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Microstructural Evolution and Wear Resistance of Silicon-Containing FeNiCrAl_0.7Cu_0.3Si_x High-Entropy Alloys

Coatings 2025, 15(6), 676; https://doi.org/10.3390/coatings15060676

by Junhong Li¹, Xuebing Han¹, Jiaxin Liu¹, Xu Wang¹ and Yanzhou Li^2,*

Reviewer 1: Anonymous

Reviewer 2:

Andrew Naylor

Reviewer 3:

Ehab AlShamaileh

Reviewer 4:

Benamara Majdi

Coatings 2025, 15(6), 676; https://doi.org/10.3390/coatings15060676

Submission received: 30 March 2025 / Revised: 28 May 2025 / Accepted: 30 May 2025 / Published: 3 June 2025

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors, I have gathered my suggestions and concerns for your consideration. This is good research, but your claims need better supporting evidence / better presented evidence before your manuscript can be published.

I would also suggest a thorough proof-read before you submit the revision, as there are multiple instances of typos and repeated sections of text in your manuscript.

Line 13 - “… silicon-free FeNiCrAl0.7Cu0.3Si0.3 …” - if it contains 0.3 % Si, its not Si free.

Line 45 - Please remove full uppercase from the referenced author’s name.

Line 51 - Line 56 - Please check the text, there is a recurring section.

Line 63 - The letter “d” is missing from the word “demonstrated”.

Line 83 - The letter “T” is missing from the word “This”.

Line 86 - Methods - Please include a table with the identifier and composition of your HEA samples. Introducing the samples only in the Results section can lead to confusion.

Line 102-103 - How many points were measured per sample? In a multiphase material, the placement of the indenter can have a serious impact on measured hardness. I would suggest taking multiple (5-8) measurements per sample and presenting both the mean and deviation.

Line 103-104 and 106-108 - You’ve repeated the description of the wear testing method. Please also add the dimensions of both base and counterbody, or at least the corresponding dimension and shape of the contact area.

Line 109 - You have not specified the contact area - neither shape, nor size. In my experience, 100N with a low frequency for 30 minutes generally leads to very low wear under lubricated conditions, where milligram resolution is not enough for gravimetric wear measurement. Based on the information presented, even taking into account dry conditions, I can’t tell if this instrument is right for the job.

Lines 116-118 - Please better highlight this on the image. I would suggest adding a letter or number to the inset figure of Fig 1.b and referencing it both in text and in the figure caption.

Line 120-121 - The manuscript would greatly benefit from some data backing your claims on the phase composition (i.e., EBSD maps or XRD spectra), not just referencing earlier studies.

Figure 1 - I would suggest using the same magnifications wherever possible. It makes the comparison and assessment of microstructure much more straightforward. I would also suggest placing the same magnifications next to each other for the same reason.

Figure 2 - I would also suggest clustering the element maps together, to ease comparison between different Si compositions. I would also suggest always showing all elements of interest, as the lack of a certain element is also valuable information. Maybe quantize your maps and present percentage compositions if possible?

Lines 154-157, 162-162 - Could you present some data to back up these claims?

Figure 3 - In multiphase materials, measuring hardness in a single point is not representative of the bulk. Please conduct multiple measurements and report both mean and deviation.

Lines 169-170 - I would argue the completion of the running in phase. In general, it’s rather challenging to assess running-in purely by looking at the friction coefficient, as with wear your contact area is constantly changing during testing, which affects contact stress, and ultimately, friction. Any means of measuring wear rate would be much better for this purpose. Si0 does show a decreasing tendency for around 7 minutes, then starts to rise. Si1 has a hump at 10 minutes, which is not preceded by a clear decrease (run-in). Si3 is nearly constant from the start, and Si5 looks like constantly increasing. What your write on lines 176-178 is not what readers see on Figure 4.

Line 182 - Figure 5a represents CoF, not wear, at least its what written on the Y axis. However, it is not indicated how this CoF was determined. Is this the value at the end? In the middle? Is this an average of the whole? Or an average of a section? Please state this information either here, or in the methods.

Line 184 - With a 10% difference I would suggest using a factual, neutral tone, rather than writing “significantly lower”, as it implies two things: you either want to underline that this is indeed a strong difference, or you have statistical proof that the difference is indeed significant. If you have done statistical testing to show the significance of the difference, report it. If not, please refrain from using “significantly lower”.

Lines 198-199 - Again, “significantly” is used on data where no statistical testing is presented. I would accept this statement for comparing Si3 and Si5 to Si0, but Si1 is a moderate decrease at best. In addition, the order of subfigures on Figure 6 (a-c-b-d) is not logical. Is it a mistake, or Si3 indeed produced a deeper wear scar compared to Si1?

Lines 200-201 - The presented images are too low magnification and resolution to assess the secondary wear mechanisms and tell if this is indeed plastic deformation (micor-ploughing) or ragged edges resulting from shear (micro-cutting). Please present higher detail images at higher magnification, if possible.

Table 1. - Does it make sense to present the wear as wear rate, where gravimetric results are multiplied by two constants, that are identical for every sample? I would suggest simply reporting the gravimetric material loss. Also, does it make sense to report width and depth alongside the total material loss? The material missing is representative of the whole wear scar, whereas a single cross section alongside the wear mark is only a part of the whole story. Again, please repeat results from multiple measurements and report an average value, or just avoid using these values.

Table 1. and Line 215 - The reported wear rate for Si3 is inconsistent.

Lines 222-224 - As before, I’d suggest consistently putting identical magnification images next to each other.

Figure 7 - I’d suggest marking the magnified region on the smaller magnification images to show the reader where the higher magnification regions correspond. Is there a way to show these images in better detail? Either enlarge them, or use a compression algorithm that results in lower loss (TIFF instead of JPEG?), as your claims are hard to assess based on the presented images. It’s also a good practice to investigate and show the surface topology of the counterbody as well. Does this composition have a tendency to adhere to WC? If not, then I’d argue that this is a more complex phenomenon where wear debris from surface A is adhering back to itself, and therefore should rather be called re-adhesion or back-transfer, to distinguish it from classical adhesive wear. Particularly with Si5 is the question of the counterbody crucial, when assessing wear rates, as these should always be taken in the context of the system. I gain nothing if I have a machine element that has 10% less wear, but in turn causes 10% higher wear on its partner.

Lines 233-234 - Where do these ceramic balls come from?

Lines 254-156 - Conclusive statements regarding phase composition are particularly troublesome if you only refer to these results as cited sources. Please either include the data in this study as well, or remove these from the conclusion.

General remark - Please don’t take this the wrong way, and I must admit, I have only noticed this based on the names in your references and have not checked the affiliations so I could be wrong, but if I count correctly, 43 from your 47 sources are written by your countrymen. A thorough literature review should represent the global state of the art in a certain topic, and your literature review is heavily based on local research. It would be nice if you could show a global overview.

Author Response

Response to Reviewer 1 Comments

Point 1: Line 13 - “… silicon-free FeNiCrAl0.7Cu0.3Si0.3 …” - if it contains 0.3 % Si, its not Si free.

Response 1: : Thank you for noticing. It was a writing mistake. I have corrected it in the revised manuscript.

Microstructural characterization reveals a progressive transformation from a dendritic structure in the silicon-free FeNiCrAl0.7Cu0.3 alloy to a chrysanthemum-like morphology in FeNiCrAl0.7Cu0.3Si0.1 and FeNiCrAl0.7Cu0.3Si0.3 alloys, and ultimately to island-like grains in FeNiCrAl0.7Cu0.3Si0.5.

Point 2: Line 45 - Please remove full uppercase from the referenced author’s name.

Response 2: The name format has been corrected in the manuscript.

Kao et al. [34] found that augmenting the Al proportion in AlxCoCrFeNi (x = 0 to 2) transforms the microstructure from a flexible FCC configuration to a more robust and rigid BCC structure.

Point3: Line 51 - Line 56 - Please check the text, there is a recurring section.

Response 3: We have made the revisions as requested.

Yang et al. [35] investigated the tribocorrosion behavior of CoCrFeNi-based HEA coatings containing Ti, Mn, Mo, and Al in 3.5 wt% NaCl solution under reciprocating friction. The study revealed that friction increased the local corrosion rate by 2–3 orders of magnitude and accelerated material loss due to the synergistic effects of wear and corrosion. Wu et al. [36] studied the wear and corrosion behavior of AlCrFeCoNi and AlCrFeCoNiTi₀.₅ HEAs in NaCl and HCl solutions. They found that Ti addition enhanced hardness and improved pitting corrosion resistance by promoting the formation of a more protective passive film.

Point 4: Line 63 - The letter “d” is missing from the word “demonstrated”.

Response 4: We have made the revisions as requested.

Lei et al. [39] demonstrated that nitrogen addition significantly refined grain size in FeCoCrNiMn HEAs from 7.6 μm to 2.5 μm.

Point 5: Line 83 - The letter “T” is missing from the word “This”.

Response 5: We have made the revisions as requested.

This study therefore further investigates the wear resistance of FeCrNiAl₀.₇Cu₀.₃Siₓ al-loys, analyzing in detail the relationship between their microstructure and wear re-sistance to comprehensively evaluate their potential engineering applications.

Point 6: Line 86 - Methods - Please include a table with the identifier and composition of your HEA samples. Introducing the samples only in the Results section can lead to confusion.

Response 6：We have made the revisions as requested.

The nominal compositions and sample abbreviations of the FeNiCrAl0.7Cu0.3Six HEAs are summarized in Table 1.

Tab.1 Nominal components of FeNiCrAl0.7Cu0.3Six HEAs (at%)

Alloy	Abbreviation	Fe	Ni	Cr	Al	Cu	Si
FeNiCrAl0.7Cu0.3	Si0	25.00	25.00	25.00	17.50	7.50	0.00
FeNiCrAl0.7Cu0.3Si0.1 0.	Si1	24.39	24.39	24.39	17.07	7.32	2.44
FeNiCrAl0.7Cu0.3Si0.3	Si3	23.26	23.26	23.26	16.28	6.98	6.98
FeNiCrAl0.7Cu0.3Si0.5	Si5	22.22	22.22	22.22	15.56	6.67	11.11

Point 7: Line 102-103 - How many points were measured per sample? In a multiphase material, the placement of the indenter can have a serious impact on measured hardness. I would suggest taking multiple (5-8) measurements per sample and presenting both the mean and deviation.

Response 7: Thank you for your suggestion. For each sample, more than six hardness measurements were conducted. A screenshot of the original hardness test report from Xi’an Jiaotong University is provided. The mean values and standard deviations have been revised accordingly in the manuscript.

(1)Microhardness tests were conducted using an HSV-1000A digital micro Vickers hardness tester. For each sample, six measurements were taken at different locations, and the average value and standard deviation were calculated.

(2)Figure 3 presents the microhardness values of FeCrNiAl₀.₇Cu₀.₃Six HEAs with varying Si content. A gradual increase in hardness is observed, from 498.2 ± 15.0 HV for the Si0 sample to 502.7 ± 32.7 HV, 577.3 ± 24.5 HV, and 863.2 ± 23.5 HV for the Si1, Si3, and Si5 samples, respectively.

Figure 3. Microhardness values of FeCrNiAl_0.7Cu_0.3Si_x HEAs (x = 0, 0.1, 0.3, 0.5)

Point 8: Line 103-104 and 106-108 - You’ve repeated the description of the wear testing method. Please also add the dimensions of both base and counterbody, or at least the corresponding dimension and shape of the contact area.

Response 8: The revisions have been made as requested. The modifications are as follows:

Microhardness tests were conducted using an HSV-1000A digital micro Vickers hardness tester. For each sample, six measurements were taken at different locations, and the average value and standard deviation were calculated.

