Microstructure Control and Friction Behavior Prediction of Laser Cladding Ni35A+TiC Composite Coatings
, Guofu Lian 1, Jibin Jiang 1, Meiyan Feng 1 and Mengning Zhou 1
Round 1
Reviewer 1 Report
The manuscript reports an analysis on the influence of four processing parameters on the geometrical characteristics of single laser cladding tracks of Ni and TiC composite on the AISI 1045 steel substrate. By means of a full factorial design of experiments, the authors investigated the influence of laser power, scanning speed, gas flow and TiC ratio on the wear resistance of the samples. Additionally, the authors analyzed the microstructure of different samples as a function of the processing parameters and relate this microstructure with wear resistance. The experimental section is complete and the number of experiments might be enough, but in the opinion of this reviewer there are some conclusions that are not clearly explained or justified. Also, some English writing issues must be addressed. For this reason, I think that this paper must address major revisions before being accepted for publication:
- Main recommendations:
- Authors infer correctly infer from their experiments that the laser power and TiC ratio are the processing parameters with higher influence on the wear resistance. However, this result may be true only in the small range of the variables that have been studied in this work. For this reason, authors should justify and explain they have chosen those range with such little variation of the processing parameters, especially in the case of laser power and scanning speed.
- The analysis of the influence of the scanning speed presented in page 10 discussing figures 9 and 10 seems somewhat confusing and at some points does not make sense to me:
- First, in the sentence in line 224 authors state that: “As can be seen that the wear rate decreases as the scanning speed increases”. However, the contour map in figure 9.b demonstrates the opposite result.
- Second. The reduction of the scanning speed keeping constant the laser power involves an increase of radiant exposure (energy input per surface area) with constant irradiance (energy input per surface area and time). The increase of radiant exposure generally implies an increase of temperature of the sample, but also a higher penetration of the isotherms, this means a greater penetration of temperature field in the substrate due to higher heat conduction in the substrate and, consequently, a more gradual temperature gradient. These effects reduce the cooling rate and, in my opinion, should favor the dendritic growth. However, the discussion of the authors in the lines 233 to 235 suggest the opposite effect. At the same time, the spherical structure of the TiC grains in the top region of the sample presented in figure 10a also suggest the opposite effect, ¿might this structure be caused by a different effect? Please, discuss, justify and clarify all these results and conclusions.
- Third. Authors state in lines 229 and 230 that near sphere structure is preferable than needle or dendritic structure to increase wear resistance, but this statement contradicts the results of other authors, see for example: “H. Wang, M. Zhang, X.M. Liu, S.Y. Qu, Z.D. Zou, Microstructure and wear properties of TiC/FeCrBSi surface composite coating prepared by laser cladding, Surf. Coat. Technol. 202 (2008) 3600–3606. https://0-doi-org.brum.beds.ac.uk/10.1016/j.surfcoat.2007.12.039.” Please, justify your statement.
- Please, detail the number of the samples analyzed in figures 7, 8 and 10 in order to identify the value of the rest processing parameters, not just the one indicated in the figure caption, so that the reader can compare and verify clearly the conclusions inferred by the authors. One may suppose that the only processing parameter changing in each couple of samples presented in these figures is the one indicated in the figure caption, but this assumption might be wrong.
- Minor changes:
- I guess that the wavelength of the laser employed is 1070 nm and it emits in continuous mode, are they correct? Please indicate the actual parameters in the experimental section.
- Please, include the units in the labels of axes of figures 4 and 9.
- I can’t understand the sentence in lines 182 to 183.
- What do the G and R symbols mean in the line 185?
- Please, indicate in their captions the relation of tables 6, 7 and 8 with the corresponding figures.
- Sentence in lines 196 and 197 is not precise since we can’t see the wear rate in the figure 8.
Author Response
Response to Reviewer 1 Comments
Point 1:Authors infer correctly infer from their experiments that the laser power and TiC ratio are the processing parameters with higher influence on the wear resistance. However, this result may be true only in the small range of the variables that have been studied in this work. For this reason, authors should justify and explain they have chosen those range with such little variation of the processing parameters, especially in the case of laser power and scanning speed.
