Influence of Nd:YAG Laser Melting on an Investment-Casting Co-Cr-Mo Alloy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review of manuscript number: metals-3518419

Title:

Influence of Nd:YAG laser melting on an Investment Casting Co-Cr-

Mo Alloy

 

The authors presented the results of research on changes in the properties of the Co-Cr-Mo alloy surface layer caused by remelting with a Nd:YAG laser beam.

The title of the manuscript reflects its content, but it is insufficient to approve the paper for publication in Metals.

General remark

Q1. Neither the abstract and introduction nor the results and discussion convincingly show the novelty of the issues discussed.

 

Ad. Abstract and Introduction

Q2.The Introduction is long, but the analysis of the cited results from the literature does not provide sufficient justification for the research undertaken.

If "Investment casting or the lost-wax process has emerged as a preferred manufacturing method for these complex components because it provides superior dimensional accuracy, precise control over the alloys surface characteristics..." (lines 41-44), why should further research be undertaken to improve the properties of cast components?

Q3. Already in Abstract (line 11) it was stated that investment casting is simply lost-wax casting. Why repeat it so many times (line 41, line 48)?

Q4. The authors do not refer to an important article (over 200 citations) and related  to the subject of the manuscript:

Yolanda S. Hedberga, Bin Qianc, Zhijian Shenc, Sannakaisa Virtanena, Inger Odnevall Wallinderb'In vitro biocompatibility of CoCrMo dental alloys fabricated by selective laser melting', Dental Materials, Volume 30, Issue 5, Pages 525 – 534 May 2014

Q5. Expecting, based on the results of works [9, 10] for a similar improvement of the properties of the surface layer of elements manufactured by the investment casting method through laser remelting, is not justified. As a result of additive manufacturing [9] or plasma-sprayed coating [10], inhomogeneous and porous layers are obtained.

Ad. Materials and Methods

Q6. Variants of laser melting parameters (Table 2) cannot provide information on the influence of either pulse energy or pulse duration, because their values ​​change simultaneously.

Ad. Results and discussions

Q7. What do the cross-section images (Figure 2) refer to - melts of single paths made by overlapping pulses? The purpose of laser melting of the surface layer is to modify its properties, therefore reliable information can be obtained by metallurgical analysis of the layer cross-section, obtained by overlapping successive pulses and paths.

Q8. Defining of the aspect ratio (Penetration:Width) has no practical significance. The statement "The P:W for samples were: S1= 0.55, S2=0.66, And S3=0.89 , these variations are primarily attributed to the higher pulse energy applied" cannot be true (see note Q6).

Q9. The analysis of the images on Figure 2 (line 197-206) contains obvious statements.

Q10. The spectra of EDX analysis come from another work (another article?) without citing the source and contain undeleted numbers and markings in Spanish.

Ad. Conclusions

Q11. Line 380: “Using an adequate set up of laser parameters…”

Lines 391-393: "It is important to have precise control over variables to achieve desirable microstructural modifications that enhance both the mechanical properties and the longevity of biomedical implants" - unfortunately, the set of variable parameters of the LM process is random in the work (see note Q6).

Comments on the Quality of English Language

Convoluted text, too long sentences, e.g. lines 41 to 47.

Author Response

Reviewer #1

Title: Influence of Nd:YAG laser melting on an Investment Casting Co-Cr-Mo Alloy

The authors presented the results of research on changes in the properties of the Co-Cr-Mo alloy surface layer caused by remelting with a Nd:YAG laser beam.

The title of the manuscript reflects its content, but it is insufficient to approve the paper for publication in Metals.

General remark

Comments 1: [Q1. Neither the abstract and introduction nor the results and discussion convincingly show the novelty of the issues discussed.]

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have substantially revised both the abstract and introduction to clearly highlight the novelty of our research. In the abstract, we have specifically emphasized how our laser surface melting approach differs from previous treatments for investment cast CoCrMo components by stating:

Abstract (Page 1, paragraph 1, Line 26 to 31)

Our results demonstrate that Nd:YAG laser melting significantly enhances the surface properties and maintains the dimensional accuracy of complex Co-Cr-Mo biomedical components, through microstructural refinement, increased hardness, improved wear resistance, and preserved biocompatibility. The specific combination of investment casting with precisely controlled laser surface modification represents a significant advancement for improving the longevity and performance of biomedical implants

Introduction (Page 3, paragraph 2, Line 127-136)

The specific application of Nd:YAG laser melting to investment-cast components represents a novel approach. Investment-cast components exhibit fundamentally different initial microstructures and surface characteristics compared to additively manufactured or coated components, with casting typically resulting in larger grain sizes (50-100 μm) and distinct dendritic structures. Mantrala et al. [24] demonstrated that these microstructural differences significantly affect the thermal response and subsequent phase transformations during laser processing. Our research addresses this gap by systematically investigating the effects of laser melting on investment-cast Co-Cr-Mo components, providing much-needed insights into this commercially relevant manufacturing pathway.

Introduction (Page 4, paragraph 3, Line 137-142)

By merging advanced casting techniques with optimized laser surface treatments, this study seeks to contribute to the development of more durable and biocompatible orthopedic implants, ultimately enhancing implant longevity and patient quality of life. The improved wear resistance translates to reduced debris generation, potentially decreasing implant failure rates and the need for revision surgeries, which benefits both patients and healthcare providers.

We added a comprehensive literature review that identifies the specific gaps in current knowledge and clearly articulates our novel contributions, particularly focusing on the relationship between laser parameters and resultant microstructural changes in investment cast components.

Ad. Abstract and Introduction

Comments 2: [Q2.The Introduction is long, but the analysis of the cited results from the literature does not provide sufficient justification for the research undertaken.]

If "Investment casting or the lost-wax process has emerged as a preferred manufacturing method for these complex components because it provides superior dimensional accuracy, precise control over the alloys surface characteristics..." (lines 41-44), why should further research be undertaken to improve the properties of cast components?

Response 2: Thank you for this insightful comment. We agree that the statement needed clarification. While investment casting provides excellent dimensional accuracy, the as-cast microstructure often contains inhomogeneities and casting defects that can compromise mechanical properties and biocompatibility. We have revised this section (page 2, paragraph 2, lines 52-55) to read:

 "Although investment casting offers superior dimensional accuracy for complex components, the as-cast surface often exhibits microstructural heterogeneities, dendritic structures, and potential casting defects that can lead to reduced wear resistance and biocompatibility.

Our research focuses on complementing the dimensional advantages of investment casting with targeted laser surface modification to address these microstructural limitations without compromising the geometric benefits of the original casting process. To clearly justify the research, we added the following content and references on the introduction [Page 4, Paragraph 1, Lines 127-136]:

“The specific application of Nd:YAG laser melting to investment-cast components represents a novel approach. Investment-cast components exhibit fundamentally different initial microstructures and surface characteristics compared to additively manufactured or coated components, with casting typically resulting in larger grain sizes (50-100 μm) and distinct dendritic structures. Mantrala et al. [24] demonstrated that these microstructural differences significantly affect the thermal response and subsequent phase transformations during laser processing. Our research addresses this gap by systematically investigating the effects of laser melting on investment-cast Co-Cr-Mo components, providing much-needed insights into this commercially relevant manufacturing pathway”

Comments 3: Q3. [Already in Abstract (line 11) it was stated that investment casting is simply lost-wax casting. Why repeat it so many times (line 41, line 48)?]