Wear performance was evaluated using an MM-10000A reciprocating wear tester in a ball-on-flat configuration under dry sliding conditions. The counterbody was a tungsten carbide (WC) ball with a diameter of 6 mm, and the base alloy samples meas-ured 20 mm × 20 mm × 3 mm. The test was conducted under a normal load of 100 N, with a reciprocating frequency of 1 Hz, a stroke length of 6 mm, and a total duration of 30 minutes.

Point 9: Line 109 - You have not specified the contact area - neither shape, nor size. In my experience, 100N with a low frequency for 30 minutes generally leads to very low wear under lubricated conditions, where milligram resolution is not enough for gravimetric wear measurement. Based on the information presented, even taking into account dry conditions, I can’t tell if this instrument is right for the job.

Response 9: Thank you for your valuable comments. We have clarified in the revised manuscript that the wear test was conducted under dry sliding conditions and have provided more detailed information about the test configuration. We had not fully realized the limitations of using a 100 N load under low-frequency conditions, but as you pointed out, increasing the applied load could result in more pronounced and distinguishable wear behavior. However, as the current manuscript is based on completed experimental work, we have reported the results as obtained under the existing conditions. We will certainly take your suggestion into consideration in future studies to further enhance experimental accuracy and resolution.

Point 10: Lines 116-118 - Please better highlight this on the image. I would suggest adding a letter or number to the inset figure of Fig 1.b and referencing it both in text and in the figure caption.

Response 10:Thank you for your suggestion. We have revised Figure 1 by adding a label (“I”) to the inset of Figure 1(b) and have referenced it accordingly in both the main text and the figure caption.

Figure 1 displays the microstructures of the various alloy samples. Figures 1(a)–(d) present the Si0–Si5 alloys at a magnification of 1000×, while Figures 1(e)–(h) show cor-responding regions at 5000× magnification. Figures 1(a) and (e) reveal that the Si0 alloy exhibits a characteristic dendritic structure. A further magnified view of the dendritic zone (Figure 1(i)) shows a well-defined grid-like configuration, indicative of a modu-lated decomposition structure. This feature results from the uphill diffusion of ele-ments during solidification, leading to compositional fluctuations and periodic struc-tural modulation[47].

Figure.1 SEM microstructures of FeCrNiAl0.7Cu0.3Six HEAs with different Si content: (a, c, i) Si0 a; (b, f) Si1 ; (c, g) Si3 ; (d, h) Si5.

Point 11:Line 120-121 - The manuscript would greatly benefit from some data backing your claims on the phase composition (i.e., EBSD maps or XRD spectra), not just referencing earlier studies.

Response 11: Thank you for the reviewer's guidance. This section has been added to the manuscript.

The phase analysis based on the XRD data is discussed in detail in our previous work [46], as shown in Figure 2. The Si0 alloy corresponds to a single BCC1 phase.Figures 1(b) and (f) illustrate that the Si1 alloy retains a dendritic morphology similar to that of Si0, but no grid-like modulated structures are observed within the dendrites. In Figures 1(c) and (g), the Si3 alloy shows a transition to a chrysanthe-mum-like dendritic morphology, along with the appearance of particulate precipitates inside the dendritic grains. Both Si1 and Si3 consist of mixed BCC1 and BCC2 phases [46], and the analysis suggests that the addition of Si promotes the transformation from dendritic BCC1 to interdendritic BCC2 phases.Figures 1(d) and (h) indicate that the Si5 alloy exhibits an island-like grain configuration, in which the particulate fea-tures within the dendritic regions have disappeared. This microstructural evolution implies that the interdendritic phase observed in Si1 has transformed into the dendrit-ic phase in the Si5 alloy. To further elucidate the phase constitution, compositional scans of the alloys were performed.

Figure.2 The XRD of FeCrNiAl0.7Cu0.3Six HEAs.

Point 12: Figure 1 - I would suggest using the same magnifications wherever possible. It makes the comparison and assessment of microstructure much more straightforward. I would also suggest placing the same magnifications next to each other for the same reason.

Response 12: Thank you for your suggestion. We have revised Figure 1 using consistent magnifications (1000× and 5000×) and rearranged the images accordingly. The text has also been updated as follows:

Figure 1 displays the microstructures of the various alloy samples. Figures 1(a)–(d) present the Si0–Si5 alloys at a magnification of 1000×, while Figures 1(e)–(h) show corresponding regions at 5000× magnification. Figures 1(a) and (e) reveal that the Si0 alloy exhibits a characteristic dendritic structure. A further magnified view of the dendritic zone (Figure 1(i)) shows a well-defined grid-like configuration, indicative of a modulated decomposition structure. This feature results from the uphill diffusion of elements during solidification, leading to compositional fluctuations and periodic structural modulation[47].

Figure.1 SEM microstructures of FeCrNiAl0.7Cu0.3Six HEAs with different Si content: (a, c, i) Si0 a; (b, f) Si1 ; (c, g) Si3 ; (d, h) Si5.

The phase analysis based on the XRD data is discussed in detail in our previous work [46], as shown in Figure 2. The Si0 alloy corresponds to a single BCC1 phase.Figures 1(b) and (f) illustrate that the Si1 alloy retains a dendritic morphology similar to that of Si0, but no grid-like modulated structures are observed within the dendrites. In Figures 1(c) and (g), the Si3 alloy shows a transition to a chrysanthemum-like dendritic morphology, along with the appearance of particulate precipitates inside the dendritic grains. Both Si1 and Si3 consist of mixed BCC1 and BCC2 phases [46], and the analysis suggests that the addition of Si promotes the transformation from dendritic BCC1 to interdendritic BCC2 phases.Figures 1(d) and (h) indicate that the Si5 alloy exhibits an island-like grain configuration, in which the particulate features within the dendritic regions have disappeared. This microstructural evolution implies that the interdendritic phase observed in Si1 has transformed into the dendritic phase in the Si5 alloy. To further elucidate the phase constitution, compositional scans of the alloys were performed.

Point 13: Figure 2 - I would also suggest clustering the element maps together, to ease comparison between different Si compositions. I would also suggest always showing all elements of interest, as the lack of a certain element is also valuable information. Maybe quantize your maps and present percentage compositions if possible?

Response 7: Thank you for the suggestion. We have rearranged the element maps, included all relevant elements, and added Table 2 based on the EDS data. The manuscript has been revised accordingly, and related test screenshots are attached:

Figure 3 illustrates the elemental distributions obtained through area scanning for each alloy sample, while the actual elemental contents from the scanned regions are summarized in Table 2. As shown in Figure 3(a), the dendritic regions of the Si0 alloy are deficient in Cr and Fe, while Cu is relatively uniformly distributed throughout the matrix. In contrast, the interdendritic areas are enriched in Cr and Fe.Figure 3(b) reveals a similar distribution pattern for the Si1 alloy, where the dendritic regions are mainly composed of Al and Ni, whereas Cr and Fe are concentrated in the interdendritic regions. In Figure 3(c), compared to the Si1 alloy, Ni is more prominently concentrated in the dendritic zones of the Si3 alloy. Si appears to co-distribute with Fe and Cr, while the intermediate granular structures are primarily composed of Al and Ni phases.In Figure 3(d), the island-like grains observed in the Si5 alloy mainly consist of Al and Ni, whereas the surrounding interdendritic regions are enriched in Fe and Cr. Unlike i Si3, Si in the Si5 alloy shows a stronger tendency to associate with Al and Ni.Across the Si1, Si3, and Si5 samples, Cu consistently tends to co-distribute with Al and Ni, suggesting a preferential segregation behavior.

Figure.3 EDS elemental mapping images of FeCrNiAl_0.7Cu_0.3Si_xalloys (a) Si0 a (b) Si1 (c)Si3 (d)Si5 alloy

Table.2 Actual elemental compositions obtained from area scanning of FeCrNiAl_0.7Cu_0.3Si_x alloys.

Alloy	Abbreviation	Fe	Ni	Cr	Al	Cu	Si
FeNiCrAl_0.7Cu_0.3	Si0	12.63	40.46	8.18	25.65	13.08	0.00
FeNiCrAl_0.7Cu_0.3Si_0.1 _0.	Si1	16.18	35.99	13.46	22.34	11.23	0.80
FeNiCrAl_0.7Cu_0.3Si_0.3	Si3	16.79	26.47	22.38	16.79	7.64	4.91
FeNiCrAl_0.7Cu_0.3Si_0.5	Si5	24.80	27.32	17.01	17.01	8.18	5.87

Point 14: . Lines 154-157, 162-162 - Could you present some data to back up these claims?

Response 14: Thank you for your comment. We reviewed a number of relevant studies. The work titled “Effects of Si content on the microstructure and properties of CoCrFeMnNiSix high-entropy alloy coatings by laser cladding” published in Materials Characterization(https://doi.org/10.1016/j.matchar.2024.114246) shows that the hardness of CoCrFeMnNiSix (x = 0, 0.4, 0.8, 1.2, 1.6) coatings increases with rising Si content. This improvement is attributed to the smaller atomic radius of Si (0.115 nm), which induces lattice distortion and solid solution strengthening. Additionally, Si atoms can partially occupy interstitial sites, reducing lattice volume, increasing atomic packing density, and hindering dislocation motion, thereby enhancing hardness.

At higher Si content, the precipitation of intermetallic compounds and BCC phases contributes to further hardness improvement through second-phase strengthening. These phases typically have higher hardness and higher Peierls stress than FCC phases, making dislocation movement more difficult.

These findings support the interpretation in our manuscript: the hardness increase in FeCrNiAl_0.7Cu_0.3Si_x alloys at low Si content results mainly from lattice distortion and dislocation hindrance, while at high Si content it is due to second-phase strengthening. We have added the relevant citation in the revised manuscript to support and formalize our interpretation.

The original text is as follows（Effects of Si content on the microstructure and properties of CoCrFeMnNiSix high-entropy alloy coatings by laser cladding” published in Materials Characterization）.

Fig. 10 (b) shows the average microhardness of CoCrFeMnNiSix high-entropy-alloy coatings. The average microhardness of Si0, Si0.4, Si0.8, Si1.2, and Si1.6 is 185.33, 416.92, 472.95, 492.3, and 513.2 HZ0.5, respectively. The microhardness of coatings increases with increased Si. Average hardness reaches the maximum (513.2 HV0.5) when x = 1.6, which is 1.77 times higher than that of the Si0 coating without Si addition. The atomic radius (0.115 nm) of Si is smaller than that of other elements in the alloy system. Different atomic radii in the alloy system intensify the distortion of the crystal lattice within coatings after Si addition. Solution strengthening is achieved, which increases coating hardness. Based on the density equation:K =nv V (6) where nis the atom number; v is the volume of an atom; Vis the volume of unit cells. With the incorporation of Si atoms with smaller atomic radii, the Si atoms occupy interstitial spaces to a certain extent, com pressing the volume of the lattice, thus increasing the densification, andtherelativeslipbetweenthecrystalsbecomesdifficult, andthus the hardness of thecoating is subsequently increased[50]. Besides, the phase structure of high-entropy-alloy coatings is characterized by a simple FCC solid solution structure with less Si. Alloys with the FCC phase structure possess favorable ductility, but strength is low. Intermetallic compound and BCC phases containing Si precipitate in alloy coatings as Si continues to increase. Intermetallic compounds containing Si exhibit high hardness and low plasticity. Moreover, the strength of BCC phases is typically higher than that of FCC phases. BCC phases exhibit a higher Peierls stress [51,52], indicating that atoms in BCC unit cells require greater force to move dislocations on the plane. In summary, Si addition improves the hardness of high-entropy-alloy coatings.

