Effect of CeO₂ Addition on the Microstructure and Properties of Laser-Prepared WC/Ni60 Composite Coatings for Cold Work Tool Steel

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents a study of the effect of CeO2 addition on the microstructure and properties of the laser-cladded tungsten carbide–nickel-60 composite coatings on cold work die steel. The study was well-designed. The process of selecting parameters for laser cladding was described. Then, the claddings were prepared using the selected parameters. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction were used to characterize the microstructure of the claddings. Microhardness and friction measurements were carried out to assess their properties.

The manuscript is suitable for publication once the suggested revisions are incorporated into a revised version, and the quality of English is improved.

 

1. The manuscript's title may suggest that the primary focus of the study was the steel onto which the cladding layer was applied, rather than the cladding layer itself. I propose changing the title to better reflect the content of the manuscript.
2. There is no description of the equipment used in the research. It should be added.
3. The discussion of the obtained results needs to be improved. Some sentences are unclear, which makes it difficult to understand the text and evaluate the entire argument in the discussion of the results.
4. Lines 154-158
   “At the same time, there are more equiaxed and significantly fewer columnar grains. Furthermore, due to the purification effect of CeO2, the fused cladding layer has fewer inclusions in the phase. This change occurs because CeO2 has a high melting point, and during the cladding process, the CeO2 particles are distributed diffusely in the cladding layer, so the dendrite encounters resistance in the growth direction”.
   It is unclear whether "this change" refers to purification or the microstructural changes described earlier. Moreover, the purification effect is not explained sufficiently.
5. Lines 185-187
   “In addition, carbides such as MC (where M is W or vanadium [V]) and chromium carbide (Cr23C6 ) precipitate in the grain boundary space, which is the same as the energy spectrum results in Fig. 4.“ There is no energy spectrum in Fig.4.
6. In line 189, the authors cite Wang and Zhong, but there is no reference to the literature
7. On page 9, the authors discuss the effect of CeO2 on microhardness. The increase in microhardness is attributed to the segregation of Ce at the grain boundaries. Nothing has been mentioned before about the dissociation of CeO2 into Ce and O. Does such a process actually occur?
8. The following sentence, cited below, is difficult to understand
   “First, Ce is preferred at the grain boundaries of the bias[29], so the impurity element bias is reduced, the grain boundaries of the purification and strengthening of the effect are obvious, and the fusion cladding layer microhardness can be improved.”
   What is the meaning of “the grain boundaries of the bias”?
   Similarly, “upper layer of the organisation “ line 216.
9. In Fig. 7, the layer thicknesses do not match the layer thicknesses in 2. The thickness of the cladding layer is approximately 0.3 mm in Fig. 7, but it is twice this thick in Fig.2
10. On page 10, some sentences need revision, e.g.
    “The specimen is conducive to the friction in the surface of the microcracks on top of the stress relaxation and there is enhanced crack extension resistance, which reduces the effect of wear.”
    or “Hence, when subjected to the wear process, there is significantly improved wear quality loss.”
11. Line 246, the term “cytocryst” is unintelligible.

Two Figures need corrections:

1. In Fig.2, the description of the vertical axis is truncated
2. Figure 6 is difficult to read. The lines overlap each other

Author Response

Dear Editor Dr. Paula Zhou:

 

Thank you very much for your letter.

Please accept our sincere thanks to you and the reviewers. Now, as you requested, I am sending you a revised manuscript of our submission "Study on the organisation and properties of cold work die steel after laser melting cerium (IV) oxide-tungsten carbide-nickel-60 composite coating" (coatings-3919000) for your consideration. This letter includes a detailed reply to the reviewers' comments. Since the issues mentioned by reviewers have been addressed as follows, we believe the manuscript has been significantly improved.

 

The following contents include detailed replies to the reviewers’ comments:

 

To Reviewer #1

This manuscript presents a study of the effect of CeO2 addition on the microstructure and properties of the laser-cladded tungsten carbide–nickel-60 composite coatings on cold work die steel. The study was well-designed. The process of selecting parameters for laser cladding was described. Then, the claddings were prepared using the selected parameters. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction were used to characterize the microstructure of the claddings. Microhardness and friction measurements were carried out to assess their properties.

The manuscript is suitable for publication once the suggested revisions are incorporated into a revised version, and the quality of English is improved.

 

1.The manuscript's title may suggest that the primary focus of the study was the steel onto which the cladding layer was applied, rather than the cladding layer itself. I propose changing the title to better reflect the content of the manuscript.