Response 1: The basis for the selection of a small range of parameters. "This study aims to analyze the relationship between various parameters on the wear rate and microstructure changes of the nickel-based titanium carbide composite coating. According to the previous research of this research group and summarize the relevant literature” Lian, G.; Zhang, H.; Zhang, Y.; Yao, M.; Huang, X.; Chen, C. Computational and Experimental Investigation of Micro-Hardness and Wear Resistance of Ni-Based Alloy and TiC Composite Coating Obtained by Laser Cladding. Materials 2019, 12, 793, doi:10.3390/ma12050793.”, select the typical The parameter interval of "explains its influence mechanism"
Point 2：The analysis of the influence of the scanning speed presented in page 10 discussing figures 9 and 10 seems somewhat confusing and at some points does not make sense to me:
- First, in the sentence in line 224 authors state that: “As can be seen that the wear rate decreases as the scanning speed increases”. However, the contour map in figure 9.b demonstrates the opposite result.
Response 2.1:There is an error in this sentence and it has been corrected in the article, the correct statement is’ As can be seen that the wear rate increases as the scanning speed increases’ in line 241.
- Second. The reduction of the scanning speed keeping constant the laser power involves an increase of radiant exposure (energy input per surface area) with constant irradiance (energy input per surface area and time). The increase of radiant exposure generally implies an increase of temperature of the sample, but also a higher penetration of the isotherms, this means a greater penetration of temperature field in the substrate due to higher heat conduction in the substrate and, consequently, a more gradual temperature gradient. These effects reduce the cooling rate and, in my opinion, should favor the dendritic growth. However, the discussion of the authors in the lines 233 to 235 suggest the opposite effect. At the same time, the spherical structure of the TiC grains in the top region of the sample presented in figure 10a also suggest the opposite effect, ¿might this structure be caused by a different effect? Please, discuss, justify and clarify all these results and conclusions.
Response 2.2: This part talks about the influence of different scanning speeds on dendrite growth, The correct statement is’Specifically, at higher scanning speed of 7mm/s, as shown in Figure 11(a), a large amount of fine TiC grain is observed at the top region of cladding layer due to the more laser energy input.’ We have corrected in the article in the lines 244 to 246.
- Third. Authors state in lines 229 and 230 that near sphere structure is preferable than needle or dendritic structure to increase wear resistance, but this statement contradicts the results of other authors, see for example: “H. Wang, M. Zhang, X.M. Liu, S.Y. Qu, Z.D. Zou, Microstructure and wear properties of TiC/FeCrBSi surface composite coating prepared by laser cladding, Surf. Coat. Technol. 202 (2008) 3600–3606. https://0-doi-org.brum.beds.ac.uk/10.1016/j.surfcoat.2007.12.039.” Please, justify your statement.
Response 2.3: Because the contact area between the spherical particles and the matrix is small and the degree of intermination is low, they are easier to fall off during the friction process, causing abrasive wear, reducing wear resistance, and increasing the wear rate per unit time in the lines 247 to 250.
Point 3: Please, detail the number of the samples analyzed in figures 7, 8 and 10 in order to identify the value of the rest processing parameters, not just the one indicated in the figure caption, so that the reader can compare and verify clearly the conclusions inferred by the authors. One may suppose that the only processing parameter changing in each couple of samples presented in these figures is the one indicated in the figure caption, but this assumption might be wrong.
Response 3 : The complete parameters and sample numbers have been added in the picture notes. Figure 7 (a) (b) in the current manuscript are group 2 and group 4 respectively figure 8 (a) (b) are group 12 and group 11 respectively figure 10 (a) (b) are the 6th and 8th groups .
Point 4 : I guess that the wavelength of the laser employed is 1070 nm and it emits in continuous mode, are they correct? Please indicate the actual parameters in the experimental section.
Response 4: The wavelength of the laser used is 1064 nm, and it emits in continuous mode.