In the study “Microstructure and dislocation density of AlCoCrFeNiSix high-entropy alloy coatings by laser cladding”, （https://doi.org/10.1016/j.matlet.2020.128746）a similar conclusion was reported. As stated: "The hardness increases linearly as the Si content increases. The microhardness increments, with the Si0 coating as a reference, are plotted in Fig. 3. The improvement of microhardness can be attributed to solid-solution strengthening, precipitation strengthening, and dislocation strengthening."

Point 15: Figure 3 - In multiphase materials, measuring hardness in a single point is not representative of the bulk. Please conduct multiple measurements and report both mean and deviation.

Response 15: We have made the requested revisions to the manuscript, as follows:

(2)Figure 4 presents the microhardness values of FeCrNiAl₀.₇Cu₀.₃Six HEAs with varying Si content. A gradual increase in hardness is observed, from 498.2 ± 15.0 HV for the Si0 sample to 502.7 ± 32.7 HV, 577.3 ± 24.5 HV, and 863.2 ± 23.5 HV for the Si1, Si3, and Si5 samples, respectively.

Figure 3. Microhardness values of FeCrNiAl_0.7Cu_0.3Si_x HEAs (x = 0, 0.1, 0.3, 0.5)

Point 16: . Lines 169-170 - I would argue the completion of the running in phase. In general, it’s rather challenging to assess running-in purely by looking at the friction coefficient, as with wear your contact area is constantly changing during testing, which affects contact stress, and ultimately, friction. Any means of measuring wear rate would be much better for this purpose. Si0 does show a decreasing tendency for around 7 minutes, then starts to rise. Si1 has a hump at 10 minutes, which is not preceded by a clear decrease (run-in). Si3 is nearly constant from the start, and Si5 looks like constantly increasing. What your write on lines 176-178 is not what readers see on Figure 4.

Response 16: Thank you for your insightful comment. Based on your suggestion, we revisited the interpretation of the friction coefficient curves and studied related literature on wear behavior. We acknowledge that the original description lacked rigor in assessing the data. Therefore, we have revised this part to more objectively reflect the actual trends shown in the data. The updated description is as follows:

Figure 5 shows the friction coefficient (COF) curves of FeCoCrAl₀.₇Cu₀.₃Six high-entropy alloys. All curves exhibit fluctuating behavior. For the Si0 sample, the COF shows a decreasing trend before 7 minutes, a peak around 10 minutes, and gradually stabilizes after 15 minutes. The Si1 sample shows a low point near 5 minutes, followed by a peak at 10 minutes, then stabilizes after 15 minutes. The Si3 sample remains relatively stable from the beginning of the test. The Si5 sample shows an increasing trend in the early stage and continues to fluctuate significantly even after 25 minutes. Overall, after 15 minutes, the COF tends to decrease with increasing Si content.

Point 17: Line 182 - Figure 5a represents CoF, not wear, at least its what written on the Y axis. However, it is not indicated how this CoF was determined. Is this the value at the end? In the middle? Is this an average of the whole? Or an average of a section? Please state this information either here, or in the methods.

Response 17: Thank you for your suggestion. We have revised the figure label accordingly. In consideration of the data trend and based on the previous review comment, the CoF value shown in Figure 6a represents the average coefficient of friction after 15 minutes of testing. This has now been clarified in both the figure caption and the experimental methods section. The revised sentence is as follows:

Figure 5(a) displays the average friction coefficients of different samples, calcu-lated over the period after 15 minutes of testing. The CoF of the Si0 alloy (0.571) is slightly higher than that of Si1 (0.551), while the CoF of the Si3 alloy (0.524) is lower than those of Si0 and Si1. The Si5 alloy exhibits the lowest CoF at 0.468

Point 18: Line 184 - With a 10% difference I would suggest using a factual, neutral tone, rather than writing “significantly lower”, as it implies two things: you either want to underline that this is indeed a strong difference, or you have statistical proof that the difference is indeed significant. If you have done statistical testing to show the significance of the difference, report it. If not, please refrain from using “significantly lower

Response 18: I have made the requested revisions to the manuscript, as follows:

Point 19: Lines 198-199 - Again, “significantly” is used on data where no statistical testing is presented. I would accept this statement for comparing Si3 and Si5 to Si0, but Si1 is a moderate decrease at best. In addition, the order of subfigures on Figure 6 (a-c-b-d) is not logical. Is it a mistake, or Si3 indeed produced a deeper wear scar compared to Si1?

Response 19: Thank you for your comment. The word “significantly” has been removed, as there was no statistical analysis. The subfigure order in Figure 6 was a labeling mistake and has been corrected. The revised sentence is:

In comparison to the Si0 sample, the samples with Si exhibit shallower and narrower wear tracks in both width and depth. Both Si0 and Si1 show local protrusions along the edges of the wear tracks, indicating potential plastic deformation during the wear process.

Point 20: Lines 200-201 - The presented images are too low magnification and resolution to assess the secondary wear mechanisms and tell if this is indeed plastic deformation (micor-ploughing) or ragged edges resulting from shear (micro-cutting). Please present higher detail images at higher magnification, if possible.

Response 20: I have supplemented the relevant data and conducted an analysis. The details are as follows: Thank you for the comment. When writing this part, we recalled a reference mentioning that local protrusions along the edges of wear tracks may indicate plastic deformation during wear. However, after checking many papers again, we were unable to find the exact source. Although we have attached the original image, it is not sufficient to clearly support this analysis. To keep the description accurate, we have removed this part from the manuscript.

Point 21: Table 1. - Does it make sense to present the wear as wear rate, where gravimetric results are multiplied by two constants, that are identical for every sample? I would suggest simply reporting the gravimetric material loss. Also, does it make sense to report width and depth alongside the total material loss? The material missing is representative of the whole wear scar, whereas a single cross section alongside the wear mark is only a part of the whole story. Again, please repeat results from multiple measurements and report an average value, or just avoid using these values.

Response 21: Thank you for the suggestion. We have revised the table to present only the gravimetric material loss. Since the experiment was not repeated multiple times, we decided to remove the wear width and depth data to ensure the accuracy and rigor of the results.

Point 22: Lines 222-224 - As before, I’d suggest consistently putting identical magnification images next to each other.

Response： I replaced image 8(h) with one at the same magnification for comparison and added marked regions as suggested later.

Figure.8 Worn surface characteristics of FeNiCrAl_0.7Cu_0.3Si_x HEAs: (a)(b) Si0, (c)(d) Si1, (e)(f) Si3, (g)(h) Si5 alloy

Point 23: Figure 7 - I’d suggest marking the magnified region on the smaller magnification images to show the reader where the higher magnification regions correspond. Is there a way to show these images in better detail? Either enlarge them, or use a compression algorithm that results in lower loss (TIFF instead of JPEG?), as your claims are hard to assess based on the presented images. It’s also a good practice to investigate and show the surface topology of the counterbody as well. Does this composition have a tendency to adhere to WC? If not, then I’d argue that this is a more complex phenomenon where wear debris from surface A is adhering back to itself, and therefore should rather be called re-adhesion or back-transfer, to distinguish it from classical adhesive wear. Particularly with Si5 is the question of the counterbody crucial, when assessing wear rates, as these should always be taken in the context of the system. I gain nothing if I have a machine element that has 10% less wear, but in turn causes 10% higher wear on its partner.

Response 23: Thank you for your guidance. We have marked the magnified regions using rectangles in the figures to clearly indicate the enlarged areas. Regarding the WC counterbody, we reviewed relevant literature and acknowledge that, in this experiment, the reduced wear observed on the samples cannot exclude the potential adhesive wear on the WC surface. We have revised the manuscript to clarify this limitation. The current study did not account for the effect of back-transfer or re-adhesion.The revised content is as follows:

In contrast, the Si5 alloy surface is smoother, without visible grooves, and covered by lamellar debris. This is likely due to increased hardness, which inhibits debris removal and promotes debris agglomeration. Under prolonged friction, local high temperatures may lead to cold welding and re-adhesion of debris to the surface. It should be noted that this interpretation does not consider possible adhesion to the WC counterbody. Therefore, the observed wear behavior may involve back-transfer effects, which require further investigation.Overall, Si addition alters the wear mechanism from abrasive to more adhesive in nature and enhances the wear resistance of the alloy, especially for the Si5 sample.

Point 24: Lines 233-234 - Where do these ceramic balls come from?

Response 24: Thank you for pointing this out. This was a writing mistake — the correct counterbody material is tungsten carbide, and we have corrected it to “WC” in the revised manuscript.

The delamination phenomenon suggests that the shear strength of the adhesive points is greater than that of the alloy but less than the shear strength of WC, resulting in shear deformation on the alloy surface, which leads to a coexistence of abrasive wear and adhesive wear.

Point 25: Lines 254-156 - Conclusive statements regarding phase composition are particularly troublesome if you only refer to these results as cited sources. Please either include the data in this study as well, or remove these from the conclusion

Response 25:The modification has been completed.

The microstructure of FeNiCrAl₀.₇Cu₀.₃Six HEAs changes with increasing Si content. The Si0 alloy shows a dendritic morphology, while the Si1 and Si3 alloys de-velop a chrysanthemum-like structure, and the Si5 alloy exhibits an island-like grain structure. Elemental mapping indicates that Al and Ni are mainly distributed in den-dritic regions, whereas Cr and Fe are enriched in interdendritic areas. With higher Si content, Si tends to co-segregate with Al and Ni. Cu shows a consistent tendency to distribute with Al and Ni in all samples.

Point 26: General remark - Please don’t take this the wrong way, and I must admit, I have only noticed this based on the names in your references and have not checked the affiliations so I could be wrong, but if I count correctly, 43 from your 47 sources are written by your countrymen. A thorough literature review should represent the global state of the art in a certain topic, and your literature review is heavily based on local research. It would be nice if you could show a global overview.

Response 26: As the reviewer noted, many of the cited references are indeed from Chinese researchers. This is partly because China currently has a high volume of publications in the field of high-entropy alloys. A search for recent literature using the keyword “high-entropy alloy” on Web of Science shows that many of the latest studies originate from China. In this manuscript, we selected references based on their relevance to the study. That said, we sincerely appreciate your suggestion and will make sure to incorporate more globally diverse sources in our future work to better reflect the international research landscape in this field.

Thank you again for your valuable suggestions！

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Abstract

It is always a challenge to limit abstracts to 200 words. I feel that the authors jump to summarising the wear results (line 18), without even mentioning that a reciprocal wear test has been conducted. This should be incorporated into the abstract without specifying full details of the wear test (keep it limited to 200 words).

Introduction

The only recommendation to the authors is to correct the formatting and typographical errors (see separate section of review).

Materials and Methods

As with all other experimental equipment, the authors need to be more specific about the make and model of SEM used, as I feel that simply stating that the “FEI SEM was employed” (line 97) does not suffice. This should be provided in full unabbreviated form first in the methods, and then can be simply referred to as SEM throughout the rest of the manuscript.

The wear testing method (line 105) looks like it is from an ISO or ASME standard. If this is the case please provide a citation for this.

The final sentence of the Materials and Methods section has confused me somewhat, and this may be down to the interchangeable use of terminology. Jumping forwards to figure 6, there are four rows of micrographs, four rows of topographs and four rows of 2D profiles. I can just about extract from the material and methods section that the micrographs were obtained by the Olympus microscope, but there are not details here regarding how the topographs or 2D profiles have been measured. I also think you are using the terms “morphology” and “topography” interchangeably.

Results, Discussion and Conclusion

The reporting of the results is good, with the authors leveraging the micrographs and roughness plots to show key findings. Figures 3, 4 and 5 would benefit from having a consistent style, and the authors should aim to have the same size font for axes and labels. The micrographs of the indentations in figure 3 are too hard to see legibly, and perhaps this should be presented as a figure 3a and figure 3b.

