.

 

Line 459-464

 

10. Ling, J.; Li, J.; Zhou, J.; Lin, M.; Huang, J.; Gao, P.; Xue, B. Evolution of the Interfacial Microstructure in 316L/AlxCoCrFeNi Composite Material Induced by High-Velocity Impact Welding. Materials Characterization 2024, 211, 113929, doi:10.1016/j.matchar.2024.113929.

 

11. Ren, X.; Sun, W.; Tian, S.; Zhu, C.; Qin, M.; Yang, Y.; Wu, W. Tribological and Electrochemical Behaviors of FeCoNiCrMox HEA Coatings Prepared by Internal Laser Cladding on 316L Steel Tube. Materials Characterization 2024, 211, 113906, doi:10.1016/j.matchar.2024.113906.

 

（3）Please explain how the samples were prepared for EBSD analysis.

Thank you for your valuable suggestions. Due to oversight during our writing process, there was insufficient description of the EBSD sample preparation procedure. In this experiment, the HEA coating was initially prepared as cross-sectional samples following standard metallographic procedures. The sample dimensions were 6 x 6 x 3 mm. The sample surfaces were polished to a mirror finish using a grinding and polishing machine (METKON). Changes in the microstructure of the coating were observed using electron backscatter diffraction (EBSD) on an LH-SEM EDX-3500. We have now included these details in the experimental methods section. The modified manuscript is as following:

 

Line 105-112

 

The HEA coatings were prepared as cross sectional samples (6 x 6 x 2 mm) according to standard metallographic procedures. The samples were polished using 600-1500 grit sandpaper, and the metallographic structure was etched using a 6% HNO3 etching solu-tion. The metallographic structure was first observed using an optical microscope (Axio Observer D1). Subsequently, changes in the microstructure of the coating were observed using a scanning electron microscope (SEM Olympus DSX1000), and phase distribution was analyzed using X-ray diffraction (XRD JDX-3530). The cross sectional sample surfac-es were polished to a mirror finish using a grinding and polishing machine (METKON).

（4）Since the surface chemical condition of powders effect on flowability, viscosity of melt and final microstructure evolution, please report the oxygen content of powders.

Thank you for your valuable suggestions. The oxygen content in the powder significantly affects the final microstructure of the coatings. Therefore, in our study, we employed gas atomization experiments using 99.99% pure argon gas to prepare CrCoFeNiMn HEA powder. The atomization equipment is designed with high sealing to prevent oxygen ingress. Additionally, we incorporated a rapid cooling system to minimize the contact time between the powder and oxygen, effectively controlling the oxygen content in the final powder. This ensures the purity of CrCoFeNiMn HEA powder and maintains the quality of the formed coatings. Details regarding oxygen content have been included in the main text and tables of our manuscript. The modified manuscript is as following:

 

Line 82-88

 

Subsequently, argon was used for atomization; the pressure was set at 3.5 MPa, with an argon flow rate of 7 L/min, and the oxygen content of the gas atomization powder was as low as 132 ppm (mg/kg). The atomization equipment is tightly sealed to prevent oxygen ingress. CrCoFeNiMn HEA powder with particle sizes ranging from 8.6 µm to 24.6 µm is produced using a rapid cooling system. The chemical analysis of the HEA powder, as shown in Table 1

 

Line 135-136

 

Table 1 . Chemical composition of gas-atomized CrCoFeNiMn powder (at%)

Element	Co	Cr	Fe	Ni	Mn	O
Nominal composition	20	20	20	20	20	0
Actual composition	19.747	20.243	19.493	20.117	20.385	0.015

 

（5）In 3.1 section the authors stated that “It is evident that the prepared powder exhibits a uniform spherical structure with a smooth surface, with some fine particles adhering to the powder surface” but it seems that there are too many satellite particles on the surface of powders which can affect the final microstructure.

In our manuscript, we lack an explanation for the phenomenon of satellite particles on the surface of HEA powder. Satellite particles appeared on the surface of the powder particles during the rapid cooling process of gas atomization experiments. We believe that the satellite particles melt first during laser cladding and subsequently merge rapidly with the main particles to form a dense coating. Scanning electron microscope images of the coated area showed a uniform distribution of the internal structure, indicating that the presence of a small number of satellite particles did not affect the microstructure of the coating significantly. This phenomenon was also observed in the study by Zheng et al (doi.org/10.1016/j.jmrt.2024.04.231).

 

Line 145-150

 

Satellite particle attachments can be seen on the surfaces of the powder particles as a re-sult of the rapid cooling during the gas atomization process. Zheng et al. also discovered satellite particle attachments on the surfaces of CrCoFeNiAl HEA powder prepared using gas atomization [29]. During the laser cladding process, the fine satellite particles melt first, and then quickly merge with the primary particles to form a dense coating.

