Transformations of the Microstructure and Phase Compositions of Titanium Alloys during Ultrasonic Impact Treatment Part III: Combination with Electrospark Alloying Applied to Additively Manufactured Ti-6Al-4V Titanium Alloy
, Marina Kazachenok 1, Konstantin Krukovskii 1, Dmitry Buslovich 1, Lyudmila Kazantseva 1, Sergey Martynov 1 and Elena Sklyarova 2
Round 1
Reviewer 1 Report
Reviewer`s comments:
This study investigates the transformations of the microstructure and phase compositions of Ti alloys during ultrasonic impact treatment. For sure, the paper is of interest to the journal readers, but it needs to be revised to be reconsidered for publication in Materials (MDPI):
1. Title: Please specify the alloy and manufacturing method.
2. Abstract: It is not informative, so it needs to be revised with more results and discussion.
3. Introduction: It is better to describe UIT as a surface severe plastic deformation (S2PD) due to the thickness of the modified layer.
4. Materials and methods: Table 1 - It is better to describe the reduction of Al in the printed sample compared to the wire, while V remained the same.
5. Materials and methods: It is difficult to understand the working principles of Figs. 1(a, b and c). Please provide a schematic view of the EBAM setup, wire feeding system and UIET setup as well.
6. Materials and methods: UIT and UIET procedures – It is necessary to describe the selection procedure of treatment parameters and passes.
7. Materials and methods: Testing distances varied from 0.1 up to 6.0 m (not km).
8. Materials and methods: What are the criteria for selecting the wear test conditions? What was the reason for selecting SAE52100 as a counterpart?
9. Materials and methods: The authors mentioned that prior to the tribological tests, the as-built samples were ground and then polished, but how did they define the grinding and polishing time in terms of surface roughness?
10. Tribological tests: The UIT did not affect the abrasive wear – it deteriorated the wear behavior.
11. Tribological tests: again km in some sentences.
12. What was the surface roughness of the samples?
13. Effect of increased surface roughness after UIT on friction behavior and wear resistance?
14. Effect of microstructural defects formed after UIT on wear resistance?
15. Correlation between friction behavior and wear resistance needs to be comprehensively discussed. The reason for the better wear resistance of UIET in air and argon than as-built and UIT samples, while UIET in air and argon demonstrated higher friction coefficient than as-built and UIT samples needs to be also discussed.
Author Response
We greatly appreciate the reviewer for careful reading of the manuscript, helpful suggestions and valuable comments. All the changes made in the revised manuscript are highlighted with a yellow marker. The point-to-point responses to the reviewer’s comments are listed as following:
- Title: Please specify the alloy and manufacturing method.
Thank You for this important suggestion. The title of the manuscript has been corrected.
- Abstract: It is not informative, so it needs to be revised with more results and discussion.
The abstract has been revised, more results and discussion have been included.
- Introduction: It is better to describe UIT as a surface severe plastic deformation (S2PD) due to the thickness of the modified layer.
The relevant information has been corrected.
- Materials and methods: Table 1 - It is better to describe the reduction of Al in the printed sample compared to the wire, while V remained the same.
This information and relevant references have been added to the revised manuscript.
- Materials and methods: It is difficult to understand the working principles of Figs. 1(a, b and c). Please provide a schematic view of the EBAM setup, wire feeding system and UIET setup as well.
We agree that the photos of EBAM and automated UIET setup do not reveal the essence of technology. Photos and schematic view of the EBAM and UIET setup have been added to the revised manuscript.
- Materials and methods: UIT and UIET procedures – It is necessary to describe the selection procedure of treatment parameters and passes.
The need for maximum surface hardening of the titanium alloy was the main reason for the selection of UIT parameters and passes. The frequency and amplitude of the oscillations are limited by the capabilities of the equipment. The maximum impact load of the striker is limited by the need to avoid plowing of the sample surface by the striker along with its cut [1]. Moreover, the sample surface was repeatedly treated in five passes because increasing the number of passes changes the hardness slightly In addition, the processing parameters were the same as in the previous work (Part I and Part II). This was done to make it possible to compare the surface finish, microstructure and phase composition of pure titanium, as-cast and EBAM-fabricated Ti-6Al-4V titanium alloys subjected to UIT. The relevant information has been corrected.
UIET parameters were also selected from the condition to obtain maximum coating thickness. An article on this issue will be published in the next.
[1]. Panin, A.V.; Kazachenok, M.S.; Kozelskaya, A.I.; Hairullin, R.R.; Sinyakova, E.A. Mechanisms of Surface Roughening of Commercial Purity Titanium during Ultrasonic Impact Treatment. Materials Science and Engineering: A 2015, 647, 43–50, doi:10.1016/j.msea.2015.08.086.
- Materials and methods: Testing distances varied from 0.1 up to 6.0 m (not km).
