Characterization of AlCrN and AlCrON Coatings Deposited on Plasma Nitrided AISI H13 Steels Using Ion-Source-Enhanced Arc Ion Plating
Round 1
Reviewer 1 Report
Dear author,
The manuscript coatings-741534-peer-review-v1, entitled ‘Characterization of AlCrN and AlCrON coatings deposited on plasma nitrided AISI H13 steel using ion source enhanced arc ion plating’ presents a comparative analysis of duplex AlCrON coatings for die casting tools. The deposited duplex coating was obtained using an industrial ion source enhanced arc ion plating PVD equipment.
Characterization methods, such as: SEM, step-profilers, XRD, XPS, TEM, RAMAN and nano-indentation were used for the study of deposited duplex coatings on the nitrited AISI H13 steel substrates.
The results are presented well, supported by adequate images and graphs revealing the infos needed to sustain the usage of duplex AlCrON coatings as die tool protection coating, with improved mechanical properties / thermal stability / wear resistance.
Overall, the manuscript is well written, with many techniques / methods described for the characterization of the coatings (deposited layers), with good correlation between the obtained results. The conclusions are in brief but sustained by the experimental findings.
Nevertheless, some aspects need to be clarified / corrected:
- Figure.1. reference in the text at page 3 line 103-104 is missing (error code). The same for all the figure references in the manuscript, it must be a compilation error in the writing machine. Please correct it.
After these minor revisions (on the text references of figures), I propose this manuscript for publishing AS IS.
Author Response
Figure.1. Reference in the text at page 3 line 103-104 is missing (error code). The same for all the figure references in the manuscript, it must be a compilation error in the writing machine. Please correct it.’’
Response: We are so sorry for our negligence in the ill-syntax error. We have rewritten all the figures referenced in the revised manuscript. All the changes made are highlighted in the text.
Reviewer 2 Report
The authors have done a thorough analysis of the AlCrN and AlCrON coatings deposited on plasma-nitride steel, including both material characterisation and tribological analysis. The manuscript is fairly well written, and most of the text and figures are clearly presented.
However, there are some points, where the authors draw strong conclusions that are not fully supported by the data, or that even contradict with the presented results. Therefore, I must recommend the Editor that this manuscript can be accepted only after a major revision.
1) Experimental section: XRD, XPS, TEM, Raman, etc lack information of the used measurement equipment and experimental details. Figures presenting 3D profile mapping would benefit from a color bar and larger font.
2) The authors claim that they have compared AlCrN and AlCrON coatings, but the experimental section tells that more than 2/3 of the AlCrON film is actually AlCrN, which has been used as an adhesion layer, and only the topmost <1um is AlCrON. Therefore, some of the results are misleading, as they consider the differences in whole films and not only on the surfaces.
For example, there are virtually no difference in the XRD patterns of the two films (figure 2), except in the shape of the peak around 44-45 degrees, but that difference is not discussed. Based on this data it is impossible to conclude any differences in the film composition.
The authors discuss also the change in the crystallite size in the films, but do not refer which peak is used in the Scherrer calculation. Just by looking at the fig, the peak attributed to (111) (which should be used in the in the analysis, as it is least affected by the instrumental broadening) seems to be of equal width (difficult to say as they overlap in the figure), which makes the claim of the decrease in the crystal size a bit questionable.
3) In XPS data the presented core scan spectra do not support what is given for the total composition of the films. The authors claim that most of the Cr-N and Al-N bonds have been replaced by oxygen bonds, but still give film compositions, where the nitrogen content in the films is reduced only from 41 to 34%, the reduction of nitrogen content in the films seems to be much greater when the individual scans are looked at. The authors also first admit that the AlCrN film can contain some oxygen due to the deposition process, but later say that the oxygen is only on the surface as it is not visible in the XRD. But the XRD patterns do not even indicate reliably the O content in the oxynitride film.
4) Like the XRD and XPS, the TEM and SAED results do not fully support the conclusions the authors made. There could be some change in the SAED patterns, but unlike the authors claim, thy do not confirm the presence of the (Al,Cr)ON solid solutions. The authors should at least identify the reference cards that they use as the basis of the analysis. The paper by Najafi et al Thin Solid Films 2014, 572, 176–183 is sited here to have reported similar results, but actually the SAED patterns presented in that paper do not match to what the authors presented here.
