Study on Friction and Lubrication Characteristics of Surface with Unidirectional Convergence Texture

Round 1

Reviewer 1 Report

Comment on article : Study on Friction and Wear and Lubrication 2 Characteristics of Surface with Unidirectional 3 Convergence Texture

First of all, article is poor written. There are too many long and incomprehensible sentences

For example : page 2  line 54-58 59 -61,  page 7 line 107-111, page 10 line 221-225

Page 2 line 64-67 why the authors evoke wear here just after the experimental methods

Section 2.1.1 to 2.1.3: it would be nice to put pictures of the textures in this section. We see the difference between the two triangles only later. In fig 1 difference between images a,b,c and d,e f is not discernible except if we look figure 2 before.

Why authors used turbulent models? are lubricant flow are turbulent? in the model, authors considered inlet pressure and outlet pressure as boundary conditions? there is no velocity at the inlet ? surfaces in contact are fixed ?  in general, in hydrodynamic lubrication a boundary condition of inlet velocity is used. 

Authors say negative pressure ? scale of pressure is in relative or total pressure ? if the second, pressure can not be negative? Cavitation phenomena occurs?

Fig 7 and 8 the two figures could be superimposed for a better comparison and analyses of influence of polishing on friction.

Fig 9, 10 and 11 : no value is inferior to the unpolished untextured surface? in this case what is the interest of texturing? In this figure, for a better analysis, the author should either overlay the curves or keep the same scale on friction axis.

Figure 14 : pits and groove are not visible. Could authors show them with arrow ?

For the surface of the non-textured polished specimen wear is abrasive and contact fatigue where as for textured surfaces wear are abrasive, adhesive and cavitation. Which is the better? Wear for untextured surfaces or textured surface ?

is there any interest in texturing the surface as the friction is higher and the wear mode is less good compared to untextured and unpolished surface?

Finally, the authors do not cite the work of Etsion et al. while he has done a lot of work on surface texturing. They are pioneer in surface texturation by for lubrication application.

Author Response

Dear Reviewer:

Thank you for comments concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Point 1: First of all, article is poor written. There are too many long and incomprehensible sentences. For example: page 2 line 54-58, 59-61, page 7 line 107-111, page 10 line 221-225.

Response 1: According to your request, I have revised some sentences of the article, including those you mentioned.

Point 2: Page 2 line 64-67 why the authors evoke wear here just after the experimental methods.

Response 2: According to your request, I have modified the introduction of the article, and mentioned lubrication and wear in the introduction.

Point 3: Section 2.1.1 to 2.1.3: it would be nice to put pictures of the textures in this section. We see the difference between the two triangles only later. In fig 1 difference between images a,b,c and d,e,f is not discernible except if we look figure 2 before.

Response 3: According to your suggestions, I have put pictures of the textures into the section 2.1 to 2.3, respectively.

Point 4: Why authors used turbulent models? are lubricant flow are turbulent? in the model, authors considered inlet pressure and outlet pressure as boundary conditions? there is no velocity at the inlet? surfaces in contact are fixed? in general, in hydrodynamic lubrication a boundary condition of inlet velocity is used. 

Response 4: The k-ɛ two-equation model was proposed in 1974 by a research team led by Professor Spalding of the British Imperial College, and became the most widely used turbulence model. It has the advantages of wide application range and reasonable precision, so it has a wide range of applications in industrial flow fields and heat exchange simulations. According to the actual working conditions, the inlet pressure of the oil is easy to control, but the flow rate of the oil entering the gap between the tool and the workpiece is difficult to obtain, thus the accurate inlet flow velocity cannot be calculated. Therefore, the inlet pressure and the outlet pressure are selected as boundary conditions. According to the Reynolds coefficient formula , although the specific Reynolds number cannot be calculated without knowing the flow velocity, the general estimated value is much larger than the critical value of laminar flow and turbulence 2800, so the turbulence model is selected. In addition, the textured surface is fixed.

Point 5: Authors say negative pressure? scale of pressure is in relative or total pressure? if the second, pressure can not be negative? Cavitation phenomena occurs?

Response 5: The scale of pressure is relative pressure. According to previous theoretical researches and experimental researches, when the fluid flows from the convergent to the divergence, the internal pressure of the fluid is reduced, bubbles are generated, and the bubbles are rapidly generated, expanded, and collapsed, forming a shock wave or a high-speed microjet in the liquid, causing impacts on the texture wall to form cavitation micro-pits. And I have marked the pits due to cavitation .