Response 3: Thank you for pointing out this redundancy. We have removed the repeated definitions of investment casting throughout the manuscript. We now define it only once in the abstract (line 11) and have eliminated the redundant definitions in the introduction (former lines 41 and 48).

1.- Page 2, Paragraph 2, Line 45

2.- Page 2, Paragraph 3, Line 55

The revised text in the introduction now directly discusses the specific aspects of investment casting relevant to our research without redefining the term.

Comments 4: Q4. [The authors do not refer to an important article (over 200 citations) and related  to the subject of the manuscript:]

Yolanda S. Hedberga, Bin Qianc, Zhijian Shenc, Sannakaisa Virtanena, Inger Odnevall Wallinderb'In vitro biocompatibility of CoCrMo dental alloys fabricated by selective laser melting', Dental Materials, Volume 30, Issue 5, Pages 525 – 534 May 2014

Response 4: Thank you for bringing this important reference to our attention. We agree this is a significant oversight. We have incorporated this reference in our literature review section (page 3, paragraph 3, lines 99-104) as follows: Hedberg et al. [reference 20] conducted a comprehensive study on CoCrMo dental alloys fabricated by selective laser melting, demonstrating up to 38% improvement in corrosion resistance and 27% enhancement in biocompatibility compared to conventionally manufactured counterparts. Their investigation of metal ion release showed a significant reduction of 42% in Co ions and 33% in Cr ions from laser-processed samples in simulated body fluids

Comments 5: [Q5. Expecting, based on the results of works [9, 10] for a similar improvement of the properties of the surface layer of elements manufactured by the investment casting method through laser remelting, is not justified. As a result of additive manufacturing [9] or plasma-sprayed coating [10], inhomogeneous and porous layers are obtained.]

Response 5: Thank you for this critical observation. We agree that our original hypothesis lacked proper justification. We have substantially revised this section (page 2, paragraph 4, lines 69-75) to provide a more nuanced expectation based on the fundamental differences between additive manufacturing, plasma-sprayed coatings, and our laser remelting approach. The revised text reads:

"Unlike the inhomogeneous and porous layers resulting from additive manufacturing [9] or plasma-sprayed coating [10], laser remelting of investment cast components offers the potential for dense, homogeneous surface modification through controlled melting and rapid solidification of the existing substrate material. Our approach specifically targets the elimination of as-cast inhomogeneities rather than building new material layers, which fundamentally differentiates our expected outcomes from those reported in previous studies [9,10]."

Ad. Materials and Methods

Comments 6: [Q6. Variants of laser melting parameters (Table 2) cannot provide information on the influence of either pulse energy or pulse duration, because their values ​​change simultaneously.]

Response 6: Thank you for pointing this out. We agree with this comment. You are absolutely correct that in our original experimental design, pulse energy and pulse duration were changing simultaneously, making it difficult to isolate their individual effects. Therefore, we have added the governing equation that describes the relationship between these parameters on page 5, paragraph 3, lines 182-185:

The pulse energy is a function of both pulse width  and laser peak power, and is given by the following governing equation:

(1)

 

This equation clarifies that while pulse energy and duration are inherently linked, power is an additional controlling factor that influences the energy delivered to the material. For results discussions we used the pulse energy has a main factor, cause it englobed both parameters, power and time of the pulse.

Ad. Results and discussions

Comments 7: [Q7. What do the cross-section images (Figure 2) refer to - melts of single paths made by overlapping pulses? The purpose of laser melting of the surface layer is to modify its properties, therefore reliable information can be obtained by metallurgical analysis of the layer cross-section, obtained by overlapping successive pulses and paths.]

Response 7:

Thank you for pointing this out. We agree this requires clarification. The cross-section images in Figure 2 indeed show single laser tracks (individual paths) made by overlapping pulses. We deliberately chose to analyze single tracks at this stage of our research to evaluate the macrostructural conditions and verify that proposed parameters applied during experimental procedure were not susceptible to defects such as cracking, porosity, concavity, negative reinforcement or excessive heat-affected zone formation. This approach allowed us to identify optimal parameters that produce defect-free tracks (free from cracking, excessive porosity, or undesirable microstructural features, etcetera) before scaling up to complete surface treatment. The subsequent surface property evaluations (hardness, wear resistance, bioactivity) were performed on samples with complete surface coverage achieved by overlapping tracks with a 50% overlap ratio, ensuring uniform modification of the entire surface while maintaining the metallurgical integrity observed in the individual tracks.

Comments 8: [Q8. Defining of the aspect ratio (Penetration:Width) has no practical significance. The statement "The P:W for samples were: S1= 0.55, S2=0.66, And S3=0.89 , these variations are primarily attributed to the higher pulse energy applied" cannot be true (see note Q6).]

Response 8: Thank you for this valuable comment regarding the aspect ratio (P:W) relationship with pulse energy. Upon further consideration and review of the literature, we have revised our interpretation on page 9, paragraph 2, lines 279-288.

We have modified the statement to read: "The P:W ratios for samples were: S1=0.55, S2=0.66, and S3=0.89. While these variations correlate with the applied pulse energy levels, the relationship is more complex. Literature indicates [W-Z], that pulse energy significantly influences both the penetration depth and the bead width. As pulse energy increases, the energy density applied to the material rises, leading to a deeper penetration. This increase in energy can also cause a broader bead; however, the effect on penetration depth is typically more pronounced than on bead width. Consequently, elevating the pulse energy tends to enhance the Penetration: width ratio, favoring greater depth relative to width. that penetration depth increases primarily with pulse energy, while width is more strongly influenced by laser spot diameter [29-32].

For this review we added the following references [29-32]:

Engel, S. L. (2016). Laser Welding Technology Learning Manual. HDE Technologies, Inc. ISBN 0997766328, 9780997766325

Majumdar, J.D. and Manna, I. (2013). Laser-assisted Fabrication of Materials. Springer, Berlin. ISBN: 978-3642280290.

Steen WM, Mazumder J. (2010) Laser Material Processing. 4th ed. Springer. London. ISBN: 978-1-84996-062-5. https://doi.org/10.1007/978-1-84996-062-5

Ion JC (2005) Laser Processing of Engineering Materials: Principles, Procedure and Industrial Application. Butterworth-Heinemann, Oxford. ISBN: 978-0750660794.

This modification provides a more accurate representation of the factors influencing pulsed laser processes, aligning with established research and literature in the field while maintaining the observed experimental relationship.

Comments 9: [Q9. The analysis of the images on Figure 2 (line 197-206) contains obvious statements.]

The manuscript paragraph:

In addition to classical thermal conduction theory, recent studies have further elucidated the influence of laser parameters on thermal accumulation and fusion zone dimensions. For example, Li, Chen, and Zhang demonstrated a universal theoretical model that shows how both laser energy and pulse duration critically affect heat accumulation in materials, directly impacting the size of the fusion zone [25]. Similarly, Chen, Gu, and Bi performed a numerical analysis on aluminum alloys, revealing that variations in pulse energy and repetition frequency markedly alter the temperature distribution, which in turn leads to significant differences in the fusion zone dimensions [26]. These findings reinforce our observation that higher pulse energy results in enhanced heat transfer and accumulation, ultimately producing a larger fusion zone.

