Review Reports - Phase Structure, Microstructure, Corrosion, and Wear Resistance of Al<sub>0.8</sub>CrFeCoNiCu<sub>0.5</sub> High-Entropy Alloy

Round 1

Reviewer 1 Report

The following comments may be incorporated before accepting the article for publication in Lubricants:

1. The introduction needs to include a few recent articles on HEA's dual-phase microstructure. The authors may refer to the below-mentioned articles:

https://doi.org/10.1080/14786435.2021.2001066

2. Authors must comment on the host lattice for BCC1 and BCC2 based on their lattice parameters. Authors must deconvolute the (110) peak of the BCC phase to clearly show the existence of BCC1 and BCC2 separately.

3. Why the intensity of the (200) reflection of the BCC phase is higher than its (110) reflection?

4. Authors need not mention the counts on the y-axis when they have already mentioned 'Intensity (a.u.)'. Please revise.

The English is acceptable. A few minor corrections can be made by the authors themselves after careful reading.

Author Response

Response to Reviewer 1 Comments

Point 1: The introduction needs to include a few recent articles on HEA's dual-phase microstructure. The authors may refer to the below-mentioned articles:

https://doi.org/10.1080/14786435.2021.2001066

Response 1: The introduction of the manuscript has been added, and the content is as follows:

In summary, HEAs have good mechanical properties and corrosion resistance, which enable them as coatings. More importantly, Al has a large solubility in HEA systems containing Co, Fe, Cr, Ni, and Cu elements, which means that the Al in the substrate and the added powder will tend to form solid solutions after the reaction reducing the susceptibility of the coating to cracking. It indicates that the HEA can potentially improve the surface properties of Al substrates. But this theory is still required to be verified by experiments. In addition, Al has been proven to improve the mechanical properties of HEA due to its large atomic radius and the ability to promote the formation of the BCC phase. It would be interesting to study the influence of Al on the properties of as-cladding HEA coating containing Fe, Co, Ni, Cr, and Cu elements. However, there are few studies on using Al-Cr-Fe-Co-Ni-Cu HEAs as a coating to improve the surface properties of aluminum.

Point 2: Authors must comment on the host lattice for BCC1 and BCC2 based on their lattice parameters. Authors must deconvolute the (110) peak of the BCC phase to clearly show the existence of BCC1 and BCC2 separately.

Response 2: Thanks for spotting it. The modifications are as follows:

Point 3: Why the intensity of the (200) reflection of the BCC phase is higher than its (110) reflection?

Response 3: Thanks for spotting it. The modifications are as follows:

The XRD pattern of Al0.8CrFeCoNiCu0.5 high-entropy alloy is shown in Figure 1(a), with Figure 1(b) and 1(c) representing the deconvolution of the BCC peaks. Diffraction peaks located at 44.8° and 65.1° are respectively attributed to the (110) and (200) planes of the BCC1 phase, which matches with the (Fe,Cr) phase. Peaks appearing at 31.3°, 44.9°, and 65.3° confirm the presence of an ordered BCC2 phase within the alloy, correspond-ing to the (100), (110), and (200) planes, consistent with the Al-Ni ``phase27. Peaks shown at 43.7°, 50.9°, and 74.7° indicate the FCC phase, which is attributed to the (111), (200), and (220) planes, matching with the Cu phase. These results are in line with previous re-search on as-cladding Al0.8CrFeCoNiCu0.5 high-entropy alloy28. Notably, the diffraction peak of the BCC phase (200) plane exhibits higher intensity than that of the (110) plane. The peak at (200) is the most intense and sharply defined, indicating a high degree of crystallinity. Moreover, it demonstrates a significant textural advantage in the (200) di-rection, which could be due to more or better-ordered grain growth in the (200) direction during the crystal's growth or processing. This can primarily be attributed to the BCC phase's preferred orientation along the （200） direction²⁹.

