Effects of Temperature and Frequency on Fretting Wear Behavior of 316L Austenitic Stainless Steel Before and After Plasma Carburization
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors presented interesting investigations concerning the effects of temperature and frequency on the fretting wear behaviour of 316L ASS – in my opinion, these results are worth considering for publishing in "Coatings”.
Unfortunately, due to the fact that I found many inaccuracies in the methodology, results analysis and conclusions I suggest a major review of this work.
My detailed remarks:
1. p. 3., l. 139: How is the reader supposed to know what a 'lower sample' is?
2. p. 4, l. 154: Why was GCr15 steel chosen as the counter sample material? Does it have practical implications - a combination of GCr15 and 316L materials?
A diagram of the friction pair would be very helpful.
3. Fig. 1 - Please note that the caption under Fig. 1 repeats 'd'.
4. p. 6, l. 216: There is no evidence that the wear mode changes between 'two-body' and 'three-body' contacts.
5. p. 6, l. 221-222: I do not agree with the statement that oxide particles can create a lubricating layer! After all, iron oxides are hard and will be an additional abrasive in the contact zone. In my opinion, the effect of the possible presence of oxide particles on the contact surface would cause exactly the opposite effect - increased wear! Moreover, you do not present any evidence that such a layer is formed.
6. Fig. 1e: I do not understand what the authors wanted to show in Fig. 1e. The presence of COF on the X-axis is incorrect - after all, it is the effect of factors causing fretting, e.g. frequency. Perhaps placing frequency on the X-axis as the driving factor, and COF and temperature on the Y-axes as friction products will show some interesting correlation.
7. Fig. 2: As I mentioned earlier, I disagree with the interpretation that suggesting a layer of wear products and damaged oxide particles would create a protective layer that reduces friction.
8. Fig. 3a1, b1 and c1 + p. 7, l. 276-288: I am not sure if the authors are interpreting the wear mechanism correctly. We are certainly dealing with fatigue here. However, spalling requires the appearance of brittle martensite in the structure as a result of local temperature increases. I would rather suggest shelling as the fatigue mechanism here.
9. p. 8, l. 302-303: ‘Loose debris particles evolved into larger, more rigid abrasive particles, leading to localized stress concentration in these areas’: how does this evolution occur?
10. Fig. 5: I would not speak here about oxidative wear but rather about the fact of high reactivity of post-damage areas, where rapid oxidation occurred after the damage. I would like to draw attention to a certain paradox in the authors' interpretation of oxidation. In the commentary to this drawing, the authors write about oxidative wear - i.e. surface destruction. It was mentioned earlier that the products of oxide decay are elements of lubricating and protective layers - therefore their presence is very positive. So what is the role of metal oxides in the wear mechanism?
11. Fig. 1, Fig. 9 and Fig. 10: The authors wrote that three repetitions were performed for each test configuration. So what do the graphs in these figures represent? Are these average trends? Do the bar graphs in Figure 10 represent average values? If so, what about the statistics?
12. Fig. 12 - This figure shows the wear mechanism only from the point of view of the sample covered with a PC layer. Meanwhile, in atmospheric conditions, steel surfaces (e.g. GCr15) are covered with oxides. Their destruction causes the formation of a hard abrasive that has a destructive effect on both surfaces in the contact area.
13. Please explain what the lubricating effect of the oxide layer is. Please prove this mechanism.
Author Response
The authors presented interesting investigations concerning the effect`ts of temperature and frequency on the fretting wear behaviour of 316L ASS – in my opinion, these results are worth considering for publishing in "Coatings”. Unfortunately, due to the fact that I found many inaccuracies in the methodology, results analysis and conclusions I suggest a major review of this work.
My detailed remarks:
1.p. 3., l. 139: How is the reader supposed to know what a 'lower sample' is?
Based on the reviewers' comments, we have added a schematic diagram of the fretting wear test in the section “Fretting friction and wear test”, which includes a diagram of the friction pair, and revises the description to make it clearer. The modifications are marked in red.
The modified contents are as follows.
Fretting wear tests were performed in ball-plane point contact. The lower sample was a Φ24 mm×8 mm 316L ASS cylinder. The upper sample was a Φ10 mm GCr15 ball. (Line 134-135)
2.p. 4, l. 154: Why was GCr15 steel chosen as the counter sample material? Does it have practical implications - a combination of GCr15 and 316L materials?A diagram of the friction pair would be very helpful.
GCr15 ball is a kind of high chromium bearing steel ball with excellent comprehensive performance, which has high and uniform hardness, good wear resistance, and high contact fatigue performance. GCr15 ball is one of the representative mating materials used in tribological tests commonly. This paper mainly focuses on the hard sealing surface fixed ball valves in the normally opened (closed) state when the valve stem / bearing, bearing / body, spool / sealing surface, and other mating places are prone to fretting wear. The valve stem and body of the ball valve is generally used in 316L stainless steel, while the bearings and spool using GCr15 steel. Therefore, the use of GCr15 ball and 316L stainless steel in friction part is not only based on tests but also has a certain practical application background.
we have added a schematic diagram of the fretting wear test in the section “Fretting friction and wear test”, which includes a diagram of the friction pair.
3.Fig. 1 - Please note that the caption under Fig. 1 repeats 'd'.
Based on the reviewer's comments, we have corrected the errors. The modifications are marked in red.
4.p. 6, l. 216: There is no evidence that the wear mode changes between 'two-body' and 'three-body' contacts.
Based on the reviewers' comments, we have added the corresponding references for literature proof. The modifications are also marked in red.
Two-body contact wear and three-body contact wear involve two classical theories in fretting tribology, namely the “Fretting Three-body Theory” and the “Kinematic Regulation Mechanism Theory”. We provide a brief explanation of these two theories to facilitate a better understanding of the transition from two-body to three-body wear. Godet [1] and Colombie [2] proposed the “Fretting Three-body theory”, as shown in Figure 1a. They considered that the generation and evolution of abrasive debris were two successive and simultaneous processes. (1) Abrasive debris generation. The contact surface is work-hardened due to adhesion and plastic deformation, accompanied by the friction transition structure formation, which is hard and brittle and can be easily crushed to form abrasive debris. There are grain refinement and migration. (2) Wear debris evolution. Further refinement of the debris causes by mechanical action and oxidation of the debris causes by chemical action. Thus, the theory suggested that wear consists of plastic deformation and fracture damage. Micro-cutting and plastic deformation are mainly for plastic materials, while fracture damage is for brittle materials. This theory can better explain the trend of friction coefficient of metallic materials. Berthier, Vincent, and Godet [3] proposed the “Kinematic Regulation Mechanism Theory”, as shown in Figure 1b. They decomposed that the contact system into five basic components: two contact bodies, a surface layer dependent on the two contact bodies, and a third body(debris).
During the fretting process, each part might undergo four types of motion regulation such as elastic deformation, normal fracture, shear, and rolling. According to the method of permutation and combination, the 5 positions and 4 kinematic regulation modes could form 20 kinematic regulation mechanisms. The theory could be used to analysis the fretting wear characteristics of the contact interface in the fretting process, such as plastic deformation, microcracks, abrasive debris morphology, wear morphology and so on. The “Kinematic Regulation Mechanism Theory” was not only applicable to dry friction, but also applicable to lubrication conditions. Zhu [4,5] summarized these fretting tribology theories and the fretting tribology system was more perfect.
References:
[1] Godet M. Third-bodies in tribology[J]. Wear, 1990, 136(1), 29-45.
[2] Colombie C., Berthier Y., Floquet A., et al. Fretting: Load Carrying Capacity of Wear Debris[J]. Journal of Tribology, 1984, 106(2), 194-201.
[3] Berthier Y., Vincent L., Godet M. Velocity Accommodation in Fretting[J]. Wear, 1988, 125(1-2), 25-38.
[4] Zhu M.H., Cai Z.B., Zhou Z.R. Fretting Wear Theory[M]. Science Press: Beijing, China, 2021.
[5] Zhu M.H., Cai Z.B., Zhou Z.R. Fretting Wear under Special Condition[M]. Science Press: Beijing, China, 2022.