Line 513-515

29. Zheng, K.; Tang, J.; Jia, W.; Wang, Y.; Wang, J.; Shi, Y.; Zhang, G. Microstructure and Mechanical Properties of Al0.5CoCrFeNi HEA Prepared via Gas Atomization and Followed by Hot-Pressing Sintering. Journal of Materials Research and Technology 2024, 30, 5323–5333, doi:10.1016/j.jmrt.2024.04.231.

 

（6）Figure 2 (c) doesn’t provide useful information it was better to prepared the FIB TEM sample from one powder and present the distribution of element.

Thank you for your valuable suggestions. Due to an oversight in our writing, we did not provide sufficient analysis and explanation for Figure 2(c). We have now revised the image, added electron diffraction patterns of the phase structure in Figure 2(c), and included the corresponding explanations in the main text. The modified manuscript is as following:

 

Line 153-158

 

Fig. 2(c) shows the TEM analysis of CrCoFeNiMn HEA powder. The electron diffrac-tion patterns in the figure indicate that the CrCoFeNiMn HEA powder prepared by gas atomization retains an FCC phase structure. Fig. 2(d) depicts the elemental analysis of the powder, which shows that no element segregation occurred, demonstrating the phase structure and elemental stability of the CrCoFeNiMn HEA.

 

Line 159-162

Fig 2. (a) displays the SEM image of atomized CrCoFeNiMn HEA powder. (b) represents the particle size distribution of atomized CrCoFeNiMn HEA powder. (c) shows the TEM image of the HEA powder, (d) presents the elemental composition analysis of the powder in the region.

（5）Please calculate the lattice parameter of alloy in powder and as coated state and discuss about peak shift and lattice distortion. Below are some references to help this:

Thank you very much for your comments. We lacked an analysis of lattice parameters and an explanation of diffraction peak shifts in our XRD analysis. Based on the references you provided, we calculated the lattice parameters of CrCoFeNiMn HEA powder and coating states and cited the relevant literature. The modified manuscript is as following:

 

Line 201-206

 

According to Equations (3-1) and (3-2) [33], the lattice parameters of CrCoFeNiMn HEA powder and CrCoFeNiMn HEA coating prepared by gas atomization are 3.602 Å and 3.611 Å, respectively. The study by Mohsen and his team found that an increase in lattice parameter and lattice strain led to a shift in the position of the (111) peak in CrCoFeNiMn HEA to a lower Bragg angle while improving the mechanical properties of the HEA [34].

 

Line 207-212

 

                                                                                                            (3-1)

n is the order of diffraction, λ is the wavelength of the incident X-ray, d is the interplanar spacing, and θ is the angle of incidence.

                                               (3-2)

a is the lattice constant, and h, k, and l represent the Miller indices of the crystallographic planes.

 

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33. Saboktakin Rizi, M.; Minouei, H.; Lee, B.J.; Toroghinejad, M.R.; Hong, S.I. Effects of Carbon and Molybdenum on the Nanostructural Evolution and Strength/Ductility Trade-off in Fe40Mn40Co10Cr10 High-Entropy Alloys. Journal of Alloys and Compounds 2022, 911, 165108, doi:10.1016/j.jallcom.2022.165108.

 

34. Jing, Q.; Hu, L.; Li, J.; Xia, S.; Huang, S.; Liu, L. Significant Strength Enhancement of High-Entropy Alloy via Phase Engineering and Lattice Distortion. Journal of Alloys and Compounds 2024, 976, 172963, doi:10.1016/j.jallcom.2023.172963.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

1) The information provided in lines 88-93 and 93-96 is repeated.

2) The selection of laser processing parameters should be justified in more detail.

3) The grammatical error in Figure 6 "misorentation angle – misorentation angle" has not been corrected.

4) It is unclear how the average friction coefficient was calculated.  Was the entire friction track from 0 s to 1800 s analyzed? Was the initial wear test region (unsteady process eg from 0 s to 40 s) analyzed to calculate the average friction coefficient? Typically, this test region is not considered when calculating the average friction coefficient.

5) Figure 13b remains the same (showing the end of the pavement wear path). The letter stated that he had been replaced.

Author Response

Response to the Reviewer 2：

Dear reviewer, Thank you for the comments and suggestions on the manuscript. We have carefully revised the manuscript and provided the point by point response below.

Response:

(1) The information provided in lines 88-93 and 93-96 is repeated.

Thank you very much for your comments. We made an error during the manuscript revision process by inadvertently repeating content that had already been described. We have since deleted the duplicated sections from the manuscript. The modified manuscript is as following:

 

Line 88-93

 

The 316L stainless steel sheets were prepared via casting process and sourced from Nan-jing Tengyao Stainless Steel Co., Ltd., with an initial surface roughness of Ra 0.3 μm. The surface of the 316L stainless steel substrate was cleaned with alcohol to ensure the removal of any oil and other contaminants. Sandpaper was used to remove the oxide layer and impurities from the substrate surface.