Point 4: Authors need not mention the counts on the y-axis when they have already mentioned 'Intensity (a.u.)'. Please revise.

Response 4: Thanks for spotting it. I have corrected the caption of Figure 1.

Author Response File: Author Response.pdf

Reviewer 2 Report

INTEREST:

Dear Editor,

I am writing to express my strong interest in the paper entitled "Phase Structure, Microstructure, Corrosion and Wear Resistance of Al0.8CrFeCoNiCu0.5 High-Entropy Alloy" by Yanzhou Li and colleagues. This research presents interesting findings with the potential for publication in the Lubricants Journal from MDPI. However, in order to meet the quality standards of this esteemed journal, significant improvements are needed in the exposition and analysis of the results. Therefore, I highly recommend that the authors undertake a major revision of the paper, incorporating the following recommendations and addressing the provided comments.

COMMENTS:

Here are some specific points for the authors to consider:

1. Abstract: It is necessary to specify the medium in which the electrochemical measurements were carried out. Clarifying this detail will provide crucial context for the readers.

2. Electrochemical tests: The description of the electrochemical tests requires improvement. Please address the following points: (i) Specify the duration for which the samples were left in conditions of open circuit potential for the electrode potential stabilization. (ii) Clearly state the potential range swept in relation to the reference electrode during the potentiodynamic polarization test. (iii) Indicate the number of samples analyzed for each test. (iv) If an average value was considered in the manuscript, it should be explicitly mentioned. Also, what was the standard deviation from the measurements? (v) Provide a detailed description of the assembly process for the working electrodes, including any specific considerations (for instance, has care been taken to avoid the presence of crevices in the working electrode?) or techniques employed.

3. Address repeatability: It is crucial to address the repeatability of the electrochemical measurements. Report the observed variation between the open circuit potential (OCP) and corrosion potential (Ecorr) measurements. Additionally, clarify whether the data presented in Figures 5 and 8 represent single results or averages of multiple data points. Reproducibility is a known issue in these systems, and it is important for the authors to explicitly address this concern.

4. In order to enhance the analysis and discussion of the polarization measurements, it is crucial to provide a comprehensive qualitative description of the polarization behavior exhibited by the samples. By offering a detailed qualitative analysis, readers will gain a better understanding of the observed polarization trends and their underlying mechanisms. Furthermore, it is highly recommended to compare the obtained polarization results with those reported in previous studies available in the literature. How would a traditional stainless steel alloy (e.g., AISI 304 stainless steel) perform in these environments? It would be very interesting to make a comparison with the materials studied. One particularly relevant reference is the work on traditional stainless alloy AISI 304 austenitic stainless steel, published in "https://doi.org/10.1016/j.matchemphys.2012.01.049". By drawing a comparison between the polarization behavior of the material under investigation and the AISI 304 stainless steel, valuable insights can be obtained regarding the performance and corrosion resistance characteristics of the studied samples. This comparative analysis will allow for a more comprehensive evaluation of the polarization measurements and help establish the unique features and the pros and cons of the tested samples.

5. Please check the drawing style of Figure 8. Redraw the x and y axes exactly on the same scale in the Nyquist plots. Additionally, the Nyquist plots should have a defined frequency axis.

6. The analysis and discussion of the EIS measurements are unfortunately very superficial and insufficient. Please present, at a minimum, the phenomena that can be observed in each frequency range and phase angle. Take the following reference as a basis: "https://doi.org/10.1016/j.corsci.2011.12.022". Additionally, consider presenting all the results obtained from fitting the EIS data by the electrical equivalent circuit in a table. This table should include the values of the CPE's parameters as well as the goodness of fit (i.e., Chi square).

7. Long-term electrochemical impedance spectroscopy (EIS) investigation: I recommend that the authors conduct long-term EIS investigations of the electrochemical corrosion behavior of the Al0.8CrFeCoNiCu0.5 High-Entropy Alloy (HEA). While many published reports focus on short-term potentiodynamic anodic polarization tests, a more comprehensive approach for engineering applications of this HEA would involve characterizing the rate of damage accumulation under free corrosion conditions. This can be achieved by analyzing pit distribution after a period of exposure or by measuring the global surface response using EIS after an extended period of free corrosion exposure.

