In Situ Ceramic Phase Reinforcement via Short-Pulsed Laser Cladding for Enhanced Tribo-Mechanical Behavior of Metal Matrix Composite FeNiCr-B₄C (5 and 7 wt.%) Coatings

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study provides valuable insights into the dynamic tribo-mechanical behavior of laser-cladded FeNiCr-B₄C metal matrix composite (MMC) coatings on an AISI 1040 steel substrate, offering a comprehensive understanding of the intricate interplay between microstructural characteristics and phase transformations. The chosen topic aligns well with the scope of the journal and significantly advances the state of the art in this field. In my opinion, the paper is suitable for publication, contingent upon the following revisions:

1. To enhance the quality of the introduction, I recommend a more thorough review of relevant literature, including references such as [13-18], [22-26], and [30-37], among others.

2. Section 3.3 would benefit from a more detailed discussion of the curves presented in Figure 4.

3. The rationale for selecting the laser cladding process parameters should be clarified.

4. The axis labels in Figure 6 are currently unclear; I suggest enlarging them for better readability.

5. The conclusions section can be strengthened by discussing potential directions for future work.

Author Response

First of all, we would like to say that we are very grateful for your high evaluation of our research – this is very important to us.

1. To enhance the quality of the introduction, I recommend a more thorough review of relevant literature, including references such as [13–18], [22–26], and [30–37], among others.

Response: We appreciate your insightful feedback regarding a more thorough discussion of the existing literature, which we acknowledge could enhance the narrative and strengthen the Introduction. To that end, we have included discussions of specific results from some of the cited studies to highlight gaps in current metal-matrix composite research and to underscore the novelty of our own contributions. In particular, we have expanded the Introduction with a more detailed justification for our choice of 5 and 7 wt.% B₄C.

We would like to clarify our approach to structuring the Introduction, which follows a deliberate plan: (1) outlining the applications and importance of enhancing FeNiCr-based austenitic stainless steels through metal-matrix composite design; (2) providing general background on the effects of each component in the alloy system to enable a comprehensive understanding of subsequent phase transformations during reinforcement; (3) justifying our specific selection and concentration of boron carbide (5 and 7 wt.%) as an effective strengthening additive; and (4) presenting an overview of various MMC coating application technologies, highlighting the advantages of the laser cladding method employed in our study.

This framework is intended to provide a comprehensive understanding of the problem addressed by our research. To avoid overwhelming the reader with excessive detail in the Introduction, we have strategically cited key publications relevant to each of these points: [13–18] for effective additives in durable steel-based MMCs; [22–26] for characterization of equiatomic FeNiCr materials (bulk and coatings); and [30–37] for high-quality research on laser cladding of composite coatings.

In light of these considerations, we respectfully request that the suggestion for further expansion of the literature review in the Introduction be reconsidered. We believe that the current structure provides a well-balanced and compelling introduction to our research, while the detailed supporting literature is appropriately referenced. We remain committed to thoroughly addressing all relevant literature throughout the remainder of the manuscript.

2. Section 3.3 would benefit from a more detailed discussion of the curves presented in Figure 4.

Response: Thank you for your comment. We’d like to clarify that the primary goal of the Raman spectroscopy analysis was to confirm the presence of the ceramic phase (B₄C) in the matrix of our FeNiCr-based coatings through peak identification and intensity analysis. Specifically, we identified, discussed, and supported with references, peaks corresponding to amorphous carbon, the stretching of C-B-C chains in B₄C, and the vibrational modes of B₁₁C icosahedra. Furthermore, we detected additional peaks related to intra-icosahedral B-B bonds, the rotational mode of the C-B-C chain in B₄C, and the breathing vibrations of B₁₁C icosahedra, providing further evidence for the presence of B₄C in both coatings. Additionally, we’ve provided further characterization and discussion of the presence of medium-intensity α-Fe₂O₃ and γ-Fe₂O₃, along with high-intensity NiFe₂O₄/NiCr₂O₄ phases. This confirmed the high concentration of the main matrix elements (Fe, Ni, and Cr) in our FeNiCr-B₄C coatings and, in conjunction with XRD analysis, supported the presence of the γ-FeNiCr phase, consistent with our earlier findings.

3. The rationale for selecting the laser cladding process parameters should be clarified.

Response: Thanks for the valuable feedback. We’ve added the laser cladding parameters and their selection rationale to the Materials and Methods section.

