Physical and Mechanical Properties of Ti-Zr-Nb Alloys for Medical Use

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 The manuscript entitled “Physical and Mechanical Properties of Ti-Zr-Nb Alloys for Medical Use”, focuses on the investigation of the physical and mechanical properties of Ti-(36-40)Zr-9Nb alloys (at.%). The authors compared the structure, phase composition and mechanical properties of the abovementioned materials. The topic of the paper is interesting and relevant. However, there are significant gaps in the text. I would like to recommend its publication in this journal after addressing the following recommendations:

 

1.     The abstract should be elaborated. In it, the authors said that “The ingots obtained had a dendritic structure” while in the text, no structure of the ingots was revealed. Conclusion is missing

The aim of the study should be clearly stated at the end of the introduction section.

2.     The spelling of the alloys must be uniform and therefore, “Ti-9Nb-36Zr alloy” should be corrected (line 99).

3.     The spelling “[Mo]экв” should be improved;

4.     No information was given about how were the alloys protected from oxidation (the white zone) during the homogenization annealing, rolling and hardening.

5.     How was the grain size of the alloys evaluated? No such methodology was mentioned in Section 2….Moreover, the authors stated a precise size: “The grain size after quenching is 170 µm”. This size seems statistically unreliable.

6.     No XRD patterns were shown in the paper. In that way, important information such as that for the texture of the samples, is missing. The crystal lattices of β` and α'' should be indicated in the text. More comments are needed.

7.     Since the Mo_eq shows that the alloys should have α + β phase structure, no explanation is given for the observed only β phase composition.

8.     How many samples of each type have been subjected to tensile tests? This size seems statistically unreliable. Moreover, tables 3, 4 and 5 should be combined in one.

9.      No information about the fractographic SEM image acquisition is given in Section 2. In Figure 10, indications of fracture origination and propagation as well as areas with ductile, brittle fracture should be added.

10. The abbreviation of the alloy “VT6” should be replaced by a proper indication.  

 

11. The reference style should also be improved following the journal’s requirements. More up-to-date references are needed. 

Author Response

Thank you for your attention and time to evaluate and help correct inaccuracies in the article.

Comments 1: The abstract should be elaborated. In it, the authors said that “The ingots obtained had a dendritic structure” while in the text, no structure of the ingots was revealed. Conclusion is missing. The aim of the study should be clearly stated at the end of the introduction section.

Response 1: We agree with this comment. The abstract has been expanded. Images of microstructure after ingot melting have been added to the main text. Conclusion has been added.Purpose has been clarified at the end of the introduction section.

Comments 2: The spelling of the alloys must be uniform and therefore, “Ti-9Nb-36Zr alloy” should be corrected (line 99).

Response 2: We agree with this comment. Fixed.

Comments 3:  The spelling “[Mo]экв” should be improved;

Response 3: We agree with this comment. Fixed.

Comments 4: No information was given about how were the alloys protected from oxidation (the white zone) during the homogenization annealing, rolling and hardening.

Response 4: We agree with this comment. The information added.

Comments 5: How was the grain size of the alloys evaluated? No such methodology was mentioned in Section 2….Moreover, the authors stated a precise size: “The grain size after quenching is 170 µm”. This size seems statistically unreliable.

Response 5: We agree with this comment. The omitted methodology has been entered in the appropriate section. The error with the indication of dimensions has been corrected.

Comments 6: No XRD patterns were shown in the paper. In that way, important information such as that for the texture of the samples, is missing. The crystal lattices of β` and α'' should be indicated in the text. More comments are needed.

Response 6: We agree with this comment. Missing X-ray diffraction analysis samples have been contributed to the article in the results section. Type of crystal lattices indicated. Stable beta and unstable beta have a similar lattice, but their behavior is different under mechanical stress.

Comments 7: Since the Mo_eq shows that the alloys should have α + β phase structure, no explanation is given for the observed only β phase composition.

Response 7: We agree with this comment. α + β phases are observed in the post annealing state. Mechanical action and quenching transfer the phase composition to other phases. Since unstable β is required in the final form of the material, the studies presented in the paper confirm that machining and quenching under the described regime bring the material to the desired state. An explanation has been added to the article.

Comments 8: How many samples of each type have been subjected to tensile tests? This size seems statistically unreliable. Moreover, tables 3, 4 and 5 should be combined in one.

Response 8: We agree with this comment. Fixed an error with the description of sample sizes. The working part was thinner than the gripping part. Tensile results between specimens were within the expected error. The tables have been merged

Comments 9: No information about the fractographic SEM image acquisition is given in Section 2. In Figure 10, indications of fracture origination and propagation as well as areas with ductile, brittle fracture should be added.