The discussion (lines 222-249) would benefit from citing some of the literature evaluated first in the introduction. As it stands, the discussion explains the phenomena from the results but does not critically evaluate through comparison to other studies.

The three concluding comments serve the manuscript well but should be updated to reflect any changes to the discussion.

Comments on the Quality of English Language

Line 40: “mainly explore on refractory HESs [24, 25],,”….. the “on” is redundant, and there is a double comma after the citation.

Line 45: “explored Fe-Cr-Ni-Co-Al alloys.KAO et al” …… space needed following the period, before “KAO”.

Line 56: “and intact regions.Chin-“…… space needed following the period.

Line 63: “Lei et al. [39] emonstrated”…… typo, should be demonstrated.

Line 83: “his study therefore further investigates”…… typos, should be “this study”.

Line 94: “arc.After achieving full melting”…… space needed following the period.

Line 99: “features.Secondary electron imaging”……. space needed following the period.

Line 102: “Microhardness tests on amples were conducted with”…… typo, should be samples.

Line 127: “interdendritic BCC2 phase.Figure 1”….. space needed following the period.

Line 159: “limiting plastic deformation.When the”….. space needed following the period.

Line 168: “FeCoCrAl0.7Cu0.3Six”….. subscript not used for elemental suffixes.

Line 170: “stage.During the early”….. space needed following the period.

Line 172: “tions.After approximately” ….. space needed following the period.

Line 173: “steady friction stage.Significant”….. space needed following the period.

Line 176: “in the friction curve.As time progresses” ….. space needed following the period.

Line 190: “emergence of the BCC phase.Meanwhile” ….. space needed following the period.

Line 196: Line space required after image caption.

Line 196: “FeCoCrAl0.7Cu0.3Six”….. subscript not used for elemental suffixes.

Line 211: Line space required after table.

Line 214: “Table 1 presents the wear results for the samples..”….. remove duplicated period.

Line 222: Line space required after image caption.

Line 251: “1.The silicon content”….. add a character space after the first numbered item.

Line 271: Add line space before funding statement.

References: Several instances where the subscript in the titles of the articles has failed. Please check your citation manager or correct each erroneous instance manually.

Author Response

Response to Reviewer 2 Comments

Point 1: Abstract

Response 1: Thank you for the helpful suggestion. Based on your comments, we have revised the abstract accordingly. We removed the wear rate values, kept the wear volume data, and clarified the description of how the wear mechanism changes with increasing silicon content. The updated abstract is as follows:

Abstract: This study investigates the influence of Si content (x = 0, 0.1, 0.3, 0.5) on the micro-structure, mechanical properties, and wear behavior of of FeNiCrAl0.7Cu0.3Six high-entropy alloys. With increasing silicon content, the microstructure evolves from a dendritic morphology the sil-icon-free FeNiCrAl0.7Cu0.3 alloy, to a transitional structure in the FeNiCrAl0.7Cu0.3Si0.1alloy that retains dendritic features, then to a chrysanthemum-like morphology in the FeNiCrAl0.7Cu0.3Si0.3 alloy, and finally to island-like grains in the FeNiCrAl0.7Cu0.3Si0.5 alloy.This evolution is accom-panied by a phase transition from a Fe and Cr-rich body-centered cubic phase to an Al and Ni-rich body-centered cubic phase, with silicon showing a tendency to segregate alongside aluminum and nickel. The microhardness increases from 484 to 864 due to solid solution strengthening and the formation of a hard sigma phase. The wear mass decreases from 1.31mg in the FeNiCrAl0.7Cu0.3 alloy to 0.78 milligrams in the FeNiCrAl0.7Cu0.3Si0.5 alloy, which is consistent with the increase in microhardness. As the silicon content increases, the dominant wear mechanism changes from abrasive wear to adhesive wear, with the high-silicon alloy exhibiting lamellar de-bris on the worn surface. These findings confirm that silicon addition enhances microstructural refinement, mechanical strength, and wear resistance of the alloy system.

Point 2: Introduction

The only recommendation to the authors is to correct the formatting and typographical errors (see separate section of review).

Response 2: I have completed the revisions.

Point 3: Materials and Methods

The wear testing method (line 105) looks like it is from an ISO or ASME standard. If this is the case please provide a citation for this.

Response 3: Thank you for the comment. We have added the full names, models, and countries of origin for all key equipment, including the scanning electron microscope. Abbreviations have been clarified on first use. In accordance with the reviewers’ collective suggestions, our wear analysis primarily focuses on mass loss measurements. Additionally, we have included detailed descriptions of how the 3D surface topography and cross-sectional profiles were obtained using the Olympus DSX1000 ultra-depth optical microscope. The extracted data were subsequently processed using Origin software to quantify wear dimensions.

Microstructural analysis was performed using a Quanta 250 FEG field emission scanning electron microscope (Thermo Fisher Scientific, USA). Prior to observation, specimens were etched with aqua regia to reveal microstructural features. Secondary electron (SE) imaging was used to observe surface morphology and contrast, and energy-dispersive spectroscopy (EDS) was applied to determine elemental distribution.

The weight of each specimen was recorded thrice both before and after testing, utilizing a JA2003N electronic balance with an accuracy of 0.001 g, and the average was used to calculate wear loss. After testing, the surface topography of the worn areas was examined using an Olympus DSX1000 ultra-depth optical microscope (Olympus Corporation, Japan), which provided 2D surface images, 3D topography maps, and cross-sectional wear profiles. The cross-sectional data obtained from the ultra-depth optical microscope were subsequently plotted using Origin software to quantify the wear dimensions. And detailed wear surface micro-morphology was analyzed via SEM.

Point 4: Results, Discussion and Conclusion

The three concluding comments serve the manuscript well but should be updated to reflect any changes to the discussion

Response 4: The microhardness images have been revised as requested. Other figures were also modified according to suggestions from other reviewers. The wear mechanism section has been rediscussed. The conclusion has been rewritten. The revised content is as follows:

1.Figure 4 presents the microhardness values of FeCrNiAl₀.₇Cu₀.₃Six HEAs with varying Si content. Figure 4b presents the microhardness values of FeCrNiAl₀.₇Cu₀.₃Six HEAs with var-ying Si content. A gradual increase in microhardness is observed, from 498.2 ± 15.0 HV for the Si0 sample to 502.7 ± 32.7 HV, 577.3 ± 24.5 HV, and 863.2 ± 23.5 HV for the Si1, Si3, and Si5 samples, respectively. The enhancement primarily stems from solid solution hardening combined with reinforcement from the second phase. As the Si content increases, more Si atoms dissolve into the matrix, substituting for other atoms or occupying interstitial sites. This leads to significant lattice distortion and generates local stress fields that hinder dislocation motion, thereby reducing dislocation mobility and limiting plastic deformation[1,2]. When the Si content reaches Si3, the solid solution strengthening effect becomes more pronounced, resulting in a marked increase in microhardness. Within the high-entropy matrix of the Si5 alloy, trace amounts of the σ phase are also generated. This hard, brittle secondary phase (σ phase) further impedes dislocation motion and contributes to the overall enhancement in microhardness[1].

Figure 4. Microhardness values of FeCrNiAl0.7Cu0.3Six HEAs (x = 0, 0.1, 0.3, 0.5)

Figure 8(a), (c), (e), and (g) depict the wear surface features of the Si0, Si1, Si3, and Si5 alloys, while the corresponding enlarged views are presented in (b), (d), (f), and (h), respectively. As the Si content increases, the wear surface and wear mechanisms gradually change. The wear surface of Si0 alloy exhibits consistent plowing grooves aligned with the wear direction, with white abrasive particles and block-like debris scattered around the grooves. The surface also shows delamination and plastic defor-mation at the edges. This type of damage is primarily caused by both abrasive wear and adhesive wear. The formation of the grooves is attributed to two factors: mi-cro-cutting of the material surface by the abrasive particles and the formation of grooves under the frictional interaction. After repeated wear, the raised parts adjacent to the grooves gradually detach from the surface. The delamination phenomenon sug-gests that the shear strength of the adhesive points is greater than that of the alloy but less than the shear strength of WC, resulting in shear deformation on the alloy surface, which leads to a coexistence of abrasive wear and adhesive wear. The Si1 alloy surface still displays plowing grooves but without the ridge-like protrusions, indicating that abrasive wear remains dominant, accompanied by some adhesive wear, with plastic deformation also occurring at the edges. The wear surface of Si3 alloy still shows pri-marily abrasive wear with the formation of granular abrasive agglomerates.

In contrast, the Si5 alloy surface is smoother, without visible grooves, and covered by lamellar debris. This is likely due to increased microhardness, which inhibits debris removal and promotes debris agglomeration. Under prolonged friction, local high temperatures may lead to cold welding and re-adhesion of debris to the surface. It should be noted that this interpretation does not consider possible adhesion to the WC counterbody. Therefore, the observed wear behavior may involve back-transfer effects, which require further investigation.Overall, Si addition alters the wear mechanism from abrasive to more adhesive in nature and enhances the wear resistance of the alloy, especially for the Si5 sample.

1. With increasing Si content, the microstructure changes from dendritic (Si₀) to a transitional structure (Si₀.₁), then to chrysanthemum-like (Si₀.₃), and finally to is-land-like grains (Si₀.₅). Al and Ni are enriched in dendrites, while Cr and Fe are in in-terdendritic areas. Si and Cu tend to co-segregate with Al and Ni.
The microhardness of FeCrNiAl₀.₇Cu₀.₃Six alloys increases with rising Si content, from 484 HV for the Si0 alloy to 864 HV for the Si5 alloy. This enhancement is at-tributed to solid-solution strengthening and the formation of the σ phase. The pres-ence of secondary phase particles in Si3 and Si5 further contributes to mechanical strengthening.
The wear resistance is significantly improved with increasing Si. The wear mass decreases from 1.31 mg for the Si0 alloy to 0.78 mg for the Si5 alloy. Si0 and Si1 alloys primarily experience abrasive wear, whereas Si3 and Si5 exhibit smoother worn sur-faces with layered wear debris, indicating a shift toward adhesive wear as the domi-nant mechanism. This transformation reflects the influence of Si on the alloy’s tribo-logical behavior and provides insight into tailoring wear properties through composi-tion design.

This study demonstrates that Si not only alters phase formation through thermo-dynamic interactions, but also provides a practical route to optimize mechanical and wear performance in Fe-based high-entropy alloys.

Point 5: Line 40: “mainly explore on refractory HESs [24, 25],,”….. the “on” is redundant, and there is a double comma after the citation..

Response 5: Thank you for the careful review. I have made the requested revisions accordingly. The updated content is as follows:

Currently, studies HEA systems mainly explore on refractory HEAs[24,25], light-weight HEAs[26,27], and transition metal-based HEAs[28,29].

Point 6: Line 45: “explored Fe-Cr-Ni-Co-Al alloys.KAO et al” …… space needed following the period, before “KAO”.

Response 6: I have made the requested revisions accordingly. The updated content is as follows:

Kao et al. ^[3] found that augmenting the Al proportion in AlxCoCrFeNi (x = 0 to 2) transforms the microstructure from a flexible FCC configuration to a more robust and rigid BCC structure.

Point 7: Line 56: “and intact regions.Chin-“…… space needed following the period.

Response 7: I have made the requested revisions accordingly. The updated content is as follows:

Chin-You Hsu et al.[37] observed that substituting Fe in AlCoCrFeₓMo0.5Ni alloys (x=0.6-2) significantly influenced their hardness and wear properties. Alloys with low-er Fe content exhibited dendritic structures and higher hardness compared to higher Fe content alloys, which displayed increased oxidation and wear at elevated tempera-tures.

