Laser Beam Welding of a Ti-15Mo/TiB Metal–Matrix Composite

Round 1

Reviewer 1 Report

Interesting investigation, however major revisions are needed:

1. “Laser beam welding (LBW) is a relatively new promising welding technology which allows …” (line 50). This technology is not relatively new…
2. In the introduction: “Aluminum-matrix composites can also be successfully joined using laser beam welding [30-32], however this joining technology of titanium metal-matrix composites was rarely considered [33, 34].” (lines 53/54). The authors should add further information related to the laser beam welding applied to titanium metal-matrix composites, describing the experiments and the results achieved.
3. In Materials and Procedure, the procedure used to measure the TiB particles.
4. The authors analysed the size of the pores based only in the macrographs results. Why the pores identified in the radiographs was not take into account? The authors should discuss about the pore formation, including both technical analysis results. The conclusion about this defect also should be revised.
5. Which is the solidification temperature of the TiB particles (line 154-155)? This information should be added to the discussion.
6. The author associated the increased of the hardness values in the RT with the presence of ω phase (line 200). However, the values of the 200ªC conditions are similar. Did the authors observe the ω phase in the pre-heat conditions? In addition, the comments about the characteristics of the ω phase formation should include other studies to support it.
7. Overall, the results obtained should be discussed and compared to other studies.

Author Response

Dear Editor, Dear Reviewers!

Many thanks for your careful revising of our manuscript and very useful comments and suggestions. We have modified the text along the comments (all modifications are highlighted by yellow). Below are our responses to the Reviewer’s comments/questions.

Reviewer #1

“Laser beam welding (LBW) is a relatively new promising welding technology which allows …” (line 50). This technology is not relatively new…

We have modified the text (lines 50-51).

In the introduction: “Aluminum-matrix composites can also be successfully joined using laser beam welding [30-32], however this joining technology of titanium metal-matrix composites was rarely considered [33, 34].” (lines 53/54). The authors should add further information related to the laser beam welding applied to titanium metal-matrix composites, describing the experiments and the results achieved.

Some information about the results of laser beam welding applied to titanium metal-matrix composites was added (lines 57-63).

In Materials and Procedure, the procedure used to measure the TiB particles.

The procedure of the TiB particles measurement was added (lines 101-103).

The authors analysed the size of the pores based only in the macrographs results. Why the pores identified in the radiographs was not take into account? The authors should discuss about the pore formation, including both technical analysis results. The conclusion about this defect also should be revised.

The analysis of pores was carried out using both the microstructure (a transverse section of the welded joints) and radiographs images (a general view of welded samples) (lines 154-158). Unfortunately, in the case of the analogous 2D X-ray radiography used in this study the resolution was not high enough to perform a quantitative analysis regarding the position of porosity and geometrical dimensions of pores. Therefore, the technique was used only for a qualitative assessment of the joints. The geometrical dimensions of the pores as well as their location in the joints are clearly visible in metallographic cross sections. A paragraph explaining the mechanism of pore formation was added to the manuscript text (lines 166-181).

Which is the solidification temperature of the TiB particles (line 154-155)? This information should be added to the discussion.

The solvus temperature of the TiB particles is ~ 2200 °C; this information was added to the text (line 185).

The author associated the increased of the hardness values in the RT with the presence of ω phase (line 200). However, the values of the 200 ªC conditions are similar. Did the authors observe the ω phase in the pre-heat conditions? In addition, the comments about the characteristics of the ω phase formation should include other studies to support it.

We observed ω phase particles after pre-heating temperature of 200°C, however, the quality of pictures were not good enough to include them into the paper. However the formation of the omega phase in this alloy (Ti-15Mo) is well known and well documented. Some additional description was added into the text (lines 250-253).

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

Thank you for an interesting paper added to the previously published series. Good luck with your further research!

Some detailed comments are available within the attached PDF manuscript file.

Regards

Your reviewer.

Comments for author File: Comments.pdf

Author Response

Dear Editor, Dear Reviewers!

Many thanks for your careful revising of our manuscript and very useful comments and suggestions. We have modified the text along the comments (all modifications are highlighted by yellow). Below are our responses to the Reviewer’s comments/questions.

Reviewer #2

In the line 29, the reviewer suggested changing from "Due to" to "Thanks to".

The text was modified.

An order of magnitude should be specified here. E.g. 'in the range of 1000 MPa'.

We have changed the wording in the sentence (lines 35-36).

The porosity of the experimental welds is understandable, given the technology used for the preparation of substrates, but it seems like a possible, significant setback to the practical use of both, the composite material and LBW method, as these discontinuities weaken the joint. Especially in figure 2 c the small pores form strands at the boundary between the weld and the base material, which is a highly unacceptable flaw in high quality welds. This promising technological advancement will need further development in order to overcome the problem.

A comment on such issues wolud improve the overall reception of the paper.

Thanks a lot for the valuable advice, a paragraph explaining the mechanism of pore formation is added to the manuscript text (lines 166-181).

Reviewer asked to correct the phrase in English version: «cracking is rather suggested high residual stresses» (line 160).

