Wear Behavior of Medium-Carbon Steel with Different Laser-Textured Densities under Starved Lubrication

Round 1

Reviewer 1 Report

Dear author,

I read the paper and, in order to improve it, I suggest the following:

The surfaces of factory equipment parts are susceptible to wear [1] and lubrication technology  is often applied to improve the tribological performance of metal surfaces [2-3].

The micro-dimples not only serve as a micro-hydrodynamic bearing under a full or mixed lubrication regime [16-17], but also as a micro-reservoir for lubricant under starved lubrication conditions and the micro-dimples can also as a micro-trap for wear debris in either lubricated or dry sliding [18-22].

The morphology of a single biomimetic unit is shown in Fig. 2, which was observed by using a laser scanning confocal microscope (LSCM) (Olympus 63 lext ols 3000, Japan). 64

The friction coefficient was  acquired directly using the MG-2000 frictiograph, and the wear weight losses were measured by  electronic balance with an accuracy of 0.0001 g and the worn surfaces of the samples were observed by SEM. To assess the effect of the textures, the smooth sample was tested for comparison.

Over time, the friction pair gradually transformed from oil lubrication to starved lubrication, and the friction coefficient curve gradually fluctuated from a relatively steady state to ?.

Fig. 7 described the properties of specimen under the condition of 100 N and 300 rpm, but in the table 4 this experiment does not exist or the table is not clear. The same in fig. 10 (The SEM images of wear scar for samples with different texture densities)

When the load was less than 100N, the friction coefficient of each specimen decreased with the increase of the load. It is only one load less than 100 N (50 N) for 100 rpm, according to table 4, so please reformulate this phrase.

Also, in table 4, why you have only 300 N load for 50, 200 and 300 rotating speed, but for 100 rpm rotating speed you have 50, 100, 200 and 300 loads.

When the load exceeded 100N, the friction coefficient rose as the load increased.

At the conclusions you said that “ As the load increased, the friction coefficient values of the biomimetic specimens first decreased  (under small loads – which are the small loads 50N, 100N?) and then increased (under large loads).”

Author Response

Manuscript ID: coatings-1029625

 

Dear Editor,

 

We deeply thank you and the reviewers for giving us the chance to revise our manuscript and providing us with constructive comments. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. Changes in the manuscript are highlighted in red. The main corrections in the manuscript and the response to the reviewers’ comments are listed as following:

 

Responses to Reviewer #1:

 

Point 1: The surfaces of factory equipment parts are susceptible to wear [1] and lubrication technology is often applied to improve the tribological performance of metal surfaces [2-3].

The micro-dimples not only serve as a micro-hydrodynamic bearing under a full or mixed lubrication regime [16-17], but also as a micro-reservoir for lubricant under starved lubrication conditions and the micro-dimples can also as a micro-trap for wear debris in either lubricated or dry sliding [18-22].

The morphology of a single biomimetic unit is shown in Fig. 2, which was observed by using a laser scanning confocal microscope (LSCM) (Olympus 63 lext ols 3000, Japan). 64

The friction coefficient was acquired directly using the MG-2000 frictiograph, and the wear weight losses were measured by electronic balance with an accuracy of 0.0001 g and the worn surfaces of the samples were observed by SEM. To assess the effect of the textures, the smooth sample was tested for comparison.

 

Response 1: Based on your suggestion, I made the same modification to the part marked in red in this article.

 

Point 2: Over time, the friction pair gradually transformed from oil lubrication to starved lubrication, and the friction coefficient curve gradually fluctuated from a relatively steady state to ?.

 

Response 2: Thank you for your suggestion. Since the description of Figure 7 is not detailed enough, I will modify it to:

 

Over time, the friction pair gradually transformed from oil lubrication to starved lubrication, and the friction coefficient of the friction pair was a relatively stable value within a certain period of time, and then increased gradually with the loss of lubricant. In this experiment, bionic samples with texture densities of 4%, 8% and 30% entered the stage of oil-deficient lubrication in a relatively short time, and the friction coefficient increased at a relatively high rate.