Point 6: Fig 7 and 8 the two figures could be superimposed for a better comparison and analyses of influence of polishing on friction.

Response 6: According to your suggestions, I have put Figure 7 and Figure 8 into a picture for a better comparison and analyses of influence of polishing on friction.

Point 7: Fig 9, 10 and 11: no value is inferior to the unpolished untextured surface? in this case what is the interest of texturing? In this figure, for a better analysis, the author should either overlay the curves or keep the same scale on friction axis.

Response 7: Fig 9, 10 and 11 are the friction coefficients of the textured surface, and the friction coefficient is only one aspect of the friction performance. The existence of texture will increase the surface roughness and friction coefficient, which is a normal phenomenon. The texture mainly improves the tribological properties of the surface by reducing the actual contact area between the friction pairs, storing wear debris and storing the lubricating fluid to achieve dynamic pressure lubrication and secondary lubrication effect. The existence of texture can effectively improve the wear condition of the surface, such as reducing the scratches and pits on the surface, thus reducing the wear volume. In addition, I have measured the amount of wear and added this part to the paper. Finally, Finally, I have also kept the scale values of the friction coefficient axis consistent.

Point 8: Figure 14: pits and groove are not visible. Could authors show them with arrow ?

Response 8: According to your requests, I have marked the scratches and pits with arrows in Figure 14, Figure 15, Figure 16 and Figure 17.

Point 9: For the surface of the non-textured polished specimen wear is abrasive and contact fatigue while as for textured surfaces wear are abrasive, adhesive and cavitation. Which is the better? Wear for untextured surfaces or textured surface? is there any interest in texturing the surface as the friction is higher and the wear mode is less good compared to untextured and unpolished surface?

Response 9: It can be seen from the surface morphology after wear that the surface scratches of the non-texture specimens are more obvious, the furrows are deeper and wider, and the pits are bigger and denser. The scratches on the surface of textured specimens are thin and shallow, and the pits are less than that of non-textured specimens. Combined with the weight loss of specimens, it can be seen that the wear performance of textured specimens are better.

Point 10: Finally, the authors do not cite the work of Etsion et al. while he has done a lot of work on surface texturing. They are pioneer in surface texturation by for lubrication application.

Response 10: According to your requests, I have already cited the research results of Etsion et al. in the introduction.

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. We appreciate for your warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very mach for your comments and suggestions.

Reviewer 2 Report

The authors used experiments and simulation to study friction and wear and lubrication characteristics of surface with unidirectional convergence texture. The manuscript can be accepted after making the suggested minor revision.

1. The introduction part needs to cover a wider range to better introduce why this work is done and attract more readers. Wear widely happens in manufacturing tools, such as machining (turning, milling and grinding) tools, and metal forming (drawing, extrusion, etc) dies where severe plastic deformation (SPD) happens especially in recently developed novel metal forming techniques. The word ‘workpieces’ in first paragraph is not appropriate, I suggest replace it with ‘tools’. I also suggest expand the first paragraph as follows:

‘‘It is estimated that about 1/3 to 1/2 of the world's energy consumption is caused by friction and wear, in conventional material removal (machining) processes such as turning, milling and grinding, the relative motion between the friction pairs can cause severe wear on the surface of tools [1], thus affecting the life and performance of tools [2,3]. Also, for other non-machining manufacturing technologies such as metal forming processes, as a result of severe plastic deformation (SPD) and high stresses of the processes such as drawing [Ceram Int 2009, 35(8):3495-3502; Trans Nonferrous Metals Soc China 2007,17:663-666], extrusion [Wear 2012, 278-279:1-8; International Journal of Machine Tools and Manufacture 2018, 126:27-43; Procedia Engineering 2017, 207:2304-2309; International Journal of Mechanical Sciences 2018, 138:524-536.], forming tools/dies are exposed to excessive wear and fatigue. How to improve the wear resistance of the surface of tools has become an urgent problem in manufacturing technologies.’’

The second paragraph should also introduce other techniques used for avoiding or improving wear of manufacturing tools, such as nitriding and surface coating, and then introduce surface texturing and patterning methods and state the advantages of this specific method that is gonna be studied in this paper. For example:

‘‘Nitriding and surface coating methods have been applied to extend the service life of manufacturing tools. Other than nitriding and surface coating methods, surface texturing and patterning methods have been widely studied these days. The advantage is the effect of enhanced friction conditions provided by surface texturing.’’

At the end of the introduction, the authors should briefly summarise the corresponding shortcomings or research gaps of existing work to introduce their own work. Then the authors should briefly state what they have done in the paper, what methods have been used.

