Characterization and Control of Residual Stress in Plasma-Sprayed Silicon Coatings on SiC/SiC Composites
, Yongjing Cui 1,3, Changliang Wang 1,3, Jian Jiao 1,3, Xiaofang Bi 2 and Chunhu Tao 1
Round 1
Reviewer 1 Report
Author as clearly explained the novlity of the work.
Abstract and conclusion part needs to be reframed to get the clarity of the work
Grammatical mistakes and discontinuity of sentences were observed in lot of places.
Manuscript needs to be throughly checked before publication.
Author Response
Dear reviewer
Thank you very much for your great work on our manuscript. We have carefully revised the manuscript point by point according to the valuable comments received, Please see the attachment.
The detailed responses to comments are listed as the following:
Point 1: Author as clearly explained the novlity of the work.
Response 1: We are pleased that you appreciate our research. In this study, Si layers on SiC-CMCs were prepared using APS technology and different parameters, with annealing at various temperatures. We aimed to reveal to increased understanding and control of residual stress in APS Si bond layers and provide valuable insights for the future development of durable EBCs.
Point 2: Abstract and conclusion part needs to be reframed to get the clarity of the work
Response 2: Thanks very much for your careful reading of our manuscript. We have revised the abstract and conclusion to clarify the works of this paper.
Point 3: Grammatical mistakes and discontinuity of sentences were observed in lot of places.
Response 3: I apologized for the mistakes. We have checked the manuscript using Grammarly and used the Specialist Editing Services in MDPI.
Point 4: Manuscript needs to be throughly checked before publication
Response 4: I apologized for the mistakes. We have checked the manuscript using Grammarly and used the Specialist Editing Services in MDPI.
I think I have improved my paper more thanks to the careful advice you gave me. Thanks again for your kind advice.
With best regards,
Mengqiu Guo
On behalf of co-authors
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Author
The article addresses one interesting topic in the plasma spraying area. Therefore the topic is interesting. According to the content Si coating was sprayed on Si fiber reinforced SiC composite by APS method. Then author mainly calculate residual stress in the coating on converting tensile stress generated during spraying to compressive stress by annealing. To support the aim, XRD, SEM, calculation of residual stress is included.
However, it need so undergo major changes before considering for publication.
such as, in experiment section, author mention about TEM, however in the content its hard to see any output from this measurement.
Which way author plt Fig. 3, is it the output from some simulation or experimental measurement from inflight particle measurement?
Fig. 6 all the section only 3 points, it looks so marginal. Why cauthors are limited to only 3 variable parameters?
Fig. 7 is from experimental measurement data? how authors include contour map , such as temp.
Fig. 8 doesnot have any error bar , so all the data are just single taken, there should be stastical distrution .
Table 4. Annealing time is fixed for all temperatures. Why?
Fig. 9 how author calculate tensile and compressive stress in material? is it from laser raman spectroscopy?
Fig. 12 residual stress decreases with annealing on the conversion of positive tensile to negative compressive stress. Hoever annealed 1 h at 1250 shows good result, what happen with depth? Whats the issue at 50 micron, stress increase with reverse trend , why ?
There are similar work in the area of plasma spraying for other materials, author should mention that , how the different version of plasma spraying commonly used in coating in materials areas
. Interfacial Adhesion of Thick NiTi Coating on Substrate Stainless Steel. Materials 2022, 15, 8598. https://doi.org/10.3390/ma15238598
Net-Shape NiTi Shape Memory Alloy by Spark Plasma Sintering Method. Appl. Sci. 2021, 11, 1802.
Fabrication of Thermal Plasma Sprayed NiTi Coatings Possessing Functional Properties. Coatings 2021, 11, 610. https://doi.org/10.3390/coatings11050610
Author Response
Response to Reviewer 2 Comments
Dear reviewer
Thank you very much for your great work on our manuscript. We have carefully revised the manuscript point by point according to the valuable comments received, and please see the attachment.