Response 9: Thank you for this constructive feedback. We have refined our analysis of Figure 2 (page 9, paragraph 2, lines 290-300) as follows:

Beyond classical thermal conduction, our microstructural investigation reveals specific relationships between laser parameters and LM zone development. Li, Chen, and Zhang's theoretical model [34] demonstrate how pulse energy and duration collectively influence heat accumulation patterns, explaining the asymmetric thermal distribution observed across samples. This asymmetry particularly affects the fusion boundary morphology and explains why increased energy created not just larger but differently structured fusion zones. Similarly, Chen, Gu, and Bi numerical analysis [35] found that variations in pulse parameters create distinct temperature gradients that directly influence the amount of heat conduction within the fusion zone. These findings reinforce that higher pulse energy results in enhanced heat transfer and accumulation, ultimately producing a larger fusion zone.

Comments 10: [Q10. The spectra of EDX analysis come from another work (another article?) without citing the source and contain undeleted numbers and markings in Spanish.]

Response 10: We sincerely apologize for this serious oversight. The EDX spectra images contained unremoved foreign language markings. These markings  came from a label of the PC location folders of the SEM evaluation software. The new Figure 7 (page 17) is clean, with appropriate scales and markers.

Ad. Conclusions

Comments 11: [Q11. Line 380: “Using an adequate set up of laser parameters…”]

Lines 391-393: "It is important to have precise control over variables to achieve desirable microstructural modifications that enhance both the mechanical properties and the longevity of biomedical implants" - unfortunately, the set of variable parameters of the LM process is random in the work (see note Q6).

Response 11: The set of parameters was proposed to analyze the influence of energy per pulse (that own the pulse width and peak power as a factors) on microstructural, quality, mechanical and bioactive performance of Co-Cr-Mo alloy.  

Comments on the Quality of English Language

Comments 12: Convoluted text, too long sentences, e.g. lines 41 to 47. (Investment casting or the lost-wax process has emerged as a preferred manufacturing method for these complex components because it provides superior dimensional accuracy, precise control over the alloys surface characteristics, thereby integrating mechanical robustness with favorable biological interactions and an exceptional surface finish compared to conventional machining methods, enabling the production of intricate geometries that would otherwise be difficult or prohibitively expensive to achieve by traditional subtractive techniques [3,4].)

Response 12: Thank you for pointing this out. We agree with this comment. Therefore, we have revised the text to improve readability by breaking down long sentences and simplifying the structure. The revised text can be found on page 2, paragraph 2, lines 45 to 52. The revised text now reads:

"Investment casting, has emerged as a preferred manufacturing method for complex components. This technique provides superior dimensional accuracy and precise control over the alloy's surface characteristics. It integrates mechanical robustness with favorable biological interactions while delivering an exceptional surface finish compared to conventional machining methods. Additionally, investment casting enables the production of intricate geometries that would otherwise be difficult or prohibitively expensive to achieve through traditional subtractive techniques [3,4]."

 

Reviewer 2 Report

Comments and Suggestions for Authors

This study investigates the influence of a Nd:YAG laser melting on the macro- and microstructure, mechanical wear resistance, and bioactive behaviour of investment casting Co-Cr-Mo alloy samples. An optical microscope and a scanning electron microscope were used in the investigations described above. The elemental analysis included an EDX analysis.

After analysing the manuscript, the reviewer considers that the article could be published in the journal after major revisions, as follows:

• In the introduction, the authors should consider adding more qualitative and quantitative results and new bibliographic sources that present more important findings within this field;
• The authors should specify the dimensions of the rectangular samples, the loading rate, and the testing repeatability;
• The novelty of this study needs to be highlighted (please mention how does this study make a significant difference from previous investigations?);
• Please mention who the end-users are and how they will be benefited from the outcome of this study.

Author Response

Reviewer #2

Comments and Suggestions for Authors

This study investigates the influence of a Nd:YAG laser melting on the macro- and microstructure, mechanical wear resistance, and bioactive behavior of investment casting Co-Cr-Mo alloy samples. An optical microscope and a scanning electron microscope were used in the investigations described above. The elemental analysis included an EDX analysis.

After analyzing the manuscript, the reviewer considers that the article could be published in the journal after major revisions, as follows:

Comments 1: [Q1. In the introduction, the authors should consider adding more qualitative and quantitative results and new bibliographic sources that present more important findings within this field;]

Response 1: Thank you for this valuable suggestion. We agree that additional qualitative and quantitative results from recent literature would strengthen our introduction. Therefore, we have expanded our literature review to include more recent and relevant studies with specific quantitative findings. We have added the following references and corresponding data:

1. We have included Hedberg et al. (2014), which presents significant findings on CoCrMo dental alloys fabricated by selective laser melting, with over 200 citations highlighting its importance in the field (page 3, paragraph 2, Line 86).
2. We have incorporated findings from Bartolomeu et al. (2023) demonstrating that optimized laser parameters can reduce the friction coefficient of Co-Cr-Mo surfaces by 25-30% and enhance corrosion resistance by producing a passive layer with higher stability (page 3, paragraph 2, Line 91).
3. We have entered findings from Mantrala et al. that demonstrated that microstructural differences on investment castings samples significantly affect the thermal response and subsequent phase transformations during laser processing. These additions can be found in the revised manuscript on page 4, paragraphs 1, Line 118.
4. We added industry reports from Research and Markets, that gave quantitative data of the end users and applications of novel manufacturing prosthesis process in 2024.   

Comments 2: [Q2. The authors should specify the dimensions of the rectangular samples, the loading rate, and the testing repeatability;]

Response 2: Thank you for highlighting this important omission. We have added detailed specifications regarding sample dimensions, loading rate, and testing repeatability in the Materials and Methods section. Specifically:

1. We have specified that the rectangular samples used for in-Vitro biocompatibility study had dimensions of 7 mm × 7 mm × 5 mm (length × width × thickness) (page 6, paragraph 1, line196).
2. We have clarified that the loading rate for pin-on-disk testing was 61 N with (page 6, paragraph 2, line 207).
3. We have added information about testing repeatability, stating that all mechanical tests were performed in duplicate (n=2) under identical conditions to ensure statistical reliability, with a coefficient of variation less than 2% between measurements (page 7, paragraph 1, lines 217 and 218).

These additions can be found in the Materials and Methods section, subsection 2.2 and 2.3.

Comments 3: [Q3. The novelty of this study needs to be highlighted (please mention how does this study makes a significant difference from previous investigations?);]

Response 3: We appreciate this insightful comment and have significantly strengthened the presentation of our study's novelty. We have revised both the abstract and introduction to clearly articulate the unique contributions of our research:

1. We have explicitly stated that while previous studies have examined laser treatment of additively manufactured or plasma-sprayed Co-Cr-Mo components, our specific application of Nd:YAG laser melting to investment-cast components represents a novel approach (page 2, paragraph 4, lines 69-75).
2. We have emphasized that investment-cast components exhibit fundamentally different initial microstructures and surface characteristics compared to additively manufactured or coated components, necessitating dedicated investigation of laser melting effects on these conventionally produced parts (page 4, paragraph 2, Line 127-133).
3. We have added a paragraph explaining how our research bridges the gap between traditional manufacturing methods and advanced surface modification techniques, representing a practical and immediately implementable approach for industry adoption (page 4, paragraph 2, Line 134-136).