 

Reply: Thank you very much for your suggestion. We have revised the manuscript's title. The new title is “Effect of CeO₂ addition on the microstructure and properties of laser-prepared WC/Ni60 composite coatings on cold-work tool steel.”

 

2.There is no description of the equipment used in the research. It should be added.

Reply: Thank you very much for your feedback. The equipment used for the laser cladding experiments has been added to the text and highlighted in yellow. The specific details are as follows: “The laser used in this experiment is a water-cooled rel-a2000d fibre laser, with a rated output power of 2000W, a central wavelength of 10-100nm, an output power stability of <3%, a QBH output connector, and a fibre core diameter of 400/600μm.

After the grinding and polishing treatments, the obtained coatings were etched with a 50% hydrochloric acid + 50% nitric acid solution for 5-7 s, and optical microscope (OM) images of the obtained coatings were taken using a DM2700M Leica microscope. A scanning electron microscope (SEM, INSPECT F50, equipped with EDS, accelerating voltage 20 kV) was used to observe the morphology, microstructure, and element distribution of the samples. X-ray diffraction (XRD, Rigaku-Ultima IV) was used to examine the phase composition of the specimens with the following test parameters: operating voltage 40 kV; current 30 mA; diffraction range 30°-100°.”

 

3.The discussion of the obtained results needs to be improved. Some sentences are unclear, which makes it difficult to understand the text and evaluate the entire argument in the discussion of the results.

 

Reply: Thank you for your thoughtful guidance. We have thoroughly revised the manuscript based on the reviewers' comments. We have refined the conclusion, clarified the research background and objectives, added descriptions of the macro-morphology of the cladding layer, and specifically supplemented the detailed mechanism through which CeO₂ influences microstructural evolution. Following these revisions, the manuscript has been significantly enhanced with regard to scientific rigor, logical coherence, and completeness. Additionally, we have engaged a professional agency to conduct a comprehensive language review to ensure both accuracy and fluency in expression.

 

4. Lines 154-158
   “At the same time, there are more equiaxed and significantly fewer columnar grains. Furthermore, due to the purification effect of CeO2, the fused cladding layer has fewer inclusions in the phase. This change occurs because CeO2 has a high melting point, and during the cladding process, the CeO2 particles are distributed diffusely in the cladding layer, so the dendrite encounters resistance in the growth direction”.
   It is unclear whether "this change" refers to purification or the microstructural changes described earlier. Moreover, the purification effect is not explained sufficiently.

 

Reply: We sincerely apologize for the lack of clarity in this section of the paper, which has caused confusion. The term “this change” refers to the microstructural changes, and has been revised in the manuscript. Additionally, a description regarding the purification effect of CeO₂ has been added to the manuscript.

 

5. Lines 185-187
   “In addition, carbides such as MC (where M is W or vanadium [V]) and chromium carbide (Cr23C6) precipitate in the grain boundary space, which is the same as the energy spectrum results in Fig. 4.“ There is no energy spectrum in Fig.4.

 

Reply: We sincerely apologize for the error in the manuscript where Fig. 5 was mistakenly labeled as Fig. 4. The correct statement should read “In addition, carbides such as MC (where M is W or vanadium [V]) and chromium carbide (Cr23C6) precipitate in the grain boundary space, which is the same as the energy spectrum results in Fig. 5.” We have made the necessary correction at the corresponding location in the manuscript and highlighted it in yellow.

 

6. In line 189, the authors cite Wang and Zhong, but there is no reference to the literature

 

Reply: We sincerely apologize for omitting these two references. They have been added to the manuscript, and the order of the references has been adjusted accordingly.

 

7.On page 9, the authors discuss the effect of CeO2 on microhardness. The increase in microhardness is attributed to the segregation of Ce at the grain boundaries. Nothing has been mentioned before about the dissociation of CeO2 into Ce and O. Does such a process actually occur?

 

Reply: Thank you for your thoughtful guidance. We mistakenly described the segregation of CeO₂ at grain boundaries as segregation of the element Ce in the article. We have made the necessary corrections and highlighted the revised sections in yellow.

 

8.The following sentence, cited below, is difficult to understand
“First, Ce is preferred at the grain boundaries of the bias[29], so the impurity element bias is reduced, the grain boundaries of the purification and strengthening of the effect are obvious, and the fusion cladding layer microhardness can be improved.”
What is the meaning of “the grain boundaries of the bias”?
Similarly, “upper layer of the organisation “ line 216.