5) The authors measured that the hardness of the AlCrON/AlCrN coating is less than the hardness of the AlCrN layer and cite papers that have measured similar results. However, others have also presented results where the hardness of the oxynitride is greater than that of the nitride. The discrepancy in the results should be discussed here, now the manuscript gives an impression of cherry-picking of references that agree with the authors’ results.
6) In Fig. 10a the RT CoF of the films is presented. There is virtually no difference between the two different films (AlCrN and AlCrON). This differs from what has been presented in the literature earlier, e.g. by Nohava et al Tribology International 81 (2015) 231–239 who saw a difference of ca. 0.2 vs 0.4 between the nitride and oxynitride films. The authors do cite this paper, but do not discuss about the possible reasons for different types of results.
Author Response
1. Experimental section: XRD, XPS, TEM, Raman, etc lack information of the used measurement equipment and experimental details. Figures presenting 3D profile mapping would benefit from a color bar and larger font.
Response: We agree with the reviewer’s suggestion quite well. We added the description about experiments and their experimental detail in the experimental section. In addition, we also revised the Figure 1 and 12 according the the reviewer’s suggestion.
2. The authors claim that they have compared AlCrN and AlCrON coatings, but the experimental section tells that more than 2/3 of the AlCrON film is actually AlCrN, which has been used as an adhesion layer, and only the topmost <1um is AlCrON. Therefore, some of the results are misleading, as they consider the differences in whole films and not only on the surfaces.
For example, there are virtually no difference in the XRD patterns of the two films (figure 2), except in the shape of the peak around 44-45 degrees, but that difference is not discussed. Based on this data it is impossible to conclude any differences in the film composition.
The authors discuss also the change in the crystallite size in the films but do not refer to which peak is used in the Scherrer calculation. Just by looking at the fig, the peak attributed to (111) (which should be used in the analysis, as it is least affected by the instrumental broadening) seems to be of equal width (difficult to say as they overlap in the figure), which makes the claim of the decrease in the crystal size a bit questionable.
Response: We apologize for our improper expression. We revised the conclusion and abstract section according to the reviewer's suggestion. We deposited monolayer AlCrN and bilayer ed AlCrN/AlCrON coating with a thickness of 3.5 µm and 3.2 µm (≈ 2.1+1.1 µm). We further extended the results and discussion section according to reviewer’s suggestions. The increase in the intensity of (200) diffraction peak increased with the addition of oxygen, which indicated the growth of plans with lower surface energy [29]. Moreover, the apparent change in the shape of (200) peak observed in the diffraction spectra can be related to the compressive residual stress, and structural defects resulting from the replacement of N3- ions by O2- ions in charge balancing mechanism and the disordered distribution of Al, and Cr ions on metal sites. The the average crystalline size was usually calculated by Scherrer formula using (111) dominant peaks from XRD spectra. We agree with the reviewer's suggestion. Due to the thin AlCrON top layer with the thickness around 1 µm, it is too difficult to evaluate the grain size of AlCrON coating from XRD results. Therefore we deleted the discussion about crystallite size calculation in the revised manuscript.
3. In XPS data the presented core scan spectra do not support what is given for the total composition of the films. The author’s claim that most of the Cr-N and Al-N bonds have been replaced by oxygen bonds, but still give film compositions, where the nitrogen content in the films is reduced only from 41 to 34%, the reduction of nitrogen content in the films seems to be much greater when the individual scans are looked at. The authors also first admit that the AlCrN film can contain some oxygen due to the deposition process, but later say that the oxygen is only on the surface as it is not visible in the XRD. But the XRD patterns do not even indicate reliably the O content in the oxynitride film.
Response: Yes, we agree with the reviewer’s suggestion quite well. We think the chemical compsotion was influenced by surface contamination due to insufficient etching during the XPS test. XPS analysis maybe unable to summarize for surface composition. So we delete the results of coating compositions in the revised manuscript. From the bonding states of the elements, we can see that the peak shift towards oxide bonds from nitride bonds. The substitution of O atom in place of N atom in the fcc-(Cr, Al)ON solid solution is confirmed in the case of AlCrN/AlCrON bilayered coating, which is consisitent with the XRD results containing strong signal from underneath AlCrN layer.
