Evolution of the Microstructure and Mechanical Properties of a Ti35Nb2Sn Alloy Post-Processed by Hot Isostatic Pressing for Biomedical Applications
Round 1
Reviewer 1 Report
In this paper, the influence of HIP post-processing steps on porosity, microstructures, and mechanical properties of a powder metallurgy Ti-Nb-Sn alloy is studied. It is shown that the HIP process is effective for reducing porosity. The influence of the cooling rate after the HIP process on phase stability and mechanical strength is also investigated. The findings of this paper should be of help for developing next-generation titanium alloys for orthopaedic and dental applications. The paper is well-written, in which the results are clearly presented (except for the flaw indicated below). For these reasons, I would recommend the paper to be accepted for publication in Metals, after the revisions indicated below.
- Figure 1 is missing.
- line 189: such us ---> such as
Author Response
The authors have download from MDPI website the article “metals-1273321” and Figure 1 appears in page three, at line 85. It seems a MS Word editor error that the figure 1 not appear on the Reviewer 1 file. But if the error is detected by MDPI editors the authors will send the Figure 1. For evidence, the article has been uploaded as PDF to avoid errors.
Authors reply to the typographical error “such us” to “such as” has been corrected at revision 2.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The work is good and presented nicely.
Unfortunately, the manuscript is inappropriate for being published under the present form. The paper could be published with minor revisions. In revising your paper please do kindly have in mind the following observations:
- In the abstract emphasize more the novelty of the research having in mind the question: why the reader should spend time to read this paper.
- In the Materials and Methods chapter may be useful a phase diagram.
- In the table 1 the text may be reorganized to fit in the table.
- Figure 1 may be reedited. It appears like a raw diagram in Word.
- Figure 4 must be relocated from Conclusions to Results and Disscutions.
- The Conclusion chapter should be rephrased. The authors may add a short phrase to give the readers an instant idea of the importance of the work. Also the limitations and the future work may be added.
Author Response
The work is good and presented nicely.
Unfortunately, the manuscript is inappropriate for being published under the present form. The paper could be published with minor revisions. In revising your paper please do kindly have in mind the following observations:
- In the abstract emphasize more the novelty of the research having in mind the question: why the reader should spend time to read this paper.
Authors reply, the following sentence have been added per reviewer recommendation:
“The HIP post-processing step is a required for developing next generation of advanced powder metallurgy titanium alloys for orthopedic and dental applications.”
- In the Materials and Methods chapter may be useful a phase diagram.
The authors reply consider that phase diagram can easily find in bibliography, additionally some phase diagrams can be found in the reference included in current article, such as for example D. Kuroka et al. (1998) or Long, M., & HJ, R. (1998).
- In the table 1 the text may be reorganized to fit in the table.
The authors agree with reviewer recommendation and in case that table 1 should be modified to fit will make the necessary reorganization to fit.
The authors have download from MDPI website the article “metals-1273321” and Table 1 seems to fit correctly. It seems a MS Word editor error that makes that Table 1 not fit correctly on the Reviewer 2 file. For evidence, the article has been uploaded as PDF to avoid errors.
- Figure 1 may be reedited. It appears like a raw diagram in Word.
The authors have download from MDPI website the article “metals-1273321” and Figure 1 appears in page three, at line 85. It seems a MS Word editor error that the figure 1 not appear on the Reviewer 2 file. But if the error is detected by MDPI editors the authors will send the Figure 1. For evidence, the article has been uploaded as PDF to avoid errors.
- Figure 4 must be relocated from Conclusions to Results and Disscutions.
The authors agree with reviewer recommendation and the Figure 4 has been relocated from “Conclusions” to “Results and Discussions”.
- The Conclusion chapter should be rephrased. The authors may add a short phrase to give the readers an instant idea of the importance of the work. Also the limitations and the future work may be added.
Per reviewer recommendation the following sentence have been updated:
“This study confirms that field-assisted consolidation processes, such as HIP, can be employed to reduce residual porosity and to increase the chemical and phase homogeneity of beta powder metallurgy titanium alloys, required for further develop advanced titanium alloys for biomedical field.”
The authors consider that the limitations and future work is currently exposed on the two last paragraphs of section ““Results and Discussions”.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript mainly presented a study on the effects of cooling rates on the microstructures and mechanical properties of Ti alloy.
1. As a classic research area, the related studies on the cooling process of HIP should be mentioned and compared to show the novelty of this study.