Response 9: We agree with this comment. Missing method information has been added. Tags are plotted and described.

Comments 10: The abbreviation of the alloy “VT6” should be replaced by a proper indication.  

Response 10: We agree with this comment. The brand of the composition is renamed to the commonly used brand.

Comments 11: The reference style should also be improved following the journal’s requirements. More up-to-date references are needed. 

Response 11: We agree with this comment. Incorrect reference 4 has been corrected. Actual links have been added.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The submitted article presents the production of three Ti-Zr-Nb alloys with varying Zr content as an alternative for common Ti alloys used for medical implants. The alloys are processed with rolling and quenching to stabilize the β-phase, followed by investigation of their mechanical properties for comparison to the mechanical properties of bones. The production steps, investigation methods and discussion is sound, while some corrections of the work might improve the manuscript before acceptance:

1. It is mentioned that Al and V may be detrimental to health when released from implant from conventional Ti alloys. The introduction should also include any documented biocompatibility risks when using Zr or Nb in alloys for implants.

2. The materials and methods section may be broken-up into several subchapters.

3. How were the Zr and Nb contribution values for stabilising the β-phase obtained in the Mo equivalent calculation?

4. The descriptions for Figures 6 and 7 are the same (Cyclic loading of the alloy Ti-36Zr-9Nb), while the images are different. Should be corrected.

5. Why was the Ti-38Zr-9Nb alloy tested with a cyclical loading of 2, 3 and 6 %, while the other alloys were not?

6. Why is superelasticity a desired property? Some explanation is missing in the text why it was measured and what are the conclusions from the obtained results.

7. Reference number 4 is not in a correct format.

Comments on the Quality of English Language

English language editing is recommended for the manuscript:

- Lines 128-133: The text mentions that the billets were rolled from a dimension of 18 mm “up to” 1 mm in three steps. This is mentioned 3x and is confusing while reading the text. Would this processing not be described as rolling “down to” 1 mm, as the final and intermediate dimensions are smaller than the initial one?

- The same sentence is repeated in lines 141-144.

- The descriptions of Figures 1 and 2 need spellchecking.

Author Response

Thank you for your attention and time to evaluate and help correct inaccuracies in the article.

Comments 1: It is mentioned that Al and V may be detrimental to health when released from implant from conventional Ti alloys. The introduction should also include any documented biocompatibility risks when using Zr or Nb in alloys for implants.

Response 1: We agree with this comment. Added information on recent safety studies of niobium and zirconium, their oxides and alloys. In general, these materials have excellent biocompatibility and no information has been found that their use poses greater risks than other materials.

Comments 2: The materials and methods section may be broken-up into several subchapters.

Response 2: We agree with this comment. Broken-up the section into 3 parts: production, research preparation, research methods.

Comments 3: How were the Zr and Nb contribution values for stabilising the β-phase obtained in the Mo equivalent calculation?

Response 3: We agree with this comment. These studies have not been conducted by our laboratory, we used the experience of other scientists described in articles and manuals. In general, according to the accumulated experience, it can be noted that this method may not be confirmed by practice under all conditions. In addition, it can be noted that the estimated phase composition is obtained only after annealing, the mode of which also needs to be selected for each composition separately. However, this method is acceptable as a first step for evaluation.

Comments 4: The descriptions for Figures 6 and 7 are the same (Cyclic loading of the alloy Ti-36Zr-9Nb), while the images are different. Should be corrected.

Response 4: We agree with this comment. The typo has been corrected.

Comments 5: Why was the Ti-38Zr-9Nb alloy tested with a cyclical loading of 2, 3 and 6 %, while the other alloys were not?

Response 5: We agree with this comment. The rationale was presented in the article. Since the Ti-38Zr-9Nb composition showed the minimum residual strain, it aroused more interest as it is necessary to understand what is the maximum value of tensile strain under cyclic deformation that does not cause residual strain.

Comments 6: Why is superelasticity a desired property? Some explanation is missing in the text why it was measured and what are the conclusions from the obtained results.

Response 6: We agree with this comment. The superelasticity is accompanied by hysteresis behavior of the load-unload line, which is characteristic of bone tissue behavior. Closer mechanical behavior to bone tissue is a priority. The information was entered in the article

Comments 7: Reference number 4 is not in a correct format.

Response 7: We agree with this comment. Fixed.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have substantially improved their manuscript.