 

Point 3: Fig. 7 described the properties of specimen under the condition of 100 N and 300 rpm, but in the table 4 this experiment does not exist or the table is not clear. The same in fig. 10 (The SEM images of wear scar for samples with different texture densities)

 

Response 3: Thank you for finding the deficiency in my experimental arrangement. I will supplement the missing contents in Table 4 and explain them in 2.2 Friction and wear examination. The revised table 4 is shown below：

Table4. The frictional experiment arrangement of smooth and different texture densities under different loads and different speeds.

	Rotating speed (rpm)	Load (N)
1	100	50
2	100	100
3	100	200
4	100	300
5	50	300
6	200	300
7	300	300
8	300	100

 

 

Point 4: When the load was less than 100N, the friction coefficient of each specimen decreased with the increase of the load. It is only one load less than 100 N (50 N) for 100 rpm, according to table 4, so please reformulate this phrase.

 

Response 4: Thanks for your advice, the description here is really not very rigorous, so we adjust these two phrases to: “When the load was 50N or 100N”and “When the load was 200N or 300N.”

 

Point 5: Also, in table 4, why you have only 300 N load for 50, 200 and 300 rotating speed, but for 100 rpm rotating speed you have 50, 100, 200 and 300 loads.

 

Response 5: In this experiment, in order to control variables, experimental arrangements of constant load and constant speed at variable load with different texture density were designed, among which experimental data of load at 100 speed 300N could be used in both experimental arrangements.

 

Point 6: When the load exceeded 100N, the friction coefficient rose as the load increased.At the conclusions you said that “As the load increased, the friction coefficient values of the biomimetic specimens first decreased (under small loads – which are the small loads 50N, 100N?) and then increased (under large loads).”

 

Response 6: Thank you for your suggestion. We will be more precise in conclusion and adjust it as follows:

“As the load increased, the friction coefficient values of the biomimetic specimens first decreased (under small loads between 50N, and 100N) and then increased (under large loads between 200N, and 300N).”

 

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript is devoted to experimental and computational studies of the wear behavior of a material after different kinds of processing, when starved lubrication is applied during wear. The authors used a laser to process the surface of the material under study (medium-carbon steel). The results are new and of interest to Coatings readers.

 

I find that the description of the details of experiments and calculations should be slightly improved. I would like to make a few comments to help the authors improve the manuscript.

 

1. Because the authors used laser texturing technology, they should provide the background and include relevant references about laser-matter interaction physics in the introduction. For example, [R1, R2, R3].

 

[R1] Povarnitsyn ME, Itina TE, Sentis M, Khishchenko KV, Levashov PR. Material decomposition mechanisms in femtosecond laser interactions with metals. Phys Rev B 2007;75:235414.

[R2] Povarnitsyn ME, Khishchenko KV, Levashov PR. Phase transitions in femtosecond laser ablation. Appl Surf Sci 2009;255:5120-5124.

[R3] Povarnitsyn ME, Itina TE, Levashov PR, Khishchenko KV. Simulation of ultrashort double-pulse laser ablation. Appl Surf Sci 2011;257:5168-5171.

 

2. The neodymium-doped yttrium-aluminum garnet laser is traditionally denoted by a colon:

Nd, YAG Laser

should be

Nd:YAG laser

 

3. Some important laser processing parameters are missing. The following parameters should be added:

- energy of one laser pulse;

- diameter of the focal spot;

- maximum laser irradiation intensity (W/cm²).

 

4. Page 2:

Olympus lext ols 3000

should be

Olympus LEXT OLS 3000

 

5. Fig. 2 is mentioned in the manuscript before Fig. 1. The order of figures 1 and 2 or the order in which figures 1 and 2 are mentioned should be changed.

 

6. Table 1: the used kind of percentage (weight %, atomic %) should be indicated.

 

7. Page 3, line 78:

Glycal

should be

Glycol

 

8. Table 5: what does SUS mean? The abbreviation should be explained on first use.

 

9. Page 4, line 99: what does XRD mean? The abbreviation should be explained on first use.

 

10. Figures 8 and 9:

Let us compare the order of curves top-down for the case 100 rpm and 300 N for the friction coefficient:

- smooth, 30%, 4%, 8%, 18%, 13%—in figure 8(a);

- smooth, 8%, 4%, 30%, 18%, 13%—in figure 9(a).

 

How is it possible?

The authors should check their results and notation.