Point 8: Line 63: “Lei et al. [39] emonstrated”…… typo, should be demonstrated.

Response 8: I have made the requested revisions accordingly. The updated content is as follows:

Lei et al. [39] demonstrated that nitrogen addition significantly refined grain size in FeCoCrNiMn HEAs from 7.6 μm to 2.5 μm.

Point 9: Line 83: “his study therefore further investigates”…… typos, should be “this study”.

Response 9: I have made the requested revisions accordingly. The updated content is as follows:

Therefore, the purpose of this study is to systematically explore the effect of Si content on the microstructure, hardness, and wear behavior of FeCrNiAl₀.₇Cu₀.₃Six high-entropy alloys, aiming to reveal the underlying wear mechanisms and evaluate their suitability for practical engineering applications.

Point 10: Line 94: “arc.After achieving full melting”…… space needed following the period.

Response 10: I have made the requested revisions accordingly.

Point 11: Line 99: “features.Secondary electron imaging”……. space needed following the period.

Response 10: I have made the requested revisions accordingly.

Point 12: Line 102: “Microhardness tests on amples were conducted with”…… typo, should be samples.

Response 12: I have made the requested revisions accordingly.

Point 13: Line 127: “interdendritic BCC2 phase.Figure 1”….. space needed following the period.

Response 13: I have made the requested revisions accordingly.

Point 14: Line 159: “limiting plastic deformation.When the”….. space needed following the period.

Response 14: I have made the requested revisions accordingly.

Point 15: Line 99: “features.Secondary electron imaging”……. space needed following the period.

Response 15: I have made the requested revisions accordingly.

Point 16: Line 102: “Microhardness tests on amples were conducted with”…… typo, should be samples.

Response 16: I have made the requested revisions accordingly.

Point 17: Line 127: “interdendritic BCC2 phase.Figure 1”….. space needed following the period.

Response 17: I have made the requested revisions accordingly.

Point 18: Line 159: “limiting plastic deformation.When the”….. space needed following the period.

Response 18: I have made the requested revisions accordingly.

Point 19: Line 168: “FeCoCrAl0.7Cu0.3Six”….. subscript not used for elemental suffixes.

Response 19: I have made the requested revisions accordingly.

Point 20: Line 170: “stage.During the early”….. space needed following the period.

Response 20: I have made the requested revisions accordingly.

Point 21: Line 172: “tions.After approximately” ….. space needed following the period.

Response 21: I have made the requested revisions accordingly.

Point 22: Line 173: “steady friction stage.Significant”….. space needed following the period.

Response 22: I have made the requested revisions accordingly.

Point 23: Line 176: “in the friction curve.As time progresses” ….. space needed following the period.

Response 23: I have made the requested revisions accordingly.

Point 24: Line 190: “emergence of the BCC phase.Meanwhile” ….. space needed following the period.

Response 24: I have made the requested revisions accordingly.

Point 25: Line 196: Line space required after image caption.

Response 25: I have made the requested revisions accordingly.

Point 26: Line 196: “FeCoCrAl0.7Cu0.3Six”….. subscript not used for elemental suffixes.

Response 26: I have made the requested revisions accordingly.

Point 27: Line 211: Line space required after table.

Response 27: I have made the requested revisions accordingly.

Point 28: Line 214: “Table 1 presents the wear results for the samples..”….. remove duplicated period.

Response 28: I have made the requested revisions accordingly.

Point 29: Line 222: Line space required after image caption.

Response 29: I have made the requested revisions accordingly.

Point 30: Line 251: “1.The silicon content”….. add a character space after the first numbered item.

Response 30: I have made the requested revisions accordingly.

Point 31: Line 271: Add line space before funding statement.

Response 31: I have made the requested revisions accordingly.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

See attached file

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Needs a lot of improvement.

It was not easy to read and comprehend.

Some remarks are in the attached file.

Author Response

Response to Reviewer 3 Comments

This is a review of the manuscript coatings-3586598-peer-review-v1 entitled: “Microstructural Evolution and Wear Resistance of Silicon-Containing FeNiCrAl0.7Cu0.3Six High-Entropy Alloys” submitted to coatings.

Point 1: After careful reading of the whole manuscript, the manuscript needs some revision and modification before it can be considered for publication in “coatings”.

Response 1: Thank you very much for taking the time to review our manuscript. We have carefully revised the manuscript according to your valuable suggestions.

Point 2: Authors should revise the whole manuscript for typographical and grammatical errors. For example: Line 102: amples → samples . Also lines 93-94: under the arc.After achieving full melting, change to “under the arc. After achieving full melting.” Please check all similar cases, such as line 99. Line 114: “Microstructural analysis”

Response 2: I have made the requested revisions accordingly

(2)Before the analysis, the alloy specimens were etched with aqua regia to reveal internal features. Secondary electron imaging was employed to reveal detailed microstructural contrast, while elemental distributions were assessed via energy-dispersive spectroscopy (EDS).

(3)Subsequently, the prepared metals were melted under the arc. After achieving full melting, electromagnetic stirring was conducted, followed by repeatedly flipping and re-melting each alloy ingot no less than four times to achieve uniform composition.

Point 3: The abstract is to be extended to about 250 words

Response 5: Thank you for the suggestion. As Reviewer #2 requested the abstract to be limited to under 200 words, we revised it based on both of your comments and the actual content of our study. Specifically, we removed the wear rate values, retained the wear volume data, and reworded the description of how the wear mechanism evolves with increasing silicon content. The revised abstract is as follows:

Abstract: This study investigates the influence of silicon content on the microstructure, mechanical properties, and wear behavior of of FeNiCrAl0.7Cu0.3Six high-entropy alloys. With increasing silicon content, the microstructure evolves from a dendritic morphology the silicon-free FeNiCrAl0.7Cu0.3 alloy to a chrysanthemum-like morphology in FeNiCrAl0.7Cu0.3Si0.1 and FeNiCrAl0.7Cu0.3Si0.3 alloys, and ultimately to island-like grains in FeNiCrAl0.7Cu0.3Si0.5.This evolution is accompanied by a phase transition from a Fe and Cr-rich body-centered cubic phase to an Al and Ni-rich body-centered cubic phase, with silicon showing a tendency to segregate alongside aluminum and nickel. The hardness increases from 484 to 864 due to solid solution strengthening and the formation of a hard sigma phase. The wear mass decreases from 1.31 milligrams in the FeNiCrAl0.7Cu0.3 alloy to 0.78 milligrams in the FeNiCrAl0.7Cu0.3Si0.5 alloy, which is consistent with the increase in hardness. As the silicon content increases, the dominant wear mechanism changes from abrasive wear to adhesive wear, with the high-silicon alloy exhibiting lamellar debris on the worn surface. These findings confirm that silicon addition enhances microstructural refinement, mechanical strength, and wear resistance of the alloy system.

Point 4: . Fig. 1: (e and f). The scale bar of “f” is not 10 µm as it should be a higher magnification of the previous “e” image.

Response 4: Thank you for your comment. We have reselected the relevant SEM images so that all samples are shown at consistent magnifications (1000× and 5000×). To ensure accuracy, we also added the original scale bars from the SEM software below each image. The revised version is shown as follows:

Figure.1 SEM microstructures of FeCrNiAl0.7Cu0.3Six HEAs with different Si content: (a, c, i) Si0 a; (b, f) Si1 ; (c, g) Si3 ; (d, h) Si5.

Point 5: The caption of fig. 1 is needs more information. There’s an extra “a” in the caption. The difference between the images should be explained and detailed. Do the same with all other figure captions.

Response 5: Revision has been completed as stated in Point 4.

Point 6: Figure.2 EDS elemental mapping images of FeCrNiAl0.7 Cu0.3 Six alloys (a) Si0 a (b) Si1

(c)Si3 (d)Si5 alloy CHANGE TO: Figure. 2 EDS elemental mapping images of FeCrNiAl0.7

Cu0.3 Six alloys, (a) Si0 a, (b) Si1, (c) Si3, and (d) Si5 alloy. Please check similar cases in the article.

Response 6: We have revised the figure caption as required and checked the manuscript for similar issues throughout.

Figure.3 EDS elemental mapping images of FeCrNiAl0.7Cu0.3Six alloys (a) Si0 (b) Si1 (c) Si3 (d) Si5 alloy

Point 7: The authors must show how to prepare the samples for SEM, hardness, and wear tests.

This is important.

Response 7: I have made the requested revisions accordingly

Before microstructural observation, all alloy ingots were sectioned using a precision low-speed diamond saw to obtain cross-sectional samples. These samples were mounted in epoxy resin and successively ground with SiC abrasive papers from 240 to 2000 grit, followed by polishing with 1 μm diamond suspension on a polishing cloth until a mirror-like surface was obtained. The polished samples were then ultrasonically cleaned in ethanol for 10 minutes and air-dried. For microstructural analysis by SEM, the cleaned samples were etched using freshly prepared aqua regia (HCl:HNO₃ = 3:1 by volume) for 30 seconds to reveal the grain boundaries and phase distribution.

For microhardness testing, the samples were coarsely ground to ensure a flat and even surface.Microhardness tests were conducted using an HSV-1000A digital micro Vickers hardness tester. For each sample, six measurements were taken at different locations, and the average value and standard deviation were calculated.

Point 8: Reconsider the conclusion to reflect the novelty of research and avoid repeating technical information mentioned in the text.

Response 8: I have made the requested revisions accordingly

The microstructure of FeNiCrAl₀.₇Cu₀.₃Six HEAs changes with increasing Si content. The Si0 alloy shows a dendritic morphology, while the Si1 and Si3 alloys develop a chrysanthemum-like structure, and the Si5 alloy exhibits an island-like grain structure. Elemental mapping indicates that Al and Ni are mainly distributed in dendritic regions, whereas Cr and Fe are enriched in interdendritic areas. With higher Si content, Si tends to co-segregate with Al and Ni. Cu shows a consistent tendency to distribute with Al and Ni in all samples.
The hardness of FeCrNiAl₀.₇Cu₀.₃Six alloys increases with rising Si content, from 484 HV for the Si0 alloy to 864 HV for the Si5 alloy. This enhancement is attributed to solid-solution strengthening and the formation of the σ phase. The presence of secondary phase particles in Si3 and Si5 further contributes to mechanical strengthening.
The wear resistance is significantly improved with increasing Si. The wear mass decreases from 1.31 mg for the Si0 alloy to 0.78 mg for the Si5 alloy. Si0 and Si1 alloys primarily experience abrasive wear, whereas Si3 and Si5 exhibit smoother worn surfaces with layered wear debris, indicating a shift toward adhesive wear as the dominant mechanism. This transformation reflects the influence of Si on the alloy’s tribological behavior and provides insight into tailoring wear properties through composition design.

Point 9: What is the proof of long term stability of the prepared samples in different environments?

Response 5: The FeCrNiAl₀.₇Cu₀.₃Six high-entropy alloys investigated in this study are designed based on the core principles of high-entropy alloy design, which emphasize structural stability and compositional uniformity. The observed formation of stable BCC phases and the presence of Si-induced σ phase contribute to their expected long-term mechanical and environmental stability.

Our previous corrosion study on this alloy system also supports its potential for good environmental durability.( Effect of Si Content on Phase Structure, Microstructure, and Corrosion Resistance of FeCrNiAl0.7Cu0.3Six High-Entropy Alloys in 3.5% NaCl Solution, DOI: 10.3390/coatings15030342)

Point 10: The mechanism of alloys formation is not clear. Summarize to show the claimed novelty.

