Aluminum Chromium Nitride Coating on a Laser Shock Micro-Molded Surface of E690 High-Strength Steel and Its Antifriction Mechanism
Round 1
Reviewer 1 Report
The manuscript reqires some minor corrections for its clarity.
First, laser wavelength and pulsewidth should be added in section2.
Second, coating thicknesses should be provided for all samples.
Third, quantitative EDX analysis of coatings in at.% should be presented along with the XRD studies.
These changes should improve and clarify the underlying conditions, procedures and results.
Author Response
The manuscript reqires some minor corrections for its clarity.
Questions and Reply
Questions 1:
First, laser wavelength and pulsewidth should be added in section2.
Reply 1：
The laser shock wavelength is 1064 nm and the pulse width is 20 ns.
According to expert suggestions. Inserted before the first paragraph of section 2.2 and labeled in red.
Questions 2:
Second, coating thicknesses should be provided for all samples.
Reply 2：
The preparation parameters of the AlCrN coatings involved in this paper are kept the same, and the coating thicknesses are also basically the same.
Questions 3:
Third, quantitative EDX analysis of coatings in at.% should be presented along with the XRD studies.
Reply 3：
Figure 3c is the corresponding SEM image of the EDX mapping, according to expert suggestions, and the corresponding elemental occupancy and energy spectrum information is provided, as shown in Figure 4. It is labeled in red font in the text.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The current article investigated friction and wear behavior of the micro-molded surface of a high-strength (E690) steel with and without AlCrN coating under a fixed linear reciprocating wear condition. Prior to coating, circular micro-pits of 2 mm diameter with varying densities and depths were formed by the laser shock peening (texturing) method. The mechanical and microstructure of the AlCrN coating developed by multi-arc ion planting were also studied.
This paper first needs substantial improvements and corrections before it can be judged again for the suitability of its publication.
Major concerns are:
A. Tribological studies, both effects of dimple density and depth, of only textured surfaces (without coating) were extensively reported earlier by these authors in Ref. 15. Yes, some parameters in that article were different, but the general inferences were essentially the same. In other words, nothing new here with regard to the uncoated sample.
These aspects were kept hidden in the present draft, which must be exclusively stated in the revised manuscript, and associated discussion should be minimal.
B. In the eagerness to show the positive influence of coating, the authors intentionally selected the wrong condition to highlight the benefits of coating with reference to the uncoated sample.
The lowest average coefficient of friction (COF) was obtained when micro-dimple density was 19.6% (Fig. 9b), and at this condition, the coating practically has no benefit on COF. However, the authors chose the data corresponding to 34.9% density because, at this condition, the difference of COF between the coated and uncoated samples was highest.
Similarly, the lowest COF was obtained when the pit depth was 7.82 micron (Fig. 11a), but the authors selected 24.72 micron depth for all types of % calculation. This was even when the cost of the processing was enhanced, and the increase of depth higher than 7.82 micron raised the COF (Fig. 11a) and no additional benefit with regard to wear loss (Fig. 11b).
Within the investigated wear conditions, the coating has no benefit with regard to friction but only marginally reduces the wear rate.
In summary, the analyses were intentionally biased, which was not acceptable. Truth needs to be mentioned. All % changes (which were repeated again and again) should be recalculated, and the related conclusion/summary statements must be altered. Accordingly, the manuscript should be thoroughly revised.
Further points for revision are:
(a) The article stressed ‘lubrication’ and retention in the pits, but it has no information about the use of lubrication in the wear test.
(b) Fig. 1 – mentioned LSP, which was undefined in this draft.
(c) Fig. 3b is unnecessary. Provide a SEM image that exactly corresponds to the EDX maps.
(d) “. The crystals in the coating were mainly composed of Cr and CrN, and the amorphous phase was AlN.” Provide citations or evidence.
(e) Fig. 7 – The ‘1.35 micron’ marked zone was not an unfirm single layer but three different layers with varying compositions. Incorporate further comment in this regard.
(f) “..and the friction process was more volatile. “ The word volatile was not proper.
(g) Page 8, 1st para – The explanation why higher dimple density was not beneficial was unclear.
(h) Comment considering the Z height (- 13.11 to + 4.89 micron) in Fig. 13 (b) and other images in this figure.
