Microstructure, Mechanical Properties, and Corrosion Resistance of NiAl-CoCrFeMo High-Entropy Alloys by Controlling Mo Co-Doping

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article is scientifically very comprehensive and detailed. I do not think that there is a technical deficiency in the article, the authors have made all the necessary technical researches in detail in all cause-effect relationships. However, I recommend that they take into account some of the points I have mentioned below.

1)The novelty of the study should be more explicitly highlighted. It is unclear how this research differs from previous studies and what new insights it provides.

2)Sample preparation details are lacking. Parameters such as temperature, duration, and pressure used in powder metallurgy or mechanical milling should be explicitly stated.

3) "2.4. Mechanical property test" can be changed as "Mechanical and wear tests" because the experimental study of wear was also mentioned in this section.

4) What is the total sliding distance for wear?

5) There are many important features in Figure 6 that you would like to point out and that you have pointed out, but these details are not visible because there are too many thumbnails. You can reduce the number of images or add extra new images for the parts you want to show details

Author Response

Response to the reviewers’ comments

Dear Editor:

Thank you for forwarding us these constructive comments and valuable suggestions from the reviewers. We have considered these comments carefully and revised our manuscript accordingly. We list below our responses to the comments below. We have also marked the revised part in red in the revised manuscript.

 

Responses to Reviewer #1 comments
1) The novelty of the study should be more explicitly highlighted. It is unclear how this research differs from previous studies and what new insights it provides.

[Response]:

Thanks for your kind advice. The addition of trace Mo to NiAl-based high-entropy alloys improved the mechanical properties, wear resistance and corrosion resistance of the alloy system. The addition of Mo produces solid solution strengthening and precipitation strengthening effects, and the precipitates of the alloy system are transforme from spherical to acicular and plate-like. The acicular phase, which maintains a co-lattice relationship with the matrix, improves the strength of the alloy at room and elevated temperatures without significantly reducing the plasticity, and the addition of Mo improves the hardness of the alloy, which reduces the wear rate of the alloy at room temperature. On the other hand, the addition of Mo improves the stability of the adhesive layer of the alloy, and the adhesive layer of the alloy is denser and stable at high temperatures, and the wear rate of the alloy at high temperatures is reduced. The addition of Mo improved the stability of the passivation film of the alloy, which enhanced its corrosion resistance of the alloy.

[In the revised manuscript]

…The addition of Mo improved the mechanical properties, wear resistance and corrosion resistance of the alloy system. With the addition of trace amounts of Mo, the precipitate phase of the alloys transformed from spherical to acicular and plate-like. The precipitated phasess in a co-lattice relationship with the matrix allow for a substantial increase in the strength of the alloy at both room and elevated temperatures without a significant loss of plasticity…

 

2) Sample preparation details are lacking. Parameters such as temperature, duration, and pressure used in powder metallurgy or mechanical milling should be explicitly stated.

[Response]:

Thanks for your kind advice. The alloys in this work were prepared via a high vacuum arc melting equipment, where the alloys were melted under a high vacuum height (1×10^-4 Pa). To ensure the homogeneity of the alloy composition, the melting was repeated five times for each sample, and the alloy was turned over after each melting, during which electromagnetic stirring was used. An electric arc generated between the electrode and the alloy material was used to heat and melt the metal. When the current passes through the protective gas (argon) between the electrode and the alloy raw material, a high-temperature arc is generated, which can reach a temperature of more than 3000 ℃, which is sufficient to melt all kinds of metal raw materials.

 

3) "2.4. Mechanical property test" can be changed as "Mechanical and wear tests" because the experimental study of wear was also mentioned in this section.

[Response]:

Thanks for your kind advice. It has been revised.

[In the revised manuscript]

…..

2.4 Mechanical and wear tests

The Vickers hardness test was performed via a Huayin HV-1000A microhardness tester with a load of 500 g and a load time of 15 s….

 

4) What is the total sliding distance for wear?

[Response]:

Thanks for your kind advice. The total sliding distance is calculated via equation (1)

where R represents the radius of the friction circle (3mm), n represents the rotational speed (600r/min), and t represents the test time (60min), which ultimately results in a total skidding distance of L= 678.58m.