«Laser cladding was performed using a ytterbium fiber laser system (UdSU, Izhevsk, Russia) to deposit MMC FeNiCr-B₄C coatings (5 and 7 wt.% B₄C) onto AISI 1040 steel substrate (Table 1, LCC “ANEP-Metal”, Ekaterinburg, Russia). Table 2 provides detailed information on the laser cladding parameters.

Table 2. Laser cladding parameters.

Parameter	Value
Material delivery method	Pre-placed powder bed
Shielding gas, Ar	10 l/min
Laser mode	Pulsed
Laser power, P	50 W
Laser wavelength, λ	1.065 µm
Scanning speed, v	5 mm/s
Pulse frequency, f	20 Hz
Pulse duration, τ	3.5 ms
Overlap rate, %	~25 %
Pulse energy, E	8,3 J
Pulse energy density, F	1057 J/cm2
Laser spot area, A	0.00785 cm²
Spot size, d	1 mm

The optimized laser cladding parameters, carefully selected for this study, promoted a desirable microstructure in the resulting coatings. The pulsed laser mode with a power of 50 W, wavelength of 1.065 µm, pulse frequency of 20 Hz, and pulse duration of 3.5 ms, combined with a scanning speed of 5 mm/s and an overlap rate of ~25%, ensured con-trolled energy input. Such precise control minimized excessive heat input (minimizing both dilution and temperature gradients), and promoted localized melting and solidification. In turn, this led to a refined grain structure and reduced residual stresses, ultimately enhancing the coating’s tribo-mechanical properties and overall performance. The calculated pulse energy of 8.3 J and resulting energy density of 1057 J/cm² over a 1 mm spot size provided sufficient energy for adequate powder consolidation and bonding to the substrate, without causing significant thermal distortion or deleterious phase transformations. The Ar shielding further minimized oxidation during the process, preserving the desired chemical composition and preventing the formation of undesirable phases. A double-pass cladding strategy was implemented to reduce substrate dilution of the coatings. The resulting coatings exhibited a consistent thickness of 250 ± 20 μm on specimens with overall dimensions of 5 × 5 × 3 mm and a roughness (R_a) of ~1 μm measured using a profilometer model 250 (JSC “Caliber”, Moscow, Russia)».

4. The axis labels in Figure 6 are currently unclear; I suggest enlarging them for better readability.

Response: We appreciate your comment. We have enlarged the text in Figure 6 to improve readability (please see the attached file).

5. The conclusions section can be strengthened by discussing potential directions for future work.

Response: We greatly appreciate your insightful recommendation. We have added general directions for future research in the Conclusion section:

«Future studies will focus on analyzing the high-temperature behavior and application-specific performance (cavitation, abrasion, and corrosion resistance) of the FeNiCr-B₄C coatings. This comprehensive investigation represents a critical avenue for advancing our understanding of these coatings’ potential in demanding environments and guiding future materials development efforts».

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Recommendations:

Lines 129-130. The dimensions of powders were measured (how, equipment?) or were provided by suppliers?

Table 1. The chemical compositions of powders were measured (how, equipment?) or were offered by suppliers?

Line 141. The ytterbium fiber laser was homemade or provided by a company?

Lines 141-148. Please provide information about the cladding optics and their processing parameters.

Line 145. Please inform about the Ar flow rate.

Line 152. Please inform about the EDS producer.

Figure 1. Increase the size of the images, dropping the side arrows, because the text in pictures a and b is too small.

The same goes for the following figures. The text in the figures should be the same size as the rest of the text.

In line 127 is specified that tests were made for 5 and 7 wt.% of B₄C powder, but in Figure are presented also 1 and 3 wt.% of B₄C powder?!?

Line 127 specifies that the tests were performed for 5 and 7% wt.% B₄C powder, but the Figure 4 and Table 4 also shows 1 and 3% wt.% B₄C powder?!?

In the Conclusions chapter, please correlate the measurements taken, do not discuss them separately.

Also, please provide some practical advice for using of this laser-cladding technology for different products.

Author Response

First of all, we are very grateful for your recommendations.

Recommendations:

Lines 129-130. The dimensions of powders were measured (how, equipment?) or were provided by suppliers?

Response: Thank you for your question. Although the powder’ sizes were provided by the suppliers, we further validated this through SEM analysis (Tescan MIRA LMS).