 

Reply: We sincerely apologize for any errors in our English translation. What we intended to convey was that CeO₂ can accumulate at structural defects such as dislocations, pores, and grain boundaries, preferentially at the latter, thereby reducing the segregation of impurity elements. This plays a very important role in the repair of the microstructure. The text has been revised accordingly. Similarly, we acknowledge that the expression “upper layer of the organization” in the article was also problematic, and we have made the necessary corrections.

 

9.In Fig. 7, the layer thicknesses do not match the layer thicknesses in 2. The thickness of the cladding layer is approximately 0.3 mm in Fig. 7, but it is twice this thick in Fig.2

 

Reply: When drawing Fig. 7, we incorrectly labeled the boundary line. Fig. 7 has been revised. The thickness of the cladding layer in Fig. 7 is approximately 0.7 mm, which deviates to a certain degree from the thickness shown in Fig. 2. This discrepancy arises from element diffusion during the cladding process, which introduces variations in the cladding layer thickness.

 

10.On page 10, some sentences need revision, e.g.
“The specimen is conducive to the friction in the surface of the microcracks on top of the stress relaxation and there is enhanced crack extension resistance, which reduces the effect of wear.”
or “Hence, when subjected to the wear process, there is significantly improved wear quality loss.”

 

Reply: Thank you very much for your suggestions. We have revised the language of the paper and highlighted the relevant sections in yellow.

 

11.Line 246, the term “cytocryst” is unintelligible.

 

Reply: The term “cytocryst” in the paper was an inaccurate translation on our part. We intended to refer to “Cellular crystals”; the text has been revised and highlighted accordingly.

 

Two Figu res need corrections:

1.In Fig.2, the description of the vertical axis is truncated

2.Figure 6 is difficult to read. The lines overlap each other

 

Reply: Figures 2 and 6 have been revised. The revised figures are as follows:

 

 

Thanks a lot for your comments and suggestions.

 

Best wishes to you and your family.

 

Sincerely yours,

 

Bo Gao

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper “Study on the organization and properties of cold work die steel after laser melting cerium (IV) oxide–tungsten carbide–nickel-60 composite coating” is devoted to the reduction of coating peeling during long-term operation by laser cladding of nickel/tungsten carbide (Ni/WC) with different cerium (IV) oxide (CeO₂) content on the surface of Cr12MoV die steel.

Traditional methods for applying coatings to the surface of Cr12MoV steel include encapsulated carburizing, thermal spraying, plasma spraying, physical vapor deposition, and chemical vapor deposition. However, the non-metallic bonds of coatings produced by these methods are prone to delamination during long-term operation. To address these issues, this study explores the potential of laser cladding for producing wear-resistant coatings. The optimum process conditions – power of 1500 W, powder feeding of 1 g/s, and a scanning speed of 7 mm/s – were derived from orthogonal experiments. Cr12MoV cast steel was used as the substrate, and composite Ni-WC-CeO₂ coatings were produced on the surface using laser cladding. To theoretically determine the optimal amount of CeO₂ in the composite coating produced by laser cladding, the effect of CeO₂ on the coating structure and properties was studied.

The following methods were used to evaluate the surfacing results: morphology assessment using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS); X-ray diffraction (XRD) technique for compositional analysis; microhardness assessment; and determination of mass loss due to frictional wear. This made it possible to determine the possibility of increasing the strength and wear resistance of the working surface using laser cladding of a nickel/tungsten carbide coating. The effect of cerium (IV) oxide CeO₂ additive (0–2.5 wt.%) on the coating microstructure, microhardness, and friction/wear was studied. When the CeO₂ mass fraction is 2.0%, the reinforcing phase is uniformly dispersed in the fusion-coated layer, and the coating appears to be significantly refined.

The work uses current literature.