4. Like the XRD and XPS, the TEM and SAED results do not fully support the conclusions the authors made. There could be some change in the SAED patterns, but unlike the author's claim, thy do not confirm the presence of the (Al,Cr)ON solid solutions. The authors should at least identify the reference cards that they use as the basis of the analysis. The paper by Najafi et al Thin Solid Films 2014, 572, 176–183 is sited here to have reported similar results, but actually the SAED patterns presented in that paper do not match to what the authors presented here.
Response: We agree quite will with the reviewer's suggestion. The coatings deposited with different deposition system yields the different structure of the same coating regarding their deferent ion source energy. We extended our discussion regarding SAED pattern collected from AlCrON layer as:
‘’Khatibi et al. (Acta Mater.2012, 60, 6494–6507) reported that in AlCrON coating the fcc- lattice can withstand a large fraction of structural defect and vacancies, exhibiting the transformation of cubic to α- (Cr, Al)2O3 phases structure with increasing oxygen content. While Najafi et al. (Thin Solid Films 2014, 572, 176–183) suggested the formation of fcc-(Cr, Al)ON phase at (O/(O+N))=53 % with B1 NaCl (200) and (220). Moreover, the intensity of (111) was sensitive to oxygen content. They reported the circular sports diffused into amorphous rings of the fcc- structure deposited by a cathodic arc deposition system. In this work, the SAED pattern in Figure 5 b shows the B1 NaCl structure with (111), (200), (220) and (311) reflection consistent with XRD analysis, suggested the formation of fcc-(Cr, Al)ON structure. The circular spots indicate the quality of crystalline structure which can be related to the depsoition method.
5. The authors measured that the hardness of the AlCrON/AlCrN coating is less than the hardness of the AlCrN layer and cite papers that have measured similar results. However, others have also presented results where the hardness of the oxynitride is greater than that of the nitride. The discrepancy in the results should be discussed here, now the manuscript gives an impression of cherry-picking of references that agree with the authors’ results.
Response: Yes, it is really true as the reviewer suggested that Hardness discussion is more or less speculation. We considered the reviewer's suggestions and revised our discussion in the mechanical properties section. The decrease of hardness with the introduction of oxygen is obvious due to the change of bonding position from mainly covalent to ionic bonds. There is a common census of various researchers in the field of the oxynitride coating. However, some studies also reported hardness peak values with the introduction of oxygen composition. Due to the smaller ratio of anion vacancies or solid solution strengthing effect, the hadness would increase by doping a small amount of oxygen, while there is a progressive decrease of hardness with increasing oxygent content (see, Acta Mater. 60 (2012) 6494–6507, Surf. Coat. Technol. 351 (2018) 153–161). Actually, the compositions of the coatings has a significant influence on the hardness including Cr and Al contents. The replacement of anion from nitrogen to oxygen in fcc- structure change the bonding position from covalence to the greater ionic bond resulted in a decrease of hardness and elastic modulus (see, Thin Solid Films 520(2011)1597–1602, ). In this study, the reduced hardness and elastic modulus of AlCrN/ACrON coating deposited by Al70Cr30 targets is related to the decrease in nitride bonding fraction as evident from XPS results.
6. In Fig. 10a the RT CoF of the films is presented. There is virtually no difference between the two different films (AlCrN and AlCrON). This differs from what has been presented in the literature earlier, e.g. by Nohava et al Tribology International 81 (2015) 231–239 who saw a difference of ca. 0.2 vs 0.4 between the nitride and oxynitride films. The authors do cite this paper, but do not discuss about the possible reasons for different types of results.