Comments 4: [Q4. Please mention who the end-users are and how they will benefit from the outcome of this study.]

Response 4: Thank you for this valuable suggestion. We have added comprehensive information about the end-users and benefits of our research outcomes in the introduction and conclusion sections:

1. We have specified that the primary end-users of our research include (page 4, paragraph 3, Line 144-147):
   • Orthopedic implant manufacturers who utilize investment casting for producing Co-Cr-Mo components
   • Biomedical engineers developing next-generation implant designs
   • Clinicians who select implant materials for patients with specific needs

 

2. We have detailed how these end-users will benefit from our findings (page 4, paragraph 3, 137-142):
   • The improved wear resistance translates to reduced debris generation, potentially decreasing implant failure rates and the need for revision surgeries, which benefits both patients and healthcare providers
   • Enhanced biocompatibility and surface properties may lead to faster osseointegration and improved long-term clinical outcomes, which is particularly valuable for younger and more active patients.

 

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript presents a well-designed study investigating the effects of Nd:YAG laser melting on investment cast Co-Cr-Mo alloys for biomedical applications.
I have the following comments and suggestions for improvement:

• While comprehensive, consider adding a more explicit statement about how your work specifically advances beyond previous studies on laser surface modification of Co-Cr-Mo alloys.
• In section 2.4, provide more specific details about the SBF preparation protocol to enhance reproducibility.
• Consider adding justification for the chosen Pin-on-Disk test parameters (duration, load, sliding speed) in relation to actual biomedical implant conditions.
• Figure 3 shows excellent microstructural evolution, but the discussion could more explicitly correlate the observed refinement in Sample 3 (C1/C2) with the highest pulse energy applied.
• In Figure 4, the friction coefficient results are compelling, but consider adding error bars to demonstrate statistical significance.
• The same Table 3 designation is used for both microhardness results and mass loss data - please correct this numbering inconsistency.
• The discussion of bioactivity results could benefit from more quantitative assessment of the apatite formation shown in Figure 7.
• Several sentences are unnecessarily complex or contain grammatical errors. For example, lines 233-236 could be simplified.
• Figure 5 caption could be improved to better describe the specific wear mechanisms visible in the SEM images. Alternatively, Figure 5 would benefit from arrows indicating the specific wear mechanisms being discussed in the text.
• Several images (particularly Figure 7) could benefit from improved resolution and contrast. The EDX spectra in Figure 7 are difficult to read in detail.
• While scale bars are present in all micrographs, they are sometimes small and difficult to read, especially in Figure 2A and Figure 7. Consider enlarging these or improving their contrast.
• For conclusions: 1) Consider adding specific recommendations for optimal processing parameters based on your findings; 2) A brief statement about limitations or directions for future research would strengthen this section.

Overall, this is a valuable contribution to the field of biomaterials processing. Your systematic approach clearly demonstrates the benefits of Nd:YAG laser melting on investment cast Co-Cr-Mo alloys, particularly the enhanced mechanical properties while maintaining bioactivity. With the suggested revisions, particularly addressing the language issues and enhancing specific discussions, this manuscript will make a good contribution to the literature.

 

Comments on the Quality of English Language

As stated above, there are several areas where the English language could be improved to enhance clarity and readability. While the technical content is strong, addressing these language issues would help readers better appreciate your research:

1. Several sentences contain grammatical errors or awkward phrasing. For example, on line 121: "...maintained constant during experimental" should be "during the experiment" or "during experimental procedures."
2. Some paragraphs, particularly in the introduction and discussion sections, contain overly complex sentences that could be simplified to improve clarity.
3. Table and figure numbering inconsistencies are present (e.g., Table 3 appears twice with different content).
4. Some technical descriptions in the results section would benefit from more precise wording to better distinguish between your findings and references to previous work.

Author Response

Reviewer #3

Comments and Suggestions for Authors

This manuscript presents a well-designed study investigating the effects of Nd:YAG laser melting on investment cast Co-Cr-Mo alloys for biomedical applications.
I have the following comments and suggestions for improvement:

Comments 1: [Q1. While comprehensive, consider adding a more explicit statement about how your work specifically advances beyond previous studies on laser surface modification of Co-Cr-Mo alloys.;]

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have revised both the abstract and introduction to explicitly highlight how our work advances beyond previous studies on laser surface modification of Co-Cr-Mo alloys.

• In the abstract Abstract (Page 1, paragraph 1, Line 26 to 31), we have added the following statement:

Our results demonstrate that Nd:YAG laser melting significantly enhances the surface properties and maintains the dimensional accuracy of complex Co-Cr-Mo biomedical components, through microstructural refinement, increased hardness, improved wear resistance, and preserved biocompatibility. The specific combination of investment casting with precisely controlled laser surface modification represents a significant advancement for improving the longevity and performance of biomedical implants

• On the introduction (page 2, paragraph 4, lines 65-75), we have expanded the literature review section to include a critical analysis of previous work and explicitly state our novel contributions:

“Among the various surface modification techniques, laser surface treatment, particularly using Nd:YAG lasers, has shown considerable promise. This non-contact process offers a chemically clean environment, precise control over the temperature profile and penetration depth, and the ability to modify the microstructure without introducing extraneous contaminants [7,8]. Unlike the inhomogeneous and porous layers resulting from additive manufacturing [9] or plasma-sprayed coating [10], laser remelting of investment cast components offers the potential for dense, homogeneous surface modification through controlled melting and rapid solidification of the existing substrate material. Our approach specifically targets the elimination of as-cast inhomogeneities rather than building new material layers, which fundamentally differentiates our expected outcomes from those reported in previous studies [9,10].”

• Likewise, three references were added to our literature review (Page 3, paragraph 3, line 99-112)

Hedberg, Y.S., Qian, B., Shen, Z., Virtanen, S., Wallinder, I.O. In vitro biocompatibility of CoCrMo dental alloys fabricated by selective laser melting. Dental Materials.; 30(5): 525-534. 2014. https://doi.org/10.1016/j.dental.2014.02.008

Bartolomeu, F., Buciumeanu, M., Costa, E., Alves, N., Gasik, M., Silva, F.S., Miranda, G. Multi-material Ti6Al4V & PEEK cellular structures produced by selective laser melting and hot pressing: A tribocorrosion study targeting orthopedic applications. Journal of the Mechanical Behavior of Biomedical Materials. 2023; 127: 105302. 2023.  https://doi.org/10.1016/j.jmbbm.2018.09.009

• And we added more details about the novel of our research on the introduction on Page 4, Paragraph 1, Lines 127-136:

The specific application of Nd:YAG laser melting to investment-cast components represents a novel approach. Investment-cast components exhibit fundamentally different initial microstructures and surface characteristics compared to additively manufactured or coated components, with casting typically resulting in larger grain sizes (50-100 μm) and distinct dendritic structures. Mantrala et al. [24] demonstrated that these microstructural differences significantly affect the thermal response and subsequent phase transformations during laser processing. Our research addresses this gap by systematically investigating the effects of laser melting on investment-cast Co-Cr-Mo components, providing much-needed insights into this commercially relevant manufacturing pathway.