2. The microstructure data are mainly presented but the mechanical data are not enough. Please add the mechanical curves and fracture morphology after tests.
3. Only two cooling rats were used, but is it possible to include more rates to show the effects?
Author Response
Comments and Suggestions for Authors
The manuscript mainly presented a study on the effects of cooling rates on the microstructures and mechanical properties of Ti alloy.
- As a classic research area, the related studies on the cooling process of HIP should be mentioned and compared to show the novelty of this study.
Author reply:
The novelty of the study is based that the HIP process was applied in ternary beta titanium alloy obtained by powder metallurgy, instead of commercial melting low alloyed titanium alloys such as Ti6Al4V. This topic is cover on the Introduction section.
- The microstructure data are mainly presented but the mechanical data are not enough. Please add the mechanical curves and fracture morphology after tests.
The mechanical results are summarized in Table 3, since the titanium alloy samples present low deformation ratios further thermomechanical treatments (hot rolling, cold drawing, and ECAP) are required to improve their mechanical properties and obtain tensile curves similar to forged titanium alloys obtained per VAM+VIR/EBM.
The authors add the tensile curves on the reviewer's reply for information purposes.
- Only two cooling rats were used, but is it possible to include more rates to show the effects?
Authors reply per project limitations no more cooling rates were studied.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Accept.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The results presention and the results analysis should be improved:
the protocole of experiment should be precised (for metallographic analysis, for SEM and EBSD observation and for tensile tests): sample preparation, sample dimension, number of used samples or analysis zones, etc...
in all captions of tables and figures, it is important to precise the treatment condition (HIP 1 and HIP 2) to lead a quick understanding.
in table 2, it is necessary to precie what is the B phase ?
In figure 3, it is important to presznt also what are the figure D,E and F.
It is necessary also to present the SEM/EBSD/EDS results for HIP 1 and Vacuum Sintering samples.
It is important to give some explanation about the microstructure evolution and the associated mechancial properties feature.
In discussion and in conclusion, it is necessary to precise the different bewteen HIP 1 and HIP 2.
Author Response
Reply on the word file.
Author Response File: Author Response.pdf
Reviewer 2 Report
The present work deals with the effects of hot isostatic pressing condition on the microstructure and mechanical properties of Ti35Nb2Sn alloys. The aim of this work and condition set of sample preparation are suitable for further advance in the PM titanium alloy field. However, the manuscript contains serious grammar flaws, scientific error, lacks of sufficient experimental analysis and scientific discussion. For example, 1) this work only contains EBSD phase map result for HIP-2 specimen, which is not enough to support the authors' claims. 2) the tensile strength obtained from tensile tests is not flexual strength but ultimate tensile strength. 3) In EDS results, the authors' claimed that the elemental distribution is homogeneous, but as seen in EBSD results, it contains a'' precipitates. The reason for that is because the scale-length and resolution of EDS analysis is not suitable for the specimen to investigate elemental distribution. 4) It lacks scientific discussion about the present results, which means lack of scientific novelty. Considering the above mentioned features, the present manuscript is not appropriate for publication in Nanomaterials.
Author Response
Reply on the word file.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper is rather interesting, but some improvements should be introduce: - The introduction section must be extended, list of references must be expanded. - Please explain the choice of tested alloy, for which medical application can be used. - Please improve the quality of Fig. 2b - there are many scratches visable. - Mechanical results should be proved by tensile curves, please add them.
Author Response
Reply on the word file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
in the revised version of the manuscript, author has made necessary corrections including all ramarks from reviewers.
Author Response
Reviewer comments: In the revised version of the manuscript, the author has made necessary corrections including all remarks from reviewers.
Author: No reply required.
Reviewer 3 Report
Authors have tried to answer some reamrks but still some imrovements are required:
- Instroduction section should be extend and complete by much more references and literature data.
- Mechanical results are still confused, how UTS results were determined?
- Please compare tensile curves for samples - vacum sintering, HIP1 and HIP2
- Vacuum sintering is the same as conventional sintering?
- SEM observations of HIP1 samples are missing.
Author Response
Reviewer 3 second reply
Authors have tried to answer some remarks but still some improvements are required:
- The introduction section must be extended, list of references must be expanded.
Authors:
The following reviewer comments the three citations have added to extend the references in the introduction section.