The detailed responses to comments are listed as the following:
The article addresses one interesting topic in the plasma spraying area. Therefore the topic is interesting. According to the content Si coating was sprayed on Si fiber reinforced SiC composite by APS method. Then author mainly calculate residual stress in the coating on converting tensile stress generated during spraying to compressive stress by annealing. To support the aim, XRD, SEM, calculation of residual stress is included.
However, it need so undergo major changes before considering for publication.
Point 1: such as, in experiment section, author mention about TEM, however in the content its hard to see any output from this measurement.
Response 1: I apologize for this mistake. We didn’t take TEM testing in this paper. I have deleted the description of TEM in Part 2.3. Thanks for your careful reading of our manuscript.
Point 2: Which way author plt Fig. 3, is it the output from some simulation or experimental measurement from inflight particle measurement?
Response 2: In this study, the system of DPV-eVOLUTION was used to measure the temperature and speed of Si particles. The principle is shown in the following figure (Ref “Investigation and Comparison of In-Flight Particle Velocity During the Plasma-Spray Process as Measured by Laser Doppler Anemometry and DPV-2000” https://doi.org/10.1007/s11666-013-9940-9).
The DPV-eVOLUTION is equipped with an automatic motion device, which can move in the X-Y plane. In this paper, we measured in a 16 mm × 16 mm rectangular plane(perpendicular to plasma flame direction) and 25 positions (5×5 matrix points with steps of 4 mm). In every position, the speed and temperature of 5000 particles were measured and calculated. When the measurements are completed, the system output a data matrix like this, including the coordinate(X, Y) and results(T,V).
At the same time, the DPV-eVOLUTION will output a contour map with lower quality. We preferred to plot a new contour map using Origin® software, according to the data matrix.
So, Fig. 3 was plotted using Origin® software based on the experimental measurement. In my opinion, it should not be a simulation.
We plotted Fig.7 in the same way.
According to this comment, we added some detail about the system in Part 2.2.
“As the measurement volume is relatively small(<1 mm3), the data can be collected for local particles and analyzed statistically. With the automatic motion device, it can also measure the matrix data in a plane. For the matrix measurements, the gun was positioned at a fixed location, and the CCD camera was moved in the plane perpendicular to the gun axis at a spray distance of 80 mm, 100 mm, and 120 mm. In this study, the 5×5 points measurement grid with a step of 4 mm was 16×16mm2 and up to 5000 inflight particles were measured per point.”
Point 3: Fig. 6 all the section only 3 points, it looks so marginal. Why cauthors are limited to only 3 variable parameters?
Response 3: Thanks very much for your careful reading of our manuscript. As you said, we selected 3 points for each parameter of plasma spraying. In this paper, we have chosen many parameters for the study, including plasma spraying and annealing. Considering more parameters, we designed fewer points for each parameter. It is beneficial to obtain preliminary results in a short time. Although this study is preliminary, we found some parameters' effects on residual stress. More work needs to be carried out to control residual stress accurately. This work can contribute to increased understanding of residual stress in APS Si bond layers. Based on the results of this paper, more research on the parameters of spraying distance, second gas (H2) flow rate and annealing is already in our plan.
According to this comment, we added some prospects in conclusion.
“Although some results were obtained, this study is preliminary, and more work needs to be carried out to achieve the control of the residual stress accurately for APS Si coatings.”
Point 4: Fig. 7 is from experimental measurement data? how authors include contour map , such as temp.
Response 4: We plotted Fig.7 in the same way as Fig.3. (Refer to the response 2 to comment 2) What is different, we measured three X-Y planes in this part, including the spray distance of 80mm, 100mm, and 120mm.
Point 5: Fig. 8 doesnot have any error bar , so all the data are just single taken, there should be stastical distrution.
Response 5: Thank you for bringing this to my attention. In this testing, the system of DPV-eVOLUTION outputted the temperature and speed of 5000 particles, and they are statistical data. We have updated Fig.8 with the error bar. Additionally, we unified the Y-coordinates. Thank you for your comment.