Table 1. The chemical compositions of powders were measured (how, equipment?) or were offered by suppliers?

Response: Thank you for your question. Although the powders’ chemical compositions were provided by the suppliers, we further validated this through SEM analysis (Tescan MIRA LMS).

Line 141. The ytterbium fiber laser was homemade or provided by a company?

Response: Thank you for your question. The ytterbium fiber laser was provided by a Chinese company, but the entire laser cell was assembled in Udmurt State University (UdSU), Izhevsk, Russia and this is an experimental complex.

Lines 141-148. Please provide information about the cladding optics and their processing parameters.

Response: Thanks for the valuable feedback. We’ve added laser cladding parameters to the Materials and Methods section.

«Laser cladding was performed using a ytterbium fiber laser system (UdSU, Izhevsk, Russia) to deposit MMC FeNiCr-B₄C coatings (5 and 7 wt.% B₄C) onto AISI 1040 steel substrate (Table 1, LCC “ANEP-Metal”, Ekaterinburg, Russia). Table 2 provides detailed information on the laser cladding parameters.

Table 2. Laser cladding parameters.

Parameter	Value
Material delivery method	Pre-placed powder bed
Shielding gas, Ar	10 l/min
Laser mode	Pulsed
Laser power, P	50 W
Laser wavelength, λ	1.065 µm
Scanning speed, v	5 mm/s
Pulse frequency, f	20 Hz
Pulse duration, τ	3.5 ms
Overlap rate, %	~25 %
Pulse energy, E	8,3 J
Pulse energy density, F	1057 J/cm2
Laser spot area, A	0.00785 cm²
Spot size, d	1 mm

The optimized laser cladding parameters, carefully selected for this study, promoted a desirable microstructure in the resulting coatings. The pulsed laser mode with a power of 50 W, wavelength of 1.065 µm, pulse frequency of 20 Hz, and pulse duration of 3.5 ms, combined with a scanning speed of 5 mm/s and an overlap rate of ~25%, ensured con-trolled energy input. Such precise control minimized excessive heat input (minimizing both dilution and temperature gradients), and promoted localized melting and solidification. In turn, this led to a refined grain structure and reduced residual stresses, ultimately enhancing the coating’s tribo-mechanical properties and overall performance. The calculated pulse energy of 8.3 J and resulting energy density of 1057 J/cm² over a 1 mm spot size provided sufficient energy for adequate powder consolidation and bonding to the substrate, without causing significant thermal distortion or deleterious phase transformations. The Ar shielding further minimized oxidation during the process, preserving the desired chemical composition and preventing the formation of undesirable phases. A double-pass cladding strategy was implemented to reduce substrate dilution of the coatings. The resulting coatings exhibited a consistent thickness of 250 ± 20 μm on specimens with overall dimensions of 5 × 5 × 3 mm and a roughness (R_a) of ~1 μm measured using a profilometer model 250 (JSC “Caliber”, Moscow, Russia)».

Line 145. Please inform about the Ar flow rate.

Response: We appreciate your insightful feedback. The Ar shielding gas was delivered at 10 l/min (please see Table 2).

Line 152. Please inform about the EDS producer.

Response: Thank you for your valuable comment. We have added the company, city and country of the EDS manufacturer.

«The microstructure and chemical composition of the FeNiCr-B₄C samples were in-ves-tigated through scanning electron microscope (SEM) Tescan MIRA LMS (Tescan Brno S.R.O., Brno, Czech Republic), coupled with energy-dispersive X-ray spectroscopy (EDS) (Oxford Instruments, Abingdon, England) to examine the interfacial characteristics and element distribution».

Figure 1. Increase the size of the images, dropping the side arrows, because the text in pictures a and b is too small. The same goes for the following figures. The text in the figures should be the same size as the rest of the text.

Response: Thank you for your valuable comment. The figures have been revised to enhance their size by eliminating purely decorative elements. We have ensured high image quality, allowing for clear visualization of all labels and annotations (arrows, lines, etc.) upon magnification. Due to the figures’ inherent detail, inscription sizes are slightly smaller than the main text, but we have selected optimized sizes to maintain optimal readability. We kindly ask for your understanding.

In line 127 is specified that tests were made for 5 and 7 wt.% of B₄C powder, but in Figure are presented also 1 and 3 wt.% of B₄C powder?!?