8. Concluding section: This section should concisely and critically summarize the key findings and fundamental outcomes of the work. Furthermore, if possible, the authors could provide recommendations for future research and advancements in the field.

By addressing these recommendations and comments, the authors can significantly enhance the quality and impact of their manuscript, making it suitable for publication in the Lubricants Journal from MDPI.

Thank you for considering these suggestions. I look forward to seeing the revised version of this promising work.

Author Response

Response to Reviewer 2 Comments

Point 1: 1Abstract: It is necessary to specify the medium in which the electrochemical measurements were carried out. Clarifying this detail will provide crucial context for the readers.

Response 1: The abstract of the manuscript has been added, and the content is as follows:

This study investigates the structure and corrosion behavior of the Al0.8CrFeCoNiCu0.5 high-entropy alloy prepared using non-consumable vacuum arc melting. XRD analysis identified BCC1 and BCC2 phases corresponding to (Fe-Cr) and Al-Ni, respectively, while the FCC phase aligned with Cu. SEM and EBSD observations confirmed an equiaxed grain structure with fishbone-like morphology at grain boundaries and modulated structures within the grains. The alloy exhibited minimal residual stress and strain. The alloy demonstrated a preferred orientation of grain growth along the <001> direction. Electrochemical testing in a 3.5% NaCl solution revealed a corrosion po-tential of -0.332V and a corrosion current density of 2.61×10-6 A/cm2.The intergranular corrosion regions exhibited significant depletion of Al and Cu elements, with the corrosion products primar-ily consisting of Al and Cu. Al and Cu elements are susceptible to corrosion. The wear scar width of Al0.8CrFeCoNiCu0.5 High-entropy alloy is 1.65mm, less than 45 # steel, and High-entropy alloy has more excellent wear resistance. Given its unique attributes, this high-entropy alloy could find potential applications in high-end manufacturing industries such as aerospace engineering, de-fense industry, energy production, and chemical processing where high corrosion resistance and wear resilience are crucial.

Point 2: Electrochemical tests: The description of the electrochemical tests requires improvement. Please address the following points: (i) Specify the duration for which the samples were left in conditions of open circuit potential for the electrode potential stabilization. (ii) Clearly state the potential range swept in relation to the reference electrode during the potentiodynamic polarization test. (iii) Indicate the number of samples analyzed for each test. (iv) If an average value was considered in the manuscript, it should be explicitly mentioned. Also, what was the standard deviation from the measurements? (v) Provide a detailed description of the assembly process for the working electrodes, including any specific considerations (for instance, has care been taken to avoid the presence of crevices in the working electrode?) or techniques employed.

Response 2: Thanks for spotting it. The section2 of the manuscript has been added, and the content is as follows:

The electrochemical workstation (Nova2, Metrohm, Switzerland) was employed to measure the samples' potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). ZView software was used for data fitting and calculations. The experimental setup involved a three-electrode system, with the sample as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum sheet electrode as the auxiliary electrode.

Before the electrochemical tests, the surface of the working electrode was carefully polished using sandpaper to achieve a smooth and flat surface. For electrochemical assessments, samples were embedded in polyester resin to establish electrical contact, with special precautions taken to prevent any crevice formation. The exposed area was strictly 1.0 cm². All electrochemical examinations were conducted at 25°C in a newly prepared 3.5% NaCl solution.

To ensure the accuracy of the results, each test was conducted more than three times. From all the prepared specimens, a set of reproducible samples was chosen. One sample from this set was then selected for further testing and analysis. During the potentiodynamic polarization curve test, the initial and final potentials were set to -0.8V and 2.3V, relative to the saturated calomel electrode, with a scanning rate of 1 mV/s. The open circuit potential (OCP) of the sample was measured and allowed to stabilize for a period of 30 minutes to ensure system stability. The frequency range for the EIS measurements was set between 100 kHz and 10 MHz, with an amplitude of 10 mV. Upon completion of the corrosion test, the surface morphology of the samples was inspected using a field-emission scanning electron microscope.