2. The scale labels of contours in Fig. 2c,f,i are hard to be seen. Also, the length scale lines in Fig.2 a,b,d,e,g,h are not clear.

3. Where do the parameters in Eqs.(8)-(9) come from? For example, why constants C1ɛ, C2ɛ and C3ɛ are taken as 1.44,147 1.92 and 0.09? The authors should give the relevant references. Also, for the determination of boundary conditions in simulation, the authors should give proper references or sources or reasons for the given parameters value.

Author Response

Response to Reviewer 1 Comments

Dear Reviewer:

Thank you for comments concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Point 1: The introduction part needs to cover a wider range to better introduce why this work is done and attract more readers. Wear widely happens in manufacturing tools, such as machining (turning, milling and grinding) tools, and metal forming (drawing, extrusion, etc) dies where severe plastic deformation (SPD) happens especially in recently developed novel metal forming techniques. The word ‘workpieces’ in first paragraph is not appropriate, I suggest replace it with ‘tools’. I also suggest expand the first paragraph as follows:

‘‘It is estimated that about 1/3 to 1/2 of the world's energy consumption is caused by friction and wear, in conventional material removal (machining) processes such as turning, milling and grinding, the relative motion between the friction pairs can cause severe wear on the surface of tools [1], thus affecting the life and performance of tools [2,3]. Also, for other non-machining manufacturing technologies such as metal forming processes, as a result of severe plastic deformation (SPD) and high stresses of the processes such as drawing [Ceram Int 2009, 35(8):3495-3502; Trans Nonferrous Metals Soc China 2007,17:663-666], extrusion [Wear 2012, 278-279:1-8; International Journal of Machine Tools and Manufacture 2018, 126:27-43; Procedia Engineering 2017, 207:2304-2309; International Journal of Mechanical Sciences 2018, 138:524-536.], forming tools/dies are exposed to excessive wear and fatigue. How to improve the wear resistance of the surface of tools has become an urgent problem in manufacturing technologies.’’

The second paragraph should also introduce other techniques used for avoiding or improving wear of manufacturing tools, such as nitriding and surface coating, and then introduce surface texturing and patterning methods and state the advantages of this specific method that is gonna be studied in this paper. For example:

‘‘Nitriding and surface coating methods have been applied to extend the service life of manufacturing tools. Other than nitriding and surface coating methods, surface texturing and patterning methods have been widely studied these days. The advantage is the effect of enhanced friction conditions provided by surface texturing.’’

At the end of the introduction, the authors should briefly summarise the corresponding shortcomings or research gaps of existing work to introduce their own work. Then the authors should briefly state what they have done in the paper, what methods have been used.

Response 1: Based on your suggestions, I have carefully revised the whole introduction, and the references have also been revised, as shown below.

It is estimated that about 1/3 to 1/2 of the world's energy consumption is caused by friction and wear, in conventional material removal processes such as turning, milling and grinding, the relative motion between the friction pairs can cause severe wear on the surface of tools [1], thus affecting the life and performance of tools [2,3]. Also, for other non-machining manufacturing technologies such as metal forming processes, as a result of severe plastic deformation and high stresses of the processes such as drawing, extrusion, forming tools are exposed to excessive wear and fatigue. How to improve the wear resistance of the surface of tools has become an urgent problem in manufacturing technologies.

Ion implantation, shot peening and surface coating methods have been applied to extend the service life of manufacturing tools. Other than ion implantation, shot peening and surface coating methods, surface texturing and patterning methods have been widely studied these days, which has obvious effects on improving the surface friction performance of tools [4]. Studies have shown that when the surface of tools has a certain texture, its wear resistance will be improved, and a certain non-smooth surface will improve the friction and lubrication properties of the lubricating fluid [5,6].

In 1942, SCHLESINGER [7] proposed that “the quality of the surface is extremely important for its correct function”, indicating that designers have long recognized that the mechanical, physical and chemical properties of the surface can be improved by changing the surface morphology, such as surface texture.

In 1966, HAMILTON [8] proposed the additional fluid dynamic pressure effect: when the liquid flows through the pits or grooves machined on the surface of the friction pair, a small convergence wedge and a divergent wedge are formed. When the friction pair is in relative motion, the fluid in the convergence wedge generates a dynamic pressure effect, thereby forming a positive pressure; while in the divergent wedge, due to the existence of "cavitation" phenomenon, the "negative pressure" of the fluid is restrained. Therefore, additional hydrodynamic pressure is formed between the friction pairs, which improves the bearing capacity of the fluid.