Line 127 specifies that the tests were performed for 5 and 7% wt.% B₄C powder, but the Figure 4 and Table 4 also shows 1 and 3% wt.% B₄C powder?!?

Response: We appreciate your comment. As we understand it, these are 2 identical questions (most likely a typo) and I hope that you would allow us to give one general answer to it. That's all correct. Figures 4 (Table 5) and 5 (Table 6) accurately present our findings. We have included results from our previous work (0, 1, and 3 wt.%) to highlight the significant progress made in optimizing the technology for creating high-strength metal-matrix coatings. Tracking the notable changes in phase composition and mechanical properties of our new FeNiCr-B₄C coatings (5 and 7 wt.% B₄C) composite coatings was crucial. The present technology leverages the synergistic combination of a moderately controlled addition of increased boron carbide and optimized laser cladding parameters to achieve advanced metal-matrix coatings.

In the Conclusions chapter, please correlate the measurements taken, do not discuss them separately.

Response: Thanks for your comment. We have revised the conclusion section according to the comments of other reviewers. We acknowledge the validity of your comment, and recognize that differing interpretations are possible. Since it is impossible to please everyone, we have left in our conclusion the consistently obtained results of the microstructural study and then the tribomechanical characteristics. We kindly ask you to treat this with deep understanding.

Also, please provide some practical advice for using of this laser-cladding technology for different products.

Response: We appreciate your insightful feedback. Short-pulsed laser cladding offers significant advantages for various product applications. This technology excels in precise deposition, minimizing heat-affected zones (HAZ) and enabling tailored microstructures. It’s particularly well-suited for repairing and enhancing the performance of high-value components like turbine blades, where localized repairs with minimal distortion are critical. Furthermore, the process is ideal for creating wear-resistant coatings on tools and dies, extending their service life and improving their efficiency. Short-pulse laser cladding can also be employed to create graded materials, improving the performance of products like medical implants, and it shows promise for additive manufacturing of complex shapes from metal powders. The flexibility and precision of this technique offer significant potential for enhancing product performance and extending service life across a wide range of industries.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This work presents a systematic investigation into the development and tribo-mechanical performance of FeNiCr metal matrix composite (MMC) coatings reinforced in situ with 5 and 7 wt.% boron carbide (B₄C), fabricated by short-pulsed laser cladding. The authors combine SEM, XRD, Raman spectroscopy, nanoindentation, and scratch testing to elucidate the role of B₄C in enhancing hardness, wear resistance, and structural integrity. The findings support the use of this composite and processing approach for high-demand engineering applications.

 

1. The novelty claim is not adequately differentiated from earlier work by the same group ([16], [18]). While this study increases B₄C content to 5 and 7 wt.%, the significance of this step is not made clear enough. A quantitative or mechanistic rationale for selecting these concentrations is missing. The authors should add a short subsection in the Introduction explicitly stating what was not known from prior FeNiCr-B₄C coatings with ≤3 wt.% and what knowledge gap is addressed here.

 

2. The laser cladding methodology (Section 2.2) lacks detail about energy density, scanning speed, overlap rate, and pulse repetition frequency. These factors heavily influence microstructure and should be reported or justified. The authors should include these critical process parameters and discuss how they affect dilution and thermal gradients.

 

3. While the XRD and Raman results confirm phase presence, the analysis remains qualitative. The authors should perform Rietveld refinement or peak area analysis to estimate relative phase fractions of B₄C and Fe₂B. In addition, the authors should discuss how phase formation is affected by B₄C content and laser thermal profile.

 

4. The paper reports excellent improvements in microhardness and HIT/E* ratios, but lacks direct evidence linking these results to local microstructure beyond general assumptions. The authorus should provide localized SEM or EDS maps of regions with different hardness levels to confirm B₄C or Fe₂B enrichment.

 

5. The scratch depth profiles are well presented, but the mechanical interpretation is lacking in depth.
   The authors should add quantitative adhesion strength estimates (e.g., critical load for delamination if observed). In addition, they should consider FIB cross-sections at scratch locations in future work to confirm interface integrity.

 

6. Sentence structure is sometimes overly long and formal. Consider simplifying for clarity, especially in the Introduction and Conclusions.

 

7. Some figures (e.g., Figure 4 and 6) would benefit from higher resolution and clearer color contrast for mapping images.

Author Response

First of all, we truly appreciate your positive assessment of our research, which we value highly.