Indeed, the friction coefficients of the samples under study were measured at the sliding distance less than 1 km (See Fig, 14, b). However the wear tests of the coatings continued until it was completely worn out. Due to the high wear resistance of the coating and its sufficiently large thickness, its complete wear was achieved only at a sliding distance of 6 km (See Fig, 14, a).
- Materials and methods: What are the criteria for selecting the wear test conditions? What was the reason for selecting SAE52100 as a counterpart?
Due to a higher hardenability, high hardness heat treatment, high contact fatigue strength, good dimensional stability and corrosion resistance, 100Cr6 hardened bearing steel is widely used in tribological tests. It is well-documented that 100Cr6 hardened bearing steel (equivalent to SAE52100) is widely used as a counterpart during the wear test of Ti-6Al-4V titanium alloy [1,2]. Moreover, Vera and co-authors [3] carried out a study of the friction and wear properties of TiN, CrN and WC/C coatings in sliding contact with AISI 52100 bearing steel balls. The possibility of comparing the obtained results with the data of other authors was the criterion for selecting the test conditions.
[1]. Mamoun Fellah, Mohamed Labaiz, Omar Assala, Leila Dekhil, Ahlem Taleb, Hadda Rezag, and Alain Iost. Tribological behavior of Ti-6Al-4V and Ti-6Al-7Nb Alloys for Total Hip Prosthesis // Advances in Tribology Volume 2014, Article ID 451387, 13 pages http://dx.doi.org/10.1155/2014/451387
[2]. X. H. Cui, Y. S. Mao, M. X. Wei and S. Q.Wang. Wear Characteristics of Ti-6Al-4V Alloy at 20–400â—¦C // Tribology Transactions, 55: 185-190, 2012 DOI: 10.1080/10402004.2011.647387
[3]. E.E. Vera, M. Vite, R. Lewis, E.A. Gallardo, J.R. Laguna-Camacho. A study of the wear performance of TiN, CrN and WC/C coatings on different steel substrates // Wear 271 (2011) 2116–2124 https://doi.org/10.1016/j.wear.2010.12.061
- Materials and methods: The authors mentioned that prior to the tribological tests, the as-built samples were ground and then polished, but how did they define the grinding and polishing time in terms of surface roughness?
The grinding and polishing time of the as-built EBAM samples has been defined in order to remove a surface roughness of cut pieces proceed by EDM Wire Cutting Machine. The information has been added to the manuscript.
- Tribological tests: The UIT did not affect the abrasive wear – it deteriorated the wear behavior.
Thank you for this relevant comment. This statement is false because of mistranslation. Indeed, the UIT did not affect only the abrasive wear mechanism of the samples. The relevant information has been corrected.
- Tribological tests: again km in some sentences.
The sliding distance really reached 6 km .
- What was the surface roughness of the samples?
The information has been added to the manuscript.
- Effect of increased surface roughness after UIT on friction behavior and wear resistance?
An increased surface roughness of the samples subjected to UIT followed by tribological test manifests itself only during running-in stage. Due to the decreased actual contact area, the samples subjected to UIT are characterized by extremely low friction coefficient (0.08) only at the sliding distance of 10 m. With its rising, the friction coefficient quickly reached its stationary level, equal to ~0.4.
- Effect of microstructural defects formed after UIT on wear resistance?
It is generally accepted that the tribological behavior of titanium is governed by the structure refinement. However, results obtained by various authors are contradictory. For example, no qualitative differences in surface topography were observed among the worn surfaces of the course-grained (CG) and ultra fine grained (UFG) Ti after wear [1]. On the other hand, despite the higher microhardness of UFG titanium, the total amount of wear in this state is twice that for CG titanium [2]. The later is due to the high density of high energy non-equilibrium grain boundaries. According to [2], since the grain boundaries are a source of defects and places of destruction, their multiple intersections lead to increased wear.
Most likely, the increase in the wear rate of the hardened surface layer of the EBAM Ti-6Al-4V sample subjected to UIT was associated with the presence of hard debris particles formed by plastic deformation of hardened surface layer. Moreover, it can be expected a more intense formation of debris particles due to the initiation and propagation of surface microcracks on the sample during the tribological test. According to the Zener-Straw model [3], interfacial boundaries and dislocation clusters were the cause of a high concentration of shear stresses. When the maximum shear stress reached a critical value, two dislocations located at the top of such a cluster, resulting in the formation of a microcrack nucleus, into which other dislocations spontaneously flew, causing its propagation.