(i) Page -7 – “Aluminum can enable generation of Al2O3 during friction and wear in a manner that forms a solid lubrication film[17],” – Recheck the statement since Al2O3 is very hard and brittle and acts as the abrasive particle.
(j) Section 2 needs further information regarding experimental procedures and the selected steel.
(k) Reduce the length of the Results and Discussion section. There is hardly any citation in this part!
Some minor improvements are desirable.
Author Response
The current article investigated friction and wear behavior of the micro-molded surface of a high-strength (E690) steel with and without AlCrN coating under a fixed linear reciprocating wear condition. Prior to coating, circular micro-pits of 2 mm diameter with varying densities and depths were formed by the laser shock peening (texturing) method. The mechanical and microstructure of the AlCrN coating developed by multi-arc ion planting were also studied.
This paper first needs substantial improvements and corrections before it can be judged again for the suitability of its publication.
Major concerns are:
Questions and Reply
Questions A:
Tribological studies, both effects of dimple density and depth, of only textured surfaces (without coating) were extensively reported earlier by these authors in Ref. 15. Yes, some parameters in that article were different, but the general inferences were essentially the same. In other words, nothing new here with regard to the uncoated sample.
These aspects were kept hidden in the present draft, which must be exclusively stated in the revised manuscript, and associated discussion should be minimal.
Reply A：
The originality of this paper is as follows:
- AlCrN-coated has the advantages of high hardness, good abrasion resistance and high interfacial bonding strength, which can make up for the defects of E690 high-strength steel with low hardness and bad abrasion resistance.
- laser impact micro-modeling can realize oil lubrication, due to the high hardness and brittleness of AlCrN-coated, directly on the surface of the AlCrN-coated laser impact micro-modeling is more difficult; in the E690 high-strength steel specimen surface laser impact micro-modeling, and then in the micro-modeling specimen surface preparation of the layered structure of the AlCrN-coated, to achieve the surface of the AlCrN-coated laser impact micro-modeling.
3.Research on the mechanism of laser impact micro-modeling AlCrN-coated synergistic wear reduction was carried out, and the experimental results showed that the AlCrN coating improved the stability of the friction process of the specimens; the friction coefficient was reduced by 8.55% and the amount of wear by 36.1% under the synergistic effect of laser impact micro-modeling-AlCrN-coated.
In summary, the research on the mechanism of laser impact micro-modeling AlCrN-coated synergistic wear reduction provides a theoretical basis for improving the tribological properties and extending the service life of E690 high-strength steel under heavy load environment, which is of great theoretical significance and engineering value.
According to expert suggestions, the introduction and conclusion parts have been revised and marked in red font.
Questions B:
In the eagerness to show the positive influence of coating, the authors intentionally selected the wrong condition to highlight the benefits of coating with reference to the uncoated sample.
The lowest average coefficient of friction (COF) was obtained when micro-dimple density was 19.6% (Fig. 9b), and at this condition, the coating practically has no benefit on COF. However, the authors chose the data corresponding to 34.9% density because, at this condition, the difference of COF between the coated and uncoated samples was highest.
Similarly, the lowest COF was obtained when the pit depth was 7.82 micron (Fig. 11a), but the authors selected 24.72 micron depth for all types of % calculation. This was even when the cost of the processing was enhanced, and the increase of depth higher than 7.82 micron raised the COF (Fig. 11a) and no additional benefit with regard to wear loss (Fig. 11b).
Within the investigated wear conditions, the coating has no benefit with regard to friction but only marginally reduces the wear rate.
In summary, the analyses were intentionally biased, which was not acceptable. Truth needs to be mentioned. All % changes (which were repeated again and again) should be recalculated, and the related conclusion/summary statements must be altered. Accordingly, the manuscript should be thoroughly revised.
Reply B：
The analysis of Figure 10 in the article yielded two conclusions regarding micro-modeling density:
1)At a micro-modeling density of 34.9%, the COF difference between coated and uncoated samples is the greatest.
2)At a density of 19.6%, the COF value of the sample is the lowest.
However, the ultimate conclusion states that a density of 19.6% exhibits the lowest COF, least wear, and best frictional performance, and does not select the 34.9% data as the optimal result.
