Friction and Wear Properties of Silicon Nitride-Based Composites with Different hBN Content Sliding against Polyether-Etherketone at Different Speeds under Artificial Seawater Lubrication
Round 1
Reviewer 1 Report
The subject matter is very interesting, important, and has a special value considering practical applications. There are still some things that could be improved, and a few questions that have to be answered before publication. Therefore, I suggest a mandatory revision of the following points to increase the quality of the paper:
1. There is no information about the names of devices used for testing. The authors should provide the names of all devices as well as parameters.
2. The authors have presented the results of the research on the friction coefficient. In my opinion, they should show curves illustrating the change of the friction coefficient as a function of time or friction distance.
3. In figures showing the worn surfaces, the observations described by the authors in the text should be marked and described.
4. The chemical composition analysis should be performed in several places. The places of analysis should be marked on the SEM photos.
5. Moreover, in Fig. 6, indescribable peaks are visible on the EDS spectrum.
6. The authors should also include articles from scientists outside of Asia.
Recommendation:
This manuscript in the presented form is not acceptable for publication in the Coatings. The major revision is necessary.
Author Response
1. There is no information about the names of devices used for testing. The authors should provide the names of all devices as well as parameters. Response: Thank you for the reminder. I have added the corresponding model number in the revised manuscript in Section 2.2. The detailed information is described below. (1) MMW-1 pin-on-disc wear tester was made by Jinan Zhongchuang Industrial Test System Co., LTD. The technical indexes of the test force of the machine are: the axial load range of the test force is 10N-1000N; the test force shows zero sensitivity ±1.5N; test force display value allowed error 0N-100N: ±2N, 100N-1000N: ±0.5%; automatic loading rate of test force 300N/min; when the test force is long, the relative error of the indicated value is automatically maintained to be ±1%. The technical indexes of friction torque of this machine are: maximum friction torque measured value of 2.5N•m; friction value tolerance of ±2%; friction load sensor of 100N; friction arm distance of 50mm. (2) The model number of Scanning Electron Microscopy (SEM) : FEI Q45, U.S.A (3) The model number of X-ray photoelectron spectroscopy (XPS): K-Alpha, U.S.A 2. The authors have presented the results of the research on the friction coefficient. In my opinion, they should show curves illustrating the change of the friction coefficient as a function of time or friction distance. Response: We have added the change curves of the friction coefficients of SN20/PEEK as a function of time or friction distance (see Fig.4 in revised manuscript). If we give all the curves, it's hard to see the friction regular, so we just present some typical curves. Fig.4 The change curves of the friction coefficients of SN20/PEEK as a function of friction distance 3. In figures showing the worn surfaces, the observations described by the authors in the text should be marked and described. Response: some typical SEM images of worn surfaces have been indicated in the figure, e.g. Fig.5a, Fig.5b, Fig.6a and Fig.6c in revised manuscript (as shown in the following). (a) (b) Figure 5 SEM images of worn surface of the PEEK disc against the SN20 pin at different speeds in artificial seawater: (a) 0.52 m/s; (b) 0.86 m/s. (a) (c) Figure 6 SEM images of worn surfaces of the SN20 pins at different speeds in artificial seawater: (a) 0.52 m/s; (c)1.73 m/s. 4. The chemical composition analysis should be performed in several places. The places of analysis should be marked on the SEM photos. Response: We tracked the averages of the chemical elements for three points in the black smooth region (which has been described in the manuscript). And, the black smooth region has also been marked in Fig.6c (as follows). 5. Moreover, in Fig. 6, indescribable peaks are visible on the EDS spectrum. Response: We have pointed out elements for the indescribable peaks in Fig.7 in revised manuscript. 6. The authors should also include articles from scientists outside of Asia. Response: I don’t quite understand your mean. Do you mean to quote more articles for the scholars from other continents? I did not notice this question before, and this article did quote many articles from Asian scholars. I will pay special attention to academic communication in the follow-up research work. Thank you very much for your reminding
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The research paper titled: Friction and wear properties of silicon nitride-based composites with different hBN content sliding against polyetheretherketone at different speed under artificial seawater lubrication is well addressed and research finding are interesting. However, some of the comments by the reviewer to improve the quality of the manuscript.
Comments:
- what is the hardness of the stationary disc and track diameter used during the wear test
- The friction coefficients decrease in Si3N4- 135 hBN with wt. 20% and again increases with hBN wt.30% during sliding speed of 0.86 and 1.73 m/s, what is the technical reason behind it and justify it.
- In Fig. 11 and Fig. 12, there is no Tribofilm formation at worn surface of the pin at increased sliding speed. please Justify with supporting SEM images. if possible include the images.
- Fig. 5(c) observed the sliding speed of 1.73 m/s leads to the emergence of black smooth areas and rough areas on the worn surface. Actually, SEM images indicates plastic deformation, material detached, abrasion of materials from the worn surface in sliding direction. please cross check it.
- In the composite material with different wt. %, mention the percentage of porosity.
Author Response
Part B (Reviewer 2#)
- What is the hardness of the stationary disc and track diameter used during the wear test.
Response: PEEK disc is commercially purchased and its hardness is Shore hardness D90. The track diameter is around 16.5cm.