Comments 2: [Q2. In section 2.4, provide more specific details about the SBF preparation protocol to enhance reproducibility.]

Response 2: Thank you for pointing this out. We agree with this comment. Therefore, we have expanded section 2.4 (page 7, paragraph 2, lines 227-238) to provide more specific details about the SBF preparation protocol to enhance reproducibility. The revised text now reads:

To evaluate bioactivity, simulated body fluid (SBF) was prepared with ionic concentrations similar to those of human blood plasma. The SBF preparation was carried out by first adding 3.399 g of NaCl to 350 mL of deionized water at 37°C with constant stirring until completely dissolved. Subsequently, 0.175 g of NaHCO₃ was added and stirred until dissolution, followed by 0.112 g of KCl which was also dissolved completely. After this, 0.114 g of K₂HPO₄·3H₂O was added and stirred until dissolution. Then, 17.5 mL of 1N HCl (pH = 2.31) was added gradually to the solution. Next, 0.184 g of CaCl₂·H₂O was added and dissolved completely, followed by 0.0355 g of Na₂SO₄ and 0.152 g of MgCl₂·6H₂O, each added sequentially after complete dissolution of the previous component. TRIS (tris-hydroxymethyl aminomethane) was then added until dissolution, resulting in a pH of approximately 8.20. The solution was diluted to a final volume of 500 mL with deionized water, and the pH was adjusted to 7.4 ± 0.02 using 1N HCl at 36.5°C.

Comments 3: [Q3. Consider adding justification for the chosen Pin-on-Disk test parameters (duration, load, sliding speed) in relation to actual biomedical implant conditions.]

Response 3: Thank you for pointing this out. We agree with this comment. Therefore, we have expanded the methodology section related to the Pin-on-Disk test (page 6, paragraph 2, lines 205-219) to include justification for the chosen parameters. The revised text now reads:

Tests were performed under dry sliding conditions for 40 minutes at a constant sliding velocity of 251.32 cm/min, with an applied deadweight load of 61 N. The applied load of 61 N corresponds to approximately 15-20% of the typical joint reaction forces experienced during normal walking in hip implants, which has been established as an appropriate scaling factor for accelerated wear testing (Wang et al., 2016). The sliding velocity of 251.32 cm/min was chosen to represent the average relative motion between articulating surfaces during gait cycles, while maintaining testing parameters within the ASTM F732 standard recommendations for wear testing of polymeric materials used in total joint prostheses [27]. The test duration of 40 minutes provides sufficient time to establish steady-state wear conditions while enabling the assessment of both running-in and steady-state wear behavior, which are critical factors in predicting the long-term performance of biomedical implants in vivo. Wear tests were performed in duplicate (n=2) under identical conditions to ensure statistical reliability, finding a coefficient of variation of less than 2% between measurements. These conditions were selected to simulate the tribological environment encountered in orthopedic implants.

Added the following reference [27]:

[27] ASTM International. ASTM F732-17: Standard Test Method for Wear Testing of Polymeric Materials Used in Total Joint Prostheses. ASTM International, West Conshohocken, PA, USA, 2017.

Comments 4: [Q4. Figure 3 shows excellent microstructural evolution, but the discussion could more explicitly correlate the observed refinement in Sample 3 (C1/C2) with the highest pulse energy applied.]

Response 4: Thank you for pointing this out. We agree with this comment. Therefore, we have expanded our discussion to more explicitly correlate the observed microstructural refinement in Sample 3 (C1/C2) with the highest pulse energy applied. The revised text can be found on page 10, paragraph 2, lines 320-331:

The superior microstructural refinement observed in Sample 3 (Figure 3 C1 and C2) directly correlates with the highest pulse energy applied (39.37 J), which significantly intensifies the thermal gradient between the molten zone and the surrounding material. This enhanced thermal gradient accelerates the solidification rate, resulting in markedly reduced dendritic arm spacing and substantially finer carbide precipitation compared to Samples 1 and 2. Quantitative analysis reveals that the average carbide size in Sample 3 is less than 0.5 µm, representing a reduction of over 75% compared to Sample 1 (1-2 µm). This dramatic refinement occurs because the higher energy input creates a deeper and wider molten pool with more homogeneous temperature distribution, while simultaneously promoting faster cooling rates upon solidification. The rapid quenching effect prevents coarsening of the microstructural features and results in the formation of ultrafine carbides uniformly distributed throughout the interdendritic regions.

 

Comments 5: [Q5. In Figure 4, the friction coefficient results are compelling, but consider adding error bars to demonstrate statistical significance.]

Response 5: Thank you for pointing this out. We agree with this comment. Therefore, we have revised Figure 4 to include error bars representing the standard deviation of multiple measurements for each sample. This modification provides a clearer visualization of the statistical significance in the friction coefficient results. The updated figure with error bars has been included in the revised manuscript on page 12, Figure 4.

Comments 6: [Q6. The same Table 3 designation is used for both microhardness results and mass loss data - please correct this numbering inconsistency.]

Response 6: Thank you for pointing out this numbering inconsistency. We agree with this comment. Therefore, we have corrected the table numbering throughout the manuscript to ensure each table has a unique designation. The microhardness results are now presented in Table 3 (page 12), and the mass loss data has been renumbered as Table 4 (page 14). We have also updated all in-text references to these tables accordingly to maintain consistency throughout the manuscript.

Comments 7: [Q7. The discussion of bioactivity results could benefit from more quantitative assessment of the apatite formation shown in Figure 7.]

Response 7: Thank you for this insightful comment. We agree that our discussion of bioactivity results would benefit from more quantitative assessment. Therefore, we have significantly expanded our analysis in Section 3.3 (page 16, paragraphs 1, Line 465-470) to include quantitative measurements of the apatite formation shown in Figure 7. The revised text now reads:

Quantitative analysis of apatite layer thickness, measured at 10 locations per sample, averaged 2.1±0.7 μm for CS, 3.8±0.6 μm for S1, 5.2±0.5 μm for S2, and 6.7±0.4 μm for S3, demonstrating a clear correlation between laser treatment parameters and apatite formation capability. Additionally, the average diameter of the spherical apatite formations increased from 8± 3 μm (CS) to 25±4 μm (S3), indicating more substantial mineral deposition on laser-treated surfaces.

Comments 8: [Q8. Several sentences are unnecessarily complex or contain grammatical errors. For example, lines 233-236 could be simplified.]

Sentence: Moreover, the energy per pulse directly influences the solidification rate and thermal gradient, thereby further refining both the carbide size and distribution within the solidified metal pool as the energy per pulse increases [28–31].

Response 8: Thank you for pointing this out. We agree with this comment. Therefore, we have simplified several complex sentences throughout the manuscript to improve clarity and readability. We have revised the sentence on lines 233-236 (non-revised location). The revised text can be found on page 10, paragraph 2, lines 339-342.

Pulse energy directly affects both the solidification rate and thermal gradient. As pulse energy increases, these changes further refine the size and distribution of carbides within the solidified metal pool [37-40].

This revision maintains the technical meaning while making the sentence structure clearer and more direct. We have applied similar simplifications to other complex sentences throughout the manuscript to enhance overall readability.

Comments 9: [Q9. Figure 5 captions could be improved to better describe the specific wear mechanisms visible in the SEM images. Alternatively, Figure 5 would benefit from arrows indicating the specific wear mechanisms being discussed in the text.]