 

11. Page 6, line 127:

The authors write that Fig. 7 corresponds to the case 100 N and 300 rpm. But there is no such combination of load and rotating speed in Table 4. Is Fig. 7 correct?

Same for Fig. 10.

 

12. Fig. 7:

Black curves are tangled.

I highly recommend using colored curves with the same notation of colors in all figures 7, 8(a), 8(b), 9(a) and 9(b).

 

13. I did not find in the manuscript an indication of the error in measuring the friction coefficient. This should be indicated in captions to figures 8 and 9 [or error bars should be added to each point in figures 8(a) and 9(a)].

 

14. I have found the error in measuring the weight loses: 0.0001 g = 0.1 mg. This should be also indicated in captions to figures 8 and 9 [or error bars should be added to each point in figures 8(b) and 9(b)].

 

15. I have not found any numerical simulation details explaining how the results shown in Fig. 12 have been obtained. What equations have been solved? What are the boundary conditions? What numerical method (or code) was used?

 

16. Caption to Table 6:

medium carbon steel, GCr15.

should be

medium carbon steel and GCr15.

 

17. Table 6, first column:

What does “Material (wt %)” mean?

In my opinion “15” in GCr15 does not mean 15 wt %, but 1.5 wt %.

 

18. To stress the difference between medium carbon steel and GCr15 steel, I recommend listing the elemental composition of the GCr15 steel in Table 1 along with the composition of the medium carbon steel.

 

19. Page 11: there are two cases of dividing of a word by word (slid/rolled, cracks/grooves). What does it mean?

I guess that

“slid/rolled” should be substituted by “slid and rolled”,

“cracks/grooves” should be substituted by “cracks or grooves”.

 

20. Page 14, line 71:

Tong X. Ren LQ Wear

should be

Tong X, Ren LQ. Wear

 

21. Page 1, line 37:

And the micro-dimples can also as

should be

And the micro-dimples can also serve as

 

22. Page 4, line 96:

Fig. 4 presents the microstructures of the biomimetic surfaces were

should be

Fig. 4 presents that the microstructures of the biomimetic surfaces were

 

It seems that the manuscript should be considered for publication in Coatings after minor improvement as listed above.

Comments for author File: Comments.pdf

Author Response

Manuscript ID: coatings-1029625

 

Dear Editor,

 

We deeply thank you and the reviewers for giving us the chance to revise our manuscript and providing us with constructive comments. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. Changes in the manuscript are highlighted in red. The main corrections in the manuscript and the response to the reviewer’s comments are listed as following:

 

Responses to Reviewer #4:

 

Point 1: Because the authors used laser texturing technology, they should provide the background and include relevant references about laser-matter interaction physics in the introduction. For example, [R1, R2, R3].

 

[R1] Povarnitsyn ME, Itina TE, Sentis M, Khishchenko KV, Levashov PR. Material decomposition mechanisms in femtosecond laser interactions with metals. Phys Rev B 2007;75:235414.

 

[R2] Povarnitsyn ME, Khishchenko KV, Levashov PR. Phase transitions in femtosecond laser ablation. Appl Surf Sci 2009;255:5120-5124.

 

[R3] Povarnitsyn ME, Itina TE, Levashov PR, Khishchenko KV. Simulation of ultrashort double-pulse laser ablation. Appl Surf Sci 2011;257:5168-5171.

 

Response 1: Thank you for your suggestions. We have cited the above literature in the introduction.

[28] M.E. Povarnitsyn, T.E. Itina, M. Sentis, K.V. Khishchenko, P.R. Levashov, Material decomposition mechanisms in femtosecond laser interactions with metals, Physical Review B, 75 (2007).

[29] M.E. Povarnitsyn, K.V. Khishchenko, P.R. Levashov, Phase transitions in femtosecond laser ablation, Applied Surface Science, 255 (2009) 5120-5124.

[30] I.T. Povarnitsyn ME, Khishchenko KV, Levashov PR, Simulation of ultrashort double-pulse laser ablation, Applied Surface Science, 257 (2011) 5168-5171.

Point 2: The neodymium-doped yttrium-aluminum garnet laser is traditionally denoted by a colon: Nd, YAG Laser should be Nd : YAG laser

 

Response 2: Thank you for your suggestion. We have corrected the wrong handwriting in the corresponding position of the manuscript.