Regarding the analysis of Figure 12 in the article, the specific details are as follows:
1)For micro-modeled samples without coating, the COF is lowest at a micro-pit depth of 7.82 micrometers. As the depth increases, the COF of the micro-modeled sample rises sharply. After coating the micro-modeled sample's surface, within the range of 7.82 to 24.72 micrometers, the COF of the micro-modeling AlCrN-coated surface remains relatively constant. The coating significantly improves the anti-friction and wear performance of the micro-modeled sample.
2)Based on Figure 12, it is evident that within the 7.82 to 24.72 micrometer range of micro-pit depth, the COF of the micro-modeling AlCrN-coated sample remains relatively constant. Combining this with the friction and wear curves of different depth samples in Figure 11, it can be inferred that within the mentioned depth range, an increased depth leads to reduced fluctuations and improved stability in the friction and wear curve of the sample. Thus, at a depth of 24.72 micrometers, the micro-modeling AlCrN-coated sample quickly enters a stable phase after a brief running-in period, showing minimal fluctuations and excellent stability.
3)Previous experimental results[14] indicate that increasing depth accommodates more abrasive particles, debris, and enhances oil retention capacity, subsequently increasing the sample's frictional lifespan.
Hence, the authors of this study chose a depth of 24.72 micrometers as the optimal parameter, According to expert suggestions, and the relevant section above Figure 12 in the article has been revised and marked in red font.
Questions a:
The article stressed ‘lubrication’ and retention in the pits, but it has no information about the use of lubrication in the wear test.
Reply a：
According to expert suggestions, incorporate the lubrication information used in the wear experiments, and marked in red within section 2.3.
Questions b:
Fig. 1 – mentioned LSP, which was undefined in this draft.
Reply b：
LSP stands for Laser Shock Peening technology. According to expert suggestions, the final modification is made at the end of Section 2.2, with the text highlighted in red font.
Questions c:
Fig. 3b is unnecessary. Provide a SEM image that exactly corresponds to the EDX maps.
Reply c：
Questions d:
“. The crystals in the coating were mainly composed of Cr and CrN, and the amorphous phase was AlN.” Provide citations or evidence.
Reply d：
Questions e:
Fig. 7 – The ‘1.35 micron’ marked zone was not an unfirm single layer but three different layers with varying compositions. Incorporate further comment in this regard.
Reply e：
According to expert suggestions, modifications in the top paragraph of Figure 8, labeled in red.
Questions f:
“..and the friction process was more volatile. ” The word volatile was not proper.
Reply f：
According to expert suggestions, replace ' and the friction process was more volatile ' with ' and the friction process fluctuates greatly’. Mark in red in the text.
Questions g:
Page 8, 1st para – The explanation why higher dimple density was not beneficial was unclear.
Reply g：
According to expert suggestions, In the paragraph above Fig. 9, it is modified in the analysis about 50.3% density at the end of the paragraph, marked with red font.
Questions h:
Comment considering the Z height (- 13.11 to + 4.89 micron) in Fig. 13 (b) and other images in this figure.
Reply h：
According to the expert suggestions, the upper two paragraphs of Fig. 13 are modified and labeled in red font.
Questions i:
Page -7 – “Aluminum can enable generation of Al2O3 during friction and wear in a manner that forms a solid lubrication film[17],” – Recheck the statement since Al2O3 is very hard and brittle and acts as the abrasive particle.
Reply i：
Questions j:
Section 2 needs further information regarding experimental procedures and the selected steel.
Reply j：
The base steel selected is American imported E690 high strength steel, obtained by wire cutting from individual teeth of the offshore platform pile leg rack.
According to expert suggestions, Added before the first paragraph of Chapter 2.1, marked in red font.
Questions k:
Reduce the length of the Results and Discussion section. There is hardly any citation in this part! （
Reply k：
According to expert suggestions, Figure 16 was changed to Figures 17 and 18, and the models with coatings and no micromodeling and with coatings and micromodeling were depicted separately and labeled in red in the text.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript has applied AlCrN coatings onto high-strength E690 steel using multi-arc ion plating to explore wear reduction mechanisms through laser impact micro-modeling surface. They conducted reciprocating friction tests, measured hardness and residual stress, and examined surface wear characteristics before and after coating using various tools. Their resultant coatings displayed a well-bonded, uniform gradient layered structure, exhibiting an engineering bond strength of 35 N. They have compared their results to micro-modeling-only samples, their results showed that the coated specimens showed 4.38% lower average coefficient of friction and 35.19% reduced wear. The best results were achieved with a micro-modeling density of 19.6%, yielding a coefficient of friction of 0.0936 and wear reduction of 38.9%. Optimal friction performance was observed at 19.6% micro-modeling density with 3× single-point impacts, effectively enhancing anti-wear functionality. The study has further established a synergistic wear reduction and lubrication model for the micro-modeling AlCrN coating.