 

5) There are many important features in Figure 6 that you would like to point out and that you have pointed out, but these details are not visible because there are too many thumbnails. You can reduce the number of images or add extra new images for the parts you want to show details

[Response]:

Thanks for your kind advice. The number of images in Figure 6 is reduced.

 

[In the revised manuscript]

 

Fig. 6. Characterization data of wear traces of Ni₃₅Al₃₀(FeCo)₂₅Cr_10-xMo_x (x=0, 5) HEAs at different temperatures. SEM images of the worn surface (a-f), local magnification (a2-f2) and EDS energy spectrum analysis of the worn surface

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Hardness should be given in Pa, not in HV

2. After the equipment, in parentheses, give the manufacturer, state, city, country.

3. The load on the Vickers hardness tester should be given in Newtons, not grams.

4. What is the experimental error in determining hardness, compression, and wear testing?

5. On page 4 in point 2.4 the authors say "To avoid experimental error, each sample was repeated three times". It is not possible to "avoid" experimental errors. Change the sentence to "to reduce experimental error...". Three repetitions are too few.

6. On page 4 in point 2.5 add the version and year of the CoView and Zview softwares.

7. Define abbreviations when first encountered in the text, for example, SAED and IFFT on page 6.

8. Increase the font size in Figure 5 because it is not visible well. On the abscissa of Figure 5 (c) and (f) should be "Temperature".

9. Increase the font size in Figure 6 because it is not visible well. 

10. Compare your results with the results for microstructure, mechanical properties and corrosion resistance of other authors.

Author Response

Response to the reviewers’ comments

Dear Editor:

Thank you for forwarding us these constructive comments and valuable suggestions from the reviewers. We have considered these comments carefully and revised our manuscript accordingly. We list below our responses to the comments below. We have also marked the revised part in red in the revised manuscript.

Responses to Reviewer #2 comments

1. Hardness should be given in Pa, not in HV

[Response]:

Thanks for your kind advice. It has been revised.

[In the revised manuscript]

Figs. 4(b) and (d) show that the average hardness values of Cr₁₀Mo₀ and Cr₅Mo₅ are 4742.5 MPa and 5474.1 MPa, respectively, and the addition of Mo significantly increases the hardness of the alloy.

 

2. After the equipment, in parentheses, give the manufacturer, state, city, country.

[Response]:

Thanks for your kind advice. It has been revised.

[In the revised manuscript]

…DHL-500II (SKY Technology Development Co; Shenyang; China) non-consumable vacuum arc furnace…

…Hitachi SU8010 cold field emission scanning electron microscope (Hitachi High-Tech Corporation; Shanghai; China) ...

…TITAN DETEM G2 transmission electron microscope (TEM, Thermo Fisher Scientific; Shanghai; China)…

…GATAN 691 precision ion polishing system (Gatan Corporation of America; Shanghai; Shanghai; China).

…Bruker D8 Advance X-ray (Bruker AXS GmbH; Shanghai; China) diffractometer with a Cu-Kα source.

…Huayin HV-1000A (Shanghai R&R Optical Technology Co; Shanghai; China) microhardness tester…

…The compression test was performed on a universal testing machine (Instron 5569, Instron (Shanghai) Test Equipment Trading Co; Shanghai; China).

…MXS-01 (Fule Instrument Technology (Shanghai) Co; Shanghai; China) high and low temperature friction and wear tester.

…Chenhua electrochemical workstation CHI660E (Shanghai Chenhua Instrument Co; Shanghai; China)…

3. The load on the Vickers hardness tester should be given in Newtons, not grams.

[Response]:

Thanks for your kind advice. It has been revised.

[In the revised manuscript]

The Vickers hardness test was performed via a Huayin HV-1000A microhardness tester with a load of 4.9 N and a load time of 15 s.

 

4. What is the experimental error in determining hardness, compression, and wear testing?

[Response]:

Thanks for your kind advice. It has been revised.