 

Point 3: Some important laser processing parameters are missing. The following parameters should be added:

- energy of one laser pulse;

 

- diameter of the focal spot;

 

- maximum laser irradiation intensity (W/cm2).

Response 2: According to your suggestion, we have supplemented the relevant parameters of laser machining, as shown below. The lasers we use are not femtosecond lasers, so the machining parameters we supplement may be different from what you require.

“During the experiment, the spot diameter was 0.4mm, the laser output energy was 4J and the maximum laser power was 800W.”

 

Point 4: Page 2: Olympus lext ols 3000 should be Olympus LEXT OLS 3000

 

Response 4: Thank you for your suggestion. We have corrected this typo in the submitted document and marked it with red font. The corrected content is as follows:

The morphology of a single biomimetic unit is shown in Fig. 2, which was observed by using a laser scanning confocal microscope (LSCM) (Olympus LEXT OLS 3000, Japan).

 

Point 5: Fig. 2 is mentioned in the manuscript before Fig. 1. The order of figures 1 and 2 or the order in which figures 1 and 2 are mentioned should be changed.

 

Response 5: Thank you for your suggestion. Figure 1 was involved in the description of the processing method, and the reference to Figure 1 has been added in the new manuscript, so we did not change the order of Figure 1 and Figure 2.As shown below：

“The biomimetic surfaces of the specimens were manufactured by an Nd: YAG Laser with a wavelength of 1.06 mm, the schematic diagram of sample preparation is shown in Figure 1.”

 

Point 6: Table 1: the used kind of percentage (weight %, atomic %) should be indicated.

 

Response 6: Thank you for your careful review of our manuscript. The chemical composition of the specimen used as a medium carbon steel consists of C0.45， Gr0.057, Ni0.016, Mn0.54, S0.002, P0.015, Si0.13, Mo0.002 and Fe as balance (all in wt.%) is presented in Table 1. We have modified Table 1 according to your comments, as shown below:

 

Table1. The chemical constituents of medium carbon steel and GCr15 were analyzed by SEM-EDS.

Elements		C	Si	Mn	S	P	Cr	Mo	Ni
Composition (wt%)	medium carbon steel	0.45	0.21	0.54	0.002	0.015	0.057	0.002	0.016
	GCr15	0.98	0.18	0.37	0.003	0.02	1.55	0.038	0.016

 

Point 7: Page 3, line 78: Glycal should be Glycol

 

Response 7: Thank you for your careful review of our manuscript. We have corrected this typo in the submitted manuscript.

 

Point 8: Table 5: what does SUS mean? The abbreviation should be explained on first use.

 

Response 8: Thanks for your suggestion. SUS stands for Saybolt universal viscosity, which we have added in Table 5, as shown below:

Table 5. The performance index of PAG lubricating oil.

viscosity index	Saybolt Universal Viscosity(SUS) 100 ℉	Viscosity 40 ℃	Viscosity 100 ℃	flash point ℃	Pour point ℃
197	170	33	7.45	232	-42

 

Point 9: Page 4, line 99: what does XRD mean? The abbreviation should be explained on first use.

 

Response 9: Thank you for your suggestion, we added an XRD explanation in 2.1 Specimens preparation and characterization, as shown below:

“X-ray diffractometer （XRD）(BRUKER D8 FOCUS X) was used to analyze the phase of medium carbon steel treated by laser and untreated.”

 

Point 10: Figures 8 and 9:

Let us compare the order of curves top-down for the case 100 rpm and 300 N for the friction coefficient:

 

- smooth, 30%, 4%, 8%, 18%, 13%—in figure 8(a);

 

- smooth, 8%, 4%, 30%, 18%, 13%—in figure 9(a).

 

How is it possible?

 

The authors should check their results and notation.

 

Response 10: We have modified Figure 8 and Figure 9 according to your suggestion:

Figure 8. Effect of different texture densities on the friction coefficient and the wear weight loss at a constant speed of 100 rpm: (a) friction coefficient, (b) wear weight losses.

Figure 9. Effect of different texture densities on friction coefficient and wear weight loss under the constant 300N load: (a) friction coefficient, (b) wear weight losses.