Liu et al. [9] used picosecond laser to achieve micro-texture on the surface of cast iron, and investigated the friction and wear properties of four different surfaces of smooth, pit textures, net textures and intermittent textures. The study found that under dry friction condition, the surface machined micro-texture can significantly improve the stability of the friction coefficient compared with smooth surface ,but different textures have different effects on the stability and initial value of the friction coefficient.

Gachot et al. [10] fabricated regular pits on the silicon surface by photolithography and wet etching, and tested the friction under boundary lubrication. The results show that the high-density pit morphology has a low coefficient of friction, and when the sliding direction and pit row When the cloth is at a 30 degree angle, the friction is reduced. Zeeshan Ur Rehman [11], Faiz Muhaffel [12] and Aliofkhazraei [13] have also done a lot of research in the field of coatings and textures.

Due to too many factors affecting the texture performance, including texture morphology, geometric parameters, friction conditions, contact methods, lubricants and environmental influences. At present, there is no certain optimal texture pattern, and most of researchers are based on experiments, lack of good theoretical explanation.

The theoretical and experimental research of the predecessors have proved that the surface texture has excellent anti-wear and lubrication performance. However, few of them have studied textures with one-way convergence morphology, such as triangle. And researches mainly focus on one aspect that affects the texture properties, such as morphology. The predecessors mainly proved the friction and lubrication effects of the surface texture by experiments, but the simulation analysis was very few. In this experiment, simulation analysis  was combined with the specific experimental methods, the simulation results were supplemented by experiments, and the effects of morphology and area occupancy ratio on texture properties were comprehensively studied.

[1]           Jianfei, S.; Shun, H.; Haitao, D.; Wuyi, C. Cutting performance and wear mechanism of Sialon        ceramic tools in high speed face milling GH4099. Ceramics International. 2019.

https://doi.org/10.1016/j.ceramint.2019.09.134.

[2]           Datta, A.; Dutta, S.; Pal, S.K.; Sen, R. Progressive cutting tool wear detection from machined            surface images using Voronoi tessellation method. Journal of Materials Processing Technology.          2013, 213(12), 2339-2349.

https://doi.org/10.1016/j.jmatprotec.2013.07.008.

[3]           Xuewei, Z.; Tianbiao, Y.; Ji, Z. Surface generation modeling of micro milling process with               stochastic tool wear. Precision Engineering. 2019.

https://doi.org/10.1016/j.precisioneng.2019.10.015.

[4]           JingHui, Z.; LiZhi, Z.; Yuying, Y.; Jie, Z. Mechanical durability of superhydrophobic surfaces: The role of surface modification technologies. Applied Surface Science. 2017, 392, 286-296.

https://doi.org/10.1016/j.apsusc.2016.09.049.

[5]           Shota, I.; Kenta, T.; Shinya, S. Generation mechanism of friction anisotropy by surface texturing     under boundary lubrication. Tribology International. 2019.

https://doi.org/10.1016/j.triboint.2019.02.006.

• Boidi, G.; Tertuliano, I.S.; Profito, F.J.; de Rossi, W.; Machado, I.F. Effect of laser surface texturing on friction behaviour in elastohydrodynamically lubricated point contacts under different          sliding-rolling conditions. Tribology International. 2019.

https://doi.org/10.1016/j.triboint.2019.02.021.

• Hongzhi, Y.; Jianxin, D.; Dongliang, G.; Xuemu, L.; Yun, Z. Effect of surface texturing on tribological performance of sliding guideway under boundary lubrication. Journal of Manufacturing Processes. 2019, 47, 172-182.

https://doi.org/10.1016/j.jmapro.2019.09.031.

[8]     Joaquin, A.; Jon-Emile, S.K.; Frederik, R.B.; Daniel, SJ.P. Dynamic prediction of fluid responsiveness during positive pressure ventilation: a review of the physiology underlying heart–lung interactions and a critical interpretation. Veterinary Anaesthesia and Analgesia. 2019.

https://doi.org/10.1016/j.vaa.2019.08.004.

• Weili, L.; Hongjian, N.; Hailong, C.; Peng, W. Numerical simulation and experimental investigation on tribological performance of micro-dimples textured surface under hydrodynamic lubrication. International Journal of Mechanical Sciences. 2019, 163.

https://doi.org/10.1016/j.ijmecsci.2019.105095.

• Gachot, C.; Rosenkranz, A.; Hsu, S.M.; Costa, H.L. A critical assessment of surface texturing for friction and wear improvement. Wear. 2017, 372–373, 21-41.

https://doi.org/10.1016/j.wear.2016.11.020.