[In the revised manuscript]

 

Fig. 4. Mechanical properties of Ni₃₅Al₃₀(FeCo)₂₅Cr_10-xMo_x (x=0, 5) HEAs at room temperature and high temperature. (a), (c) Engineering stress‒strain curves; (b), (d) corresponding mechanical property parameters.

Fig. 5. Data used to characterize the wear resistance. (a) Friction coefficient curves of Cr₁₀Mo₀ at different temperatures. (b) Wear rate and average friction coefficient of Cr₁₀Mo₀ at different temperatures. (c) Depth and width of the wear scars at different temperatures for Cr₁₀Mo₀. (d) Friction coefficient curves of Cr₅Mo₅ at different temperatures. (e) Wear rate and average friction coefficient of Cr₅Mo₅ at different temperatures. (f) Depth and width of the wear scars at different temperatures for Cr₅Mo₅.

5. On page 4 in point 2.4 the authors say "To avoid experimental error, each sample was repeated three times". It is not possible to "avoid" experimental errors. Change the sentence to "to reduce experimental error...". Three repetitions are too few.

[Response]:

Thanks for your kind advice. It has been revised.

[In the revised manuscript]

The compression test was performed on a universal testing machine (Instron 5569) at a compression rate of 0.36 mm/min. To reduce experimental error, each sample was repeated three times.

 

6. On page 4 in point 2.5 add the version and year of the CoView and Zview softwares.

[Response]:

Thanks for your kind advice.

[In the revised manuscript]

The impedance spectra were tested in the frequency range of 0.01-100 kHz. the experimental data were analyzed by using CoView software to process the polarization curves and ZView software (version 3.1,2012) to fit the impedance spectra, respectively.

 

7. Define abbreviations when first encountered in the text, for example, SAED and IFFT on page 6.

[Response]:

Thanks for your kind advice.

[In the revised manuscript]

To further confirm the crystal structure and microstructure of the alloy, bright field (BF), dark field (DF), selected area electron diffraction (SAED), fast Fourier transform (FFT), and high-resolution transmission electron microscopy (HRTEM) images…

 

8. Increase the font size in Figure 5 because it is not visible well. On the abscissa of Figure 5 (c) and (f) should be "Temperature".

[Response]:

Thanks for your kind advice. The font size in Figure 5 has been modified.

[In the revised manuscript]

Fig. 5. Data used to characterize the wear resistance. (a) Friction coefficient curves of Cr₁₀Mo₀ at different temperatures. (b) Wear rate and average friction coefficient of Cr₁₀Mo₀ at different temperatures. (c) Depth and width of the wear scars at different temperatures for Cr₁₀Mo₀. (d) Friction coefficient curves of Cr₅Mo₅ at different temperatures. (e) Wear rate and average friction coefficient of Cr₅Mo₅ at different temperatures. (f) Depth and width of the wear scars at different temperatures for Cr₅Mo₅.

 

9. Increase the font size in Figure 6 because it is not visible well. 

[Response]:

Thanks for your kind advice. Figure 6 has been modified

[In the revised manuscript]

Fig. 6. Characterization data of wear traces of Ni₃₅Al₃₀(FeCo)₂₅Cr_10-xMo_x (x=0, 5) HEAs at different temperatures. SEM images of the worn surface (a-f), local magnification (a2-f2) and EDS energy spectrum analysis of the worn surface

 

10. Compare your results with the results for microstructure, mechanical properties and corrosion resistance of other authors.

[Response]:

Thanks for your kind advice. The comparison of relevant mechanical properties and corrosion resistance is shown in the following table.