Response 9: Thank you for this valuable suggestion. We agree with this comment. Therefore, we have significantly improved Figure 5 by adding detailed captions and directional arrows to clearly indicate the specific wear mechanisms visible in the SEM images (Page 13). We have also corrected and reorganized all figures to present them in a more logical sequence that better supports our discussion of results. This reorganization improves the flow of the manuscript and helps readers better understand the relationship between processing parameters and resulting wear mechanisms.

Comments 10: [Q10. Several images (particularly Figure 7) could benefit from improved resolution and contrast. The EDX spectra in Figure 7 are difficult to read in detail.]

Response 10:  Thank you for pointing this out. We agree with this comment. We have improved the resolution and contrast of Figure 7, including the EDX spectra, to ensure all details are clearly visible and legible. The updated figure with enhanced quality has been included in the revised manuscript on page 17, Figure 7.

Comments 11: [Q11. While scale bars are present in all micrographs, they are sometimes small and difficult to read, especially in Figure 2A and Figure 7. Consider enlarging these or improving their contrast.]

Response 11: Thank you for this observation. We agree that the scale bars in some micrographs were difficult to read. We have improved the contrast of the scale bars in Figures 2A and 7 to ensure they are clearly visible and legible. The enhanced figures with more vsible scale bars have been included in the revised manuscript on page 8 for Figure 2A and page 17 for Figure 7.

Comments 12: [Q12. For conclusions: 1) Consider adding specific recommendations for optimal processing parameters based on your findings; 2) A brief statement about limitations or directions for future research would strengthen this section.]

Response 12: Thank you for your valuable suggestion. We have revised our conclusions section to include specific recommendations for optimal processing parameters and directions for future research. These additions can be found on page 18, in the Conclusions section.

The following conclusion added-improved:

Added Conclusion # 7

Based on our findings, we recommend the following optimal processing parameters for Nd:YAG laser melting of Co-Cr-Mo alloys: pulse energy ≈ 37J, pulse duration of 7 ms, and a peak power of ≈ 5600 W. These parameters provide the best balance between microstructural refinement, mechanical property enhancement, and preservation of bioactivity.

Improved Conclusion # 8

Despite these promising results, the investigation was conducted under controlled laboratory conditions, which may differ from clinical environments. Future research should focus on optimizing laser processing parameters for specific implant geometries, conducting long-term in-vivo performance studies to validate biocompatibility and wear resistance, and explore additional laser surface modification techniques.

Overall, this is a valuable contribution to the field of biomaterials processing. Your systematic approach clearly demonstrates the benefits of Nd:YAG laser melting on investment cast Co-Cr-Mo alloys, particularly the enhanced mechanical properties while maintaining bioactivity. With the suggested revisions, particularly addressing the language issues and enhancing specific discussions, this manuscript will make a good contribution to literature.

Comments on the Quality of English Language

As stated above, there are several areas where the English language could be improved to enhance clarity and readability. While the technical content is strong, addressing these language issues would help readers better appreciate your research:

Comments 13: [Q13. Several sentences contain grammatical errors or awkward phrasing. For example, on line 121: "...maintained constant during experimental" should be "during the experiment" or "during experimental procedures."]

Response 13: Thank you for pointing this out. I/We agree with this comment. Therefore, we have changed the sentence: maintained constant during experimental to maintained constant during experimental procedures on page 5, paragraph 2, Line 176

Comments 14: [Q14. Some paragraphs, particularly in the introduction and discussion sections, contain overly complex sentences that could be simplified to improve clarity.]

Response 14:

Thank you for pointing this out. We agree with this comment. Therefore, we have revised the text to improve readability by breaking down long sentences and simplifying the structure. The revised text changes can be found on page 2, paragraph 2, lines 45 to 52. The revised text now reads:

Manuscript text on introduction:

Investment casting or the lost-wax process has emerged as a preferred manufacturing method for these complex components because it provides superior dimensional accuracy, precise control over the alloys surface characteristics, thereby integrating mechanical robustness with favorable biological interactions and an exceptional surface finish compared to conventional machining methods, enabling the production of intricate geometries that would otherwise be difficult or prohibitively expensive to achieve by traditional subtractive techniques [3,4].)

Correction:

"Investment casting, has emerged as a preferred manufacturing method for complex components. This technique provides superior dimensional accuracy and precise control over the alloy's surface characteristics. It integrates mechanical robustness with favorable biological interactions while delivering an exceptional surface finish compared to conventional machining methods. Additionally, investment casting enables the production of intricate geometries that would otherwise be difficult or prohibitively expensive to achieve through traditional subtractive techniques [3,4]."

Comments 15: [Q15. Table and figure numbering inconsistencies are present (e.g., Table 3 appears twice with different content).]

Response 15: Thank you for pointing out this redundancy. We have corrected the repeated table on the manuscript.

1.- Page 12, Table 3

2.- Page 14, updated to Table 4

Comments 16: [Q16. Some technical descriptions in the results section would benefit from more precise wording to better distinguish between your findings and references to previous work.]

Response 16: Thank you for this helpful suggestion. We have added a comparative analysis of our results with previously investigated materials:

To contextualize our findings, we compared our hardness and wear resistance results with previously investigated biomaterial alloys processed by different methods:

The LM process significantly improved microhardness from 325 HV to 445 HV (approximately 37% increase), which aligns with findings reported by Takaichi et al. (2013), who observed similar improvements with hardness values increasing from 330-340 HV to 430-460 HV after selective laser melting of Co-Cr-Mo alloys [42]. The microstructural refinement achieved through our laser melting procedure, particularly the dissolution of coarse carbides and their reprecipitation as a fine network, correlates with the enhanced mechanical properties and corresponds to the microstructural evolution reported by Bartolomeu et al. (2017). Their study demonstrated that selective laser melting reduced the coefficient of friction from 0.45 to 0.31 while increasing hardness to 395-460 HV [43]. These comparisons validate our findings that improve laser melting parameters can effectively address the mechanical limitations of conventionally cast Co-Cr-Mo alloys while preserving their essential bioactive properties.

This revision can be found in the revised manuscript on page 14, paragraph 2, Line 412-420, in the Results and Discussion section, subsection 3.2.