1. The novelty claim is not adequately differentiated from earlier work by the same group ([16], [18]). While this study increases B₄C content to 5 and 7 wt.%, the significance of this step is not made clear enough. A quantitative or mechanistic rationale for selecting these concentrations is missing. The authors should add a short subsection in the Introduction explicitly stating what was not known from prior FeNiCr-B₄C coatings with ≤3 wt.% and what knowledge gap is addressed here.

Response: Thank you for your valuable comment. We have incorporated a short subsection within the Introduction that provides a detailed justification for our selection of 5 and 7 wt.% B₄C.

«The FeNiCr alloy system, especially in its equiatomic configuration, has garnered significant research interest [16,18,22–26]. As reported in [16,18], equiatomic FeNiCr coatings (3.2 GPa) exhibit a 50% higher microhardness than AISI 1040 steel (2.2 GPa), thereby highlighting their potential for various industrial applications. The addition of 1 and 3 wt.% B₄C to the FeNiCr matrix [16] failed to induce the anticipated in situ formation of iron boride intermetallic compounds (FeB/Fe₂B) and the associated synergistic strengthening effect from the B₄C/FeB(Fe₂B) composite. When aiming for in situ formation of FeB/Fe₂B, the Fe₂B phase is preferable to FeB due to the latter’s greater brittleness and tendency to form continuous, embrittling networks along grain boundaries, particularly at higher B₄C concentrations. This can significantly reduce ductility and toughness. However, B₄C additions must be carefully controlled, as excessive concentrations can be detrimental to material properties. The increased volume fraction of residual B₄C particles in the matrix, while enhancing hardness, can also act as crack nucleation sites, com-promising the overall strength of the composite. Such MMC coatings exhibit increased brittleness, limited load-bearing capacity, and a propensity for premature failure under stress. In this study, building upon the authors’ prior investigations, the B₄C concentration was systematically increased to 5 and 7 wt.% to promote the in-situ formation of FeB and Fe₂B intermetallic phases while mitigating any deleterious effects on the coating micro-structure and tribo-mechanical behavior».

2. The laser cladding methodology (Section 2.2) lacks detail about energy density, scanning speed, overlap rate, and pulse repetition frequency. These factors heavily influence microstructure and should be reported or justified. The authors should include these critical process parameters and discuss how they affect dilution and thermal gradients.

Response: Thanks for the valuable feedback. We’ve added the laser cladding parameters and their selection rationale to the Materials and Methods section.

«Laser cladding was performed using a ytterbium fiber laser system (UdSU, Izhevsk, Russia) to deposit MMC FeNiCr-B₄C coatings (5 and 7 wt.% B₄C) onto AISI 1040 steel substrate (Table 1, LCC “ANEP-Metal”, Ekaterinburg, Russia). Table 2 provides detailed information on the laser cladding parameters.

Table 2. Laser cladding parameters.

Parameter	Value
Material delivery method	Pre-placed powder bed
Shielding gas, Ar	10 l/min
Laser mode	Pulsed
Laser power, P	50 W
Laser wavelength, λ	1.065 µm
Scanning speed, v	5 mm/s
Pulse frequency, f	20 Hz
Pulse duration, τ	3.5 ms
Overlap rate, %	~25 %
Pulse energy, E	8,3 J
Pulse energy density, F	1057 J/cm2
Laser spot area, A	0.00785 cm²
Spot size, d	1 mm

The optimized laser cladding parameters, carefully selected for this study, promoted a desirable microstructure in the resulting coatings. The pulsed laser mode with a power of 50 W, wavelength of 1.065 µm, pulse frequency of 20 Hz, and pulse duration of 3.5 ms, combined with a scanning speed of 5 mm/s and an overlap rate of ~25%, ensured con-trolled energy input. Such precise control minimized excessive heat input (minimizing both dilution and temperature gradients), and promoted localized melting and solidification. In turn, this led to a refined grain structure and reduced residual stresses, ultimately enhancing the coating’s tribo-mechanical properties and overall performance. The calculated pulse energy of 8.3 J and resulting energy density of 1057 J/cm² over a 1 mm spot size provided sufficient energy for adequate powder consolidation and bonding to the substrate, without causing significant thermal distortion or deleterious phase transformations. The Ar shielding further minimized oxidation during the process, preserving the desired chemical composition and preventing the formation of undesirable phases. A double-pass cladding strategy was implemented to reduce substrate dilution of the coatings. The resulting coatings exhibited a consistent thickness of 250 ± 20 μm on specimens with overall dimensions of 5 × 5 × 3 mm and a roughness (R_a) of ~1 μm measured using a profilometer model 250 (JSC “Caliber”, Moscow, Russia)».