5.p. 6, l. 221-222: I do not agree with the statement that oxide particles can create a lubricating layer! After all, iron oxides are hard and will be an additional abrasive in the contact zone. In my opinion, the effect of the possible presence of oxide particles on the contact surface would cause exactly the opposite effect - increased wear! Moreover, you do not present any evidence that such a layer is formed.
Oxygen from the air penetrates and diffuses into the metal surface during fretting wear to produce oxides. When the oxides are firmly bonded to the substrate, it provides a protecting effect and slows down wear damage. When the oxide film reaches a certain thickness, it is easy to become brittle, friction instantaneous rupture, and fall off. The spalling materials will be refined to form oxide particles in the process of repeated radial movement of the upper specimen. The number of hard oxide particles are small in the early wear stage and scatter in the contact area, which play a role in the abrasive grains and cause the abrasive wear [1,2]. However, the oxide film will be regenerated after peeling off, the generation and destruction of oxides are alternating, which leads to the accumulation and regeneration of oxides. The oxides particles will be migrated, adhesion, and agglomeration to form an oxide debris layer. The frictional temperature rise in the contact area will play a sintering effect, the abrasive layer will continue to accumulate and reach a certain thickness, filling in the contact area, reducing the direct contact of friction pair, and slowing down the fretting wear [3,4,5]. Therefore, metal oxides have both effects of intensifying and slowing down the fretting wear, which depends on the state of metal oxides (size, shape, viscosity).
In this paper, we examined the distribution of oxygen elements within the wear marks (see Figure 6 and Figure 7). Through the aggregation of oxygen within the wear marks, we generally believe that an oxidation reaction occurs and oxidative wear exists during the fretting wear process. Since 316L stainless steel is a passivated metal, it will react with oxygen to generate iron oxide film in the air or during the friction wear, which may contain oxygen and iron solid solution, granular oxides, solid solution of eutectic, or different forms of oxides [2,3,6], such as FeO, Fe2O3, Fe3O4, etc. We have supported this viewpoint through the corresponding literatures and refined this section. The modifications are marked in red.
The modified contents are as follows.
(1) At lower frequencies, the generation and expulsion of debris were competitive processes, causing the contact mode to alternate between two-body and three-body stages [9,10]. The number of hard oxide particles were small in the early wear stage and scattered in the contact area, which played a role in the abrasive grains, resulting in abrasive wear [5]. This oxide debris layer filled into the wear interface to provide lubrication and protection for the carburized layer [31,42]. (Line 200-203)
(2) These oxide particles accumulated and participated in the wear process, forming a bed of oxide abrasive debris in the wear interface (the third body layer), which could provide a lubricating and friction-reducing effect [50,51]. (Line 575-577)
References：
[1] Godet M. Third-bodies in Tribology[J]. Wear, 1990, 136(1), 29-45.
[2] Wen S.Z. Principles of Tribology[M]. Tsinghua University Press: Beijing, China, 1990.
[3] He J.F., Ren Y.P., Bai C.C., et al. Fretting Wear Mechanism of Plasma Nitride 35CrMo Steel under Dry and Lubricated Conditions[J]. Tribology, 2023, 43(1): 18-29.
[4] Zheng J.P., Shen M.X., Li G., et al. Friction and Wear Characteristics of Acrylonitrile-butadiene Rubber under Hard Particles Condition[J]. Journal of Materials Engineering, 2015, 43(10): 79-84
[5] Yuan C.Q., Guo Z.W., Tao W., et al. Effects of Different Grain Sized Sands on Wear Behaviours of NBR/Casting Copper Alloys[J]. Wear, 2017, 384-385: 185-191.
[6] Li B., Huang J., Yang T., et al. Analysis on High Temperature Fretting Wear Behaviour of 20Cr13 Stainless Steel[J]. Tribology, 2024, 44(04), 494-508.
6.Fig. 1e: I do not understand what the authors wanted to show in Fig. 1e. The presence of COF on the X-axis is incorrect - after all, it is the effect of factors causing fretting, e.g. frequency. Perhaps placing frequency on the X-axis as the driving factor, and COF and temperature on the Y-axes as friction products will show some interesting correlation.
We are very grateful to the reviewer for making questions. Figure 1e shows the average friction coefficient of 316L and PC at different frequencies and temperatures. It reflects the effect of temperature and frequency on the average friction coefficient of 316L and PC. To some extent, it can reflect the roughness of the friction interface and the size of the contact pressure under different temperatures and frequencies. We set the X-axis represents the temperature and frequency respectively, and the Y-axis as the average friction coefficient, so that the figure is clearer and simpler to illustrate the trend of the average friction coefficient of 316L and PC under different temperatures and frequencies (see Figure 2e, f). The modifications are marked in red.
7.Fig. 2: As I mentioned earlier, I disagree with the interpretation that suggesting a layer of wear products and damaged oxide particles would create a protective layer that reduces friction.
The displacement amplitude of conventional friction wear is large (the order of magnitude is millimeter). It is easy to discharge the abrasive debris during the wear process, and it is difficult to accumulate the abrasive debris in the contact area. The metal particles in the contact area will play the role of abrasive grains to aggravate the wear at this time. The displacement amplitude of fretting wear is very small (order of microns). The friction pair is similar to be the “closed” contact, the abrasive debris is very difficult to be discharged from the contact area, and is very easy to be accumulated and fill into the contact area to form a unique abrasive debris layer (the third body layer), which reduces the direct contact of the friction pair (See Figure 1), and slows down the fretting wear [1,2,3,4]. With the development of fretting wear, the frictional heat and stress in the wear interface increase and accumulate continuously. The accumulation of abrasive debris in the contact area is more and more significant. This provides the contact surface with a higher activation energy. The wear surface undergoes a frictional glazing effect under the combined action of heat and chemical reactions [5,6]. Fretting wear is controlled by the formation and discharge process of abrasive debris from the contact area [7]. This is due to the “fretting” characteristic of fretting wear.
References：
[1] Wen S.Z. Principles of Tribology[M]. Tsinghua University Press: Beijing, China, 1990.
[2] He J.F., Ren Y.P., Bai C.C., et al. Fretting Wear Mechanism of Plasma Nitride 35CrMo Steel under Dry and Lubricated Conditions[J]. Tribology, 2023, 43(1): 18-29.
[3] Zheng J.P., Shen M.X., Li G., et al. Friction and Wear Characteristics of Acrylonitrile-butadiene Rubber under Hard Particles Condition[J]. Journal of Materials Engineering, 2015, 43(10): 79-84.
[4] Yuan C.Q., Guo Z.W., Tao W., et al. Effects of Different Grain Sized Sands on Wear Behaviours of NBR/Casting Copper Alloys[J]. Wear, 2017, 384-385: 185-191.
[5] Zhang C.C., Neu Richard W. Temperature-Frequency Wear Mechanism Maps for a Heat-Resistant Austenitic Stainless Steel[J]. Wear, 2023, 522.
[6] Jin X., Shipway H.P., Sun W. The Role of Temperature and Frequency on Fretting Wear of a Like-on-Like Stainless Steel Contact[J]. Tribology Letters, 2017, 65(3).
[7] Paulin C., Fouvry S., Deyber S. Wear Kinetics of Ti-6Al-4V under Constant and Variable Fretting Sliding Conditions[J]. Wear, 2019, 428: 366-375.
8.Fig. 3a1, b1 and c1 + p. 7, l. 276-288: I am not sure if the authors are interpreting the wear mechanism correctly. We are certainly dealing with fatigue here. However, spalling requires the appearance of brittle martensite in the structure as a result of local temperature increases. I would rather suggest shelling as the fatigue mechanism here.
