Effects of Al and Heat Treatment on the Microstructure and Hardness of Ti–Al Synthesized via In Situ Melting using LENS

Round 1

Reviewer 1 Report

The paper entitled "Effects of Al and heat treatment on the microstructure and hardness of Ti-Al synthesised via in-situ melting using LENS” by Zhang et al deals with the laser heat treatment of an iron-nickel based alloy” by Tlotlengand Pityana deals with the production of Ti-Al parts by a directed energy deposition method (LENS®) and their microstructural analysis. Microhardness of produced parts has been also analysed. The influence of the post heat treatment on the microstructure and microhardness has been also analysed.

Results are in the scope of the Metals journal. These are interesting, but after reading the paper, I have some comments about it:

  

GENERAL COMMENTS:

             

1) The main problem of this paper is that general results can not be deduced or extrapolated for other experiments. For higher supplying of Al powder to the processing region the results indicate that the Al content does not increases in the corresponding parts. Instead, the Al content randomly varies. Therefore, subsequent results are hard to interpret. For example, after heat treatment the microhardness is maximum for sample D (mass flow rate 0.2 g/min); however, for a mass flow rate of 0.26 g/min (sample E) the microhardness drops. Therefore, the deduction of a trend related to the Al content is extremely difficult. Authors should, first, try to explain by the Al content randomly varies in samples from A to F. Then, a better connection of the microhardness with the microstructure should be done.

2) In general, the quality of the figures should be improved. It is rather difficult to observe the details in most of the figures.

 

PARTICULAR COMMENTS:

 

1) (Page 2, Line 62) Which is FGM? Functionally graded materials? Production of functionally graded materials is difficult with SLM, but it is not impossible (see. e.g.: Mumtaz, Kamran Aamir, and Neil Hopkinson. "Laser melting functionally graded composition of Waspaloy® and Zirconia powders." Journal of materials science 42.18 (2007): 7647-7656).

2)  (Page 2, Lines 109-110) Please, change “flowrate” with “flow rate”

3)  (Page 2, Table 1) Please, include the focal spot position and focal length

4)  (Page 2, Table 1) Why were the values provided in Table 1 selected? Are the optimum processing parameters? Which were the optimization criteria?

5)  (Page 6, Table 2) Aluminium content randomly varies with the increment of the Al flow rate; however, Ti content also varies (and is not decreasing as expected). Please, comment also this. Add errors to the Al and Ti content. Were these values measured in a very localized point? Were measured at similar locations for all the samples?

6) (Page 6, Line 177) The vaporization of Al is possible, but why is there a higher vaporization when the Al flow rate increases? Please, provide a plausible explanation. This part is very relevant for the subsequent explanations and should not be a future task.

7)   (Page 10, Figure 10) Please, add error bars.

8)    (Page 10, Lines 279-280) The higher hardness of sample D is attributed to the excess aluminium; however, why is not observed this in other samples? Why is not observed this is sample E with a much higher aluminium content?

Author Response

The rebuttal is attached as pdf file.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, the effects of Al content and post heat treatment on the microstructure of binary Ti-Al alloys produced via LENS system have been studied. Before further consideration the following issues should be considered and addressed:

1.      The structure and tense of some sentences are not appropriate for a scientific paper and so this aspect should be modified. For instance page 2 line 79-80, ‘I did not…..’

2.      In the introduction, a paragraph regarding the introduction of the LENS process should be inserted.

3.      According to the ISO standard, all the blown powder processes are recognized as directed energy deposition (DED) process and this definition should be clarified in the introduction.

For this aspect the following paper can be useful:

·        Saboori et al., An overview of additive manufacturing of titanium components by directed energy deposition: Microstructure and mechanical properties, Applied Sciences, vol. 7, issue 9, 883, 2017.  

4.      The resolution of all the Figures is very low and is not readable.

5.      The metallography procedure should be explained in details.

6.      Controlling the chemical composition by EDS is not precise and recommended so the presented results in table 2 are not reliable.

7.      The conclusion part is too short and should be expanded according to the findings of this work.

Author Response

Rebuttal is submitted as an pdf file attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In its present state, the paper entitled “Effects of Al and heat treatment on the microstructure and hardness of Ti-Al synthesised via in-situ melting using LENS” is acceptable for publication. Authors have addressed most of the concerns of the reviewer; however, some points should be corrected prior to the final publication of this paper:

Please, replace “laser in-situ      alloying” with “in-situ laser alloying” along the whole manuscript.

Reviewer 2 Report

The revision is satisfactory and thus this paper can be accepted in this form.