The corresponding text was modified (line 157).

Line 167: Microstostures → Microstructures.

Thanks for the valuable comment, the slip was corrected.

Figure 4:  footnote separated from the figure.

The corresponding modifications was done.

Line 178: Was that the intended word ('wearily' ???) ? Perhaps 'rarely"?

The slip was corrected.

The Authors are correctly making it obvious that the primary intention behind this work was to gain insight into the crystallographic structure of Ti based composite materials fabricated with the use of SBS and LBW technologies. The nano and micro-scale effects are described in an impressive manner. However, it is worth mentioning the adverse impact of the more macroscopic effects observed, such as porosity and cracking of the experimental welds, which are unacceptable in case of attempts at applying the new technology in real life. The problem is likely to be overcome as the development of the method progresses, nevertheless it deserves a mention and a short commentary.

Many thanks for this comment: a short remark was added: lines 179-181.

Author Response File: Author Response.pdf

Reviewer 3 Report

1. The subject corresponds to the content of the work
2. The selected research methodology is appropriate. The description of procedures does not require improvement.
3. The authors in the abstract write that they used pre-heating temperatures: 20, 200, 400 or 600 °C and that "The quality of laser beam welded joints was not found to be dependent noticeably on the pre-heating temperature". The next sentence: "... cracks can form during welding at room temperature". In my opinion, the two sentences do not match. It follows that the heating temperature affects the quality. I believe 20 °C should be removed from the list of pre-heating temperatures as this is not the pre-heating temperature (it is room temperature).
4. Please avoid collective citations, e.g. line from 37-42 present brief information without details, and in this short excerpt there are 6 references.
5. Line 69: what exactly was the difference before and after additional annealed at 1200 ° C in 24 h.
6. No numbering of photos in Figures in the form of (a), (b) etc.
7. Why the Figure 4 is in the table?
8. The authors used a 1 kg (1000 g) load to the hardness test. Therefore, hardness was tested and not microhardness. Microhardness is measured up to <200 g (some standards state <500g). Everything above is called hardness, so changes in this aspect are required. Please also correct the y-axis marking in the hardness diagram (Fig. 7).
9. Conclusions are clear presented in my opinion.

Author Response

Dear Editor, Dear Reviewers!

Many thanks for your careful revising of our manuscript and very useful comments and suggestions. We have modified the text along the comments (all modifications are highlighted by yellow). Below are our responses to the Reviewer’s comments/questions.

Reviewer #3

The authors in the abstract write that they used pre-heating temperatures: 20, 200, 400 or 600 °C and that "The quality of laser beam welded joints was not found to be dependent noticeably on the pre-heating temperature". The next sentence: "... cracks can form during welding at room temperature". In my opinion, the two sentences do not match. It follows that the heating temperature affects the quality. I believe 20 °C should be removed from the list of pre-heating temperatures as this is not the pre-heating temperature (it is room temperature).

Thank you, this phrase has been removed from the abstract.

Please avoid collective citations, e.g. line from 37-42 present brief information without details, and in this short excerpt there are 6 references.

We have reduced the number of collective citations.

Line 69: what exactly was the difference before and after additional annealed at 1200 ° C in 24 h.

Annealing at 1200 in 24 h was carried out to obtain a more chemically homogeneous structure in the composite; a short description has been added to the text (line 77).

No numbering of photos in Figures in the form of (a), (b) etc.

Numbering of photos in Figures in the form of (a), (b) is given with the text below under each figure.

Why the Figure 4 is in the table?

We have removed this table.

The authors used a 1 kg (1000 g) load to the hardness test. Therefore, hardness was tested and not microhardness. Microhardness is measured up to <200 g (some standards state <500g). Everything above is called hardness, so changes in this aspect are required. Please also correct the y-axis marking in the hardness diagram (Fig. 7).

We are sorry for this mistake. This part was rewritten as follows: Microhardness profiles across the joints were obtained using an automated Vickers hardness testing machine FALCON 5000 (INNOVATEST Europe BV, Maastricht, The Netherlands) with 2.942 N load (lines 106-107).

Author Response File: Author Response.pdf

Reviewer 4 Report

Very interesting work in the field of joining materials that are difficult to weld, such as metal composites. Based on the literature review, the authors correctly formulated the purpose and scope of the work. It is also good to describe the methodology of the experiment and the obtained results on the basis of which they formulated conclusions On this basis, I conclude that the article may be published in this form. 

Author Response

Dear Editor, Dear Reviewers!

Many thanks for your careful revising of our manuscript and very useful comments and suggestions. We have modified the text along the comments (all modifications are highlighted by yellow). Below are our responses to the Reviewer’s comments/questions.

Reviewer #4

Very interesting work in the field of joining materials that are difficult to weld, such as metal composites. Based on the literature review, the authors correctly formulated the purpose and scope of the work. It is also good to describe the methodology of the experiment and the obtained results on the basis of which they formulated conclusions On this basis, I conclude that the article may be published in this form.

Thank you very much for the appreciation of our work.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors hace changed the manuscript and now it can be accepeted in the present form.