Response: Yes, we agree with the reviewer’s suggestion quite well. It is known that the conditions for wear test significantly influence the COF and wear rate specifically for hard coatings, Nohava et al Tribology International 81 (2015) 231–239 reported resulted of COF in the cited paper is different due to different loading condition 10N vs 7N, and sliding speed 0.2 ms-1 vs 0.25 ms-1. The reasonable wear resistance at 600 ℃ was observed in cubic AlCrN and AlCrON coatings, and oxynitride coating exhibited improving wear resistance due to the high ability of a coating to resist oxidation and to delay substrate oxidation. Although the as-deposited AlCrON bilayered coating present dense structure and excellent thermal stability, both coatings exhibited severe wear at evaluated temperature. It could be attributed to the low thickness of the coatings. When the thin AlCrON coating failed, the coating would wear out rapidly. Based on the above results, the AlCrN/AlCrON bilayered coating with the fcc-AlCrON structure presents better tribological performance compared to the AlCrN coating, making it a suitable candidate for the HPDC application. The thick AlCrON coatings with optimal properties will be investigated systematically in future.
Reviewer 3 Report
Topic: Characterization of AlCrN and AlCrON coatings deposited on plasma nitrided AISI H13 steel using ion source enhanced arc ion plating
Interesting and relevant work on the characterization of AlCrN and AlCrON coatings deposited on plasma nitrided AISI H13 steel using an ion source-enhanced arc ion coating.
In this article, the AlCrN and AlCrON duplex coatings on plasma nitrided AISI – H13 tool steels were investigated, graphically characterized and evaluated through ion source enhanced arc ion. The AlCrN and AlCrON coatings consisted mainly of solid solution phases fcc-AlCrN and fcc-AlCrON, respectively. As a result, the average crystallite size for oxygen incorporation could be reduced from 27.8 to 22.7 nm for AlCrN or AlCrON coatings. The deposited AlCrN coating shows a lower surface roughness than the AlCrON coating. Results from XRD and Raman spectroscopy showed that the AlCrON and AlCrN coatings were stable by a temperature of T = 700 °C 293. The AlCrON coatings have a higher thermal stability than the AlCrN coatings. Furthermore, the AlCrON coatings showed better adhesion to the substrate and improved oxidation resistance than the AlCrN coatings by a temperature of T = 700 °C. Both coatings have high wear rates at high temperatures in dry conditions. Therefore, it is possible to utilize AlCrON coatings deposited on plasma nitrided AISI – H13 steel to protect metalworking tools with improved mechanical properties, thermal stability and wear resistance.
The scope of the work is well detailed and the methods are most often well explained, along with some mentioned in the comments below. This work is certainly valuable for industrial users and researchers who work in the field of surface protection of mechanical components.
Before accepting, it is recommended to consider the following suggestions: state the terms, symbols and abbreviations used on the front page.
In this contribution I miss a short description of the experimental investigations and their parameters. Furthermore, an information on the relationships and interaction between the process parameters used for the PVD coatings and the resulting AlCrN and AlCrON duplex coatings is lacking.
Comments for author File: 
Comments.pdf
Author Response
Before accepting, it is recommended to consider the following suggestions: state the terms, symbols and abbreviations used on the front page.
In this contribution, I miss a short description of the experimental investigations and their parameters. Furthermore, an information on the relationships and interaction between the process parameters used for the PVD coatings and the resulting AlCrN and AlCrON duplex coatings is lacking
Response: We agree with the reviewer’s suggestion quite well. We checked the abbreviations on the front page, and added the description of the ion source enhanced arc ion plating system in the revised manuscript according to the reviewer’s suggestion. The ion source enhanced arc ion plating was based on the multi-arc ion plating method combined with high energy Ar ion cleaning pretreatment. During the ion source cleaning procedure, Ar gas was ionized assisted by using a rotating cathode of Ti target with a shield plate, which would create a highly efficient argon etching to enhance the adhesive strength between coating and substrate. The detail process parameter about our ion source enhanced arc ion plating deposition system is reported elsewhere (see, Ceramics International 44 (2018) 18894-18902).
Reviewer 4 Report
An interesting paper, but I would like to see more analysis of the coating. Several points should be considered in more details.
The section about the preparation of the samples has to be improved. There is no information about the PVD system (in the text).
There is no information about statistical confidence interval or tolerance interval of the measurements.
The discussion should be extended and the data should be compared to the up to date literature.
The conclusion of this work contains the list of the results obtained without any conclusion.
The paper can only accepted for publication after major improvements.
Author Response
1. The section about the preparation of the samples has to be improved. There is no information about the PVD system (in the text).