Response 5: We have added a summary of the alloy formation mechanism in the conclusion section to clarify the role of Si in driving the observed microstructural and phase evolution.

Conclusion

The microstructure of FeNiCrAl₀.₇Cu₀.₃Six HEAs changes with increasing Si content. The Si0 alloy shows a dendritic morphology, while the Si1 and Si3 alloys de-velop a chrysanthemum-like structure, and the Si5 alloy exhibits an island-like grain structure. Elemental mapping indicates that Al and Ni are mainly distributed in den-dritic regions, whereas Cr and Fe are enriched in interdendritic areas. With higher Si content, Si tends to co-segregate with Al and Ni. Cu shows a consistent tendency to distribute with Al and Ni in all samples.
The hardness of FeCrNiAl₀.₇Cu₀.₃Six alloys increases with rising Si content, from 484 HV for the Si0 alloy to 864 HV for the Si5 alloy. This enhancement is attributed to solid-solution strengthening and the formation of the σ phase. The presence of sec-ondary phase particles in Si3 and Si5 further contributes to mechanical strengthening.
The wear resistance is significantly improved with increasing Si. The wear mass decreases from 1.31 mg for the Si0 alloy to 0.78 mg for the Si5 alloy. Si0 and Si1 alloys primarily experience abrasive wear, whereas Si3 and Si5 exhibit smoother worn sur-faces with layered wear debris, indicating a shift toward adhesive wear as the domi-nant mechanism. This transformation reflects the influence of Si on the alloy’s tribo-logical behavior and provides insight into tailoring wear properties through composi-tion design.

Point 11: Include error bars where appropriate.

Response 11: Thank you for the comment. Error bars have been added to the hardness data, and the text has been updated accordingly.

Figure 4 presents the microhardness values of FeCrNiAl₀.₇Cu₀.₃Six HEAs with varying Si content. A gradual increase in hardness is observed, from 498.2 ± 15.0 HV for the Si0 sample to 502.7 ± 32.7 HV, 577.3 ± 24.5 HV, and 863.2 ± 23.5 HV for the Si1, Si3, and Si5 samples, respectively.

Figure 4. Microhardness values of FeCrNiAl_0.7Cu_0.3Si_x HEAs (x = 0, 0.1, 0.3, 0.5)

Point 12: Redraw figure 4. Start the y-axis from 0.3 or similar. This shows the curves better.

Response 12: I have made the requested revisions accordingly

Figure 5. The COF for FeCrNiAl_0.7Cu_0.3Si_x HEAs (x = 0, 0.1, 0.3, 0.5)

Point 13: Line 20-22: The statement is not clear! Missing information.

Response 13: I have made the requested revisions accordingly

Point 14: Line 83: Explain “his study”?

Response 14: I have made the requested revisions accordingly

Point 15: .Line 17: “FeNiCrAl₀.₇Cu₀.₃Si₀.₅ alloy” 0.5 not ₀.₅

Response 15: I have made the requested revisions accordingly

The wear mass decreases from 1.31 milligrams in the FeNiCrAl_0.7Cu_0.3 alloy to 0.78 milligrams in the FeNiCrAl_0.7Cu_0.3Si_0.5 alloy

Point 16: The alloys “Si0-Si5” are first mentioned in the Results and Discussion section. This is not acceptable since these are the main studied and prepared alloys. Authors need to describe the differences between them and how to prepare them and the rationale behind using such percentages in the introduction and materials/experimental section.

Response 16: Thank you for your suggestion. We have added Table 1 in the experimental section to clearly list the compositions and abbreviations (e.g., Si0–Si5) of the studied alloys. These alloys are designed as Fe-based transitional high-entropy alloys. Fe, Cr, Ni, and Cu were selected as the base elements due to their similar atomic radii, which support the formation of solid solution phases according to high-entropy alloy design principles. Al was introduced to enhance strength, and Cu, as an FCC-phase stabilizer, helps improve ductility. The overall composition was designed based on a 1:1 molar ratio of Fe and Cu, and we varied the Si content to systematically study its effect on mechanical and wear properties.

FeNiCrAl0.7Cu0.3Six alloys were designed. Among them, Fe, Ni, and Cr were selected as the principal elements due to their similar atomic radii and high mutual solubility, which are favorable for forming solid solution phases in high-entropy alloys. Al was introduced to enhance the strength of the alloy[47] while Cu was added as an FCC phase-forming element to improve ductility[48]. Si was varied systematically to study its effect on the microstructure and wear resistance of the alloy.The nominal compositions and sample abbreviations of the FeNiCrAl0.7Cu0.3Six HEAs are summarized in Table 1.

Tab.1 Nominal components of FeNiCrAl0.7Cu0.3Six HEAs (at%)

Alloy	Abbreviation	Fe	Ni	Cr	Al	Cu	Si
FeNiCrAl0.7Cu0.3	Si0	25.00	25.00	25.00	17.50	7.50	0.00
FeNiCrAl0.7Cu0.3Si0.1 0.	Si1	24.39	24.39	24.39	17.07	7.32	2.44
FeNiCrAl0.7Cu0.3Si0.3	Si3	23.26	23.26	23.26	16.28	6.98	6.98
FeNiCrAl0.7Cu0.3Si0.5	Si5	22.22	22.22	22.22	15.56	6.67	11.11

Point 17: Why not a higher percentage of Si is was not tested since as claimed that corrosion and wear changes with increasing Si concentration.

Response 17: In this study, Si was used as a minor alloying element to investigate its effect on the microstructure and properties of FeNiCrAl0.7Cu0.3Six high-entropy alloys. When the Si content reached 0.5, intermetallic compounds such as Cr₅Si₃ were already observed, which could negatively affect the alloy’s ductility and corrosion resistance. According to high-entropy alloy theory, the mixing enthalpy between Si and other principal elements is relatively large, and its atomic radius differs significantly from those of Fe, Cr, and Ni. A higher Si concentration would disrupt the formation of solid solution phases and promote brittle intermetallics. Therefore, we did not further increase the Si content in this alloy system.

If Si is considered as a major element—at levels comparable to or exceeding those of Fe, Cr, or Ni—it would constitute a different type of high-entropy alloy. Such Si-rich systems may be studied separately in the future to explore the effects of silicon as a principal component on alloy design and performance.

Point 18: In the abstract, the mention of “highest Si content” is misleading. State the

values explicitly.

Response 18: I have made the requested revisions accordingly

Point 19: Figure 5 caption: wear mass losses. This changes the meaning. Corrct

Response 19: I have made the requested revisions accordingly

Figure 6. Friction and wear properties of FeCoCrAl_0.7Cu_0.3Si_x HEA alloys with different Si contents: (a) COF; (b) wear mass.

Point 20: Many references are not cited correctly. Extra text and strange fonts. Make clearer.

Response 20: Thank you for the comment. Due to issues with the reference management software, some references currently appear with formatting errors or unreadable characters. These will be corrected during the proofreading stage using the journal's editing tools.

Point 20: Many references are not cited correctly. Extra text and strange fonts. Make clearer.

Point 21: Improve the discussion when describing figures and the drawn conclusions from results and comparisons.

Response 21: We have revised the discussion related to the microhardness results and wear performance to enhance clarity and depth of analysis. Corresponding conclusions have also been updated to better reflect the experimental findings.

(1)Figure 4 presents the microhardness values of FeCrNiAl₀.₇Cu₀.₃Six HEAs with varying Si content. A gradual increase in hardness is observed, from 498.2 ± 15.0 HV for the Si0 sample to 502.7 ± 32.7 HV, 577.3 ± 24.5 HV, and 863.2 ± 23.5 HV for the Si1, Si3, and Si5 samples, respectively. The enhancement primarily stems from solid solution hardening combined with reinforcement from the second phase. As the Si content increases, more Si atoms dissolve into the matrix, substituting for other atoms or occupying interstitial sites. This leads to significant lattice distortion and generates local stress fields that hinder dislocation motion, thereby reducing dislocation mobility and limiting plastic deformation^[50,51]. When the Si content reaches Si3, the solid solution strengthening effect becomes more pronounced, resulting in a marked increase in hardness. Within the high-entropy matrix of the Si5 alloy, trace amounts of the σ phase are also generated. This hard and brittle second phase further impedes dislocation motion and contributes to the overall enhancement in hardness^[50].

It can be seen that alloys with higher Si content have lower COF. Figure 6(b) shows the wear mass of each sample, which are 1.31mg, 1.28mg, 1.11mg, and 0.78mg, and the trend is consistent with the wear coefficient.

(2)This reduction is consistent with the increasing hardness, supporting the inverse relationship between hardness and wear volume described by the Archard wear theory. The Si5 alloy, with the highest hardness, shows a 40.46% reduction in wear mass and a 19.61% decrease in friction coefficient compared to the Si0 sample. These improvements can be attributed to enhanced resistance against plastic deformation and the protective effect of hard secondary phases, which collectively reduce material removal during sliding wear.

Point 22: What are the compositions of Fe, Cr, Ni and so on in the different prepared alloys?

Response 22: Thank you for the question. We have added a table (Table 1) in the Materials and Methods section, listing the nominal compositions (in molar ratio) of Fe, Cr, Ni, Al, Cu, and Si for each alloy (Si0–Si5).

Tab.1 Nominal components of FeNiCrAl0.7Cu0.3Six HEAs (at%)

Alloy	Abbreviation	Fe	Ni	Cr	Al	Cu	Si
FeNiCrAl0.7Cu0.3	Si0	25.00	25.00	25.00	17.50	7.50	0.00
FeNiCrAl0.7Cu0.3Si0.1 0.	Si1	24.39	24.39	24.39	17.07	7.32	2.44
FeNiCrAl0.7Cu0.3Si0.3	Si3	23.26	23.26	23.26	16.28	6.98	6.98
FeNiCrAl0.7Cu0.3Si0.5	Si5	22.22	22.22	22.22	15.56	6.67	11.11

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript presents a systematic investigation of the microstructure and wear behavior of FeNiCrAl₀.₇Cu₀.₃Six high-entropy alloys. The topic is relevant to the field of advanced metallic materials and coatings, and the experimental approach is sound. However, several areas require significant improvement in clarity, consistency, methodology presentation, and depth of discussion.

Major Comments:

Abstract

[Q1] In the abstract, consider specifying the exact compositions tested (e.g., x = 0, 0.1, 0.3, 0.5) instead of repeating the full formula multiple times.
[C1] The sentence "chrysanthemum-like morphology in Si1 and Si3" should be clarified—Si1 is also said to retain dendritic form in the results.

Introduction

[Q1] The introduction is well-referenced but it is still needed an introduction focuse on the materia behaviours bason on the content. There is some relevente references talking about many materials behaviours would be cited in your paper.

https://www.sciencedirect.com/science/article/pii/S0254058408006457

https://www.sciencedirect.com/science/article/pii/S0167577X06006136

https://www.sciencedirect.com/science/article/pii/S0257897225002130

[C2] Repeated content: Lines 54–55 repeat nearly verbatim from lines 51–52.
[C3] Grammar/clarity issues in sentences like “These alloys exhibit superior properties compared to conventional alloys...” — consider rephrasing for smoother flow.

Materials and Methods

[Q3] How was the actual composition of the HEAs verified after melting (e.g., via EDS or XRF)? Please clarify.
[Q4] What was the surface roughness/preparation protocol for the wear samples before testing?
[C4] The Vickers hardness load is listed as 100 N, which seems unusually high for microhardness. Please confirm if it was 100 gf or 1 N instead.
[C5] The wear test setup appears more like a macro-wear test. If so, rephrase "microhardness" consistently across the text.
[C7] There are relevant references that discuss other preparation methods. Please compare them with your method of preparation, cite these references appropriately, and highlight the advantages of the method you used.