- The friction coefficients decrease in Si3N4- 135 hBN with wt. 20% and again increases with hBN wt.30% during sliding speed of 0.86 and 1.73 m/s, what is the technical reason behind it and justify it.
Response: When the hBN content reached 30%, severe deterioration of the mechanical properties caused an extremely rough wear surface with a more serious mechanical wear. Once the speed increased, the mechanical wear became more severe under the action of shear force. Hence, the friction coefficient and wear rate of the SN30/PEEK pair increased with the increase of the sliding speed.
The description has been presented in the manuscript.
- In Fig. 11 and Fig. 12, there is no Tribofilm formation at worn surface of the pin at increased sliding speed. please Justify with supporting SEM images. if possible include the images.
Response: In fact, no tribofilm was formed on the worn surface of SN0/PEEK pairs. Fig.11 (Fig.12 in revised manuscript) shows the morphologies of the worn surfaces for SN0 pin at the speeds of 0.52m/s and 1.73m/s. only rougher surfaces with some splling pits could be observed. Correspondingly, Fig.12 shows the morphology of the worn surface of PEEK disc at the speed of 1.73 m/s, revealing the furrow, trivial peeling off, and tiny particles. The rough surfaces suggest that mechanical meshing occurs on the wear surface when SN0 pin slides against PEEK disc, and is not avoided by the lubrication of seawater and the generation of tribochemical product (e.g. SiO2). So, higher friction coefficient of SN0/PEEK pair was at a range from 0.1 to 0.22.
- Fig. 5(c) observed the sliding speed of 1.73 m/s leads to the emergence of black smooth areas and rough areas on the worn surface. Actually, SEM images indicates plastic deformation, material detached, abrasion of materials from the worn surface in sliding direction. please cross check it.
Response: Fig.5c (Fig.6c in revised manuscript) shows the worn surface of SN20 pin at the speed of 1.73m/s, as follows. On the whole, the worn surface is mainly composed of black smooth area and gray rough area. Certainly, material detached and abrasion of materials can be observed in the edges of smooth areas and rough regions (this sentence has been added into the revised manuscript).
In this paper, we indicated tha, when SN20 pin slid against PEEK at a speed of 1.73m/s, the hard ceramic micro-bulge would damage the PEEK surfaces at the initial stage of friction process, causing the spalling pits andthe wear particles (which generally came from the hBN agglomeration area of the pin surface, namely material detached and abrasion of materials). One part of wear particles were carried away from the wear interface by the seawater, and some wear particles could be reacted with the seawater contributing to the formation of tribochemical products (enough tribochemical reaction products could aggregate to form a surface film). So, the worn surface of SN20 against PEEK at the speed of 1.73 was composed of smooth region and rough region.
- In the composite material with different wt. %, mention the percentage of porosity.
Response: the porosities of the composite materials have been given in Table 1.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper deals with the evaluation of friction and wear behaviors of Si3N4-hBN composites/ PEEK pair immerged in seawater using pin-on-disc tester at different speed rotations.
The work is well written and structured but it requires revisions to be suitable for publication.
1/ Some English mistakes should be corrected:
The last paragraph from line 89 to line 96 is duplicated in paragraph (line 101 to 108).
Line 110 should be revised.
2/The analysis of XRD results are very poor. The authors should describe and analyze the XRD spectra thoroughly.
3/The reviewer is asking about the assessment of the experimental errors in the determination of the friction and wear rates? i.e., Pin -on-disc experiments present scatter results, which should be evaluated. This question is critical in such case.
Author Response
Part C (Reviewer 3#)
1/ Some English mistakes should be corrected:
The last paragraph from line 89 to line 96 is duplicated in paragraph (line 101 to 108).
Line 110 should be revised.
Response: Thank you for your reminder, and we have revised in the manuscript. The sentence has been changed to “All the pin and disc samples were dried after ultrasonic cleaning for the wear test”.
2/The analysis of XRD results are very poor. The authors should describe and analyze the XRD spectra thoroughly.
Response: The XRD results of the sintered specimens for Si3N4 and Si3N4-30%hBN were shown in Fig.1, and it can be seen that pure Si3N4 specimen is composed of β-Si3N4, and the ceramic composite is composed of β-Si3N4 and hBN. Thus, it can be concluded that, the α-Si3N4 raw powder has been completely transformed to β-Si3N4 during sintering process, and the hBN powder did not undergo any phase transformation. So, the composite ceramics was composed of β-Si3N4 columnar crystal and hBN sheets.
The above analysis has been added to the revised manuscript.
3/The reviewer is asking about the assessment of the experimental errors in the determination of the friction and wear rates? i.e., Pin -on-disc experiments present scatter results, which should be evaluated. This question is critical in such case.
Response: Yes, in our study, the scatter results of the wear experiment occasionally appeared in the friction and wear test due to environmental interference and equipment failure and other uncontrollable causes. When the scatter result occurred, we chose to increase the test amount to find the real tribological law. Therefore, we use many repeatable tests to remove the bad spots.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have taken into account the reviewer's comments and they have made corrections in this article. They have responded to all comments of the reviewer. The authors have performed significant positive changes to the manuscript. The work is clear and very interesting.
Recommendation:
This manuscript in the presented form is acceptable for publication in the Coatings.