Table 1. Mechanical property parameters of Cr₁₀Mo₀, Cr₅Mo₅ and typical superalloys

	Cr10Mo0	Cr5Mo5	Co-30Ni-10Al-5Mo-2Ta (Co-based superalloy) [1]	Mar-M-247 (Ni-based superalloy) [2]	Co-30Ni-2Nb-7Al-2Ti (Ni-Co based superalloy) [3]	NiAl-28Cr-6Mo [4]
RT	1322±15.8	1670±18.7	890	820	1060	1120
500℃	---	---	---	---	---	800
600℃	986±13.6	1320±15.4	---	---	---	---
650℃	---	---	---	850	---	---
670℃	---	---	750	---	950	---
700℃	---	---	---	---	---	600
750℃	---	---	---	870	---	---
770℃	---	---	660	---	760	---
850℃	260±10.2	537±10.9	---	---	---	---

 

References

[1] Makineni, S.K.; Samanta, A.; Rojhirunsakool, T.; Banerjee, R.; Chattopadhyay, K. A new class of high strength high temperature Cobalt based γ–γ′ Co–Mo–Al alloys stabilized with Ta addition. Acta Mater. 2015, 97, 29-40.

[2] Baldan, R.; Tomasiello, R.B.; Rosenthal, R. Solutioning and aging of Mar-M247 Nickel-based superalloy. J. Mater. Eng. Perform. 2013, 22, 2574-2579.

[3] Mazumder, N.; Kumar, D, Singh M. P, Makineni, S. K.; et al. Synergistic effect of multimodal γ' precipitates tuned through Ti addition on phase stability and strength of Co-Ni based superalloy. Scripta Mater. 2023, 223, 115105.

[4] Mathiou, C.; Giorspyros, K.; Georgatis, E.; Karantzalis, A.E. Microstructural verification of the theoretically predicted morphologies of the NiAl-Cr pseudo-binary alloy systems and NiAl-Cr eutectic structure modification by Mo addition. SN. Appl. Sci. 2019, 1, 1292.

 

 

 

 

 

 

Table 2. Wear performance parameters of Cr₁₀Mo₀, Cr₅Mo₅ and typical alloys

Alloy	Counterparts	Load (N)	Sliding speed (m/s)	Wear rate (mm3/Nm)	Reference
TiZrNbMo0.6	Si3N4	10	0.1	1.3×10-5	[5]
TiAl-10Ag	Si3N4	10	0.234	3.26×10-4	[6]
NiAl-5Ag-5WS2	Si3N4	10	0.2	7.78×10-6	[7]
VNbTa	Si3N4	5	0.188	3.9×10-6	[8]
Cr10Mo0	Si3N4	10	0.188	7.64×10-5	This work
Cr5Mo5	Si3N4	10	0.188	3.89×10-5	This work

 

References

[5] Jin, C.; Li, X.L.; Li, H.Z.; Li, Q.; Wang, H.F. Tribological performance of a TiZrNbMo refractory high entropy alloy at elevated temperatures. J. Alloys Compd. 2022, 920, 165915.

[6] Shi, X.L.; Xu, Z.S.; Wang, M.; Zhai, W.Z.; Yao, J.; Song, S.Y.; Din, A.Q.; Zhang, Q.X. Tribological behavior of TiAl matrix self-lubricating composites containing silver from 25 to 800℃. Wear. 2013, 303, 486-494.

[7] Mahto, N.K.; Tyagi, R.; Sinha, S.K. Synergistic effect of Ag and WS₂ on high temperature tribological performance of Ni₃Al based composites. Tribol. Int. 2023,183, 108408.

[8] Wei, Q.; Zhang, A.J.; Xin, B.B.; Han, J.S.; Su, B.; Wang, X.C.; Meng, J.H. Observation of low friction and high wear resistance in the ductile VNbTa refractory medium-entropy alloy at 800 ℃. Intermetallics. 2024, 175, 108497.

 

Table 3. Corrosion property parameters of Cr₁₀Mo₀, Cr₅Mo₅ and typical alloys

Alloy	Ecorr (V)	Icorr (A/cm2)	Reference
A356	-1.14	3.29×10-6	[9]
Al-Zn-Mg-Cu	-0.7	20.8×10-6	[10]
AlCrCuFeNi	-0.137	9.65×10-6	[11]
Cr10Mo0	-0.758	6.57×10-6	This Work
Cr5Mo5	-0.785	5.7×10-6	This Work

References

[9] Chen, W.; Xu, X.R.; Jiang, P.P.; Qiu, W.; Gan, L.; Chen, K.; Li, C.; Chen, J.; He, D.G.; Lin, Y.C. Investigation into the role of rare earth oxides in controlling the microstructure and enhancing the mechanical and corrosion properties of as-cast Al-Si-Mg alloys. J. Alloy. Compd. 2025,1021, 179708.