• Zeeshan, U.R.; Bon, H.K. Effect of Na2SiO.5H2O concentration on the secondary step coating produced on AZ91 magnesium alloy in the K2ZrF6-based el3ectrolyte solution. Surface and coating technology. 2017, 317, 117-124.
• Faiz, M.; Mertcan, K.; Grzegorz, C.; Bora, D.; Adam, K.; Erdem, A.; Huseyin, C. Influence of alumina and zirconia incorporations on the structure and wear resistance of titania-based MAO coatings. Surface & Coatings Technology. 2019, 377.

https://doi.org/10.1016/j.surfcoat.2019.124900.

• Aliofkhazraei, M.; Sabour Rouhaghdam, A. Wear and coating removal mechanism of alumina/titania nanocomposite layer fabricated by plasma electrolysis. Surf.Coatings Technol. 2011, 205, S57–S62.

https://doi.org/10.1016/j.surfcoat.2011.02.058.

• Edeling, W.N.; Cinnella, P.; Dwight, R.P.; Bijl, H. Bayesian estimates of parameter variability in the k–ε turbulence model. Journal of Computational Physics. 2014, 258, 73-94.

https://doi.org/10.1016/j.jcp.2013.10.027.

Point 2: The scale labels of contours in Fig. 2c,f,i are hard to be seen. Also, the length scale lines in Fig.2 a,b,d,e,g,h are not clear.

Response 2: According to your request, I have replaced Fig. 2c,f,i to make the scale labels of contours in figures clearer. Also, the length scale lines in Fig.2 a,b,d,e,g,h have been relabeled.

Point 3: Where do the parameters in Eqs.(8)-(9) come from? For example, why constants C1ɛ, C2ɛ and C3ɛ are taken as 1.44,147 1.92 and 0.09? The authors should give the relevant references. Also, for the determination of boundary conditions in simulation, the authors should give proper references or sources or reasons for the given parameters value.

Response 3: The k-ɛ two-equation model was proposed in 1974 by a research team led by Professor Spalding of the British Imperial College, and became the most widely used turbulence model. The k-ɛ model assumes that turbulent viscosity is related to turbulent kinetic energy and dissipation rate. The standard k-ɛ equation is of the form:

In the formula: k, ɛ are the turbulent kinetic energy and turbulent dissipation rate, respectively. ρ is the density, t is the time, and G_k and G_b are the turbulent flow energy affected by the velocity and buoyancy, respectively. μ_t is the viscosity coefficient, Y_M is the degree to which the dissipation rate is affected by the pulsation expansion, σ_k and σ_ɛ represent the Prandtl numbers of the turbulent flow energy k and the dissipation rate ɛ, respectively. The model constants are: C_1ɛ=1.44, C_2ɛ=1.92 and C_3ɛ=0.09.

Because the fluid is not compressible, the boundary conditions select the inlet pressure and the outlet pressure. In order to correspond to the friction and wear test conditions, the fluid is Mobil No. 1 lubricant, which has a density of 900kg/m³, and a viscosity of 0.045Pa·s. The loading force F is 300N, the wear area S is 28.06πmm², The inlet pressure is 3.403MPa by the formula P=F/S. And the reference pressure at the outlet is taken as the atmospheric pressure 101325 Pa.

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. We appreciate for your warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very mach for your comments and suggestions.

Reviewer 3 Report

Comments

The author has carried out interesting experiment and liable to be published in this journal, however the following comments should be taken into account.

Please modify the title by removing the repeating words Author should present the abstract in more brief form and remove the sentence which have been also mentioned in the introduction part. The author should follow the format of the current journal and imply relevant modifications The author should the modify the format of the references The author should add more reasons and relevant details in the introduction part as well include many current references in the introduction to improve the innovation impact of the article. How did the author concluded that non textured surface has abrasive wear and contact fatigue wear, while the textures surface has mainly adhesive wear, abrasive wear and cavitation? The author should correct the labels of Fig. 14, 15, 16, 17. Please modify fig. 9, 10, 11, 12, 13, by increasing the font size of the labels, line and symbols. The author should include the following article in the introduction part.

a. Zeeshan Ur Rehman , Bon Heun Koo, Effect of Na2SiO.5H2O concentration on the secondary step coating produced on AZ91 magnesium alloy in the K2ZrF6-based el3ectrolyte solution, Surface and coating technology, (2017) 317, 117-124.

b. Faiz Muhaffel, Mertcan Kaba, Grzegorz Cempura, Bora Derin, Adam Kruk, Erdem Atar, Huseyin Cimenoglu, Influence of alumina and zirconia incorporations on the structure and wear resistance of titania-based MAO coatings, Surface & Coatings Technology 377 (2019) 124900.

c. Aliofkhazraei, A.S. Rouhaghdam, Wear and coating removal mechanism of alumina/titania nanocomposite layer fabricated by plasma electrolysis, Surf.Coatings Technol. 205 (2011) S57–S62, https://doi.org/10.1016/j.surfcoat.2011.02.058

Response to Reviewer 2 Comments

Dear Reviewer:

Thank you for comments concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Point 1: Please modify the title by removing the repeating words.