Response: We agree with the reviewer’s suggestion quite well. We added the description of the PVD sysytem and coating depsosition in the revised manuscript according to the reviewer’s suggestion. The coatings were deposited by an industrial ion source enhanced arc ion plating system using two AlCr alloy targets with 70 at.% Al composition. The ion source enhanced arc ion plating was based on the multi-arc ion plating method combined with high energy Ar ion cleaning pretreatment. During the ion source cleaning procedure, Ar gas was ionized assisted by using a rotating cathode of Ti target with a shield plate, which would create a highly efficient argon etching to enhance the adhesive strength between coating and substrate. We have reported this technology about substrate cleaning effect in elsewhere (see, Ceramics International 44 (2018) 18894-18902). Before coating deposition, the nitrided specimens substrates were preheated to 450 °C and the base pressure was kept below 1×10−3 Pa. The substrates were firstly sputter cleaned in Ar plasma at 4.0 Pa pressure with a bias of −400 V for 10 min, and then the ion source cleaning was performed at a substrate bias of −300 V for 30 min to etch the substrate by the high density and energy Ar ions. The monolayer AlCrN and AlCrN/AlCrON bilayered coatings were prepared using the same arc current of 140 A and substrate bias voltage of -50 V.
2. There is no information about statistical confidence interval or tolerance interval of the measurements.
Response: We are so sorry about our incorrect expression. We applied the advice and did the modification in the revised manuscript. We define the limitations of this study and concluded our results accordingly. In this study, we characterized monolayer AlCrN and bilayered AlCrN/AlCrON duplex coatings deposited with ion source enhance arc ion plating technology. The main objective of this study was to compare the well-developed single-layered nitride coating with bi-layered oxi-nitride coating for high temperature wear resistance application ( specifically for die tools). AlCrN coating was prepared in a pure N2 environment while a constant O2/N2 gases flow ratio of 1:10 was used for the deposition of AlCrON top layer. The trace amounts of oxygen is ineffective, and higher oxygen content would reduce the mechanical properties of AlCrON coatings (see, Thin Solid Films 688 (2019) 137252). In this work, both coatings with appropriate compositions were compared to investigate the effect of oxygen addition. The influence of oxygen content on the structure and properties of AlCrON coating will be studied in future.
3. The discussion should be extended and the data should be compared to the up to date literature.
Response: We appreciate the reviewer’s suggestion it helped us to improve our work. We applied the advice and did the modification according to the reviewers’ suggestion. We extended our discussion section and also present up to date reference for comparison as follows:
We improved the discussion about ‘’micro structure analysis, Mechanical properties and thermal stability’’. We also extended our discussion in wear test analysis section and added updated references (presented bellow) for the comparison of results. Moreover, the changes are highlighted in our revised manuscript.
[43]A.Y. Adesina, Z.M. Gasem, A.S. Mohammed, Comparative Investigation and Characterization of the Scratch and Wear Resistance Behavior of TiN, CrN, AlTiN and AlCrN Cathodic Arc PVD Coatings, Arab. J. Sci. Eng. 44 (2019) 10355–10371.
[44]P.S. Souza, A.J. Santos, M.A.P. Cotrim, A.M. Abrão, M.A. Câmara, Analysis of the surface energy interactions in the tribological behavior of AlCrN and TiAlN coatings, Tribol. Int. 146 (2020) 106206.
[45]M. Antonov, H. Afshari, J. Baronins, E. Adoberg, T. Raadik, I. Hussainova, The effect of temperature and sliding speed on friction and wear of Si3N4, Al2O3, and ZrO2 balls tested against AlCrN PVD coating, Tribol. Int. 118 (2018) 500–514.
4. The conclusion of this work contains the list of the results obtained without any conclusion.
Response: We agree with the reviewer’s suggestion quite well. We have added the conclusive sentences according to the reviewer’s advice. So we did the modification in the abstract and conclusion.
Round 2
Reviewer 2 Report
The authors have done an adequate job in improving the paper and sufficiently addressed all the concerns expressed by the reviewers. Therefore I can recommend the Editor to accept this revised manuscript to be published in Coatings.
Reviewer 4 Report
I do not see the statistical confidence interval of the measurements in the text (for example, line 200-201).