We are very grateful to the reviewer for making questions. The wear mechanism and wear morphology involved here can be explained by the delamination theory. Firstly, wear is classified as abrasive wear, adhesive wear, fatigue wear, and corrosive wear. Fretting wear is the result of the composite effect of the above wear types. Among them, fatigue wear refers to the pitting or spalling caused by plastic deformation of the wear interfaces under the action of alternating contact stresses, which leads to fatigue crack sprouting, crack expansion, and material fracture [1]. According to the different degree of wear damage, fatigue wear can be divided into three forms: pitting, shallow peeling, and deep peeling. On this basis, Suh [2] proposed the “Fatigue Peeling Wear Theory” in 1973 for the first time. This theory suggested that dislocations are the main reason for the occurrence of microcrack expansion and material wear, microcracks form spalling pits after expanding to the material surface under tangential forces. Pitting occurs when a small area of material at the contact interface is dislodged by cracks or other defects. Spalling occurs when there is a large range of shedding material. Pitting and Spalling coexist in the wear morphology generally. Spalling and Pitting occur repeatedly during fretting wear [3]. Therefore, we have described this morphology as material spalling, microcracks, and wear pits. With increasing temperature, the wear mechanism of 316L ASS changed from adhesive and abrasive wear to adhesive wear, accompanied by plastic deformation, fatigue peeling and oxidative wear. The carburized layer had an adhesive wear, plastic de-formation, fatigue peeling, and oxidative wear mechanism. We have added the corresponding literatures to support this viewpoint. The modifications are marked in red.
References:
[1] Wen S. Z. Principles of Tribology[M]. Tsinghua University Press: Beijing, China, 1990.
[2] Suh N. P. The Delamination Theory of Wear[J]. Wear, 1973, 25(1): 111-124.
[3] Kulka M., Mikolajczak D., Makuch N., et al. Wear Resistance Improvement of Austenitic 316L Steel by Laser Alloying with Boron[J]. Surface & Coatings Technology, 2016, 291: 292-313.
9.p. 8, l. 302-303: ‘Loose debris particles evolved into larger, more rigid abrasive particles, leading to localized stress concentration in these areas’: how does this evolution occur?
Due to the low displacement amplitudes, abrasive debris from fretting wear may be trapped in the contact area. Metal oxide particles can cause abrasive wear (increasing the wear rate) or form a stable oxide abrasive debris layer (decreasing the wear rate). Godet [1] put forward the “Third Body Theory” to clarify the significant impact of wear debris in the fretting wear process, and debris formation and evolution. (1) In the early stage of fretting wear, the oxide film on the surface is broken, the metal surface is in direct contact, and adhesion wear increases. The particle peeling occurs on the metal surface. Loose abrasive particles undergo “migration - agglomeration - crushing - refinement - oxidation”, in which some abrasive particles agglomerate and adhere to form larger and harder abrasive debris, leading to the stress concentration in these areas as the interfacial friction temperature rises [2]. (2) As the fretting wear proceeds, the metal abrasive debris are continuously crushed and oxidized to become very small particles. Most of the abrasive debris are compacted and built up to form the third body layer until the balance between the abrasive debris generation and overflow is reached in the contact area. The formation of the third body at the friction interface will prevent direct metal-to-metal contact. If the oxide abrasive debris layer can be formed quickly, it can act as a solid lubricant in the frictional contact, protecting the surface and reducing fretting wear. However, if it cannot be formed, the oxide abrasive debris acts as an abrasive to increase fretting wear. Fretting wear is controlled by the formation and discharge process of abrasive debris from the contact area [3] (see Figure 1). Paulin and Iwabuchi [4,5] suggested that load, displacement amplitude, frequency, and temperature may affect the debris discharge, which affects the formation of the oxide debris layer and the overall fretting wear behavior.
References:
[1] Godet M. Third-bodies in Tribology[J]. Wear, 1990, 136(1), 29-45.
[2] Li B., Huang J., Yang T., et al. Analysis on High Temperature Fretting Wear Behaviour of 20Cr13 Stainless Steel[J]. Tribology, 2024, 44(04), 494-508.
[3] Paulin C., Fouvry S., Deyber S. Wear Kinetics of Ti-6Al-4V under Constant and Variable Fretting Sliding Conditions[J]. Wear, 2019, 428: 366-375.
[4] Paulin C., Fouvry S., Meunier C. Finite Element Modelling of Fretting Wear Surface Evolution: Application to a Ti-6Al-4V Contact[J]. Wear, 2008, 264(1-2): 26-36.
[5] Iwabuchi A. The Role of Oxide Particles in the Fretting Wear of Mild Steel[J]. Wear, 1991, 151(2): 301-311.
10.Fig. 5: I would not speak here about oxidative wear but rather about the fact of high reactivity of post-damage areas, where rapid oxidation occurred after the damage. I would like to draw attention to a certain paradox in the authors' interpretation of oxidation. In the commentary to this drawing, the authors write about oxidative wear - i.e. surface destruction. It was mentioned earlier that the products of oxide decay are elements of lubricating and protective layers - therefore their presence is very positive. So what is the role of metal oxides in the wear mechanism?
Oxygen from the air penetrates and diffuses into the metal surface to produce oxides during the fretting wear. When the oxides are firmly bonded to the substrate, it acts as a protector and slows down fretting wear. The thickness of the oxide film grows gradually and the growth of the oxide is parabolic with time. When the oxide film reaches a certain thickness, it is easy to become brittle, friction instantaneous rupture and fall off, the spalling (peeling) material will be refined to form oxide particles by repeated radial movement of the upper specimen. The number of hard oxide particles are small in the early wear stage and scatter in the contact area, which play a role in the abrasive grains, resulting in the abrasive wear [1,2]. However, the oxide film will be regenerated after peeling off, the generation and destruction of oxides are alternating, which leads to the accumulation of oxides will continue to produce. The oxides particles will be migrated, adhesion, and agglomeration of the formation of an abrasive debris layer (the third body layer). The frictional temperature rise in the contact area will play a sintering effect, the abrasive layer will continue to accumulate to a certain thickness, filling in the contact area, reducing the friction mating direct contact, and slowing down the fretting wear [3,4,5]. Therefore, metal oxides have both effects of intensifying and slowing down wear, which depends on the state of metal oxides (size, shape, viscosity).
In addition, Wen [2] believed that when the oxide film generate on the surface of the metal friction pair is worn off during the wear process, a new oxide film will be formed very quickly. Oxidative wear is a process in which both chemical oxidation and mechanical wear occur in friction wear. The size of oxidative wear depends on the strength of the oxide film connection and the oxidation rate. Brittle oxide film and the shear strength is poor, or oxide film generation rate is lower than the wear rate, wear damage is severe. When the oxide film toughness and the shear strength is high, or the oxidation rate is higher than the wear rate, the oxide film can reduce the friction wear, the oxidative wear is slight. The oxidation reaction is related to the surface contact deformation state for the steel friction pair.
References:
[1] Godet M. Third-bodies in Tribology[J]. Wear, 1990, 136(1), 29-45.
[2] Wen S.Z. Principles of Tribology[M]. Tsinghua University Press: Beijing, China, 1990.
[3] He J.F., Ren Y.P., Bai C.C., et al. Fretting Wear Mechanism of Plasma Nitride 35CrMo Steel under Dry and Lubricated Conditions[J]. Tribology, 2023, 43(1): 18-29.
[4] Zheng J.P., Shen M.X., Li G., et al. Friction and Wear Characteristics of Acrylonitrile-butadiene Rubber under Hard Particles Condition[J]. Journal of Materials Engineering, 2015, 43(10): 79-84.
[5] Yuan C.Q., Guo Z.W., Tao W., et al. Effects of Different Grain Sized Sands on Wear Behaviours of NBR/Casting Copper Alloys[J]. Wear, 2017, 384-385: 185-191.
11.Fig. 1, Fig. 9 and Fig. 10: The authors wrote that three repetitions were performed for each test configuration. So what do the graphs in these figures represent? Are these average trends? Do the bar graphs in Figure 10 represent average values? If so, what about the statistics?
The fretting wear tests involved in this paper are repeated three times, but we have chosen to illustrate the data set where the test process is more stable and reasonable (considering that the test process is smoother, without violent vibration and noise, etc.). Therefore, the results in Figure 1, Figure 9 and Figure 10 are not average values. We also considered whether to use the average value or not, but the friction coefficient, wear volume, wear morphology, and wear volume have correlation. If we use the average value, the wear morphology and wear profile will not be able to explain the illustration, there is no corresponding correlation between them.
12.Fig. 12 - This figure shows the wear mechanism only from the point of view of the sample covered with a PC layer. Meanwhile, in atmospheric conditions, steel surfaces (e.g. GCr15) are covered with oxides. Their destruction causes the formation of a hard abrasive that has a destructive effect on both surfaces in the contact area.