Response 1: According to your requests, I have modified the title of the paper to “Study on Friction and Lubrication Characteristics of Surface with Unidirectional Convergence Texture”.

Point 2: Author should present the abstract in more brief form and remove the sentence which have been also mentioned in the introduction part.

Response 2: Based on your request, I have refined the abstract, as shown below.

Abstract: In order to study the influence of texture on the wear and lubrication performance of the surface of the tools, three kinds of textures with unidirectional convergence morphology were processed on the surface of the samples, and each texture was designed with different area occupancy ratios. Simulation analysis shows that: due to the reflow and convection effect of liquid in the texture, the lubricating film flowing through the textured surface has a high hydrodynamic pressure value, and the semicircular ring texture is the most prominent. By comparing the friction coefficient: When the area occupancy ratio of  texture on the surface is 10%, the surface of the samples with different morphology has the lowest coefficient of friction, especially the friction coefficient of the semicircular ring textured surface is very low. Surface textures reduce the direct contact area between the friction pairs, and generate dynamic pressure lubrication and secondary lubrication, so that the surface friction coefficient of the samples is obviously reduced. The surface of the non-textured samples have abrasive wear and contact fatigue wear, and the surface of the textured samples have adhesive wear, abrasive wear and cavitation.

Point 3: The author should follow the format of the current journal and imply relevant modifications. The author should the modify the format of the references.

Response 3: According to your request, I have modified the paper according to the format of the current journal, and the format of the references have also been revised.

Point 4: The author should add more reasons and relevant details in the introduction part as well include many current references in the introduction to improve the innovation impact of the article. 

Response 4: Based on your request, I have already supplemented the introduction part and referred to some of the latest literature, as shown below.

It is estimated that about 1/3 to 1/2 of the world's energy consumption is caused by friction and wear, in conventional material removal processes such as turning, milling and grinding, the relative motion between the friction pairs can cause severe wear on the surface of tools [1], thus affecting the life and performance of tools [2,3]. Also, for other non-machining manufacturing technologies such as metal forming processes, as a result of severe plastic deformation and high stresses of the processes such as drawing, extrusion, forming tools are exposed to excessive wear and fatigue. How to improve the wear resistance of the surface of tools has become an urgent problem in manufacturing technologies.

Ion implantation, shot peening and surface coating methods have been applied to extend the service life of manufacturing tools. Other than ion implantation, shot peening and surface coating methods, surface texturing and patterning methods have been widely studied these days, which has obvious effects on improving the surface friction performance of tools [4]. Studies have shown that when the surface of tools has a certain texture, its wear resistance will be improved, and a certain non-smooth surface will improve the friction and lubrication properties of the lubricating fluid [5,6].

In 1942, SCHLESINGER [7] proposed that “the quality of the surface is extremely important for its correct function”, indicating that designers have long recognized that the mechanical, physical and chemical properties of the surface can be improved by changing the surface morphology, such as surface texture.

In 1966, HAMILTON [8] proposed the additional fluid dynamic pressure effect: when the liquid flows through the pits or grooves machined on the surface of the friction pair, a small convergence wedge and a divergent wedge are formed. When the friction pair is in relative motion, the fluid in the convergence wedge generates a dynamic pressure effect, thereby forming a positive pressure; while in the divergent wedge, due to the existence of "cavitation" phenomenon, the "negative pressure" of the fluid is restrained. Therefore, additional hydrodynamic pressure is formed between the friction pairs, which improves the bearing capacity of the fluid.

Liu et al. [9] used picosecond laser to achieve micro-texture on the surface of cast iron, and investigated the friction and wear properties of four different surfaces of smooth, pit textures, net textures and intermittent textures. The study found that under dry friction condition, the surface machined micro-texture can significantly improve the stability of the friction coefficient compared with smooth surface ,but different textures have different effects on the stability and initial value of the friction coefficient.