3. While the XRD and Raman results confirm phase presence, the analysis remains qualitative. The authors should perform Rietveld refinement or peak area analysis to estimate relative phase fractions of B₄C and Fe₂ In addition, the authors should discuss how phase formation is affected by B₄C content and laser thermal profile.

Response: Thanks for the useful comment. We performed a Rietveld refinement (X’Pert HighScorePlus 3.0.5) to estimate the relative phase fractions of B₄C and Fe₂B, and discussed in detail how phase formation is affected by B₄C content and laser thermal profile.

«Rietveld refinement quantified the phase compositions of both coatings. The FeNiCr + 5 wt.% B₄C coating consisted of 3.1% α-Fe, 80.3% γ-FeNiCr, 7% B₄C, 9.6% Fe₂B, while the FeNiCr + 7 wt.% B₄C coating comprised 4.6% α-Fe, 72% γ-FeNiCr, 10.4% B₄C, 13% Fe₂B. These phase ratios, notably the increased presence of B₄C and Fe₂B, were achieved through the controlled addition of B₄C and optimization of the laser thermal profile. Increasing the B₄C concentration to 5 and 7 wt.% directly impacts the available boron, driving the formation of Fe₂B intermetallic phases, as evidenced by the observed XRD patterns. Concurrently, the laser thermal profile, determined by parameters such as power, scanning speed, and pulse duration, governs the local temperature distribution and cooling rates during the laser cladding process. These thermal conditions dictate the kinetics of phase transformations, affecting the size, morphology, and distribution of both B₄C and Fe₂B phases within the FeNiCr matrix. For example, a higher energy input promotes more extensive melting and mixing, potentially leading to more uniform phase distributions, while faster cooling rates may favor the formation of finer microstructures. By carefully controlling both the B₄C content and the laser parameters, we successfully tailored the phase composition and microstructure, thereby achieving optimized tribo-mechanical properties of the FeNiCr-B₄C coatings».

4. The paper reports excellent improvements in microhardness and H_IT/E* ratios, but lacks direct evidence linking these results to local microstructure beyond general assumptions. The authorus should provide localized SEM or EDS maps of regions with different hardness levels to confirm B₄C or Fe₂B enrichment.

Response: Thank you for your valuable feedback. Indeed, it would be appropriate to identify localized SEM or EDS maps of areas with different hardness levels to confirm enrichment in B₄C or Fe₂B. However, it must be recognized that obtaining specific localized SEM or EDS maps that directly correlate microhardness variations with specific enrichments of B₄C or Fe₂B in these coatings presents several significant challenges rooted in the material properties, analytical limitations, and the nature of the microstructure itself. Therefore, while SEM-EDS analysis can provide some qualitative information about the distribution of elements, the limitations related to light element detection, spatial resolution, spectral interferences, phase identification, and sample preparation artifacts make it difficult to establish a definitive, quantitative correlation between localized hardness variations and the precise enrichment of B₄C or Fe₂B using only these techniques. A multi-technique approach, combining SEM-EDS with XRD, TEM, EBSD, or even atom probe tomography (APT) is usually used to provide more robust and convincing evidence.

• Here it is worth immediately clarifying that in our previous study with 1-3 wt.% B₄C, a multi-technique approach (SEM-EDS, XRD, TEM) failed to identify the B₄C phase, either qualitatively or quantitatively. Therefore, Raman microscopy was essential for definitive (only qualitative) B₄C identification within our FeNiCr-based MMC coatings.
• Utilizing 5 and 7 wt.% B₄C, we successfully induced the in-situ formation of Fe₂B phase within our MMC FeNiCr-B₄C coatings and were able to qualitatively and quantitatively identify B₄C and Fe₂B phases through SEM-EDS, XRD, and Raman spectroscopy methods. However, to identify localized areas with different hardness levels to confirm enrichment in B₄C or Fe₂B, is difficult to achieve in our case, as explained by the limitations outlined earlier.
• In support of our arguments, we also refer to the available literature and research by one of our co-authors, Prof. Kharanzhevsky, who studied in detail the formation of carbide (B₄C) and intermetallic compounds of the FeB/Fe₂B type in a steel matrix and convincingly characterized, and compared the dependence of improved mechanical properties of coatings with a formed composite microstructure enriched in boron carbide and iron boride phases.