Although the manuscript is well written and organized and presents interesting results, the originality of the work is not clear. Below is a summary list of suggestive minor revisions that might help improve the manuscript.
1. The “Abstract” section needs to outline the work; and briefly present what is given in the manuscript by answering what, why, how the research work was carried out; and possibly with a very brief reference to the results. The abstract, at its current state, reads more like a summary of results. It may need to include a few sentences to provide clear explanations and emphasis on the originality of the work.
2. The “Introduction” section needs to include a clear problem statement followed by clear emphasis on the originality of the work in the last paragraphs.
3. The “Experiments and Methods” section needs some minor revisions listed below:
3.1. Clear chemical composition of the E690 steel as well as the coating.
3.2. The ISO/ASTM standard procedure citation for the metallography and mechanical testing (wear resistance and hardness test).
3.3. The details of metallography (such as the griding SiC sandpaper grit sizes and the applied forces used) and the electron microscopy (such as the kV and working distance used for the SEM and EDS, X-ray analysis).
4. In the “Results and discussion” section, some figures need attention.
4.1. I would suggest revising figure 16. It looks too busy. It needs more clear presentation re-arrangement.
Author Response
The manuscript has applied AlCrN coatings onto high-strength E690 steel using multi-arc ion plating to explore wear reduction mechanisms through laser impact micro-modeling surface. They conducted reciprocating friction tests, measured hardness and residual stress, and examined surface wear characteristics before and after coating using various tools. Their resultant coatings displayed a well-bonded, uniform gradient layered structure, exhibiting an engineering bond strength of 35 N. They have compared their results to micro-modeling-only samples, their results showed that the coated specimens showed 4.38% lower average coefficient of friction and 35.19% reduced wear. The best results were achieved with a micro-modeling density of 19.6%, yielding a coefficient of friction of 0.0936 and wear reduction of 38.9%. Optimal friction performance was observed at 19.6% micro-modeling density with 3× single-point impacts, effectively enhancing anti-wear functionality. The study has further established a synergistic wear reduction and lubrication model for the micro-modeling AlCrN coating.
Although the manuscript is well written and organized and presents interesting results, the originality of the work is not clear. Below is a summary list of suggestive minor revisions that might help improve the manuscript.
Question and Reply
Question 1:
The “Abstract” section needs to outline the work; and briefly present what is given in the manuscript by answering what, why, how the research work was carried out; and possibly with a very brief reference to the results. The abstract, at its current state, reads more like a summary of results. It may need to include a few sentences to provide clear explanations and emphasis on the originality of the work.
Reply 1：
According to expert suggestions, the authors have updated the text with a new abstract, and the updated parts are marked in red font.
Question 2:
The “Introduction” section needs to include a clear problem statement followed by clear emphasis on the originality of the work in the last paragraphs.
Reply 2：
Question 3.1:
Clear chemical composition of the E690 steel as well as the coating.
Reply 3.1：
Question 3.2:
3.2. The ISO/ASTM standard procedure citation for the metallography and mechanical testing (wear resistance and hardness test).
Reply 3.2：
Question 3.3:
The details of metallography (such as the griding SiC sandpaper grit sizes and the applied forces used) and the electron microscopy (such as the kV and working distance used for the SEM and EDS, X-ray analysis).
Reply 3.3：
According to expert suggestions, Revised in front of the first paragraph of section 2.1 and 2.4, marked in red font in the text.
Question 4.1:
In the “Results and discussion” section, some figures need attention.I would suggest revising figure 16. It looks too busy. It needs more clear presentation re-arrangement.
Reply 4.1：
According to expert suggestions, Figure 16 was changed to Figures 17 and 18, and the models with coatings and no micro-modeling and with coatings and micro-modeling were depicted separately and labeled in red in the text.
Author Response File: Author Response.pdf