Results and Discussion

[Q5] Was XRD or EBSD used to confirm the phase transformation (BCC1 to BCC2 and σ-phase formation)? SEM + EDS is not conclusive alone.
[C7] The description of “modulated decomposition” (line 117) could use references or further explanation.

[Q6] Were standard deviations or error bars calculated for hardness measurements? Please include them in Figure 3.
[C8] Rephrase “hard and brittle second phase” as “hard, brittle secondary phase (σ phase)” for technical accuracy.

[Q7] Please clarify whether wear volume was calculated from profilometry or weight loss. The method of calculating wear volume should be more explicit.
[Q8] The wear equation in line 212 has unreadable formatting. Please correct.
[C9] In Table 1, please include uncertainty/error estimates for width, depth, and wear rate.

[Q9] The transition from abrasive to adhesive wear is central to your discussion. Could this be supported by more quantified observations (e.g., roughness, wear track cross-section profiles)?
[C10] Figures 6 and 7 should have consistent scale bars and higher resolution for clearer visualization.
[C11] Consider organizing wear mechanism descriptions into a comparative table.

Please cite the following references, as they support the interpretation of microstructure, hardness, and wear behavior in the studied alloys:

The paper ‘Structure and Electrical Properties of (111)-Oriented Pb(Mg₁/₃Nb₂/₃)O₃—PbZrO₃—PbTiO₃ Thin Film for Ultra-High-Frequency Transducer Applications’ demonstrates how crystallographic orientation affects functional and structural performance, aligning with the role of phase orientation in the current HEA system.
The work ‘Lead Zirconate Titanate Thick Film with Enhanced Electrical Properties for High-Frequency Transducer’ Applications emphasizes the influence of microstructure tailoring on mechanical enhancement, supporting the observed increase in hardness due to Si-induced phase changes.
The study ‘Corrosion Behaviors and Mechanism of AlxCrFeMnCu High-Entropy Alloys in a 3.5 wt% NaCl Solution’ provides valuable insight into phase stability and compositional influence in multi-principal element alloys, which parallels the wear resistance trends discussed in the present work.

Conclusion

[C12] Conclusion point 1 is very long and could be divided into two sentences for better readability.
[Q10] Could you briefly comment on how this alloy system compares to similar compositions in literature regarding cost-performance ratio?

Minor and Technical Issues:

Numerous typographical errors are present (e.g., “amples” → “samples”; “emonstrated” → “demonstrated”).
The repeated phrase “wear resistance is improved with Si” could be varied for better readability.
Ensure consistent notation for phases (e.g., BCC1 vs. BCC-1).

The manuscript presents promising findings but requires improved clarity, technical corrections, and more robust discussion of phase verification and methodology to reach publication standards.

Author Response

Response to Reviewer 4 Comments

The manuscript presents a systematic investigation of the microstructure and wear behavior of FeNiCrAl₀.₇Cu₀.₃Six high-entropy alloys. The topic is relevant to the field of advanced metallic materials and coatings, and the experimental approach is sound. However, several areas require significant improvement in clarity, consistency, methodology presentation, and depth of discussion.

Point 1: Abstract

[Q1] In the abstract, consider specifying the exact compositions tested (e.g., x = 0, 0.1, 0.3, 0.5) instead of repeating the full formula multiple times.

[C1] The sentence "chrysanthemum-like morphology in Si1 and Si3" should be clarified—Si1 is also said to retain dendritic form in the results.

Response 1: Thank you for your guidance. I have incorporated the feedback from all the reviewers and rewritten the abstract, removing the repetitive content and adding specific research data. The revised version is as follows:

This study investigates the influence of Si content (x = 0, 0.1, 0.3, 0.5) on the microstructure, mechanical properties, and wear behavior of of FeNiCrAl0.7Cu0.3Six high-entropy alloys. With in-creasing silicon content, the microstructure evolves from a dendritic morphology the silicon-free FeNiCrAl0.7Cu0.3 alloy, to a transitional structure in the FeNiCrAl0.7Cu0.3Si0.1alloy that retains dendritic features, then to a chrysanthemum-like morphology in the FeNiCrAl0.7Cu0.3Si0.3 alloy, and finally to island-like grains in the FeNiCrAl0.7Cu0.3Si0.5 alloy.This evolution is accompanied by a phase transition from a Fe and Cr-rich body-centered cubic phase to an Al and Ni-rich body-centered cubic phase, with silicon showing a tendency to segregate alongside aluminum and nickel. The hardness increases from 484 to 864 due to solid solution strengthening and the formation of a hard sigma phase. The wear mass decreases from 1.31mg in the FeNiCrAl0.7Cu0.3 alloy to 0.78 milligrams in the FeNiCrAl0.7Cu0.3Si0.5 alloy, which is consistent with the increase in hardness. As the silicon content increases, the dominant wear mechanism changes from abrasive wear to adhesive wear, with the high-silicon alloy exhibiting lamellar debris on the worn surface. These findings confirm that silicon addition enhances microstructural refinement, mechanical strength, and wear resistance of the alloy system.

Point 2: Introduction

[Q1] The introduction is well-referenced but it is still needed an introduction focuse on the materia behaviours bason on the content. There is some relevente references talking about many materials behaviours would be cited in your paper.

https://www.sciencedirect.com/science/article/pii/S0254058408006457

https://www.sciencedirect.com/science/article/pii/S0167577X06006136

https://www.sciencedirect.com/science/article/pii/S0257897225002130

[C2] Repeated content: Lines 54–55 repeat nearly verbatim from lines 51–52.

[C3] Grammar/clarity issues in sentences like “These alloys exhibit superior properties compared to conventional alloys...” — consider rephrasing for smoother flow.

Response 2:

[Q1] I have made the requested revisions accordingly

[C2] I have made the requested revisions accordingly.

Yang et al. [38] investigated the tribocorrosion behavior of CoCrFeNi-based HEA coatings containing Ti, Mn, Mo, and Al in 3.5 wt% NaCl solution under reciprocating friction. The study revealed that friction increased the local corrosion rate by 2–3 orders of magnitude and accelerated material loss due to the synergistic effects of wear and corrosion. Wu et al. [39] studied the wear and corrosion behavior of AlCrFeCoNi and AlCrFeCoNiTi₀.₅ HEAs in NaCl and HCl solutions. They found that Ti addition enhanced hardness and improved pitting corrosion resistance by promoting the formation of a more protective passive film.

[C3] I have made the requested revisions accordingly.

These alloys offer a combination of high strength [5-8], excellent toughness [9-12], superior high-temperature performance [13-15], strong corrosion resistance [16-18] and outstanding wear resistance [19,20] , making them advantageous over conventional alloys.

Point 3: Materials and Methods

[Q3] How was the actual composition of the HEAs verified after melting (e.g., via EDS or XRF)? Please clarify.

[Q4] What was the surface roughness/preparation protocol for the wear samples before testing?

[C4] The Vickers hardness load is listed as 100 N, which seems unusually high for microhardness. Please confirm if it was 100 gf or 1 N instead.

[C5] The wear test setup appears more like a macro-wear test. If so, rephrase "microhardness" consistently across the text.

[C7] There are relevant references that discuss other preparation methods. Please compare them with your method of preparation, cite these references appropriately, and highlight the advantages of the method you used.

Response 3:

[Q3] We used EDS area scanning to verify the actual composition of the prepared high-entropy alloys after melting. Some of these data are shown below:

[Q4] I have made the requested revisions accordingly.

Wear performance was evaluated using an MM-10000A reciprocating wear tester in a ball-on-flat configuration under dry sliding conditions. The counterbody was a tungsten carbide (WC) ball with a diameter of 6 mm, and the base alloy samples meas-ured 20 mm × 20 mm × 3 mm. Prior to testing, the sample surfaces were ground se-quentially with SiC abrasive papers up to 2000 grit and then polished.The test was conducted under a normal load of 100 N, with a reciprocating frequency of 1 Hz, a stroke length of 6 mm, and a total duration of 30 minutes.

[C4] The load of 100 N was applied during the wear test. We have revised the manuscript to clarify this.

[C5] I have made the requested revisions accordingly.

Figure 4 presents the microhardness values of FeCrNiAl₀.₇Cu₀.₃Six HEAs with varying Si content. A gradual increase in microhardness is observed, from 498.2 ± 15.0 HV for the Si0 sample to 502.7 ± 32.7 HV, 577.3 ± 24.5 HV, and 863.2 ± 23.5 HV for the Si1, Si3, and Si5 samples, respectively.

[C7] I have made the requested revisions accordingly.

Compared to methods like laser cladding[50], mechanical alloying[51], and spark plasma sintering[52], arc melting is a simpler and more cost-effective way to prepare bulk high-entropy alloys. While laser cladding is good for surface coatings with fine structures, it often causes composition segregation. Arc melting, on the other hand, al-lows repeated melting and better composition control, making it more suitable for studying alloy design and bulk properties.

Point 4: [Q5] Was XRD or EBSD used to confirm the phase transformation (BCC1 to BCC2 and σ-phase formation)? SEM + EDS is not conclusive alone.

[C7] The description of “modulated decomposition” (line 117) could use references or further explanation.

[Q6] Were standard deviations or error bars calculated for hardness measurements? Please include them in Figure 3.

[C8] Rephrase “hard and brittle second phase” as “hard, brittle secondary phase (σ phase)” for technical accuracy.

[Q7] Please clarify whether wear volume was calculated from profilometry or weight loss. The method of calculating wear volume should be more explicit.

[Q8] The wear equation in line 212 has unreadable formatting. Please correct.

[C9] In Table 1, please include uncertainty/error estimates for width, depth, and wear rate.

[Q9] The transition from abrasive to adhesive wear is central to your discussion. Could this be supported by more quantified observations (e.g., roughness, wear track cross-section profiles)?

[C10] Figures 6 and 7 should have consistent scale bars and higher resolution for clearer visualization.

[C11] Consider organizing wear mechanism descriptions into a comparative table.

Please cite the following references, as they support the interpretation of microstructure, hardness, and wear behavior in the studied alloys:

The paper ‘Structure and Electrical Properties of (111)-Oriented Pb(Mg₁/₃Nb₂/₃)O₃—PbZrO₃—PbTiO₃ Thin Film for Ultra-High-Frequency Transducer Applications’ demonstrates how crystallographic orientation affects functional and structural performance, aligning with the role of phase orientation in the current HEA system.
The work ‘Lead Zirconate Titanate Thick Film with Enhanced Electrical Properties for High-Frequency Transducer’ Applications emphasizes the influence of microstructure tailoring on mechanical enhancement, supporting the observed increase in hardness due to Si-induced phase changes.
The study ‘Corrosion Behaviors and Mechanism of AlxCrFeMnCu High-Entropy Alloys in a 3.5 wt% NaCl Solution’ provides valuable insight into phase stability and compositional influence in multi-principal element alloys, which parallels the wear resistance trends discussed in the present work.

Response 4:

[Q5] In our previously published work, we used XRD to confirm the phase composition of the FeNiCrAl₀.₇Cu₀.₃Six alloys. To clarify this point, we have now included the XRD patterns in the revised manuscript (as Figure 2) and updated the corresponding description in the text accordingly.