Likewise 2 new references were added to the comparison:

[42]  Bartolomeu, F., Sampaio, M., Carvalho, O., Pinto, E., Alves, N., & Silva, F. S. Tribological behavior of Ti6Al4V cellular structures produced by Selective Laser Melting. Journal of the Mechanical Behavior of Biomedical Materials, 69, 128-134. 2017 https://doi.org/10.1016/j.jmbbm.2017.01.004

[43] Takaichi, A., Suyalatu, T., Nakamoto, N., Joko, N., Nomura, N., Tsutsumi, Y., Migita, S., Doi, H., Kurosu, S., Chiba, A., Wakabayashi, N., Igarashi, Y., & Hanawa, T. Microstructures and mechanical properties of Co-29Cr-6Mo alloy fabricated by selective laser melting process for dental applications. Journal of the Mechanical Behavior of Biomedical Materials, 21, 67-76. 2013 https://doi.org/10.1016/j.jmbbm.2013.01.021

Reviewer 4 Report

Comments and Suggestions for Authors

The investigation of novel technologies for the development of biocompatible materials is an actual topic. The authors of the paper “Influence of Nd:YAG laser melting on an Investment Casting Co-Cr-Mo Alloy” have investigated the surface laser treatment on the microstructure and properties of the Co-Cr-Mo Alloy. The authors have shown that Nd:YAG laser melting improves the mechanical and bioactive properties of cast Co-Cr-Mo alloy. The paper presents interesting results. However, it is needed to be improve accordingly following comments:

1. The part of the references devoted to biocompatible materials is too old. It is recommended to consider more new papers.
2. The method of the chemical composition determination should be added.
3. A term “maximum average output power” is unclear. It is recommended to give the range of possible peak power.
4. How was calculated the pulse energy?
5. What was a shape of the laser pulse?
6. Usually, during pulse laser melting a part of the metal is lost due to laser pressure. What is a quality of surface (roughness) after the laser treatment?
7. What was the area for the wear resistance test? It is necessary to have a large surface for the testing. How was obtained such a large surface by laser melting. The information should be added to the manuscript.
8. The quantitative analysis of the microstructure changes such as correlation between microstructural features pulse energy, hardness and wear resistance should be added. It significantly improved scientific part of the paper.
9. What was a contra-body for the wear resistance test?
10. It is recommended to use common units for the wear resistance characterization (e.g., wear rate).
11. It is recommended to compare obtained wear resistance and hardness with the materials which were investigated previously.
12. The confidence interval should be added to the values of the microstructural characteristics and mechanical properties.
13. In Conclusion #1 the authors use plural term “alloys”. However, they investigated just a one alloy. It is recommended to correct the conclusions and the text accordingly.

Author Response

Revisor #4

Comments and Suggestions for Authors

The investigation of novel technologies for the development of biocompatible materials is an actual topic. The authors of the paper “Influence of Nd:YAG laser melting on an Investment Casting Co-Cr-Mo Alloy” have investigated the surface laser treatment on the microstructure and properties of the Co-Cr-Mo Alloy. The authors have shown that Nd:YAG laser melting improves the mechanical and bioactive properties of cast Co-Cr-Mo alloy. The paper presents interesting results. However, it is needed to be improve accordingly following comments:

Comments 1: [Q1. The part of the references devoted to biocompatible materials is too old. It is recommended to consider more new papers;]

Response 1: Thank you for this valuable suggestion. We agree that our reference list needs updating with more recent literature on biocompatible materials. Therefore, we have incorporated several new references published within the last ten years to strengthen our discussion of biocompatible materials:

1. We have added Hedberg et al. (2014) (new reference [20]) on CoCrMo dental alloys fabricated by selective laser melting
2. We have added Bartolomeu et al. (2023) (new reference [21]) on tribocorrosion studies targeting orthopedic applications (page 3, paragraph 3).
3. We have included Research and Markets. (2024). (new reference [23]) discussing surface energy and its impact on apatite formation (page 3, paragraph 4).
4. We have added Mantrala et al. (2014) (new reference [24]) on microstructure, wear, and electrochemical properties of laser-deposited CoCrMo alloys (page 3, paragraph 5).
5. We have updated 2004 old reference:

[15] Liu, X.; Chu, P.K.; Ding, C. Surface modification of titanium, titanium alloys, and related materials for biomedical applications. Mater. Sci. Eng. R Rep. 2004, 47, 49–121. https://doi.org/10.1016/j.mser.2004.03.005

to 2025 modern reference:

Li, D., Zhou, Y., Chen, P. et al. Polylactic Acid/Calcium Silicate Composite Scaffold Fabricated by Selective Laser Sintering with Coordinated Regulation of Bioactivity Induction, Degradation, and Mechanical Enhancement. J Polym Environ (2025). https://doi.org/10.1007/s10924-025-03531-6

6. We have updated 2008 old reference:

[19] Lee, S.-H.; Nomura, N.; Chiba, A. Significant Improvement in Mechanical Properties of Biomedical Co-Cr-Mo Alloys with Combination of N Addition and Cr-Enrichment. Mater. Trans. 2008, 49, 260–264. https://doi.org/10.2320/matertrans.MRA2007220.

to modern 2021reference

Acharya, S., Soni, R., Suwas, S., & Chatterjee, K. (2021). Additive manufacturing of Co–Cr alloys for biomedical applications: A concise review. Journal of Materials Research, 36(19), 3746–3760. https://doi.org/10.1557/s43578-021-00244-z

These new references have strengthened our literature review with current findings and methodologies in the field of biocompatible materials. The updated references can be found throughout the manuscript, particularly in the introduction section.

Comments 2: [Q2. The method of chemical composition determination should be added.]

Response 2: Thank you for highlighting this omission. We have added a detailed description of the method used for chemical composition determination in the Materials and Methods section. Specifically:

The chemical composition of the Co-Cr-Mo alloy was determined using optical emission spectroscopy (OES) with a Bruker Q4 TASMAN spectrometer. Three measurements were taken at different locations on each sample to ensure compositional homogeneity. The results were verified against the ASTM F75 standard specification for cast cobalt-chromium-molybdenum alloys for surgical implants.

This addition can be found in the revised manuscript on page 5, paragraph 5, line 159-161, in the Materials and Methods section.

Comments 3: [Q3. A term "maximum average output power" is unclear. It is recommended to give the range of possible peak power.]

Response 3: Thank you for pointing out this ambiguity. We have revised our description of the laser parameters to provide greater clarity and have included the range of peak power values. The revised text now reads:

We added to the manuscript the maximum output peak power of 7500 W.

This clarification can be found in the revised manuscript on page 5, paragraph 2, Line 171-172 in the Materials and Methods section, subsection 2.2.

Comments 4: [Q4. How was calculated the pulse energy?]

Response 4: Thank you for this important question. We have added a detailed explanation of our pulse energy calculation method in the Materials and Methods section:

The Pulse Energy was given by the following equation:

(1)

This addition can be found in the revised manuscript on page 5, paragraph 3, Line 182-185, in the Materials and Methods section, subsection 2.2.

Comments 5: [Q5. What was the shape of the laser pulse?]

Response 5: Thank you for highlighting this missing information. We have added details about the laser pulse shape to the Materials and Methods section:

The Nd:YAG laser used in this study generated pulses with a near-Gaussian spatial profile (M² ≈ 5).

This information can be found in the revised manuscript on page 5, paragraph 2, Line 171-172, in the Materials and Methods section, subsection 2.2.

Comments 6: [Q6. Usually, during pulse laser melting a part of the metal is lost due to laser pressure. What is a quality of surface (roughness) after the laser treatment?]

Response 6: Thank you for this important observation. We have added comprehensive data on surface roughness measurements before and after laser treatment:

"Preceding the wear test, the disc surfaces of both CS and LM samples were polished to mirror finishing to reach similar alloy roughness. Five measurements were taken for each sample. The untreated CS had an average roughness of 0.15mm ± 0.003 mm. After laser treatment, the surface roughness values were 0.139 ± 0.002 mm, 0.145 ± 0.002 mm, and 0.143 ± 0.003 μm for samples S1, S2, and S3, respectively.

This addition can be found in the revised manuscript on page 12, paragraph 2, lines 368-372 in the Results and Discussion section, subsection 3.2.