Based on the reviewers' comments, we have added the schematic diagram of the fretting wear mechanism of 316L stainless steel in Figure12, which makes the fretting wear mechanism of 316L and PC clearer and more explicit (see Figure 1). The modifications are marked in red.
13.Please explain what the lubricating effect of the oxide layer is. Please prove this mechanism.
With the development of fretting wear, the frictional heat and stress at the wear interface increase and accumulate continuously. The accumulation of abrasive debris in the contact area is more and more significant. This provides the contact surface with a higher activation energy. The wear surface undergoes a frictional glazing effect under the combined action of heat and chemical reactions [1-4]. This may allow high temperature-induced agglomeration, adhesion, and free-state oxide abrasives accumulation, which generating a plastic flow-like layer or a special “glaze layer”, providing its lubricating and friction-reducing effect, and decreasing the wear damage [2,3]. A greater load leads to more significant glazing on the wear surface and a thicker glaze layer [1,2]. (2) Some oxide abrasive debris layer (the third body layer) is further refined and transforms into amorphous products (highly brittle) and spalls to form abrasive debris during fretting wear. The formation of these abrasive debris accelerates the oxidative wear in the contact area and plays a lubricating role. The oxide particles accumulate and participate in the fretting wear process, forming a bed of oxide abrasive debris in the wear interface and providing its lubricating and friction-reducing effect [5-8].
In the next step of our research work, we will study and characterize the sub-surface (cross-section) in detail to demonstrate the evolution mechanism of oxidative wear, crack initiation and extension, and the competitive relationship between wear and fatigue in fretting wear. In this paper, we focus on the surface damage characteristics of wear marks in fretting wear, the evolution mechanism of oxidative wear is supported by the corresponding literature. Since the accumulation of oxygen elements in the wear marks are examined (see Figure 5 and Figure 6), we generally consider that oxidative wear occurs in the fretting wear.
References:
[1] Pearson S.R., Shipway P.H., Abere J.O., et al. The Effect of Temperature on Wear and Friction of a High Strength Steel in Fretting[J]. Wear, 2013, 303(1-2): 622-631.
[2] Viat A., Bouchet M.I.D.B., Vacher B., et al. Nanocrystalline Glaze Layer in Ceramic-metallic Interface under Fretting Wear[J]. Surface and Coatings Technology, 2016, 308: 307-315.
[3] Zheng H., Zhuang W.H., Yang S.L., et al. Effect of Displacement Amplitude on Tangential Fretting Wear of Alloy 690 Tube in High Temperature and High Pressure Water[J]. China Surface Engineering, 2022, 35(4): 57-64.
[4] Chu Q.H., Huang Q., Zhang M.Y., et al. Study on Fretting Wear of 690TT Alloy Heat Transfer Tube in High Temperature and High Pressure Water Environment[J]. Atomic Energy Science and Technology, 2023, 57(10): 1964-1971.
[5] Yin C.H., Liang Y.L., Liang Y., et al. Formation of a Self-lubricating Layer by Oxidation and Solid-state Amorphization of Nano-lamellar Microstructures During Dry Sliding Wear Tests[J]. Acta materialia, 2019,166: 208-220.
[6] Li C.R., Deng X.T., Wang Z.D., et al. Friction Behaviour and Self-lubricating Mechanism of Low Alloy Martensitic Steel during Reciprocating Sliding[J]. Wear, 2021,482/483:203972.
[7] Yin C., Qin X., Li S., et al. Amorphization Induced by Deformation at Ferrite-cementite Nanointerfaces in a Tribolayer and Its Effect on Self-lubricating[J]. Materials & Design, 2020, 192: 108764.
[8] Kirk M.A., Shipway H.P., Sun W., Bennett C.J. The Effect of Frequency on Both the Debris and the Development of the Tribologically Transformed Structure during Fretting Wear of a High Strength Steel[J]. Wear, 2019, 426-427(Pt A), 694-703.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsGeneral comments
This paper examines the impact of frequency and temperature on the wear mechanism and damage behavior of 316L ASS before and after plasma carburization. The authors position the study as theoretical support for improving the anti-fretting properties of key ball valve components in harsh environments. The manuscript is well-structured, clear, and relevant to the field. The references cited are recent, with no indication of excessive self-citations.
The manuscript is technically sound, with an experimental design appropriate for achieving the stated objectives. However, the novelty and significance of the results are not clearly articulated. The methods section provides enough detail for reproducing the results.
The figures, tables, and images effectively present the data overall, but Figure is difficult to interpret and requires clarification. The conclusions require some revision. The data availability statement is adequate.
Specific comments
1) The terms "friction coefficient" and "frictional coefficient" are used interchangeably. To improve clarity and consistency, it would be better to standardize the terminology.
2) The meaning of the plus and minus symbols in Figure 2 is unclear to the reader. Consider revising the figure or providing a clear explanation to ensure better understanding.
3) In the abstract and conclusions (Lines 35 and 673), "vibration noise pollution" is mentioned as a cause of "abnormal failure of the film layer" or "wear instability." However, these terms do not appear to be thoroughly discussed or supported by the findings in the paper. It seems that these points are presented as general knowledge rather than specific findings of this work. Consider clarifying their relevance or removing them if they are not directly supported by the study's results.
Author Response
General comments: This paper examines the impact of frequency and temperature on the wear mechanism and damage behavior of 316L ASS before and after plasma carburization. The authors position the study as theoretical support for improving the anti-fretting properties of key ball valve components in harsh environments. The manuscript is well-structured, clear, and relevant to the field. The references cited are recent, with no indication of excessive self-citations. The manuscript is technically sound, with an experimental design appropriate for achieving the stated objectives. However, the novelty and significance of the results are not clearly articulated. The methods section provides enough detail for reproducing the results.
The figures, tables, and images effectively present the data overall, but Figure is difficult to interpret and requires clarification. The conclusions require some revision. The data availability statement is adequate.
Specific comments
1.The terms "friction coefficient" and "frictional coefficient" are used interchangeably. To improve clarity and consistency, it would be better to standardize the terminology.
Based on the reviewers' comments, we have sexed up the description of the friction coefficients to the same specification and modified the content in Figure 1. The modifications are marked in red.
2.The meaning of the plus and minus symbols in Figure 2 is unclear to the reader. Consider revising the figure or providing a clear explanation to ensure better understanding.
Based on the reviewers' comments, we have provided additional explanations of what the arrow (↑), plus sign (+) and negative sign (-) represent in Figure 2. The modifications are marked in red.
The modified contents are as follows.
the arrows (↑) represented an increase in temperature or frequency, the plus signs (+) meant that the mechanism was facilitated positively, and the negative signs (-) meant that the mechanism was inhibited negatively. (Line 220-222)
3.In the abstract and conclusions (Lines 35 and 673), "vibration noise pollution" is mentioned as a cause of "abnormal failure of the film layer" or "wear instability." However, these terms do not appear to be thoroughly discussed or supported by the findings in the paper. It seems that these points are presented as general knowledge rather than specific findings of this work. Consider clarifying their relevance or removing them if they are not directly supported by the study's results.
Based on the reviewers' comments, we acknowledge that the content of this section is only speculation based on the phenomena observed in our tests and is not verified by informative literatures and test characterization methods. It is not sufficient to be presented as the conclusion. We have decided to remove this section from the abstract and conclusions.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript entitled “Effects of temperature and frequency on fretting wear behavior of 316L ASS before and after plasma carburization” is devoted to research on the wear resistance of 316L steel. This steel enjoys great interest in many scientific centers around the world due to its properties, especially corrosion resistance. Each attempt to modify the surface layer of this steel allows for obtaining more information about it. Therefore, it is highly appreciated that the authors have taken up this research topic. The article is interesting and worth publishing in the Coatings journal. Below are a few comments that should be taken into account when improving the article:
1. What was the reason for choosing 316L austenitic steel? Why was a corrosion-resistant steel from the martensitic steel group (for example X39Cr13) not selected? These steels are characterized by much higher strength properties than austenitic steels.
2. The percentage of carbon should be added to Table 1.
3. Were the properties listed in Table 2 tested? Were they taken from the literature? If they were tested, the research methods should be described. If the data were taken from the literature, it should be stated from which literature.