Point 3: Address repeatability: It is crucial to address the repeatability of the electrochemical measurements. Report the observed variation between the open circuit potential (OCP) and corrosion potential (Ecorr) measurements. Additionally, clarify whether the data presented in Figures 5 and 8 represent single results or averages of multiple data points. Reproducibility is a known issue in these systems, and it is important for the authors to explicitly address this concern.

Response 3: I appreciate the expert's input, which has been crucial in enhancing the precision of the manuscript's content. For our samples, we conducted over three measurements each to ensure the reproducibility of our results. In the manuscript, we chose one among the reproducible samples for analysis. Additional descriptions have been incorporated into Figures 5 and 8, the details of which are as follows:

Figure 5 depicts the polarization test curve of Al_0.8CrFeCoNiCu_0.5 high-entropy alloy , derived from a single selected sample.

Figure 8 illustrates the Nyquist plot, impedance modulus curve, and phase angle plot for the Al_0.8CrFeCoNiCu_0.5 high-entropy alloy, all of which are based on a single chosen sample.

Point 4: In order to enhance the analysis and discussion of the polarization measurements, it is crucial to provide a comprehensive qualitative description of the polarization behavior exhibited by the samples. By offering a detailed qualitative analysis, readers will gain a better understanding of the observed polarization trends and their underlying mechanisms. Furthermore, it is highly recommended to compare the obtained polarization results with those reported in previous studies available in the literature. How would a traditional stainless steel alloy (e.g., AISI 304 stainless steel) perform in these environments? It would be very interesting to make a comparison with the materials studied. One particularly relevant reference is the work on traditional stainless alloy AISI 304 austenitic stainless steel, published in "https://doi.org/10.1016/j.matchemphys.2012.01.049". By drawing a comparison between the polarization behavior of the material under investigation and the AISI 304 stainless steel, valuable insights can be obtained regarding the performance and corrosion resistance characteristics of the studied samples. This comparative analysis will allow for a more comprehensive evaluation of the polarization measurements and help establish the unique features and the pros and cons of the tested samples.

Response 4: Thanks for spotting it. The section 3.2 of the manuscript has been added, and the content is as follows:

The corrosion current density is calculated via the Tafel extrapolation method. The cor-rosion potential of the alloy is measured at -0.332V, and the corrosion current density stands at 2.61×10-6A/cm2. In a study conducted by Rovere et al.³⁵, the corrosion resistance of AISI 304 stainless steel was compared to that of three Fe–Mn–Si–Cr–Ni–Co shape memory stainless steels (SMSSs). AISI 304 showed a lower corrosion potential in a 3.5% NaCl solution, signifying superior corrosion resistance compared to the SMSSs, but infe-rior when compared to the Al0.8CrFeCoNiCu0.5 high-entropy alloy investigated in this study. This alloy exhibited superior corrosion resistance in the same environment, as ev-idenced by its higher corrosion potential.Rovere et al. attributed the relatively better cor-rosion resistance of AISI 304, compared to the SMSSs, to its higher Cr content. Similarly, the Al0.8CrFeCoNiCu0.5 high-entropy alloy, which has an even higher Cr content, can be seen as the reason for its superior corrosion resistance when compared to both the AISI 304 and the SMSSs. Furthermore, high-entropy alloys benefit from the cocktail effect. Therefore, the higher content of Cr and Ni in the Al0.8CrFeCoNiCu0.5 alloy is another sig-nificant factor contributing to its superior corrosion resistance compared to both AISI 304 stainless steel and the SMSSs.