The phase analysis based on the XRD data is discussed in detail in our previous work [49], as shown in Figure 2. The Si0 alloy corresponds to a single BCC1 phase.Figures 1(b) and (f) illustrate that the Si1 alloy retains a dendritic morphology similar to that of Si0, but no grid-like modulated structures are observed within the dendrites. In Figures 1(c) and (g), the Si3 alloy shows a transition to a chrysanthe-mum-like dendritic morphology, along with the appearance of particulate precipitates inside the dendritic grains. Both Si1 and Si3 consist of mixed BCC1 and BCC2 phases[49], and the analysis suggests that the addition of Si promotes the transformation from dendritic BCC1 to interdendritic BCC2 phases. Figures 1(d) and (h) indicate that the Si5 alloy exhibits an island-like grain configuration, in which the particulate features within the dendritic regions have disappeared. This microstructural evolution implies that the interdendritic phase observed in Si1 has transformed into the dendritic phase in the Si5 alloy. To further elucidate the phase constitution, compositional scans of the alloys were performed.

Figure.2 The XRD of FeCrNiAl0.7Cu0.3Six HEAs.

[C7] I have made the requested revisions accordingly.

A further magnified view of the dendritic zone (Figure 1(i)) shows a well-defined grid-like configuration, indicative of a modulated decomposition structure[55]. This structure arises from the uneven distribution of elements during solidification, where certain elements tend to enrich in specific regions, while others accumulate in adjacent zones, resulting in periodic compositional fluctuations. These periodic variations give rise to modulated microstructures. In high-entropy alloys, such structures are more prone to form due to the complex interactions among multiple principal elements and their relatively slow diffusion kinetics[55,56].

[Q6] I have made the requested revisions accordingly.

Figure 4. Microhardness values of FeCrNiAl_0.7Cu_0.3Si_x HEAs (x = 0, 0.1, 0.3, 0.5)

[C8] I have made the requested revisions accordingly.

This hard, brittle secondary phase (σ phase) further impedes dislocation motion and contributes to the overall enhancement in microhardness[57].

[Q7] In response to this and related reviewer suggestions, we have unified the analysis method across the manuscript. Wear performance is now consistently evaluated using mass loss measurements. The corresponding text has been clarified as follows:

Figure 6(b) shows the wear mass of each sample, which are 1.31mg, 1.28mg, 1.11mg, and 0.78mg, and the trend is consistent with the wear coefficient. This reduction is consistent with the increasing microhardness, supporting the inverse relationship between microhardness and wear volume described by the Archard wear theory. The Si5 alloy, with the highest microhardness, shows a 40.46% reduction in wear mass and a 19.61% decrease in friction coefficient compared to the Si0 sample. These improvements can be attributed to enhanced resistance against plastic deformation and the protective effect of hard secondary phases, which collectively reduce material removal during sliding wear.

[Q8] According to the reviewers' comments, this equation is not adopted for evaluating friction and wear in this study.

[C9] According to the reviewers' comments, this equation is not adopted for evaluating friction and wear in this study.

[Q9] Since our wear mechanism analysis in this study is primarily based on SEM surface morphology, it is difficult to provide additional quantitative data such as roughness measurements or wear track cross-sectional profiles. However, considering the importance of this point, we have revised the corresponding section to more clearly describe the observed transition from abrasive to adhesive wear based on surface features. The revised content is as follows:

Figure 8(a), (c), (e), and (g) depict the wear surface features of the Si0, Si1, Si3, and Si5 alloys, while the corresponding enlarged views are presented in (b), (d), (f), and (h), respectively. As the Si content increases, the wear surface and wear mechanisms gradually change. The wear surface of Si0 alloy exhibits consistent plowing grooves aligned with the wear direction, with white abrasive particles and block-like debris scattered around the grooves. The surface also shows delamination and plastic defor-mation at the edges. This type of damage is primarily caused by both abrasive wear and adhesive wear. The formation of the grooves is attributed to two factors: mi-cro-cutting of the material surface by the abrasive particles and the formation of grooves under the frictional interaction. After repeated wear, the raised parts adjacent to the grooves gradually detach from the surface. The delamination phenomenon sug-gests that the shear strength of the adhesive points is greater than that of the alloy but less than the shear strength of WC, resulting in shear deformation on the alloy surface, which leads to a coexistence of abrasive wear and adhesive wear. The Si1 alloy surface still displays plowing grooves but without the ridge-like protrusions, indicating that abrasive wear remains dominant, accompanied by some adhesive wear, with plastic deformation also occurring at the edges. The wear surface of Si3 alloy still shows pri-marily abrasive wear with the formation of granular abrasive agglomerates.

[C10] I have revised the figures and replaced several images as shown below.

Figure.7 Wear track characterization of FeCoCrAl_0.7Cu_0.3Si_x HEAs: macroscopic morphology, laser confocal topography, and geometric profile for (a) Si0, (b) Si1, (c) Si3, (d) Si5 alloy.

Figure.8 Worn surface characteristics of FeNiCrAl_0.7Cu_0.3Si_x HEAs: (a)(b) Si0, (c)(d) Si1, (e)(f) Si3, (g)(h) Si5 alloy

[C11] I have made the requested revisions accordingly.

Point 5: Conclusion

[C12] Conclusion point 1 is very long and could be divided into two sentences for better readability.

[Q10] Could you briefly comment on how this alloy system compares to similar compositions in literature regarding cost-performance ratio?

Minor and Technical Issues:

Numerous typographical errors are present (e.g., “amples” → “samples”; “emonstrated” → “demonstrated”).

The repeated phrase “wear resistance is improved with Si” could be varied for better readability.

Ensure consistent notation for phases (e.g., BCC1 vs. BCC-1).

The manuscript presents promising findings but requires improved clarity, technical corrections, and more robust discussion of phase verification and methodology to reach publication standards.

Response 5:

[C12] I have made the requested revisions accordingly.

With increasing Si content, the microstructure changes from dendritic (Si₀) to a transitional structure (Si₀.₁), then to chrysanthemum-like (Si₀.₃), and finally to is-land-like grains (Si₀.₅). Al and Ni are enriched in dendrites, while Cr and Fe are in in-terdendritic areas. Si and Cu tend to co-segregate with Al and Ni.

[Q10] In this work, we removed cobalt to reduce cost and used more economical elements such as Fe, Cr, and Ni. The resulting alloy still exhibits good strength and wear resistance. However, its corrosion resistance and toughness still require further comprehensive evaluation.

Point 6:

Minor and Technical Issues:

Numerous typographical errors are present (e.g., “amples” → “samples”; “emonstrated” → “demonstrated”).

The repeated phrase “wear resistance is improved with Si” could be varied for better readability.

Ensure consistent notation for phases (e.g., BCC1 vs. BCC-1).

The manuscript presents promising findings but requires improved clarity, technical corrections, and more robust discussion of phase verification and methodology to reach publication standards.

Response 6: Thank you for the suggestions. We have carefully checked the manuscript and corrected typographical and formatting errors.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

thank you for your dedication, the manuscript has been significantly improved.

I've noticed you've stated the use of Olympus DSX1000 for topography characterization. Regarding your future work, I would advise to look for partners who possess either a laser scanning microscope, confocal microscope, white light interferometer, or a traditional stylus profilometer and cooperate with them to acquire surface topography data with adequate resolution. Despite all advances in computational photography, the focus variation technique still has an inherent limit in resolution due to the characteristics of traditional optical imaging systems. I have experience with both focus variation, confocal and interferometry; focus variation is inferior when it comes to resolving fine details, as it smudges surface features. When possible, aim for interferometry and support the analysis with high magnification scanning electron microscopy, to have concrete evidence of the wear mechanisms.

Author Response

Response to Reviewer 1 Comments

Point :

Dear Authors,

thank you for your dedication, the manuscript has been significantly improved.

Response：Thank you very much for your detailed comments. We sincerely appreciate your recognition of the improvements made to our manuscript.Regarding the wear tests, our high-entropy alloy samples were made at Northwestern Polytechnical University, and the friction and wear experiments were carried out at Shenyang University of Technology, where the available equipment was used.

In future work, we’ll try to cooperate with teams that have better surface measurement tools. We’ll also read more literature in this area to improve our experiments and understanding of wear behavior in high-entropy alloys.

Thanks again for your valuable suggestions!

Reviewer 3 Report

Comments and Suggestions for Authors

The authors did a very good job improving the manuscript to a better level. However, some points are still not answered and need careful attention.

The abstract should contain some numerical results.
Point 12 was not done although the authors said that they did it. Redo figure 5 (figure 4 in the last version).
Make sure that all newly added text and tables are accurate.

Comments on the Quality of English Language

Good

Author Response

Response to Reviewer 3 Comments

The authors did a very good job improving the manuscript to a better level. However, some points are still not answered and need careful attention.

Point 1: Thank you for your guidance. I have revised the abstract as required. The updated content is as follows:

Response 1: Thank you very much for taking the time to review our manuscript. We have carefully revised the manuscript according to your valuable suggestions.

Abstract: This study investigates the influence of Si content (x = 0, 0.1, 0.3, 0.5) on the micro-structure, mechanical properties, and wear behavior of of FeNiCrAl0.7Cu0.3Six high-entropy alloys. With increasing silicon content, the microstructure evolves from a dendritic morphology the sil-icon-free FeNiCrAl0.7Cu0.3 alloy, to a transitional structure in the FeNiCrAl0.7Cu0.3Si0.1alloy that retains dendritic features, then to a chrysanthemum-like morphology in the FeNiCrAl0.7Cu0.3Si0.3 alloy, and finally to island-like grains in the FeNiCrAl0.7Cu0.3Si0.5 alloy.This evolution is accom-panied by a phase transition from a Fe and Cr-rich body-centered cubic phase to an Al and Ni-rich body-centered cubic phase, with silicon showing a tendency to segregate alongside aluminum and nickel. The microhardness increases from 498.2 ± 15.0 HV for the FeNiCrAl0.7Cu0.3 alloy, to 502.7 ± 32.7 HV for FeNiCrAl0.7Cu0.3Si0.1, 577.3 ± 24.5 HV for FeNiCrAl0.7Cu0.3Si0.3, and 863.2 ± 23.5 HV for FeNiCrAl0.7Cu0.3Si0.5. The average friction coefficients are 0.571, 0.551, 0.524, and 0.468, respectively. The wear mass decreases from 1.31 mg in the FeNiCrAl0.7Cu0.3 alloy to 1.28 mg, 1.11 mg, and 0.78 mg in the FeNiCrAl0.7Cu0.3Si0.1, FeNiCrAl0.7Cu0.3Si0.3, and FeNiCrAl0.7Cu0.3Si0.5 samples, respectively. These trends are consistent with the increase in microhardness, supporting the inverse relationship between hardness and wear. As the silicon content increases, the dom-inant wear mechanism changes from abrasive wear to adhesive wear, with the high-silicon alloy exhibiting lamellar debris on the worn surface. These findings confirm that silicon addition en-hances microstructural refinement, mechanical strength, and wear resistance of the alloy system.

Point 2: Point 12 was not done although the authors said that they did it. Redo figure 5 (figure 4 in the last version).

Response 2: We apologize for the oversight. I misunderstood the original meaning of Point 12. The figure has now been revised as requested. The updated content is as follows:

Figure 5. The COF for FeCrNiAl_0.7Cu_0.3Si_x HEAs (x = 0, 0.1, 0.3, 0.5)

Point 3: Make sure that all newly added text and tables are accurate.

Response 3: I have carefully rechecked the manuscript to ensure the accuracy of all newly added text and tables. Figure 1 has been cropped accordingly, and all figure labels have been verified.

Thank you again for taking the time to review and guide the revision.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Thanks to the authors for including the needed corrections.

Author Response

Response to Reviewer 4 Comments

Point : Thanks to the authors for including the needed corrections.

Response : Thank you very much for your careful review. We truly appreciate the time and effort you spent on our manuscript.

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Microstructural Evolution and Wear Resistance of Silicon-Containing FeNiCrAl_0.7Cu_0.3Si_x High-Entropy Alloys

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