4. It would be worth adding information on other methods of testing resistance to abrasive wear (Archives of Metallurgy and Materials 54(1), 2009, 241-246; Surface & Coatings Technology 291, 2016, 292-313).
Author Response
The manuscript entitled “Effects of temperature and frequency on fretting wear behavior of 316L ASS before and after plasma carburization” is devoted to research on the wear resistance of 316L steel. This steel enjoys great interest in many scientific centers around the world due to its properties, especially corrosion resistance. Each attempt to modify the surface layer of this steel allows for obtaining more information about it. Therefore, it is highly appreciated that the authors have taken up this research topic. The article is interesting and worth publishing in the Coatings journal. Below are a few comments that should be taken into account when improving the article:
1.What was the reason for choosing 316L austenitic steel? Why was a corrosion-resistant steel from the martensitic steel group (for example X39Cr13) not selected? These steels are characterized by much higher strength properties than austenitic steels.
This paper is based on the actual background that a hard sealing surface fixed ball valves in the normally opened (closed) state when the stem / bearing, bearing / body, spool / sealing surface and other mating places are very susceptible to fretting wear. Stainless steel ball valves are often used materials such as 304, 304L, 316L, and 316. Considering that ball valves are used in Liquefied Natural Gas (LNG) environment, which is prone to occur low-temperature cold embrittlement phenomenon in LNG environment. Once the austenitic organization is transformed into martensite organization will lead to a decrease in corrosion resistance and an increase in brittleness of the workpiece, which is very prone to fracture, thus affecting the performance and safety of the valves. Since the austenitic stainless steel has a small deformation in the low temperature environment, there is no obvious low -temperature cold embrittlement critical temperature. It can still maintain high toughness below -200 ℃, so we choose 316L stainless steel as the test material.
2.The percentage of carbon should be added to Table 1.
Based on the reviewers' comments, we have added the carbon content of 316L ASS in Table 1. The modifications are marked red.
3.Were the properties listed in Table 2 tested? Were they taken from the literature? If they were tested, the research methods should be described. If the data were taken from the literature, it should be stated from which literature.
The properties of 316L and PC listed in Table 2 are derived from the corresponding test characterizations [1], which have been published in public. In order to ensure academic norms and ethics, we have tabulated this section with additional citations to the corresponding references. The modifications are marked red.
References:
[1] Sun L., Li Y.D., Cao C., et al. Effect of Low-Temperature Plasma Carburization on Fretting Wear Behavior of AISI 316L Stainless Steel[J]. Coatings, 2024, 14(2), 158.
4.It would be worth adding information on other methods of testing resistance to abrasive wear (Archives of Metallurgy and Materials 54(1), 2009, 241-246; Surface & Coatings Technology 291, 2016, 292-313).
Based on the reviewers' comments, we have added a schematic diagram of the fretting wear test in the section “Fretting friction and wear test”, which includes a diagram of the friction pair, and revises the description of the relevant part to make it clearer. The modifications are marked in red.
The modified contents are as follows.
Fretting wear tests were performed in ball-plane point contact. The lower sample was a Φ24 mm×8 mm 316L ASS cylinder. The upper sample was a Φ10 mm GCr15 ball. The main chemical composition of GCr15 ball were as follows (wt.%): 1.60% Cr, 1.00% C, 0.30% Si, 0.30% Mn, 0.08% Mo, and 96.72% Fe. The surface hardness of GCr15 ball was 62-65 HRC. The machining accuracy of GCr15 balls was G5. The above performance values were provided by the supplier. The upper and lower sample surfaces were cleaned before each test. Friction pair was abbreviated as GCr15/316L and GCr15/PC. (Line 134-140)
By reading the literatures provided by the reviewer, we will use other variety evaluation methods to test the resistance to abrasive wear in our future research work. These literatures have significant academic value for our subsequent research work. We have cited the literatures provided by the reviewer.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe process of low-temperature plasma carburization of 316L steel is investigated. In particular, the effect of the carbide layer on the wear process at different temperatures and frequencies of action is investigated. The data are of certain practical value, but the theoretical part needs significant revision. In particular, I recommend paying attention to the following:
1. The Abstract looks too cumbersome and overloaded with unnecessary details. I recommend that authors focus on the problem statement, solution methods, and key results.
2. Also constructions like " μPC > μ316L" or "M-V-W type" "arc-W type" make it difficult to understand the meaning. What is GCr15/316L? This requires explanation, but then the Abstract will become even more cumbersome. Everything needs to be formulated more simply and clearly. Non-key conclusions can be removed.
3. Lines 42 - 48. There should be appropriate references.
4. austenitic stainless steel (ASS) - you must first enter the abbreviation and then use it. (Line 56)
5. "μPN＞μ31CrMoV9" - this needs some explanation
6. "low temperatures" and "high temperatures" (lines 84-85) - what temperatures are these?
7. "critical temperature required..." - what temperature exactly? What is it connected with?
8. The introduction lists the main results of previous works, but it is poorly systematized. Systematization is needed, not just a list of results, and often repeated ones.
9. The authors' names (for example, Li [27], but also many others) do not match those listed in the References.
10. References 16, 20, 25 - do the last names of all the authors consist of only one letter?
11. In general, the list of References is compiled carelessly, there are many errors and typos.
12. Line 116 - "With decreasing temperature, the amount of wear increased..." - why? What is the reason? The temperature changed by only 40 degrees... Once again: there is no point in simply listing facts, we need to analyze the information!
13. "This steel plate undergoes abrasive, fatigue, and adhesive wear" - what is the use of this information? In almost all similar conditions, these are the wear mechanisms that will occur!
14. "Ding [30] coated a 316L surface with a Co-based composite coating and studied fretting wear behavior on both the uncoated and coated surfaces. The Cr23C6, α-Co, and WC phases contained ..." - but where did the chromium and tungsten carbides come from? There is nat tungsten in the 316L steel, and <0.03% carbon. Where did the WC come from?
15. What is "SRV-V"?
16. wear rates (K) - what is it? what units of measurement? how is it determined?
17. In general, the Introduction does not solve the main task - justification of the purpose and objectives of the study, its scientific novelty. In its current form, the Introduction simply contains a list of facts and results (not always adequately presented). The Introduction should be completely rewritten.
18. Table 1 - the values must have an equal number of decimal places.
19. Line 174 "...oxide films on their surfaces were crushed" - how is this proven? What kind of oxide films are formed?
20. Lines 172 - 193 - Is this a hypothesis? How is it confirmed?
21. How does the section "3. Results and analysis" differ from the section "4. Results and Discussion" - in both sections "Results". Maybe it is worth using traditional section names?
22. Line 359 "that led to strong stress concentration at internal defects" - but where is the measurement of the stress magnitude?
23. Fig. 5 and 6 are described very little and superficially. "Significant oxygen accumulation..." - due to what? Externally it looks like for all temperatures approximately identical spots saturated with oxygen are formed. But due to what does "significant oxygen accumulation" occur - the same for different temperatures? The iron oxide film is very loose and does not perform a protective function. What processes occur during friction and how does temperature affect them?
24. The samples are not examined during the wear resistance test, but after the tests are completed. Accordingly, oxides may form after the tests are completed.
25. Of course, oxidation processes have been very little studied. In particular, the study of the cross-section of the wear zone boundary could allow a better study of the wear mechanisms.
26. Section 4.1 Fretting wear analysis - the authors present a hypothesis, but it would be worthwhile to confirm it by examining real cross-sections, including mapping the distribution of elements. That is, what is presented in Fig. 12, but with experimental confirmation.
Author Response
The process of low-temperature plasma carburization of 316L steel is investigated. In particular, the effect of the carbide layer on the wear process at different temperatures and frequencies of action is investigated. The data are of certain practical value, but the theoretical part needs significant revision. In particular, I recommend paying attention to the following:
1.The Abstract looks too cumbersome and overloaded with unnecessary details. I recommend that authors focus on the problem statement, solution methods, and key results.
Based on the reviewers' comments, we have rewritten the abstract. The modifications are marked in red.
The modified content are as follows.