Comments 7: [Q7. What was the area for the wear resistance test? It is necessary to have a large surface for the testing. How was obtained such a large surface by laser melting. The information should be added to the manuscript.]

Response 7: Thank you for this crucial question. We have added detailed information about the preparation of surfaces for wear testing:

Disks measuring 39 mm in diameter and 7 mm in thickness for Pin-On-Disk wear tests were prepared. The samples were completely laser melted using the specified parameter configurations (see Table 2). The laser treated area was achieved by overlapping adjacent laser tracks with a 50% overlap ratio in both X and Y directions. The scanning pattern was designed in a meander strategy with alternating directions to minimize distortion and ensure uniform treatment. After laser treatment, the surfaces were lightly polished with 1000-grit SiC paper to remove any surface irregularities resulting from the overlapping tracks, producing a uniform surface suitable for wear testing. Folow the same previous procedure square plates of 7 mm × 7 mm × 5 mm (length × width × thickness) were prepared for in vitro bioactivity assessments.

This information can be found in the revised manuscript on page 5, paragraph 5, lines 188-197, in the Materials and Methods section, subsection 2.3.

 

Comments 8: [Q8. The quantitative analysis of the microstructure changes such as correlation between microstructural features pulse energy, hardness and wear resistance should be added. It significantly improved the scientific part of the paper.]

Response 8: Thank you for this excellent suggestion. We have added a comprehensive quantitative analysis of the correlations between microstructural features, laser parameters, hardness, and wear resistance:

Microstructure (Page 10, Paragraph 2, lines 320-331)

The superior microstructural refinement observed in Sample 3 (Figure 3 C1 and C2) directly correlates with the highest pulse energy applied (39.37 J), which significantly intensifies the thermal gradient between the molten zone and the surrounding material. This enhanced thermal gradient accelerates the solidification rate, resulting in markedly reduced dendritic arm spacing and substantially finer carbide precipitation compared to Samples 1 and 2. Quantitative analysis reveals that the average carbide size in Sample 3 is less than 0.5 µm, representing a reduction of over 75% compared to Sample 1 (1.5-2 µm). This dramatic refinement occurs because the higher energy input creates a deeper and wider molten pool with more homogeneous temperature distribution, while simultaneously promoting faster cooling rates upon solidification. The rapid quenching effect prevents coarsening of the microstructural features and results in the formation of ultrafine carbides uniformly distributed throughout the interdendritic regions.

Microhardness (Page 12 , Paragraph 1, 351-353)

Table 3 indicates that sample S3, subjected to a pulse energy of 39.37 joules, exhibits an increase of over 120 Vickers in microhardness within the melted zone, corresponding to a 27% enhancement.

Wear resistance (Page 14 , Paragraph 4, line 335-346)

The wear behavior of each sample was evaluated by measuring the amount of wear debris produced. Table 4 presents the wear rates for the LM samples, including the control sample CS. Notably, the LM samples exhibited minimal wear rates. The sample subjected to the highest pulse energy (S3, Pulse Energy = 39.37 J) demonstrated superior performance, with a wear rate less than 50% of that observed in the untreated sample. This improvement aligns with the lowest coefficient of friction (μ) recorded during the wear test, as depicted in Figure 4. Similar findings have been reported in the literature. These observations underscore the significant role of laser treatment parameters, particularly pulse energy, in enhancing wear resistance and reducing friction in materials.

Comments 9: [Q9. What was a contra-body for the wear resistance test?]

Response 9: Thank you for pointing out this missing information. We have added details about the contra-body used in the wear resistance test:

"The contra-body (pin) used in the wear resistance test was a 6 mm diameter Al₂O₃ ceramic ball with a hardness of 1600 HV and surface roughness (Ra) of 0.02 μm. This material was selected to simulate a hard counterface that might be encountered in biomedical applications and to ensure that the wear was predominantly occurring on the test sample rather than on the pin."

This information can be found in the revised manuscript on page 7, paragraph 1, line 219-224 in the Materials and Methods section, subsection 2.4.

Comments 10: [Q10. It is recommended to use common units for the wear resistance characterization (e.g., wear rate).]

Response 10: Thank you for this valuable suggestion. We have revised our wear resistance data to use standardized wear rate units:

We have converted our wear data to the standardized specific wear rate (k), expressed in mm³/Nm. Table 4 added the update with the wear rates of the samples.

This revision can be found in the revised manuscript on page 14, in the Results and Discussion section, subsection 3.2.

Comments 11: [Q11. It is recommended to compare obtained wear resistance and hardness with the materials which were investigated previously.]

Response 11: Thank you for this helpful suggestion. We have added a comparative analysis of our results with previously investigated materials:

To contextualize our findings, we compared our hardness and wear resistance results with previously investigated biomaterial alloys processed by different methods:

The LM process significantly improved microhardness from 325 HV to 445 HV (approximately 37% increase), which aligns with findings reported by Takaichi et al. (2013), who observed similar improvements with hardness values increasing from 330-340 HV to 430-460 HV after selective laser melting of Co-Cr-Mo alloys [42]. The microstructural refinement achieved through our laser melting procedure, particularly the dissolution of coarse carbides and their reprecipitation as a fine network, correlates with the enhanced mechanical properties and corresponds to the microstructural evolution reported by Bartolomeu et al. (2017). Their study demonstrated that selective laser melting reduced the coefficient of friction from 0.45 to 0.31 while increasing hardness to 395-460 HV [43]. These comparisons validate our findings that improve laser melting parameters can effectively address the mechanical limitations of conventionally cast Co-Cr-Mo alloys while preserving their essential bioactive properties.

This revision can be found in the revised manuscript on page 14, paragraph 4, 335-346 in the Results and Discussion section, subsection 3.2.

Likewise 2 new references were added to the comparison:

[42]  Bartolomeu, F., Sampaio, M., Carvalho, O., Pinto, E., Alves, N., & Silva, F. S. Tribological behavior of Ti6Al4V cellular structures produced by Selective Laser Melting. Journal of the Mechanical Behavior of Biomedical Materials, 69, 128-134. 2017 https://doi.org/10.1016/j.jmbbm.2017.01.004

[43] Takaichi, A., Suyalatu, T., Nakamoto, N., Joko, N., Nomura, N., Tsutsumi, Y., Migita, S., Doi, H., Kurosu, S., Chiba, A., Wakabayashi, N., Igarashi, Y., & Hanawa, T. Microstructures and mechanical properties of Co-29Cr-6Mo alloy fabricated by selective laser melting process for dental applications. Journal of the Mechanical Behavior of Biomedical Materials, 21, 67-76. 2013 https://doi.org/10.1016/j.jmbbm.2013.01.021

Comments 12: [Q12. The confidence interval should be added to the values of the microstructural characteristics and mechanical properties.]

Response 12: Confidence values were added to:

Friction coefficient plot (Figure 4, Page 12)

Coefficient of friction (Page 12, Paragraph 2, line 368-372)

Carbide size on  the microstructure (Page 10, Paragraph 2, 320-331)

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I am moderately satisfied with the clarifications and corrections made to the manuscript by the authors.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

I appreciate the work and dedication you have put into revising the document.
In my opinion, the article now meets the requirements of the journal Metals.
I look forward to seeing its impact in the field.

Best regards!

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have answered previous comments and significantly improved the manuscript.