5. The scratch depth profiles are well presented, but the mechanical interpretation is lacking in depth. The authors should add quantitative adhesion strength estimates (e.g., critical load for delamination if observed). In addition, they should consider FIB cross-sections at scratch locations in future work to confirm interface integrity.

Response: We appreciate your insightful feedback. The scratch test results in our study effectively complement the mechanical characterization (Section 3.4), yielding a strong basis for the conclusions. It’s important to emphasize that the cross-sectional scratch tests on the FeNiCr-B₄C coatings were specifically designed to evaluate the failure behavior of both the coating material and the substrate, with a particular focus on the interface region. The resulting penetration depth versus distance curves proved invaluable for identifying these distinct zones within the cross-section – clearly delineating the coating, interface, and substrate regions. Furthermore, beyond simply measuring penetration depth, the SEM images allowed us to estimate the scratch profile widths and calculate average values for both the coating and substrate. Critically, we didn’t observe the delamination of the coating material, and no significant visual defects were apparent in the coating compared to the substrate. This lack of delamination and defects strongly suggests excellent interfacial adhesion between the coating and substrate. It may also indicate that the B₄C reinforcement does not introduce significant stress concentrations or weaknesses within the coating itself. This observation could further imply that the coating is well-integrated with the substrate, potentially contributing to enhanced overall mechanical performance and durability of the composite system under tribological loading conditions.

Further analysis and characterization techniques will be necessary to fully validate these findings. We will definitely take your valuable recommendation into consideration and include FIB cross-sectioning in our future study to confirm the interface integrity.

6. Sentence structure is sometimes overly long and formal. Consider simplifying for clarity, especially in the Introduction and Conclusions.

Response: We appreciate your comment. We have revised the manuscript text and broke long sentences into shorter ones, especially in the Introduction and Conclusions sections, to improve comprehension and readability (highlighted in red).

      7. Some figures (e.g., Figure 4 and 6) would benefit from higher resolution and clearer color contrast for mapping images.

Response: Thanks for the valuable feedback. All figures originally had high resolution; the current blurriness likely stems from the PDF compression process. We have revised our Figures 4 and 6 to improve readability (please see the attached file).

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

1. The study evaluates coatings with 5 wt.% and 7 wt.% B₄C content, demonstrating improved hardness and wear resistance. I suggest the authors consider discussing whether further increases in B₄C content (e.g., 10 wt.%) were explored or are feasible. Could excessive B₄C lead to embrittlement or reduced coating integrity? Providing insights into the upper limits of B₄C incorporation would enhance the applicability of this work.
2. While the improved wear resistance and adhesion are demonstrated, the specific wear mechanisms (e.g., adhesive, abrasive, oxidative) are insufficiently discussed. I encourage the authors to provide SEM images of wear tracks and friction coefficient data to clarify the dominant wear processes. Furthermore, given the potential industrial applications, preliminary corrosion resistance tests (e.g., electrochemical analysis) would substantiate the claimed protective capabilities.
3. The short-pulsed laser cladding approach shows promising laboratory results. However, the authors should discuss potential challenges in scaling up for industrial applications, including coating uniformity, throughput, and cost-effectiveness. Clarifying process repeatability and stability in high-volume production would greatly enhance the study’s practical relevance.

Author Response

Response to Review 4

First of all, we thank you for your constructive comments on our study.

1. The study evaluates coatings with 5 wt.% and 7 wt.% B₄C content, demonstrating improved hardness and wear resistance. I suggest the authors consider discussing whether further increases in B₄C content (e.g., 10 wt.%) were explored or are feasible. Could excessive B₄C lead to embrittlement or reduced coating integrity? Providing insights into the upper limits of B₄C incorporation would enhance the applicability of this work.