Double-glow low-temperature plasma carburization (LTPC) was utilized to prepare a carburized layer (PC) on 316L austenitic stainless steel (ASS) surface, and the fretting wear behavior was evaluated at various temperatures and frequencies. The friction coefficient curves could be divided into running-in, wear, and stable stages. With increasing temperature, the wear mechanism of 316L ASS changed from adhesive and abrasive wear to adhesive wear, accompanied by plastic deformation, fatigue peeling and oxidative wear. The carburized layer had an adhesive wear, plastic deformation, fatigue peeling, and oxidative wear mechanism. As the frequency increased, 316L ASS showed an adhesive wear, fatigue peeling, and oxidative wear mechanism. With increasing frequency, the wear mechanism of PC changed from abrasive and adhesive wear to abrasive wear, adhesive wear, and fatigue peeling, accompanied by oxidative wear. The carburized layer generally showed lower frictional energy dissipation coefficients and wear rates than 316L ASS. This work demonstrated that plasma carburization could improve the fretting wear stability and resistance of 316L ASS. The rise in frictional temperature, the tribo-chemical reaction time, and the evolution of debris collectively influenced the wear mechanisms and wear morphologies of 316L ASS before and after plasma carburization. This could provide theoretical support for the fretting damage behaviors of ball valves under severe service conditions. (Line 13-30)
2.Also constructions like " μPC > μ316L" or "M-V-W type" "arc-W type" make it difficult to understand the meaning. What is GCr15/316L? This requires explanation, but then the Abstract will become even more cumbersome. Everything needs to be formulated more simply and clearly. Non-key conclusions can be removed.
GCr15/316L represents the material type of friction pair. In this paper, the lower sample is Φ24 mm×8 mm 316L ASS cylinder and the upper sample is Φ10 mm GCr15 ball. For the convenience of description, we have written the friction pair as GCr15/316L and GCr15/PC. In order to express more clearly and explicitly, we have explained it in the paper.
Based on the reviewers' comments, we have rewritten the abstract. The modifications are marked in red.
The modified content are as follows.
Friction pair was abbreviated as GCr15/316L and GCr15/PC. (Line 126-127)
3.Lines 42 - 48. There should be appropriate references.
Based on the reviewers' comments, we have added the corresponding references for literature proof. The modifications are marked in red.
4.austenitic stainless steel (ASS) - you must first enter the abbreviation and then use it.
Based on the reviewers' comments, we have made changes to the descriptions. The modifications are marked in red.
The modified content are as follows.
316L austenitic stainless steel (316L ASS) was commonly utilized in the petrochemical, aerospace, marine engineering, nuclear, biomedical, civil, and other fields due to its good comprehensive performance. (Line 49-51)
5."μPN＞μ31CrMoV9" - this needs some explanation.
Based on the reviewers' comments, we have made changes to the descriptions. The modifications are marked in red.
“μPN＞μ31CrMoV9” indicated that the friction coefficient of the nitride layer is higher than that of 31CrMoV9 steel. The author suggests that this phenomenon is related to the abrasive debris generated at the contact interface. As the hard abrasive particles generated in the nitride layer rupture the stripped layer during the fretting wear process, leading to the continuous alternation of the abrasive debris layer and stripped layer, the friction coefficient fluctuates greatly in the falling stage, resulting in the friction coefficient of the nitride layer being higher than that of 31CrMoV9 steel.
References：
[1] Long Y.H., Ren Y.P., He T., et al. Study on Fretting Wear Behaviour of Plasma Nitriding Layer of 31CrMoV9 Steel[J]. Tribology, 2024, 44(05), 633-643.
6."low temperatures" and "high temperatures" (lines 84-85) - what temperatures are these?
Jin [1] considered that the low temperature is room temperature (RT), the high temperature is T = 275 °C, and the critical transition temperature is T = 125 °C. Jin mainly investigated the wear mechanism transformation and the oxides evolution of stainless steel during fretting wear at different temperatures and frequencies. Under low temperatures, wear damage is mainly generated through the formation and expulsion of oxides in the contact areas. At high temperatures, wear damage is reduced because an oxide protective layer (glaze layer) is generated in the contact area, and the transition temperature of the wear mechanism depends on the frequency.
References：
[1] Jin X., Shipway H.P., Sun W. The Role of Temperature and Frequency on Fretting Wear of a Like-on-Like Stainless Steel Contact[J]. Tribology Letters, 2017, 65(3).
7."critical temperature required..." - what temperature exactly? What is it connected with?
The critical temperature proposed by Zhang [1] is the temperature at which the transition from severe oxidized wear to mild oxidized wear occurs. The critical transition temperature is related to the formation of the glaze layer at the wear interface. Under low temperatures, wear is mainly generated through the formation and expulsion of oxides in the contact areas. At high temperatures, wear damage is reduced because an oxide protective layer (glaze layer) is generated in the contact area. Temperature plays a decisive role in the wear behavior of stainless steel, followed by frequency.
References：
[1] Zhang C.C., Neu Richard W. Temperature-Frequency Wear Mechanism Maps for a Heat-Resistant Austenitic Stainless Steel[J]. Wear, 2023, 522.
8.The introduction lists the main results of previous works, but it is poorly systematized. Systematization is needed, not just a list of results, and often repeated ones.
Based on the reviewers' comments, we have rewritten the introduction. The modifications are marked in red (see Line 35-112).
9.The authors' names (for example, Li [27], but also many others) do not match those listed in the References.
Based on the reviewers' comments, we have rechecked and corrected the references. The modifications are marked in red.
10.References 16, 20, 25 - do the last names of all the authors consist of only one letter?
Based on the reviewers' comments, we have rechecked and corrected the references. The modifications are marked in red.
11.In general, the list of References is compiled carelessly, there are many errors and typos.
Based on the reviewers' comments, we have rechecked and corrected the references. The modifications are marked in red.
12.Line 116 - "With decreasing temperature, the amount of wear increased..." - why? What is the reason? The temperature changed by only 40 degrees... Once again: there is no point in simply listing facts, we need to analyze the information!
Sun [1] concluded that FH36 marine steel is prone to low-temperature cold embrittlement at low temperatures, resulting in decreasing the wear resistance of the FH36 steel and increasing its brittleness, which leads to the wear damage increase. Therefore, for the steel used in polar ships and platforms, it is necessary to conduct its ice load friction resistance test based on the evaluation of low-temperature mechanical properties to ensure structural safety.
Low-temperature cold embrittlement refers to the property of the material to exhibit its brittle fracture at low temperatures (T＜0). When the temperature decreases, the impact absorption work of the material decreases, causing the material to change from the ductile state to the brittle state. At low temperatures, the plasticity and toughness of the steel decreases, resulting in brittle fracture easily. Factors affecting the low-temperature cold embrittlement are the properties of the steel, the stress state, and the structure form.
References：
[1] Sun S.B., Qiang Q., Wang D.S., et al. Friction and Wear Properties of TMCP FH36 Marine Steel Plate at Different Temperatures[J]. Tribology, 2024, 43(04), 421-428.
13."This steel plate undergoes abrasive, fatigue, and adhesive wear" - what is the use of this information? In almost all similar conditions, these are the wear mechanisms that will occur!
Abrasive wear, adhesive wear, fatigue wear, and corrosive wear may occur during the wear process. In actual wear phenomena, several forms of wear are usually present at the same time, and the occurrence of one form of wear often induces other forms of wear [1]. It is necessary to pay attention to the wear mechanisms of materials during the wear process to better understand the wear behavior of materials. That is why we illustrate the wear mechanism of the steel plates in the paper.
Based on the reviewers' comments, we have rewritten the introduction. The modifications are marked in red (see Line 35-113).
References:
[1] Wen, S.Z. Principles of Tribology[M]. Tsinghua University Press: Beijing, China, 1990.
14."Ding [30] coated a 316L surface with a Co-based composite coating and studied fretting wear behavior on both the uncoated and coated surfaces. The Cr23C6, α-Co, and WC phases contained ..." - but where did the chromium and tungsten carbides come from? There is nat tungsten in the 316L steel, and <0.03% carbon. Where did the WC come from?
Ding [1] used laser cladding to prepare the Co-based alloy/WC/CaF2 composite coating on 316L surface, in which the WC particles come from the coating.
Based on the reviewers' comments, we have modified the corresponding content to make it clearer and more explicit. The modifications are marked in red.