There are recommendations for clarifying the text, improving the figures, and increasing the detail in the table description:

1. The powder feed parameters need to be clarified. The abstract states that laser cladding is effective with the following process parameters: 1500 W power, 24 mm defocus distance, 6 mm/s scan speed, 5 mm spot diameter, and 6 g/min powder feed. However, Table 4 shows different results, specifically, varying the powder feed rate from 0.5 to 1.5 g/s. The conclusion also states a powder feeding of 1 g/s. These parameters need to be adjusted accordingly.
2. The text of the work does not clearly explain all the values indicated in Table 4. In particular, the following designations need to be clarified: k₁, k₂, k₃, K₁, K₂, and K₃. The remaining values at the bottom of the table also require clarification.
3. Table 4 lists 9 samples. Experimental results are shown for only five. It is necessary to indicate why it is not necessary to consider other samples.
4. Figure 2. It is necessary to improve the quality. The name of the axes is cropped. It is recommended to arrange all drawings uniformly according to the example of Figure 7.
5. Excessive use of the "/" symbol. When correcting, you can follow Figure 7.
6. Figure 8. It is better to make the signature of the ordinate axis with a capital letter.
7. It is recommended to provide abbreviated names for some methods in the work: SEM, EDS and XRD. This will make the text accessible to a wider range of readers.

Author Response

Dear Editor Dr. Paula Zhou:

 

Thank you very much for your letter.

Please accept our sincere thanks to you and the reviewers. Now, as you requested, I am sending you a revised manuscript of our submission "Study on the organisation and properties of cold work die steel after laser melting cerium (IV) oxide-tungsten carbide-nickel-60 composite coating" (coatings-3919000) for your consideration. This letter includes a detailed reply to the reviewers' comments. Since the issues mentioned by reviewers have been addressed as follows, we believe the manuscript has been significantly improved.

 

The following contents include detailed replies to the reviewers’ comments:

 

To Reviewer #2

The paper “Study on the organization and properties of cold work die steel after laser melting cerium (IV) oxide–tungsten carbide–nickel-60 composite coating” is devoted to the reduction of coating peeling during long-term operation by laser cladding of nickel/tungsten carbide (Ni/WC) with different cerium (IV) oxide (CeO₂) content on the surface of Cr12MoV die steel.

Traditional methods for applying coatings to the surface of Cr12MoV steel include encapsulated carburizing, thermal spraying, plasma spraying, physical vapor deposition, and chemical vapor deposition. However, the non-metallic bonds of coatings produced by these methods are prone to delamination during long-term operation. To address these issues, this study explores the potential of laser cladding for producing wear-resistant coatings. The optimum process conditions – power of 1500 W, powder feeding of 1 g/s, and a scanning speed of 7 mm/s – were derived from orthogonal experiments. Cr12MoV cast steel was used as the substrate, and composite Ni-WC-CeO₂ coatings were produced on the surface using laser cladding. To theoretically determine the optimal amount of CeO₂ in the composite coating produced by laser cladding, the effect of CeO₂ on the coating structure and properties was studied.

The following methods were used to evaluate the surfacing results: morphology assessment using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS); X-ray diffraction (XRD) technique for compositional analysis; microhardness assessment; and determination of mass loss due to frictional wear. This made it possible to determine the possibility of increasing the strength and wear resistance of the working surface using laser cladding of a nickel/tungsten carbide coating. The effect of cerium (IV) oxide CeO₂ additive (0–2.5 wt.%) on the coating microstructure, microhardness, and friction/wear was studied. When the CeO₂ mass fraction is 2.0%, the reinforcing phase is uniformly dispersed in the fusion-coated layer, and the coating appears to be significantly refined.

The work uses current literature.

There are recommendations for clarifying the text, improving the figures, and increasing the detail in the table description:

1.The powder feed parameters need to be clarified. The abstract states that laser cladding is effective with the following process parameters: 1500 W power, 24 mm defocus distance, 6 mm/s scan speed, 5 mm spot diameter, and 6 g/min powder feed. However, Table 4 shows different results, specifically, varying the powder feed rate from 0.5 to 1.5 g/s. The conclusion also states a powder feeding of 1 g/s. These parameters need to be adjusted accordingly.

 

Reply: Due to our oversight, the unit for “Powder feeding capacity” in Table IV was incorrectly listed as g/s. The unit should be 10^-1 g/s. We have corrected this error in both the table and the conclusions.

 

2.The text of the work does not clearly explain all the values indicated in Table 4. In particular, the following designations need to be clarified: k₁, k₂, k₃, K₁, K₂, and K₃. The remaining values at the bottom of the table also require clarification.

 

Reply: We apologize for any confusion caused by the lack of clarity in Table 4.

The final column of Table 4 presents microhardness data measured for the clad layer under different process parameters in the orthogonal experiment. Microhardness refers to the average hardness value between the clad layer surface and the heat-affected zone, serving as an indicator for evaluating the clad layer's wear resistance.

In the manuscript, A represents laser power, B denotes the powder feeding capacity,

and C indicates scanning speed.