Point 6. Annealing time is fixed for all temperatures. Why?
Response 6: In this paper, we tried to reveal the relationship between residual stress in Si layers on SiC/SiC composites and the different parameters. So we designed experiments with single-variable as much as possible. In order to study the effect of temperature, we fixed the annealing time for all temperatures.
Point 7: Fig. 9 how author calculate tensile and compressive stress in material? is it from laser raman spectroscopy?
Response 7: Thank you very much for your very detailed advice. Fig.9 is the surface stress with different annealing temperatures and times. In this part, the surface stress was tested by XRD using the sin2ψ method. For the sin2ψ method, >0 represents the tensile, and <0 represents the compressive.
According to this comment, we added more explanation in Part 2.3.
“ >0 represents the tensile stress, while <0 represents the compressive stress.”
We also revised the caption of Fig.9.
“Figure 9. Residual stress (tested using the sin2ψ method) variation with differences in annealing temperature and time.”
Point 8: Fig. 12 residual stress decreases with annealing on the conversion of positive tensile to negative compressive stress. However annealed 1 h at 1250 shows good result, what happen with depth? Whats the issue at 50 micron, stress increase with reverse trend , why ?
Response 8: Thanks very much for your careful reading of our manuscript. Figure 12 shows the Residual stress variation along the depth of the as-sprayed and annealed Si layer. It is obvious that after annealing at 1100 and 1250 °C, the residual stress of the cross-section close to the surface transferred from tensile to compressive. Compared with the as-sprayed layer, all the compressive stress in the cross-section at the depth >20μm increased obviously after annealing. But unfortunately, we didn’t observe a law on how much the compressive stress increased. And the distribution of compressive stress at a depth >20μm seems to fluctuate irregularly.
Point 9: There are similar work in the area of plasma spraying for other materials, author should mention that , how the different version of plasma spraying commonly used in coating in materials areas.
- Interfacial Adhesion of Thick NiTi Coating on Substrate Stainless Steel. Materials2022, 15, 8598. https://doi.org/10.3390/ma15238598
- Net-Shape NiTi Shape Memory Alloy by Spark Plasma Sintering Method. Sci.2021, 11, 1802.
- Fabrication of Thermal Plasma Sprayed NiTi Coatings Possessing Functional Properties. Coatings2021, 11,610. https://doi.org/10.3390/coatings11050610
Response 9: Thanks very much for your information about similar works. I have studied the papers and realized they are significant. We mentioned the information in the introduction.
“Generally, the coatings could be prepared by several processes, such as spark plasma sintering[14] and thermal spraying.[15] Plasma spraying has emerged as one of the potential routes to deposit thick coating layers on the structure material.[16]”
I think I have improved my paper, and thanks again for your kind advice.
With best regards,
Mengqiu Guo
On behalf of co-authors
Author Response File: Author Response.pdf
Reviewer 3 Report
The article is devoted to the study of the properties of SiC/SiC composites, which are one of the promising materials for protection against corrosion and degradation. In general, the presented direction is quite promising, and the results obtained are of great importance for a large number of readers and research groups. To characterize the obtained results, the authors used a fairly large number of different methods of analysis. The article is suitable for this journal and can be accepted for publication after the authors answer a number of questions that the reviewer has after reading this article and analyzing it.
1. In the abstract, the authors should provide more details about the method of obtaining the objects under study.
2. The authors should give an explanation for such large measurement errors in strength characteristics, taking into account which the changes are practically indistinguishable with varying synthesis conditions.
3. The authors report that the use of high-temperature annealing leads to a change in the type of deformation distortions and structural changes, but this phenomenon should be described in more detail.
4. The authors should provide a more detailed description of the reasons for choosing the annealing temperatures, as well as the annealing time, which made it possible to change the properties of the structures under study.