Bolzoni, L., Ruiz-Navas, E. M., Zhang, D., & Gordo, E. (2012). Modification of sintered titanium alloys by hot isostatic pressing. Key Engineering Materials, 520(July 2014), 63–69. https://doi.org/10.4028/www.scientific.net/KEM.520.63
Molaei, R., Fatemi, A., & Phan, N. (2018). Significance of hot isostatic pressing (HIP) on multiaxial deformation and fatigue behaviors of additive manufactured Ti-6Al-4V including build orientation and surface roughness effects. International Journal of Fatigue, 117(July), 352–370. https://doi.org/10.1016/j.ijfatigue.2018.07.035
Lopez, M., Pickett, C., Arrieta, E., Murr, L. E., Wicker, R. B., Ahlfors, M., Godfrey, D., & Medina, F. (2020). Effects of postprocess hot isostatic pressing treatments on the mechanical performance of EBM fabricated TI-6Al-2Sn-4Zr-2Mo. Materials, 13(11). https://doi.org/10.3390/ma13112604
Mechanical results are still confused, how UTS results were determined?
Authors reply:
The UTS values were determined three points bending test, following standard ISO 3325 at a crosshead speed of 0.5 mm/min following standard ISO 3325.
The following sentence has been updated per reviewer recommendation:
“Tensile specimens were tested by a Shimadzu AG-X plus mechanical tester (Shimadzu, Kyoto, Japan) at a crosshead speed of 0.5 mm/min on three points bending test per standard ISO 3325.”
Please compare tensile curves for samples - vacum sintering, HIP1 and HIP2
Authors reply:
The strain values obtain on the three points bending test are summarized in Table 3, since the titanium alloy samples present low deformation ratios (around 3%) the authors consider that the graphical representation of the tensile curves for the three conditions studied are not required and it will be duplicated per Table 3 information.
Vacuum sintering is the same as conventional sintering? Yes
Authors reply:
The word “Vacuum” has been added on the following sentence to avoid misunderstandings per reviewer recommendation:
“The present paper proposes a processing route to obtain Ti35Nb2Sn based on conventional powder metallurgy (compact and vacuum sintering) and HIP post-processing. It aims to evaluate the effect of the HIP route on beta titanium powder metallurgy alloys (Ti35Nb2Sn) at different cooling rates.”
“A new beta titanium alloy with a nominal Ti35Nb2Sn composition was fabricated by using a conventional powder metallurgical route (press and vacuum sintering).”
“Figure 2. The microstructure of Ti35Nb2Sn according to its manufacturing condition. A) Conventional vacuum sintering at 1350 °C for 180 minutes. B) HIPed under 1200 ◦C, 150 MPa and cooling rate 500 °C/min. (HIP 1) C) HIPed under 1200 ◦C, 150 MPa and cooling rate 100 °C/min (HIP 2).”
SEM observations of HIP1 samples are missing.
Authors reply:
The author only to add the EBSD phase map result and SEM for HIP 2 to show the influence of the cooling rate on the α” phase precipitation that previously on the optical microscopy was considered as α phase. To support the author's claims the HIP 1 EBSD phase maps results have been added to this reply, present the same behavior observed on the etched Ti35Nb2Sn alloy observed by optical microscopy.
Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
The manuscript can be published, but authors should state in the paper if the tested alloys meet the criteria for biomedical applications. If yes, which biomedical uses can be proposed? Moreover, can we classified the tested titanium alloys as nanostructural metallic materials?
Author Response
Reviewer 3 third reply
The manuscript can be published, but authors should state in the paper if the tested alloys meet the criteria for biomedical applications. If yes, which biomedical uses can be proposed?
Moreover, can we classified the tested titanium alloys as nanostructural metallic materials?
Authors:
The closure of residual porosity allows the PM parts to be processed through plastic deformation metallurgical process required to obtain nanostructural metallic materials.
The following paragraph has been revised per reviewer recommendation:
“Developing an appropriate nanograin microstructure with optimum mechanical properties and good corrosion resistance is a challenging problem in the low modulus β-type titanium alloys field, which should be addressed in the biomedical industrial sector to obtain nanostructured materials for dental applications. This would imply the inclusion of an advanced thermo-mechanical process on the PM alloys after HIPing, such as hot drawing and working or ECAP, and heat treatments to improve ductility (≥ 10%) and meet the properties required for titanium alloys employed to manufacture prothesis [22-29].”
Additionally, on the chapter “4 Conclusion”:
“The HIPing post-process is a feasible treatment to eliminate the PM residual porosity, allowing to be processed on further plastic deformation metallurgic techniques to obtain a nanostructured titanium alloy, which are required to withstand long-time performance of implants.”
Author Response File: 
Author Response.docx