Point 5: Please check the drawing style of Figure 8. Redraw the x and y axes exactly on the same scale in the Nyquist plots. Additionally, the Nyquist plots should have a defined frequency axis.

Response 5: Thanks for spotting it. I have corrected Figure 8. The modifications are as follows:

Point 6: The analysis and discussion of the EIS measurements are unfortunately very superficial and insufficient. Please present, at a minimum, the phenomena that can be observed in each frequency range and phase angle. Take the following reference as a basis: "https://doi.org/10.1016/j.corsci.2011.12.022". Additionally, consider presenting all the results obtained from fitting the EIS data by the electrical equivalent circuit in a table. This table should include the values of the CPE's parameters as well as the goodness of fit (i.e., Chi square).

Response 6: Thanks for spotting it. The modifications are as follows:

Figure 8 illustrates the Nyquist plot, impedance modulus curve, and phase angle plot for the Al0.8CrFeCoNiCu0.5 high-entropy alloy, all of which are based on a single chosen sample. The scattered data points in the Nyquist plot (Figure 8a) represent the experimental measurements, while the curve represents the fitted data. The diameter of the capacitive semicircle is related to the charge transfer resistance. A larger capacitive semicircle diameter indicates better corrosion resistance, and the capacitance radius of this sample is approximately 3000Ω·cm². The Bode plot's higher |Z| value signifies better corrosion resistance. From the Bode plot of the sample (Figure 8b), it can be observed that the sample's highest |Z| value reaches 56710Ω·cm² in the low-frequency region. Generally, the higher the |Z| value in the Bode diagram, the better the corrosion resistance. As shown in Figure 8b, the |Z| value of the sample exhibits an increasing trend in the high-frequency range (0.01 Hz to 0.1 Hz), reaching a maximum value of 7153Ω·cm². The Bode value continuously decreases in the mid-frequency range (0.1 Hz to 10000 Hz), ending at 5.918Ω·cm². The high phase angle indicates good oil repellency in the high-frequency range, whereas the large modulus in the low-frequency range suggests enhanced corrosion resistance. The sample shows high phase angles in both the high-frequency and low-frequency ranges, indicating a certain degree of corrosion re-sistance.The high phase angle in the high-frequency range indicates good repellent performance, while the large modulus in the low-frequency range suggests enhanced corrosion resistance. The sample exhibits high phase angles in both the high-frequency and low-frequency ranges, indicating a certain level of corrosion resistance. This may be attributed to the formation of a dense chromium oxide film on the sample surface and the synergistic effect with other elements in forming a passive film. The phase angle plot shows that in the high-frequency range (0.01 Hz to 0.1 Hz), the phase angles are close to 10 degrees, indicating that the impedance is predominantly determined by electrolytic resistance. Within a narrow band in the mid-frequency region (10 Hz to 20 Hz), the phase angle values reach their maximum, which is indicative of capacitive behavior characteristics³⁶.

Point 7: Long-term electrochemical impedance spectroscopy (EIS) investigation: I recommend that the authors conduct long-term EIS investigations of the electrochemical corrosion behavior of the Al0.8CrFeCoNiCu0.5 High-Entropy Alloy (HEA). While many published reports focus on short-term potentiodynamic anodic polarization tests, a more comprehensive approach for engineering applications of this HEA would involve characterizing the rate of damage accumulation under free corrosion conditions. This can be achieved by analyzing pit distribution after a period of exposure or by measuring the global surface response using EIS after an extended period of free corrosion exposure

Response 7: Thank you for your valuable suggestion. We agree that a long-term Electrochemical Impedance Spectroscopy (EIS) study would provide deeper insights into the free corrosion behavior of the Al0.8CrFeCoNiCu0.5 High-Entropy Alloy. However, due to limitations in our current experimental setup, we are unable to conduct long-term EIS investigations at this time. Nonetheless, we appreciate your suggestion and will consider incorporating such investigations in our future work. This would indeed be an important step forward in understanding and describing the accumulation of damage and corrosion behaviors of HEAs in engineering applications

Point 8: Concluding section: This section should concisely and critically summarize the key findings and fundamental outcomes of the work. Furthermore, if possible, the authors could provide recommendations for future research and advancements in the field.