5. The authors report a change in the shift of the Raman lines, however, for a more detailed explanation, an analysis of the obtained spectral lines in comparison should be given.
Author Response
Dear reviewer
Thank you very much for your great work on our manuscript. We have carefully revised the manuscript point by point according to the valuable comments received, and please see the attachment.
The detailed responses to comments are listed as the following, and Please see the attachment.
The article is devoted to the study of the properties of SiC/SiC composites, which are one of the promising materials for protection against corrosion and degradation. In general, the presented direction is quite promising, and the results obtained are of great importance for a large number of readers and research groups. To characterize the obtained results, the authors used a fairly large number of different methods of analysis. The article is suitable for this journal and can be accepted for publication after the authors answer a number of questions that the reviewer has after reading this article and analyzing it.
Point 1: In the abstract, the authors should provide more details about the method of obtaining the objects under study.
Response 1: Thanks for your advice.
①At first, we refined the abstract with more details about the methods, and the total number was also reduced to less than 200 words.
“In order to reveal the relationship between residual stress in Si layers of SiC/SiC composites and the different parameters used in their preparation, the residual stress of the coating surface was tested using X-ray sin2ψ technology and laser Raman spectroscopy. Then, the Raman shift–stress coefficient ( ) and the Raman shift with free stress ( ) were calculated as −201.41 MPa/cm−1 and 520.591 cm−1 via linear fitting with the least squares method. The results show that all the as-sprayed Si coatings exhibited tensile stress on the surface, ranging from 53.5 to 65.9 MPa. The parameters of the spraying distance and second gas (H2) flow rate were considered to be the most important for controlling the residual stress on the coating surface. Additionally, the surface tensile stress of the Si layers could be eliminated and even changed into compressive stress by annealing above 800 °C. Furthermore, the residual stress distribution in the cross-section of the Si layers was evaluated using laser Raman spectroscopy. Additionally, the particle characteristics, such as in-flight velocity and temperature, were investigated using a diagnostic system. The results of this research contribute to increasing the understanding and control of residual stress in APS Si bond layers.”
②Due to the limit of the abstract, we added some detail about the test methods in Part 2.2 and 2.3.
Part 2.2: Inflight Particle Measurement
“As the measurement volume is relatively small (<1 mm3), the data can be collected for local particles and analyzed statistically. With the automatic motion device, it can also measure the matrix data in a plane. For the matrix measurements, the gun was positioned at a fixed location, and the CCD camera was moved in the plane perpendicular to the gun axis at spray distances of 80 mm, 100 mm, and 120 mm. In this study, the 5×5 points measurement grid with a step of 4 mm was 16×16mm2 and up to 5000 inflight particles were measured per point.”
Part 2.3: Analysis Methods
“ >0 represents the tensile stress, while <0 represents the compressive stress.”
Part 3.2: The Influence of Spraying and Annealing Parameters on the Residual Surface Stress
“In this study, seven couples of – were detected for all samples, and the angles included -1.54°, 4.40°, 13.66°, 18.46°, 23.27°, 32.52°, and 38.47°.”
Point 2: The authors should give an explanation for such large measurement errors in strength characteristics, taking into account which the changes are practically indistinguishable with varying synthesis conditions.
Response 2: Thanks very much for your careful reading of our manuscript. According to your comment, we realized the limitations of this part of the study. We have added an explanation around Fig.6.
“Additionally, the reasons for the relatively large errors seen in this experiment are two-fold. Firstly, the sample was tested as-sprayed, with certain anisotropy, which affected the 2 measured at different angles. Secondly, the X-ray could penetrate to a depth of approximately 10μm, and there was a stress gradient in the depth direction of the coating. In this part, the correlation study between surface stress and spraying parameter was simplified without considering the information on the depth and anisotropy”
Point 3: The authors report that the use of high-temperature annealing leads to a change in the type of deformation distortions and structural changes, but this phenomenon should be described in more detail.