 

Point 11: Page 6, line 127: The authors write that Fig. 7 corresponds to the case 100 N and 300 rpm. But there is no such combination of load and rotating speed in Table 4. Is Fig. 7 correct? Same for Fig. 10 .

 

Response 11: Figures 7 and 10 are right. Thank you for finding the deficiency in my experimental arrangement. I will supplement the missing contents in Table 4 and explain them in 2.2 Friction and wear examination. The revised table 4 is shown below：

 

 

Table4. The frictional experiment arrangement of smooth and different texture densities under different loads and different speeds.

	Rotating speed (rpm)	Load (N)
1	100	50
2	100	100
3	100	200
4	100	300
5	50	300
6	200	300
7	300	300
8	300	100

 

 

Point 12: Fig. 7: Black curves are tangled. I highly recommend using colored curves with the same notation of colors in all figures 7, 8(a), 8(b), 9(a) and 9(b).

 

Response 12: According to your suggestion, we have modified the color of the curve in Figure 7:

Figure 7. The friction coefficient curves of biomimetic specimens.

 

Point 13: I did not find in the manuscript an indication of the error in measuring the friction coefficient. This should be indicated in captions to figures 8 and 9 [or error bars should be added to each point in figures 8(a) and 9(a)].

 

Point 14:I have found the error in measuring the weight loses: 0.0001 g = 0.1 mg. This should be also indicated in captions to figures 8 and 9 [or error bars should be added to each point in figures 8(b) and 9(b)].

 

Response 13 and 14: Thank you for your suggestions. We rearranged the experimental data and added error bars in Figure 8 and Figure 9, as shown below:

Figure 8. Effect of different texture densities on the friction coefficient and the wear weight loss at a constant speed of 100 rpm: (a) friction coefficient, (b) wear weight losses.

Figure 9. Effect of different texture densities on friction coefficient and wear weight loss under the constant 300N load: (a) friction coefficient, (b) wear weight losses.

 

Point 15: I have not found any numerical simulation details explaining how the results shown in Fig. 12 have been obtained. What equations have been solved? What are the boundary conditions? What numerical method (or code) was used?

 

Response 15: According to your suggestion, we have supplemented the numerical research method and related formulas in the manuscript, and pointed out the constraints. The revised content is as follows:

“The constraint condition of the models is shown in Fig 11, consists of two parts: a fixed block and a test block above it.”

“Equivalent stress (Von Mises stress) is an important cause of wear. In this experiment, the numerical study was carried out by Workbench to analyze the influence of three main stresses on plastic damage. The expression can be written as follows:

                                                                                                                   (1)

where is the Von Mises stress. , and are the first, second and third main stress, respectively.”

Point 16: Caption to Table 6: medium carbon steel, GCr15 should be medium carbon steel and GCr15.

Point 17: Table 6, first column: What does “Material (wt %)” mean? In my opinion “15” in GCr15 does not mean 15 wt %, but 1.5 wt %.

 

Response 16 and 17: Thank you for your suggestions. We have modified Table 6：

 

Table 6. The performance parameters of medium carbon steel and GCr15.

Material	Density (g/cm3)	Elasticity (GPa)	Tensile strength (MPa)	Yield strength (MPa)	Poisson’s ratio	Young’s modulus (GPa)
Medium carbon steel	7.84	207	650	400	0.278	206
GCr15	7.81	210	861.3	518.4	0.300	210

 

Point 18: To stress the difference between medium carbon steel and GCr15 steel, I recommend listing the elemental composition of the GCr15 steel in Table 1 along with the composition of the medium carbon steel.

 

Response 18: Thank you for your suggestion. We have added the Composition of GCr15 in Table 1. The revised Table 1 is as follow:

 

Table 1. The chemical constituents of medium carbon steel and GCr15 were analyzed by SEM-EDS.

Elements		C	Si	Mn	S	P	Cr	Mo	Ni
Composition (wt%)	medium carbon steel	0.45	0.21	0.54	0.002	0.015	0.057	0.002	0.016
	GCr15	0.98	0.18	0.37	0.003	0.02	1.55	0.038	0.016

 

Point 19: Page 11: there are two cases of dividing of a word by word (slid/rolled, cracks/grooves). What does it mean? I guess that“slid/rolled” should be substituted by “slid and rolled”, “cracks/grooves” should be substituted by “cracks or grooves”.