⑴ Determining the optimal level and best combination of experimental factors

Analyze the impact of power on experimental metrics under each parameter. As shown in the table, the effects of A1, A2, and A3 are reflected in experiments 1-3, 4-6, and 7-9, respectively.

The experimental metric sum for power factor Level 1 is:

K_A1 = Y₁ + Y₂ + Y₃ = 2313

Average metric KA1 is:

k_A1 = K_A1/3 = 771

The experimental indicator sum for the 2nd level of power factor is:

K_A2 = Y₄ + Y₅ + Y₆ = 2518.9

Average indicator KA2 is: k_A2 = K_A2/3 = 839.6

The experimental indicator sum for the 3rd level of power factor is:

K_A3 = Y₇ + Y₈ + Y₉ = 2477.2

The average indicator KA3 is: K_A3 = K_A3/3 = 825.7

Orthogonal experiments are a method for simultaneously evaluating multiple factors. Through the orthogonal experimental design in Table 4, we can compare the three sets of data A₁, A₂, and A₃. However, the differences in K_A1, K_A2, and K_A3 indicate that variations in factor A affect the experimental results. Simultaneously, by comparing the magnitudes of K_A1, K_A2, and K_A3, we can determine the relative impact of A₁, A₂, and A₃ on the experimental indicators, thereby identifying A₂ as the optimal level for factor A. The same method can be used to determine the optimal levels for factors B and C as B₂ and C₂, respectively. K_A3 to determine the relative impact of A₁, A₂, and A₃ on the experimental metric, thereby identifying A₂ as the optimal level for factor A. Similarly, the optimal levels for factors B and C are determined as B₂ and C₂, respectively. Ultimately, A₂B₂C₂ is identified as the optimal level combination for this experiment. Thus, statistical analysis of data in orthogonal experimental designs aids in determining optimal level combinations for factors, achieving the goal of optimizing experimental outcomes.

(2) Determining the Hierarchy of Factors

By comparing the range R of power, powder feed rate, and scanning speed, the relative importance of each factor on hardness can be assessed.

R = max - min

Calculations show R₁ > R₂ > R₃. Thus, power has the greatest impact on hardness in this experiment, followed by powder feed rate, while scanning speed has the least effect.

Through comprehensive analysis of how different process parameters affect the morphology and properties of the clad layer, combined with statistical analysis of the orthogonal experimental data, the following conclusion is reached: In the ninth experiment, the process parameter combination yielding the highest clad layer hardness is: power 1500W, powder feed rate 0.1g/s, scanning speed 6mm/s.

 

3.Table 4 lists 9 samples. Experimental results are shown for only five. It is necessary to indicate why it is not necessary to consider other samples.

 

Reply: During our experiments, we discovered that three process parameters—laser power, scanning speed, and powder feed rate—significantly impact the quality of cladding specimens. Therefore, we need to identify optimal cladding parameters. Conducting simple repeated tests for each condition would be excessively labor-intensive, and comprehensive experiments would be both wasteful and impractical. Orthogonal experiments meet the requirements for rapid and cost-effective process optimization. Therefore, we employed an orthogonal experimental design (3³), comprising nine data sets corresponding to the nine positions shown in Figure 1. This approach identifies the optimal laser cladding process parameters and subsequently investigates the effects of varying the CeO₂ concentration (five different CeO₂ content levels) on the microstructure and properties of the cladding layer.

 

4.Figure 2. It is necessary to improve the quality. The name of the axes is cropped. It is recommended to arrange all drawings uniformly according to the example of Figure 7.

 

Reply: Figure 2 has been revised. The revised figures are as follows:

 

 

5.Excessive use of the "/" symbol. When correcting, you can follow Figure 7.

 

Reply: Figure 2 has been revised. The revised figures are as follows:

 

 

6.Figure 8. It is better to make the signature of the ordinate axis with a capital letter.

 

Reply: Figure 8 has been revised. The revised figure is as follows:

 

 

7.It is recommended to provide abbreviated names for some methods in the work: SEM, EDS and XRD. This will make the text accessible to a wider range of readers.

 

Reply: Thank you very much for your suggestion. We have replaced the relevant content in the text with the corresponding abbreviations.

 

 

 

 

 

Thanks a lot for your comments and suggestions.

 

Best wishes to you and your family.

 

Sincerely yours,

 

Bo Gao

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript was improved by the authors' revisions. I suggest publishing it as it is.