In our previous work [4] the UIT effect on the microstructure, deformation and fracture mechanisms of the wire-feed EBAM Ti-6Al-4V samples subjected to uniaxial tension was studied. It was shown that, since dislocation sliding in the ultrasonically treated surface layer of the wire-feed EBAM Ti-6Al-4V samples was hindered, the non-crystallographic shear bands nucleated in the underlying layers propagated in the ultrasonically treated surface layer. It can be expected that during the wear of the samples, numerous shear bands are formed beneath the wearing surface along the sliding direction and, in addition, cracks were initiated along the shear bands. Similar simultaneous increase in hardness and decrease in wear resistance of aluminum-based alloys after processing by ECAP due to the lack of a strain hardening capability was observed in Ref. [5].
The information has been added to the manuscript.
[1]. Nong Gao, Chuanting Wang, Robert Wood, Terence G. Langdon. Tribological properties of ultrafine-grained materials processed by severe plastic deformation // Journal of Materials Science, 2012 ,47(12):4779-4797 DOI: 10.1007/s10853-011-6231-z
[2]. M A Pakhomov, D Gorlov and V Stolyarov. Features of wear and friction in titanium // IOP Conf. Ser.: Mater. Sci. Eng., 2020, 996 012017 doi:10.1088/1757-899X/996/1/012017
[3]. Zhang, Y.; Ma, L. Surface Zener–Stroh Crack Model to Slip Band Due to Contact. Arch. Appl. Mech. 2020, 90, 221–234, doi:10.1007/s00419-019-01606-0.
[4]. A.V. Panin, M.S. Kazachenok, A.I. Dmitriev, A.Yu. Nikonov, O.B. Perevalova, L.A. Kazancheva, E.A. Sinyakova, S.A.Martynov. The effect of ultrasonic impact treatment on deformation and fracture of electron beam additive manufactured Ti-6Al-4V under uniaxial tension // Mater. Sci. Eng, A.- 2022.- V. 832,- P. 142458. https://doi.org/10.1016/j.msea.2021.142458.
[5]. Chuanting Wang, Nong Gao, , Robert Wood, Terence G. Langdon. Wear behavior of an aluminum alloy processed by equal-channel angular pressing // Journal of Materials Science 46(1):123-130 DOI: 10.1007/s10853-010-4862-0
- Correlation between friction behavior and wear resistance needs to be comprehensively discussed. The reason for the better wear resistance of UIET in air and argon than as-built and UIT samples, while UIET in air and argon demonstrated higher friction coefficient than as-built and UIT samples needs to be also discussed.
In general, the higher wear rate is not always correlated with higher friction coefficient. The friction coefficient is a tribosystem property and not materials related. Therefore the normal load and sliding velocity only govern the friction coefficient, while for the wear behavior it necessary to consider surface roughness, hardness, adhesion, wear debris temperature, normal load and also sliding velocity. Despite the high friction coefficient, the extremely high hardness is the main reason for the better wear resistance of the EBAM Ti-6Al-4V samples subjected to UIET in air and argon. It is interesting to mention at this point that high velocity oxygen fuel spray process enable to produce WC-(nano WC-Co) coatings composed of micro-sized WC strengthening phase and nano WC strengthened cobalt matrix [1]. A similar simultaneous increase in friction coefficient and wear resistance of the WC-(nano WC-Co) coatings was observed.
The information has been added to the manuscript.
[1]. Pei-Hu Gao, Bai-Yang Chen, Wei Wang, Han Jia, Jian-Ping Li, Zhong Yang, Yong-Chun Guo. Simultaneous increase of friction coefficient and wear resistance through HVOF sprayed WC-(nano WC-Co) // Surface and Coatings Technology, Volume 363, 15 April 2019, Pages 379-389 https://doi.org/10.1016/j.surfcoat.2019.02.042
Reviewer 2 Report
Congratulations on your work, which is focused on an interesting subject. Only the novelity is not emphasized enough in your work. Please be clear about what is new to the readers.
1. What is the novelity in this work?
2.The topic is relevant in the field.
3.The authors compare the effect of the ultrasonic impact treatment with the ultrasonic electrospark treatment on the Ti-6Al-4V samples manufactured with additional manufacturing process in terms of the mechanical and tribological properties.
4.The metodology are well defined and the controls are well done.
5.The conclusions are consistent, only the novelity is missing.
6.The references are mostly news, relevant and appropriate.
7.The figures and tables are appropriate.
Author Response
Thank you for attentive reading and valuable comments. They have allowed us to improve the manuscript a lot. Please find the replies below. We also made some minor changes in the manuscript according to most of the comments and suggestions of other reviewers. All the modifications were marked in yellow in the revised manuscript.
- What is the novelty in this work?
The novelty of this work is related to the use of shielding gas in the process of UIET. Moreover, ultrasonic impact electrospark treatment has been used for the first time to increase the wear resistance of Ti-6Al-4V samples fabricated by wire-feed electron beam additive manufacturing.
…
5.The conclusions are consistent, only the novelty is missing.
The information has been added to the manuscript.
Round 2
Reviewer 1 Report
Please refer to the email from MDPI.