Point 5 :Please, include the units in the labels of axes of figures 4 and 9.
Response 5: We have included the units in the labels of axes of figures 4 and 9.
Point 6 :I can’t understand the sentence in lines 182 to 183.
Response 6 : The correct statement is ‘Part of Fe elements and Ti elements left by the decomposition of TiC are concentrated in the grain boundaries, and this grain boundary structure with relatively weak mechanical properties will further reduce the inter-grain bonding strength and increase the wear rate’ in the lines 184 to 187.
Point 7 :What do the G and R symbols mean in the line 185?
Response 7 : G is the temperature gradient and R is the solidification rate.
Point 8 :Please, indicate in their captions the relation of tables 6, 7 and 8 with the corresponding figures
Response 8 : We have indicated in their captions the relation of tables 6, 7 and 8 with the corresponding figures.
Point 9: Sentence in lines 196 and 197 is not precise since we can’t see the wear rate in the figure 8.
Response 9: We have added the wear rate in figure 8.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors have done a good work in designing a full factorial experimental study to study the influence of process parameters in the laser cladding process on the coatings’ wear performance. However, the study lacks a deep scientific discussion about how microstructure/ microstructural features impact the mechanical properties (hardness, fracture toughness) and hence the wear performance. I recommend that authors should select few samples from their long list of samples preferably the best and the worst and may be one more somewhere with mediocre performance and discuss them in detail with experimental proofs (shape and size of hard phase, hardness, fracture toughness etc.).
Some more comments are as follows:
- Please quantify the dark grey hard phase in selected samples using image analysis and discuss their role on properties and performance.
- Please show the hardness and fracture toughness (which can also be calculated by simple indentation method) of selected samples and correlate them with the microstructure and wear performance.
- Please also show the post wear tracks of the selected samples while discussing the results.
- Please mark all the figures, tables, and their cations accordingly in the results and discussion section to show that which samples the data belong to. Please mark them with the sample # from the experimental design table.
- Please mention in the caption of the EDS tables which figures (with SEM micrographs) they are referring to.
Author Response
Response to Reviewer 2 Comments
Point 1:Please quantify the dark grey hard phase in selected samples using image analysis and discuss their role on properties and performance.
Response 1: Combining the results of XRD phase analysis and EDS element analysis, it is inferred that the dark phase is TiC phase, whose main function is to enhance the hardness of the cladding layer and improve the wear resistance of the cladding layer.
Point 2:Please show the hardness and fracture toughness (which can also be calculated by simple indentation method) of selected samples and correlate them with the microstructure and wear performance.
Response 2: We use the indentation method to calculate the fracture toughness by looking at the shape of the surrounding cracks under different loads. The hardness data of the sample is shown in Table 4. It can be seen from the table that the hardness and wear resistance are positively correlated under the same friction form.
Point 3:Please also show the post wear tracks of the selected samples while discussing the results.
Response 3: The wear 3D topography is shown in Figure 8, Figure 10 and Figure 13.
Point 4:Please mark all the figures, tables, and their cations accordingly in the results and discussion section to show that which samples the data belong to. Please mark them with the sample # from the experimental design table.
Response 4 : The sample numbers and corresponding test parameters have been marked in Figure 6, Figure 7, Figure 8, Figure 9, Figure 10, Figure 12 and Figure 13.
Point 5:Please mention in the caption of the EDS tables which figures (with SEM micrographs) they are referring to.
Response 5: We have mentioned the numbers they refer to in the headings of the EDS tables (table 6, table 7 and table 8).
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Major revision recommended for acceptance:
Point 1: The small range of the variables that have been studied in this work is still not correctly justified in the manuscript. Furthermore, the short range of variation is already included in their own previous work cited by the authors: Lian, G.; Zhang, H.; Zhang, Y.; Yao, M.; Huang, X.; Chen, C. Computational and Experimental Investigation of Micro-Hardness and Wear Resistance of Ni-Based Alloy and TiC Composite Coating Obtained by Laser Cladding. Materials 2019, 12, 793, doi:10.3390/ma12050793.