Response 3: Thanks very much for your comment. I am sorry that we didn’t pay much attention to the structural characterization. According to your comment, we redescribed the change in the type of residual stress and discussed the possible causes by adding an XRD figure in the end of Part 3.2.
“Figure 9 shows the variations in the residual surface stress with different annealing temperatures and times. It can be seen that when the sample was annealed at 500°C ° for 1 h and 5 h, the stress slightly reduced from 68.9 MPa to 65.8 and 60.3 MPa. When the annealing temperature reached 800 °C, the coating stress level decreased rapidly to 66.5 MPa and changed from tensile to compressive at -4.1 MPa after 5 h. When the annealing temperature increased to 1100 °C, the residual stress on the Si layer surface transformed from a tensile stress of 56.2 MPa into a compressive stress of -45.2 MPa after 1 h and then stabilized over time. The same phenomenon was also observed in the annealing temperature of 1200-1300 ℃. Hence, we conclude that for the Si coating sprayed on the SiC-CMCs, annealing can be carried out above 800 °C to eliminate tensile stress and, thus, promote the bonding of the coating with the substrate.”
“Figure 10 shows the XRD measurements of the as-sprayed and annealed silicon coatings. The results indicate that the deposited layers were cubic polysilicon, and no phase change occurred during the annealing process at a temperature up to 1300 ℃. It can be seen that the intensity of the (400), (331), and (422) diffraction peaks increased significantly after annealing, as compared to those of the as-sprayed Si layers. The enhancement in diffraction peaks may contribute to the changes in residual stress.”
Point 4: The authors should provide a more detailed description of the reasons for choosing the annealing temperatures, as well as the annealing time, which made it possible to change the properties of the structures under study.
Response 4: Thanks very much for your comment. Ref[26](Zhang, X.; Zhang, T.-Y.; Wong, M.; Zohar, Y. Residual-stress relaxation in polysilicon thin films by high-temperature rapid thermal annealing. Sensors Actuators A Phys. 1998, 64, 109–115. https://doi.org/10.1016/s0924-4247(97)01661-0.) investigated the effects of regular furnace annealing on the residual stress of LPCVD polysilicon thin film. The results showed that after annealing at a temperature varying from 600 to 1100 ℃, the film stress decreased gradually with increasing temperature. Additionally, the compressive stress varied very little with annealing time from 30 to 120 min. So, the annealing temperatures of 500, 800 and 1100 ℃ were set in this study. Furthermore, we chose higher temperatures of 1200, 1250 and 1300℃ too, which are lower than the melting point of Si(~1400 ℃). Actually, we have no special reasons for the choice of annealing time, and we just want to obtain some preliminary results.
According to this comment, we added some descriptions before table 4.
“Zhang et al.[26] investigated the effects of regular furnace annealing on the residual stress of LPCVD polysilicon thin film. The results showed that after annealing at a temperature varying from 600 to 1100 ℃, the film stress decreased gradually with increasing temperature. Additionally, the compressive stress varied very little with annealing time from 30 to 120 min.”
Point 5: The authors report a change in the shift of the Raman lines, however, for a more detailed explanation, an analysis of the obtained spectral lines in comparison should be given.
Response 5: Thanks very much for your careful reading of our manuscript. In this study, an average of five measured Raman shifts was used for one point, as mentioned in Part 2.3. The typical spectra are like the figure following, and we read the data from the centre(circled by the black line) for every measurement. It is statistical data, which is used to calculate the stress by . So, I think it is hard and has little significance to compare the one-time obtained spectral lines of different parameter. If you have any further suggestions for improving the quality of the paper, we would be glad to hear from you.
Finally, we have performed a Specialist Editing Services in MDPI to improve the quality of the English Language.
I think I have improved my paper, and thanks again for your kind advice.
With best regards,
Mengqiu Guo
On behalf of co-authors
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors replied to the queries very briefly. So the article is improved and accepted for publication.