Gachot et al. [10] fabricated regular pits on the silicon surface by photolithography and wet etching, and tested the friction under boundary lubrication. The results show that the high-density pit morphology has a low coefficient of friction, and when the sliding direction and pit row When the cloth is at a 30 degree angle, the friction is reduced. Zeeshan Ur Rehman [11], Faiz Muhaffel [12] and Aliofkhazraei [13] have also done a lot of research in the field of coatings and textures.

Due to too many factors affecting the texture performance, including texture morphology, geometric parameters, friction conditions, contact methods, lubricants and environmental influences. At present, there is no certain optimal texture pattern, and most of researchers are based on experiments, lack of good theoretical explanation.

The theoretical and experimental research of the predecessors have proved that the surface texture has excellent anti-wear and lubrication performance. However, few of them have studied textures with one-way convergence morphology, such as triangle. And researches mainly focus on one aspect that affects the texture properties, such as morphology. The predecessors mainly proved the friction and lubrication effects of the surface texture by experiments, but the simulation analysis was very few. In this experiment, simulation analysis  was combined with the specific experimental methods, the simulation results were supplemented by experiments, and the effects of morphology and area occupancy ratio on texture properties were comprehensively studied.

[1]           Jianfei, S.; Shun, H.; Haitao, D.; Wuyi, C. Cutting performance and wear mechanism of Sialon        ceramic tools in high speed face milling GH4099. Ceramics International. 2019.

https://doi.org/10.1016/j.ceramint.2019.09.134.

[2]           Datta, A.; Dutta, S.; Pal, S.K.; Sen, R. Progressive cutting tool wear detection from machined            surface images using Voronoi tessellation method. Journal of Materials Processing Technology.          2013, 213(12), 2339-2349.

https://doi.org/10.1016/j.jmatprotec.2013.07.008.

[3]           Xuewei, Z.; Tianbiao, Y.; Ji, Z. Surface generation modeling of micro milling process with               stochastic tool wear. Precision Engineering. 2019.

https://doi.org/10.1016/j.precisioneng.2019.10.015.

[4]           JingHui, Z.; LiZhi, Z.; Yuying, Y.; Jie, Z. Mechanical durability of superhydrophobic surfaces: The role of surface modification technologies. Applied Surface Science. 2017, 392, 286-296.

https://doi.org/10.1016/j.apsusc.2016.09.049.

[5]           Shota, I.; Kenta, T.; Shinya, S. Generation mechanism of friction anisotropy by surface texturing     under boundary lubrication. Tribology International. 2019.

https://doi.org/10.1016/j.triboint.2019.02.006.

• Boidi, G.; Tertuliano, I.S.; Profito, F.J.; de Rossi, W.; Machado, I.F. Effect of laser surface texturing on friction behaviour in elastohydrodynamically lubricated point contacts under different          sliding-rolling conditions. Tribology International. 2019.

https://doi.org/10.1016/j.triboint.2019.02.021.

• Hongzhi, Y.; Jianxin, D.; Dongliang, G.; Xuemu, L.; Yun, Z. Effect of surface texturing on tribological performance of sliding guideway under boundary lubrication. Journal of Manufacturing Processes. 2019, 47, 172-182.

https://doi.org/10.1016/j.jmapro.2019.09.031.

[8]     Joaquin, A.; Jon-Emile, S.K.; Frederik, R.B.; Daniel, SJ.P. Dynamic prediction of fluid responsiveness during positive pressure ventilation: a review of the physiology underlying heart–lung interactions and a critical interpretation. Veterinary Anaesthesia and Analgesia. 2019.

https://doi.org/10.1016/j.vaa.2019.08.004.

• Weili, L.; Hongjian, N.; Hailong, C.; Peng, W. Numerical simulation and experimental investigation on tribological performance of micro-dimples textured surface under hydrodynamic lubrication. International Journal of Mechanical Sciences. 2019, 163.

https://doi.org/10.1016/j.ijmecsci.2019.105095.

• Gachot, C.; Rosenkranz, A.; Hsu, S.M.; Costa, H.L. A critical assessment of surface texturing for friction and wear improvement. Wear. 2017, 372–373, 21-41.

https://doi.org/10.1016/j.wear.2016.11.020.

• Zeeshan, U.R.; Bon, H.K. Effect of Na2SiO.5H2O concentration on the secondary step coating produced on AZ91 magnesium alloy in the K2ZrF6-based el3ectrolyte solution. Surface and coating technology. 2017, 317, 117-124.
• Faiz, M.; Mertcan, K.; Grzegorz, C.; Bora, D.; Adam, K.; Erdem, A.; Huseyin, C. Influence of alumina and zirconia incorporations on the structure and wear resistance of titania-based MAO coatings. Surface & Coatings Technology. 2019, 377.

https://doi.org/10.1016/j.surfcoat.2019.124900.