(2) The selection of laser processing parameters should be justified in more detail.

Thank you for your valuable suggestions. The laser parameters selected for this study were determined based on literature review and preliminary experimental results. Additional clarification has been provided on the relevant literature and specific experimental parameters. The modified manuscript is as following:

 

Line 95-101

 

Based on researchers' experimental experience, laser powers ranging from 1200 W to 1500 W, scan speeds from 4 mm/s to 8 mm/s, and an overlap rate of 40% can effectively melt CrCoFeNiMn powder and form a dense coating [29,30]. After multiple experiments and observation of coating quality, we ultimately chose a laser power of 1300 W, a scan speed of 6 mm/s, and an overlap rate of 40%. To prevent oxidation of the molten metal, argon gas was used as the protective atmosphere. The specific experimental parameters are shown in Table 2.

 

Line 135-136

Table 2 . Laser Processing Parameters

Process	Parameters	Values
	Spot size/mm	3
	Scannig speed/(mm/s)	6
Laser Cladding	Power/W	1300
	Argon flow rate(min/L)	5
	Defocus(mm)	5
	Overlap rate(%)	40

 

Line 513-518

 

29. Luo, F.; Wang, S.; Shi, W.; Xiong, Z.; Huang, J. Analysis of the Wear Behavior and Corrosion Resistance of CoCrFeNiMn-2% CNTs Laser Cladding Composite Coating. Journal of Materials Research and Technology 2024, 30, 6910–6923, doi:10.1016/j.jmrt.2024.05.105.
30. Liu, H.; Wang, R.; Hao, J.; Liu, X.; Chen, P.; Yang, H.; Zhang, T. Microstructural Evolution and Wear Characteristics of Laser-Clad CoCrFeNiMn High-Entropy Alloy Coatings Incorporating Tungsten Carbide. Journal of Alloys and Compounds 2024, 976, 173124, doi:10.1016/j.jallcom.2023.173124.

 

(3) The grammatical error in Figure 6 "misorentation angle – misorentation angle" has not been corrected.

 

Thank you for your valuable suggestions. This was an error during our manuscript preparation where we mistakenly uploaded images that hadn't been properly edited, leading to the issue not being addressed in a timely manner. We apologize again for this oversight. The images have now been re-edited to ensure grammatical accuracy. The modified manuscript is as following:

 

Line 269-272

 

Fig 6. (a) Misorientation angle distribution in the substrate region (b) Misorientation angle distribution in the coating region (c) Grain size distribution in the substrate region (d) Grain size distribution in the coating region

 

(4) It is unclear how the average friction coefficient was calculated.  Was the entire friction track from 0 s to 1800 s analyzed? Was the initial wear test region (unsteady process eg from 0 s to 40 s) analyzed to calculate the average friction coefficient? Typically, this test region is not considered when calculating the average friction coefficient.

 

Thank you very much for your comments. In this experiment, the average friction coefficient was calculated using Formula (3-4) , where n represents the number of measurement points during the steady state stage (800-1800 s). The analysis did not cover the entire friction trajectory from 0 to 1800 s. We apologize for omitting the description of the average friction coefficient calculation region in the main text. We have thoroughly reviewed the manuscript and added an explanation of the wear phase The modified manuscript is as following:

 

Line 322-330

 

In Figure 11, the period from 0 to 800s represents the running-in stage of the wear process, where the friction coefficient increases sharply within a short time and then fluctuates. This is due to the initially small friction contact area, causing fractures and fragmentation on the friction surfaces.As the friction time increases, the wear process enters a steady state stage (800-1800s), during which the fluctuation range of the friction coefficient decreases and stabilizes. According to the instantaneous friction coefficient µ_i in the steady state stage shown in Figure 11, the average friction coefficient µ for the coating and substrate regions is calculated using Formula (3-4).

 

Line 336-337

 

                                                   （3-4）

Where n is the number of measurement points in the steady state stage.

 

Line 338-339

 

Fig. 11 Variation in coating and substrate coefficients of friction under 10N loading.

 

(5) Figure 13b remains the same (showing the end of the pavement wear path). The letter stated that he had been replaced.

 

Thank you for your valuable suggestions. We apologize for the mistake in uploading the images, where the corrected versions were not properly uploaded initially. We have now rectified this error by uploading the updated images.The modified manuscript is as following:

 

Line 388-391

Fig. 13 3D morphology of wear areas. (a) localized area wear morphology of substrate, (a1) substrate wear depth and contour curve, (b) localized area wear morphology of coating, (b1) coating wear depth and contour curve.

 

 

Thank you again for your valuable suggestions to improve the quality of our manuscript！

Author Response File: Author Response.pdf