Response: Thank you for your valuable comment. We have incorporated a short subsection within the Introduction that provides a detailed justification for our selection of 5 and 7 wt.% B₄C:

«The FeNiCr alloy system, especially in its equiatomic configuration, has garnered significant research interest [16,18,22–26]. As reported in [16,18], equiatomic FeNiCr coatings (3.2 GPa) exhibit a 50% higher microhardness than AISI 1040 steel (2.2 GPa), thereby highlighting their potential for various industrial applications. The addition of 1 and 3 wt.% B₄C to the FeNiCr matrix [16] failed to induce the anticipated in situ formation of iron boride intermetallic compounds (FeB/Fe₂B) and the associated synergistic strengthening effect from the B₄C/FeB(Fe₂B) composite. When aiming for in situ formation of FeB/Fe₂B, the Fe₂B phase is preferable to FeB due to the latter’s greater brittleness and tendency to form continuous, embrittling networks along grain boundaries, particularly at higher B₄C concentrations. This can significantly reduce ductility and toughness. However, B₄C additions must be carefully controlled, as excessive concentrations can be detrimental to material properties. The increased volume fraction of residual B₄C particles in the matrix, while enhancing hardness, can also act as crack nucleation sites, com-promising the overall strength of the composite. Such MMC coatings exhibit increased brittleness, limited load-bearing capacity, and a propensity for premature failure under stress. In this study, building upon the authors’ prior investigations, the B₄C concentration was systematically increased to 5 and 7 wt.% to promote the in-situ formation of FeB and Fe₂B intermetallic phases while mitigating any deleterious effects on the coating micro-structure and tribo-mechanical behavior».

Thus, our decision to use a moderate B₄C addition of 5 and 7 wt.% is based on the existing knowledge base, including Prof. Kharanzhevsky’s earlier investigations, where he supervised the short-pulsed laser cladding process with additions ranging from 8–12 wt.%. This approach allows us to avoid the negative consequences of embrittlement observed at higher B₄C concentrations.

1. While the improved wear resistance and adhesion are demonstrated, the specific wear mechanisms (e.g., adhesive, abrasive, oxidative) are insufficiently discussed. I encourage the authors to provide SEM images of wear tracks and friction coefficient data to clarify the dominant wear processes. Furthermore, given the potential industrial applications, preliminary corrosion resistance tests (e.g., electrochemical analysis) would substantiate the claimed protective capabilities.

Response: We value your feedback and acknowledge your point of view. However, the primary focus of this work was to evaluate the synergistic potential of optimizing short-pulse laser cladding parameters in conjunction with moderate reinforcement of the coating matrix using 5 and 7 wt.% B₄C. This approach, unlike our previous work (0.1 and 3 wt.%), enabled the in-situ formation of strengthening iron-boron intermetallic phases while retaining the B₄C phase within the coating matrix. This was comprehensively confirmed by SEM, XRD, and Raman spectroscopy. As a result, we achieved exceptional mechanical properties, coupled with the expected wear-resistant behavior compared to the AISI 1040 steel substrate, as evidenced by the scratch test. While we recognize the importance of comprehensive wear testing, we will incorporate additional wear resistance evaluations in future study, as noted in the Conclusion section:

«Future studies will focus on analyzing the high-temperature behavior and application-specific performance (cavitation, abrasion, and corrosion resistance) of the FeNiCr-B₄C coatings. This comprehensive investigation represents a critical avenue for advancing our understanding of these coatings’ potential in demanding environments and guiding future materials development efforts».

1. The short-pulsed laser cladding approach shows promising laboratory results. However, the authors should discuss potential challenges in scaling up for industrial applications, including coating uniformity, throughput, and cost-effectiveness. Clarifying process repeatability and stability in high-volume production would greatly enhance the study’s practical relevance.

Response: We acknowledge the reviewer’s valid point regarding scalability. While our short-pulsed laser cladding approach demonstrates promising laboratory results, we recognize that significant challenges exist in transitioning to industrial applications. Specifically, maintaining coating uniformity, achieving acceptable throughput, and ensuring cost-effectiveness in high-volume production environments require further investigation. Future studies will focus on addressing these challenges by exploring techniques such as automated multi-pass cladding strategies, optimized powder delivery systems, and process parameter optimization to enhance repeatability, stability, and overall efficiency for large-scale manufacturing. These efforts will be crucial in realizing the full potential of this technology for real-world applications.

We agree that clarification is warranted, and we plan to address this in our next study through additional cavitation, abrasion, and corrosion resistance testing, as indicated in our previous response.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed my comments.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors modified manuscript in accordance with reviewer's comment. The manuscript can be consider for publication in this form.