Response 8: The wear mechanism has been added, and the content is as follows:

This study presents a comprehensive investigation of the Al0.8CrFeCoNiCu0.5 high-entropy alloy, exploring its structural characteristics, electrochemical behavior, and wear resistance. The principal findings from this research are:

(1) The Al0.8CrFeCoNiCu0.5 high-entropy alloy exhibits the presence of BCC1 and BCC2 phases, corresponding to (Fe-Cr) and Al-Ni, respectively. The identified FCC phase aligns with the Cu element.

(2) Te Al0.8CrFeCoNiCu0.5 high-entropy alloy exhibits an equiaxed grain structure with a fishbone-like morphology at the grain boundaries and the presence of modulated structures within the grains. The intragranular regions predominantly comprise the BCC, while the intergranular areas primarily comprise the FCC. The alloy demonstrates minimal residual stress and strain within its internal structure. The alloy grains tend to grow along the <001> direction.

(3) The Al0.8CrFeCoNiCu0.5 high-entropy alloy showed a corrosion potential of -0.332V and a corrosion current density of 2.61×10-6A/cm2. The corrosion surface of the al-loy remained relatively intact, with some areas exhibiting intergranular corrosion. The intergranular corrosion regions exhibited significant depletion of Al and Cu elements, while the corrosion products primarily consisted of Al and Cu elements. Al and Cu phases contribute to the alloy's susceptibility to corrosion.

(4) The wear scar width of Al0.8CrFeCoNiCu0.5 High-entropy alloy is 1.65mm, less than 45 # steel, and High-entropy alloy has more excellent wear resistance. Compared with 45# steel, the wear surface of Al0.8CrFeCoNiCu0.5 high entropy alloy is more intact, and the wear form is mainly adhesive wear.

These findings offer significant insights into the behavior of the Al0.8CrFeCoNiCu0.5 high-entropy alloy, pointing out its potential for applications that require high corrosion and wear resistance. Future studies are recommended to focus on a more in-depth understanding of the corrosion behavior of the alloy through long-term Electrochemical Impedance Spectroscopy and other advanced methods. This could potentially lead to further enhancements in the design and performance of the alloy in harsh environments.

Author Response File: Author Response.pdf

Reviewer 3 Report

The author must incorporate the below suggestions/comments in their manuscript.

1. The application line can be added to the abstract.

2. The research gap followed by the objective should be elaborated more.

3. Sample preparation and sample must be included.

4. Fig 2 scale is not visible. It can be improved.

5. Fig 3, the author should include the observation in SEM images.

6. Fig 8, visibility of scale should be improved.

7. The author can include the raw data of friction coefficient.

8. The author should include the wear mechanism in the last paragraph of Sec 3.4.

Author Response

Point 1: 1. The application line can be added to the abstract.

Response 1: The abstract of the manuscript has been added, and the content is as follows:

Point 2: The research gap followed by the objective should be elaborated more.

Response 2: Thanks for spotting it. The conclusion of the manuscript has been added, and the content is as follows:

The study offers valuable insights into the Al0.8CrFeCoNiCu0.5 high-entropy alloy, highlighting its potential in applications requiring high corrosion and wear resistance. However, the research identified gaps in the understanding of the alloy's long-term cor-rosion behavior, specifically the lack of extended Electrochemical Impedance Spectros-copy (EIS) studies.To fill this gap, future research should focus on long-term EIS investi-gations of the alloy and explore its behavior under varied conditions. This would con-tribute to the alloy's design optimization, enhancing its performance in harsh operation-al environments.

Point 3: Sample preparation and sample must be included.