• Aliofkhazraei, M.; Sabour Rouhaghdam, A. Wear and coating removal mechanism of alumina/titania nanocomposite layer fabricated by plasma electrolysis. Surf.Coatings Technol. 2011, 205, S57–S62.

https://doi.org/10.1016/j.surfcoat.2011.02.058.

Point 5: How did the author concluded that non textured surface has abrasive wear and contact fatigue wear, while the textures surface has mainly adhesive wear, abrasive wear and cavitation? 

Response 5: Definition of abrasive wear: in the process of friction, the material loss caused by the extrusion of hard particles or hard micro protrusion on the surface of friction pair and the movement of hard particles along the surface of friction pair. The main feature of abrasive wear is scratches on the friction surface or grooves formed by obvious plows. There are significant wear scratches on the surface of non-textured specimen, which is consistent with the characteristics of abrasive wear, and I have already marked the scratches.

Definition of contact fatigue wear: When the surface of friction pairs move in rolling or sliding, due to the effect of alternating contact stress, the surface material is fatigued and fractured, resulting in pitting or peeling off. The characteristic of pitting is that the initial crack appears on the surface of the part, the surface crack gradually expands and produces fatigue failure. The damage depth of the material is shallow, the material falls off in small pieces, and finally forms pits on the surface of the parts. In addition, when the surface contact compressive stress is large and the friction coefficient is small, the initial crack tends to sprout and expand below the surface, and the fatigue damage mostly occurs suddenly. The material is flaky and the damage zone is large, this form of fatigue wear is called peeling. There are significant pits of different sizes on the surface of specimen, which conform to the characteristics of pitting and peeling.

So I concluded that non textured surface has abrasive wear and contact fatigue wear.

Definition of adhesive wear: Adhesive wear refers to the local adhesion of the friction pair during the relative sliding process. In the subsequent relative sliding, the adhesion is broken and the metal particles are pulled from the surface of the part.

Definition of cavitation: The process of formation, development and collapse of vapor or gas voids at the internal or liquid-solid interface of a liquid when the local pressure in the liquid is reduced. In the movement of liquid, after the surface is impacted by cavitation, there will be deformation and material erosion on the surface, which is also called erosion or cavitation. When the fluid flows from the convergent to the divergence, the internal pressure of the fluid is reduced, bubbles are generated, and the bubbles are rapidly generated, expanded, and collapsed, forming a shock wave or a high-speed microjet in the liquid, causing impacts on the texture wall to form cavitation micro-pits.

According to the definition and characteristics of adhesive wear, abrasive wear and cavitation, as well as the real working condition of the test, I concluded that textures surface has mainly adhesive wear, abrasive wear and cavitation, and I have marked the location of scratches and pits. 

Point 6: The author should correct the labels of Fig. 14, 15, 16, 17. Please modify fig. 9, 10, 11, 12, 13, by increasing the font size of the labels, line and symbols.

Response 6: According to your requirements, I have corrected the labels of Fig. 14, 15, 16, 17 and modified Fig. 9, 10, 11, 12, 13 by increasing the font size of the labels, line and symbols.

Point 7: The author should include the following article in the introduction part.

124. Zeeshan Ur Rehman , Bon Heun Koo, Effect of Na2SiO.5H2O concentration on the secondary step coating produced on AZ91 magnesium alloy in the K2ZrF6-based el3ectrolyte solution, Surface and coating technology, (2017) 317, 117-124.
125. Faiz Muhaffel, Mertcan Kaba, Grzegorz Cempura, Bora Derin, Adam Kruk, Erdem Atar, Huseyin Cimenoglu, Influence of alumina and zirconia incorporations on the structure and wear resistance of titania-based MAO coatings, Surface & Coatings Technology 377 (2019) 124900.
126. Aliofkhazraei, A.S. Rouhaghdam, Wear and coating removal mechanism of alumina/titania nanocomposite layer fabricated by plasma electrolysis, Surf.Coatings Technol. 205 (2011) S57–S62, https://doi.org/10.1016/j.surfcoat.2011.02.058.

Response 7: According to your suggestion, I have already added these articles in the introduction.

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. We appreciate for your warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very mach for your comments and suggestions.

Round 2

Reviewer 3 Report

The article can be accepted for publication in the current form.