[10] Li, K.Z.; Wang, Y.Z.; Su, R.M.; Li, G.L.; Qu, Y.D. Cyclic non-isothermal aging: An aging method to simultaneously improve mechanical properties and corrosion resistance of Al-Zn-Mg-Cu alloys. J. Alloy. Compd. 2025, 1022, 179970.

[11] Rekabizadeh, A.; Yeganeh, M.; Baghal Lari, S. M. Effect of Ti content on the microstructure, hardness, wear properties, and corrosion resistance of AlCrCuFeNi high entropy alloy. Mater. Today. Commun. 2025, 42, 111121.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 Without a doubt, the subject of this manuscript is highly relevant, given the extensive research conducted nowdays in the field of HEAs. I would like to congratulate the authors for the professional manner in which they have structured the manuscript and for their detailed description of the processes involved, particularly in the case of wear mechanisms. However, I have a few minor points of clarification that I would appreciate the authors' assistance in addressing.
- Regarding the Vickers hardness values, the authors state (line 140) that: " to reduce measurement error, each sample was measured seven times, the lowest value was removed, and the average value was taken as the hardness value of the sample."
Please explain the algorithm used to remove the lowest value. What if the lowest value is close to the rest of the values? And maybe the highest value is out of the specific range or seem to be an error? What about the reasoning in choosing to perform 7 indents on each sample? The aim should be to perform as manny indents are necessarry in order to reduce as much as possible the measurement error.  And, of course, it would be nice to provide the measurement errors and/or error bars on the charts.
- Correct the notations in the manuscript. Example, line 149, Si4N3 - subscript needed
- Could you include references throughout the manuscript, for example related to the hardness and yield strength values? - ofcourse, if there are simillar works reported in the literature

Author Response

Response to the reviewers’ comments

Dear Editor:

Thank you for forwarding us these constructive comments and valuable suggestions from the reviewers. We have considered these comments carefully and revised our manuscript accordingly. We list below our responses to the comments below. We have also marked the revised part in red in the revised manuscript.

 

Responses to Reviewer #3 comments
1) Regarding the Vickers hardness values, the authors state (line 140) that: " to reduce measurement error, each sample was measured seven times, the lowest value was removed, and the average value was taken as the hardness value of the sample."
Please explain the algorithm used to remove the lowest value. What if the lowest value is close to the rest of the values? And maybe the highest value is out of the specific range or seem to be an error? What about the reasoning in choosing to perform 7 indents on each sample? The aim should be to perform as manny indents are necessarry in order to reduce as much as possible the measurement error.  And, of course, it would be nice to provide the measurement errors and/or error bars on the charts.

[Response]:

Thanks for your kind advice. High entropy alloys often do not consist of a single phase and the hardness of each phase will varies. The average value of the hardness of the different parts was used to represent the hardness value of the alloy. Seven measurements were taken to avoid the influence of chance errors on the experimental results. Notably, several times are also possible, and there is no limit to the number of measurements, the greater the number of measurements is, the more accurate the results.

2) Correct the notations in the manuscript. Example, line 149, Si4N3 - subscript needed

[Response]:

Thanks for your kind advice. It has been revised.

[In the revised manuscript]

…Si₄N₃ ceramic balls with a diameter of 5 mm were used as the upper phase….

3) Could you include references throughout the manuscript, for example related to the hardness and yield strength values? – of course, if there are simillar works reported in the literature

[Response]:

Thanks for your kind advice. Both hardness and yield strength are related to the resistance of dislocation motion. The more difficult the dislocation is to move (for example, owing to grain boundaries, solution strengthening, etc.), the higher the hardness and yield strength are usually. Chen et al. provided a linear regression analysis chart showing a positive correlation between microhardness (Hv) and yield strength (σy).

[In the revised manuscript]

…There is a positive correlation between yield strength and hardness [35].

 

Author Response File: Author Response.pdf