References：
[1] Ding H.T., Cao, Y., Ke H., et al. Fretting Wear Resistance at Ambient and Elevated Temperatures of 316 Stainless Steel Improved by Laser Cladding with Co-based Alloy/WC/CaF2 Composite Coating[J]. Optics and Laser Technology, 2023, 163, 109428.
15.What is "SRV-V”?
SRV-V is the model number of this fretting friction and wear tester. The machine is manufactured by Optimol Company, Germany. This machine is used for friction and wear testing, lubricant, and additive performance evaluation. It is mainly used for testing the fretting friction and wear performance of materials at room temperature or high temperature with lubrication or under dry friction conditions (see Figure 1).
The machine can also be used to evaluate the lubricating medium bearing capacity and high temperature friction reduction performance. The main technical specifications of the machine are shown in Table 1. The types of friction pair used in this machine are generally cylinder/disc, disc/disc, and ball/disc. The data that can be measured are friction coefficient, load, travel, temperature, torque, and speed.
16.wear rates (K) - what is it? what units of measurement? how is it determined?
Wear rate is the amount of wear mass on the surface of an object per unit of time or per unit of distance (in terms of the wear mass). Wear rate can also be calculated in terms of the wear volume, defined as the ratio of the wear volume of the specimen to the friction work. The volume of the specimen loses per unit of friction work. Wear rate is an important indicator that describes the wear resistance of different materials and is often used to assess the degree of wear resistance[1].
The wear rate of the coating refers to the ratio of the thickness or mass of the coating reduced due to friction, abrasion, and so on in the service process, indicating the wear resistance degree of the coating. The magnitude of the wear rate depends on the material properties of the coating, the service environment, and the operating conditions. A higher wear rate means that the coating has lower wear resistance and requires more frequent repair or replacement.
References:
[1] Pearson S.R., Shipway, P.H. Is the Wear Coefficient Dependent upon Slip Amplitude in Fretting? Vingsbo and Soderberg Revisited[J]. Wear, 2015, 330, 93-102.
17.In general, the Introduction does not solve the main task - justification of the purpose and objectives of the study, its scientific novelty. In its current form, the Introduction simply contains a list of facts and results (not always adequately presented). The Introduction should be completely rewritten.
Based on the reviewers' comments, we have rewritten the introduction to explain the purpose and content of the study, and to summarize the shortcomings of the current study and the novelty of this study. The modifications are marked in red (see Line 35-113).
18.Table 1 - the values must have an equal number of decimal places.
Based on the reviewers' comments, we have standardized the number of decimal points for the values in Table 1, retaining two decimal points. The modifications are marked in red.
19.Line 174 "...oxide films on their surfaces were crushed" - how is this proven? What kind of oxide films are formed?
Since stainless steel is a passivated metal, it is placed in the air will react with oxygen to generate iron oxide film, which may contain oxygen and iron solid solution, granular oxides and solid solution of eutectic or different forms of oxides, such as FeO, Fe2O3, Fe3O4, etc. [1-3].
The “Fretting three Body Theory” [4] can explain the evolution of wear debris during fretting wear process. Godet proposed the “Fretting Third Body Theory” to clarify the significant impact of wear debris in the fretting wear process and the formation and evolution of debris. In the early stage of fretting wear, the oxide film on the surface is broken, the metal surface is in direct contact, the adhesion is increased, and the particle flaking occurs on the metal surface. Loose abrasive particles undergo the process of “migration - agglomeration - crushing - refinement - oxidation”, in which some abrasive particles agglomerate and adhere to form larger and harder abrasive debris, leading to the stress concentration in these areas as the interfacial friction temperature rises. As the fretting wear proceeds, the metal abrasive debris are continuously crushed and oxidized to become oxide abrasive debris with very small dimensions. Most of the abrasive debris are compacted and built up to form the debris layer (the third body layer) until the balance between the abrasive debris generation and overflow is reached in the contact area.
References:
[1] Li B., Huang J., Yang T., et al. Analysis on High Temperature Fretting Wear Behaviour of 20Cr13 Stainless Steel[J]. Tribology, 2024, 44(04), 494-508.
[2] Wen S.Z. Principles of Tribology[M]. Tsinghua University Press: Beijing, China, 1990.
[3] He J.F., Ren Y.P., Bai C.C., et al. Fretting Wear Mechanism of Plasma Nitride 35CrMo Steel under Dry and Lubricated Conditions[J]. Tribology, 2023, 43(1): 18-29.
[4] Godet M. Third-bodies in Tribology[J]. Wear, 1990, 136(1), 29-45.
20.Lines 172 - 193 - Is this a hypothesis? How is it confirmed?
Hurricks [1] and Waterhouse [2] divided the fretting wear process into three stages. (1) Initial stage. An oxide film is formed on the metal surface and the friction coefficient was low. As the wear proceeds, the oxide film is removed with the fretting wear, resulting in direct contact with the metal surface and thus the friction coefficient increases rapidly. The fretting process is accompanied by material adhesion and transfer. (2) Intermediate stage. Wear marks will increase with the process of fretting wear. The abrasive debris will be dislodged from the wear interface and oxidation occurs with the surrounding environment. The abrasive debris generated can avoid direct contact between the metal surfaces and has a ploughing effect. Due to the drastic changes in the wear interface, the friction coefficient is unstable and can be fluctuated drastically. (3) Stabilization stage. The friction coefficient is relatively stable. The abrasive debris inside the wear mark formed a dense oxide layer, which has a lubricating effect. The “Third Body Theory” proposed by Godet [3] completed the evolution of fretting wear. On the basis of these classical fretting tribology theories, we have compared and analyzed the friction coefficient curves of 316L and PC. We have added the corresponding references for literature proof.
References:
[1] Hurricks P.L. The mechanism of fretting[J]. Wear, 1970, 15(6), 389-409.
[2] Waterhouse R.B. Fretting Wear[J]. Wear, 1984, 1984, 100(1), 107-118.
[3] Godet M. Third-bodies in tribology[J]. Wear, 1990, 136(1), 29-45.
21.How does the section "3. Results and analysis" differ from the section "4. Results and Discussion" - in both sections "Results". Maybe it is worth using traditional section names?
“3. Result” analyses the friction coefficient, wear mark morphology, element distribution, wear profile, and wear amount of 316L and PC at different temperatures and frequencies. “4. Discussion” analyses the fretting wear process of 316L and PC at different temperatures and frequencies from mechanical and energetic, and is a summary and in-depth study of “3. Result”.
Based on the reviewers' comments, we have revised the chapter titles. The modifications are marked in red.
22.Line 359 "that led to strong stress concentration at internal defects" - but where is the measurement of the stress magnitude?
The stress concentration is defined as the presence of an abnormal increase in localized stress in a structure or material. The stress concentration occurs when sharp geometric features (holes, defects, projections, etc.) are present in the structure. In the vicinity of these geometrical features, the distribution of stress can change significantly, resulting in the localized stress are much higher than in other areas of the structure.
Since wear pits, cracks, bumps, and other defects occur in the wear contact interfaces. Based on the definition of stress concentration, scholars have found that there is a high probability of stress concentration at these defects [1,2,3,4]. We have added the corresponding references for the literature proof. The modifications are marked in red (see Line 348-350).
Due to the extremely small size of fretting wear marks, there is no good way to measure the stress magnitude, and the SRV-V fretting friction and wear tester we used does not support the installation of a stress measurement system, so it is not possible to monitor the change of stress magnitude in real time during the fretting wear process.
References：
[1] Wen S.Z. Principles of Tribology[M]. Tsinghua University Press: Beijing, China, 1990.
[2] Li B., Huang J., Yang T., et al. Analysis on High Temperature Fretting Wear Behaviour of 20Cr13 Stainless Steel[J]. Tribology, 2024, 44(04), 494-508.
[4] Zhu M.H., Cai Z.B., Zhou Z.R. Fretting Wear Theory[M]. Science Press: Beijing, China, 2021.
[5] Zhu M.H., Cai Z.B., Zhou Z.R. Fretting Wear under Special Condition[M]. Science Press: Beijing, China, 2022.