A sound explanation and justification of the reasons to select this range of processing parameters and the novelty of the present experiments must be included and should be convincing to accept this manuscript for publication.
Minor revisions:
Point 4 : Please include the data of the wavelength of the laser and temporal mode of emition in the experimental section of the manuscript.
Point 7 :Please include the explanation of the G and R symbols in the manuscript.
Point 9: Former sentence in lines 196 and 197, now in lines 208 and 209, does refer now to figure 10 rather than 9, doesn't it?
Author Response
Point 1: The small range of the variables that have been studied in this work is still not correctly justified in the manuscript. Furthermore, the short range of variation is already included in their own previous work cited by the authors: Lian, G.; Zhang, H.; Zhang, Y.; Yao, M.; Huang, X.; Chen, C. Computational and Experimental Investigation of Micro-Hardness and Wear Resistance of Ni-Based Alloy and TiC Composite Coating Obtained by Laser Cladding. Materials 2019, 12, 793, doi:10.3390/ma12050793.
A sound explanation and justification of the reasons to select this range of processing parameters and the novelty of the present experiments must be included and should be convincing to accept this manuscript for publication.
Response 1: In this range, a relatively excellent coating can be obtained: large microhardness (maximum value of 75.2HRC), small defects and good wear resistance. This article focuses on the analysis of the mechanism of the microstructure of the composite coating on the performance of the cladding layer , Using typical XRD, organizational structure analysis, and elemental analysis of its influence on performance.
Minor revisions:
Point 4 : Please include the data of the wavelength of the laser and temporal mode of emition in the experimental section of the manuscript.
Response 4: The wavelength of the laser used is 1064 nm, and it emits in continuous mode,in line 86.
Point 7 :Please include the explanation of the G and R symbols in the manuscript.
Response 7: G is the temperature gradient and R is the solidification rate，in lines 190 and 191.
Point 9: Former sentence in lines 196 and 197, now in lines 208 and 209, does refer now to figure 10 rather than 9, doesn't it?
Response 9: Former sentence in lines 196 and 197, now in lines 213 and 214, it refers to figure 10.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors have revised the manuscript to a some extent but few aspects are still missing which are:
- Fracture toughness is not calculated and shown. This needs to be measured and discussed.
- Image analysis is not done to quantify the dark grey hard phase. It must be done and also correlated with the properties and performance.
Author Response
Point 1: Fracture toughness is not calculated and shown. This needs to be measured and discussed.
Response 1: The Ni35+TiC composite coating prepared in this experiment is a high-plasticity coating, and cracks cannot appear when Vickers indenter is used. The main reason for failure is not low fracture toughness.
Point 2:Image analysis is not done to quantify the dark grey hard phase. It must be done and also correlated with the properties and performance.
Response 2: The quantitative analysis of the dark gray hard phase of the image has been supplemented.The dark grey hard phase at the top region of Figure 7(a) (2# sample) accounts for 16.84%,and the dark gray hard phase at the top of Figure 7(b) (4# sample) accounts for 15.29%.In Table 4 , the hardness of the 2# sample is 59.7 HRC, the hardness of the 4# sample is 52.6 HRC，in lines 195 to 200. The dark grey hard phase at the top region of Figure 9(a) (12# sample) accounts for 18.57%,and the dark gray hard phase at the top of Figure 9(b) (11# sample) accounts for 71.8%. In Table 4 , the hardness of the 12# sample is 55.4 HRC, the hardness of the 11# sample is 70 HRC,in lines 223 to 226.The dark grey hard phase at the top region of Figure 12(a) (6# sample) accounts for 15.89%,and the dark gray hard phase at the top of Figure 12(b) (8# sample) accounts for 16.52%. In Table 4 , the hardness of the 6# sample is 58.7 HRC, the hardness of the 8# sample is 59.7 HRC,in lines 269 to 272.
Author Response File: Author Response.docx
Round 3
Reviewer 2 Report
Thanks to the Authurs for their efforst in revising the manuscript. The manuscript can be publsihed in its current form.