Response 3: Thanks for spotting it. The section 2 of the manuscript has been added, and the content is as follows:

The observation surface was sequentially polished with 400#, 800#, 1500#, and 2500# water sandpaper, and then the EBSD sample was prepared using electrolytic polishing. The electrolytic polishing solution is a mix of 10% acetic acid and 90% perchloric acid. The polishing temperature was controlled at -30℃, the polishing voltage was set at 20 V, and the polishing current was approximately 0.3 A. After polishing for 60 seconds, the sample was rapidly removed, and the corroded surface was rinsed with running water. It was then cleaned with anhydrous ethanol for the final wash. After drying with cold air, a flat and shiny EBSD sample surface was obtained.

Before the electrochemical tests, the surface of the working electrode was carefully polished using sandpaper to achieve a smooth and flat surface. For electrochemical as-sessments, samples were embedded in polyester resin to establish electrical contact, with special precautions taken to prevent any crevice formation. The exposed area was strict-ly 1.0 cm². All electrochemical examinations were carried out at 25°C in a newly pre-pared 3.5% NaCl solution.

Point 4: Fig 2 scale is not visible. It can be improved.

Response 4: Thanks for spotting it. I have corrected the scale of Figure 2. The modifications are as follows:

Point 5: Fig 3, the author should include the observation in SEM images.

Response 5: Thanks for spotting it. I have corrected Figure 3. The modifications are as follows:

Point 6: Fig 8, visibility of scale should be improved.

Response 6: Thanks for spotting it. I have corrected Figure 8. The modifications are as follows:

Point 7: The author can include the raw data of friction coefficient.

Response 7: The raw data of friction coefficient has been added, and the content is as follows:

Figure 9 presents the friction coefficient curve of Al_0.8CrFeCoNiCucc high-entropy alloy and 45# steel. As observed, there are significant fluctuations in the curve during the initial phase of wear. This is primarily due to the unevenness of the worn surface, which affects the workpiece during wear.The surface contact occurs mainly at points or lines, leading to an unstable frictional performance throughout the wear experiments. The friction coefficients of Al_0.8CrFeCoNiCu_0.5 high-entropy alloy and 45 # steel is 0.519 and 0.514, respectively, showing a minimal difference.

Point 8: The author should include the wear mechanism in the last paragraph of Sec 3.4.

Response 8: The wear mechanism has been added, and the content is as follows:

Figure 10 shows the wear surface morphology of 45# steel and Al_0.8CrFeCoNiCu_0.5high entropy alloy under dry friction conditions. Figures 10(a) and 10(c) respectively show the wear mark morphology of 45# steel and Al0.8CrFeCoNiCu0.5 high entropy alloy. The wear mark width of Al_0.8CrFeCoNiCu_0.5high entropy alloy is 1.65mm, smaller than the 1.88mm of 45# steel, indicating that the high entropy alloy has superior wear resistance. Figures 10(b) and 10(d) are magnified images of their wear morphology. The surface of 45# steel shows severe plastic deformation and has wider furrows, with the worn form mainly being adhesive wear and abrasive wear. During the friction wear process, a significant extent of plastic deformation first occurs along the direction of shear stress on the friction block. Under the continued action of shear forces, the material fractures, and some of the elongated plastic surfaces shrink after being torn, forming ductile dimples. The newly formed surfaces contact the friction block and continue to repeat the above process, resulting in severe plastic deformation. This outcome confirms that No. 45 steel has a higher toughness, lower hardness, and inferior wear resistance.In contrast, the wear surface of Al_0.8CrFeCoNiCu_0.5 high entropy alloy is more intact, and the worn condition is mainly adhesive wear. The Al_0.8CrFeCoNiCu_0.5 high entropy alloy mainly comprises BCC components, and its higher hardness gives it superior wear resistance.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I have thoroughly reviewed the authors' responses to the reviewer's comments and noted that they have effectively addressed all the raised concerns. Based on this comprehensive evaluation, I strongly recommend moving forward with the acceptance of the article.

Reviewer 3 Report

No Comments