 

Response 19: Thank you for your suggestion. We have corrected this typo in the submitted document and marked it with red, as shown:

“Due to the biomimetic units, when the abrasive particles slid and rolled on the surfaces and produced grooves, the units could prevent the moving path of the particles or make the movement path segregated, thereby effectively stopping the expansion of the cracks and grooves.”

 

Point 20: Page 14, line 71: Tong X. Ren LQ Wear should be Tong X, Ren LQ. Wear

 

Response 20: Thank you for your suggestion. We have modified the quotation format of this reference and marked it in red font in the submitted document.

 

Point 21: Page 1, line 37: “And the micro-dimples can also as” should be “And the micro-dimples can also serve as”

 

Response 21: Thank you for your careful examination of the manuscript. We have revised it in the manuscript:

“The micro-dimples not only serve as a micro-hydrodynamic bearing under a full or mixed lubrication regime [16-17], but also as a micro-reservoir for lubricant under starved lubrication conditions and the micro-dimples can also serve as a micro-trap for wear debris in either lubricated or dry sliding [18-22].”

 

Point 22: Page 4, line 96: “Fig. 4 presents the microstructures of the biomimetic surfaces were” should be “Fig. 4 presents that the microstructures of the biomimetic surfaces were”

 

Response 22: Thank you for your careful examination of the manuscript. We have revised it in the manuscript:

“Fig. 4 presents that the microstructures of the biomimetic surfaces were different from those of the smooth surfaces.”

 

 

 

 

Author Response File: Author Response.docx

Reviewer 3 Report

The preparation of five densities of textured on the surfaces of medium carbon steel, by laser, is described, along with the friction tests. The influence of some synthesis parammeters is analyzed in order to describe an analysis of the tribological mechanism. The main objective is to reduce wear cracks and it deserves publication in this journal.

 

Some minor comments:

 

Table 1 caption must show the analytical technique used to determine the chemical composition of the samples. Such information has to be added to the experimental section.

 

Table 4 caption is not complete.

 

XRD and SEM equipments must be described in the experimental section.

The preparation of five densities of textured on the surfaces of medium carbon steel, by laser, is described, along with the friction tests. The influence of some synthesis parammeters is analyzed in order to describe an analysis of the tribological mechanism. The main objective is to reduce wear cracks and it deserves publication in this journal.

 

Some minor comments:

 

Table 1 caption must show the analytical technique used to determine the chemical composition of the samples. Such information has to be added to the experimental section.

 

Table 4 caption is not complete.

 

XRD and SEM equipments must be described in the experimental section.

Author Response

Manuscript ID: coatings-1029625

 

Dear Editor,

 

We deeply thank you and the reviewers for giving us the chance to revise our manuscript and providing us with constructive comments. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. Changes in the manuscript are highlighted in red. The main corrections in the manuscript and the response to the reviewers’ comments are listed as following:

Responses to Reviewer #2:

 

Point 1: Table 1 caption must show the analytical technique used to determine the chemical composition of the samples. Such information has to be added to the experimental section.

 

Response 1: Thank you for your suggestions to make our research more rigorous and credible. Therefore，Table 1 caption was modified to:

Table 1. Chemical composition of medium carbon steel by SEM-EDS.

Elements	C	Cr	Ni	Mn	S	P	Si	Mo
Composition（at%）	0.45	0.057	0.016	0.54	0.002	0.015	0.13	0.002

 

 

Point 2: Table 4 caption is not complete.

 

Response 2: Thank you for finding the deficiency in my experimental arrangement. I will supplement the missing contents in Table 4 and explain them in 2.2 Friction and wear examination. The revised table 4 is shown below：

 

Table4. The frictional experiment arrangement of smooth and different texture densities under different loads and different speeds.

	Rotating speed (rpm)	Load (N)
1	100	50
2	100	100
3	100	200
4	100	300
5	50	300
6	200	300
7	300	300
8	300	100

 

 

Point 3: XRD and SEM equipments must be described in the experimental section.

 

Response 3: In 2.1, we marked the model of SEM equipment and supplemented the model of XRD equipment.

Author Response File: Author Response.docx