23.Fig. 5 and 6 are described very little and superficially. "Significant oxygen accumulation..." - due to what? Externally it looks like for all temperatures approximately identical spots saturated with oxygen are formed. But due to what does "significant oxygen accumulation" occur - the same for different temperatures? The iron oxide film is very loose and does not perform a protective function. What processes occur during friction and how does temperature affect them?
Due to the fretting wear process, the oxygen in the air and the contact interface materials will be occurred oxidative wear. As the fretting wear proceeds, the temperature rise of the wear interface will accelerate the friction chemical action time, increasing the formation of the oxide film. The oxidative wear of wear interfaces is severe, resulting in the internal wear marks appear oxygen element aggregation. Wear debris during fretting wear is highly susceptible to accumulation at the contact interface. As wear progresses, the debris undergoes oxidation, which can also lead to the accumulation of oxygen element at the contact interface. Differences in oxygen element occur between worn and unworn areas. The oxygen element comes from the oxidation reaction that occurs at the contact surfaces during fretting wear, resulting in the formation of an oxide layer.
Abrasive wear, adhesive wear, fatigue wear, and corrosive wear may occur during the wear process. In actual wear phenomena, several forms of wear are usually present at the same time, and the occurrence of one form of wear often induces other forms of wear [1]. Fretting wear is the result of the composite effect of the above wear types, and the materials have different wear mechanisms as the working conditions change.
Temperature affected the fretting wear process in four ways [2-5] (see Figure 2). the arrows (↑) represent an increase in temperature, the plus signs (+) mean that the mechanism is facilitated positively, and the negative signs (-) mean that the mechanism is inhibited negatively. (1) Frictional temperature rise. increasing the temperature exacerbates the frictional temperature rise at the contact interface, which promotes material softening, reduces hardness and shear strength, and causes severe plastic deformation. A sustained increase in interfacial temperature may lead to the recrystallization of the surface structure. On one hand, increasing the interfacial temperature facilitates the agglomeration and formation of a debris layer, which provides a “solid lubricant” effect that decreases the fretting wear. On the other hand, a higher interfacial temperature also enhances material adhesion effects, which increases the fretting wear. (2) Tribo-chemical reaction time. Decreasing the temperature can limit the duration of tribo-chemical reactions at the contact interface, which reduces the formation of the interfacial oxide film and consequently increases the fretting wear. (3) Debris generation and ejection rates. Lower temperatures can accelerate the sliding velocity at the interface. Consequently, the rate at which debris is ejected from the contact interface increases, leading to a corresponding increase in the fretting wear.
References：
[1] Wen S.Z. Principles of Tribology[M]. Tsinghua University Press: Beijing, China, 1990.
[2] Zhang S.Z., Liu L.Y., Ma X., et al. Effect of the Third Body Layer Formed at Different Temperature on Fretting Wear Behavior of 316 Stainless Steel in the Composite Fretting Motion of Slip and Impact[J]. Wear, 2022, 492-493.
[3] Guo X.L., Lai P., Li L., et al. Progress in Studying the Fretting Wear/Corrosion of Nuclear Steam Generator Tubes[J]. Annals of Nuclear Energy, 2020, 144, 107556.
[4] Fouvry S., Arnaud P., Mignot A., et al. Contact Size, Frequency and Cyclic Normal Force Effects on Ti-6Al-4V Fretting Wear Processes: An Approach Combining Friction Power and Contact Oxygenation[J]. Tribology International, 2016, 113: 460-473.
[5] Yin H.C., Liang Y.L., Yun J., et al. Formation of Nano-Laminated Structures in a Dry Sliding Wear-Induced Layer under Different Wear Mechanisms of 20CrNi2Mo Steel[J]. Applied Surface Science, 2017, 423: 305-313.
24.The samples are not examined during the wear resistance test, but after the tests are completed. Accordingly, oxides may form after the tests are completed.
In order to minimize errors, we usually characterize the morphology and element distribution of the wear marks immediately after the fretting wear tests, but wear marks will inevitably continue to oxidize in the air, leading to change in the oxygen content. This phenomenon is bound to occur， but the amount of oxides formed at the end of the tests are very small (because the short contact time with the air) , We still believe that the accumulation of oxygen content at the wear interface is the result of an oxidation reaction and oxide debris accumulation during the fretting wear process. We generally combine the literatures on the distribution of oxygen in the wear marks to make a simple description.
25.Of course, oxidation processes have been very little studied. In particular, the study of the cross-section of the wear zone boundary could allow a better study of the wear mechanisms.
We are very grateful to the reviewer for making questions. Therefore, in the next step of our research work, we will examine and characterize the sub-surfaces (cross-sectional morphology) of above samples in detail. We will study the crack initiation and expansion in the sub-surfaces, the competition between wear and fatigue, and the effect of tribology transformed structure (TTS) on the fretting wear behavior. Oxidative wear on sub-surface is analyzed in more detail. These ideas will be reflected in detail in the next paper.
26.Section 4.1 Fretting wear analysis - the authors present a hypothesis, but it would be worthwhile to confirm it by examining real cross-sections, including mapping the distribution of elements. That is, what is presented in Fig. 12, but with experimental confirmation.
We are very grateful to the reviewer for making questions. We believe that the sub-surface formed in the fretting wear is very valuable for research. Therefore, in the next step of our research work, we will examine and characterize the sub-surfaces (cross-sectional morphology) of the above samples in detail. We will study the crack initiation and expansion in the sub-surfaces, the competition between wear and fatigue, and the effect of tribology transformed structure (TTS) on the fretting wear behavior. Wear characteristics on sub-surfaces are verified by tests and finite elements. These ideas will be reflected in detail in the next paper. The surface morphologies of fretting wear are the focus in this paper.
Based on the reviewers' comments, we have added a schematic diagram of the fretting wear mechanism of 316L stainless steel in Figure12, which makes the fretting wear mechanism of 316L and PC clearer and more explicit (see Figure 1). The modifications are marked in red.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe explanations and additions of the authors are satisfactory. I can recommend this article for publication.
Author Response
The explanations and additions of the authors are satisfactory. I can recommend this article for publication.
We sincerely appreciate your review and valuable comments on our paper. We have been able to improve and enhance our paper significantly with your help. We appreciate your recognition of our paper. We would like to express our deep appreciation for your conscientiousness and patience in guiding us!
We will continue our efforts in future research work and look forward to more opportunities for cooperation!
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe authors have corrected and supplemented the manuscript, making it acceptable for publication. I recommend that you also review the following before publishing:
"SRV-V fretting friction and wear" - it is unclear, it is necessary to more clearly designate SRV-V as a device model.
The authors have corrected and supplemented the manuscript, making it acceptable for publication. I recommend that you also review the following before publication:
"SRV-V fretting friction and wear" - unclear, SRV-V should be more clearly designated as a device model.
In future work, I recommend that the authors not only use the works of other researchers to confirm their hypotheses, but also conduct their own research for the purpose of such confirmation. What was true under some experimental conditions may turn out to be false under other conditions.
Author Response
The authors have corrected and supplemented the manuscript, making it acceptable for publication. I recommend that you also review the following before publishing:
"SRV-V fretting friction and wear" - it is unclear, it is necessary to more clearly designate SRV-V as a device model.
The authors have corrected and supplemented the manuscript, making it acceptable for publication. I recommend that you also review the following before publication:
"SRV-V fretting friction and wear" - unclear, SRV-V should be more clearly designated as a device model.
In future work, I recommend that the authors not only use the works of other researchers to confirm their hypotheses, but also conduct their own research for the purpose of such confirmation. What was true under some experimental conditions may turn out to be false under other conditions.
We sincerely appreciate your review and valuable comments on our paper. We have been able to improve and enhance our paper significantly with your help. We appreciate your recognition of our paper. We would like to express our deep appreciation for your conscientiousness and patience in guiding us!
Based on the reviewers' comments, we have added the model number of the machine to make the presentation clearer and more explicit. The modifications are marked in red.
The modified contents are as follows.
Fretting wear tests were performed with an SRV-V fretting friction and wear tester (SRV-V, Optimol Company, Germany), which automatically recorded the friction coefficient. The SRV-V is the model number of the machine. (Line 129-131)
We will continue our efforts in future research work and look forward to more opportunities for cooperation!
Author Response File: Author Response.pdf
