Effect of Reaction Temperature and Heat Treatment Time on Electrical and Mechanical Performance of TiB2 Particles and TiB Whiskers Reinforced Copper Matrix Composites
Round 1
Reviewer 1 Report
The paper presents the effect of reaction temperature and heat treatment time on electrical and mechanical performance of Copper composites with TiB2 particle + TiB whisker (TiB2p + TiBw) reinforcements. The results of the paper are interesting. However, to strengthen the article's scientific and presentation quality - the following changes are recommended.
(1) Use of abbreviation TiB2p + TiBw
(a) Title: Please avoid using abbreviations TiB2p + TiBw in the title. It is not a standard abbreviation known to all journal readers. Please explicitly mention that TiB2p is TiB2 particles and TiBw is TiB whiskers.
(b) Abstract and main text: Once again - please define what is TiB2p and TiBw in the first instance separately in abstract and main text. Then, please use the abbreviation consistently throughout.
Currently, the authors have directly used the abbreviation in line 12 (abstract) and line 64 (main text) without prior definition.
(2) Introduction
(a) To lead the readers into the material of focus in this study i.e., TiB2p + TiBw/Cu composites - the authors are to include in the introduction section (after line 29) why TiB2p + TiBw reinforcements are interesting compared to other reinforcements listed. The authors are also to provide some background on why they have chosen a system that combines particulate and whisker fillers. The related discussion is to be added in the manuscript.
(b) The authors have provided some description of prior work [Line 46-69] on in situ reaction casting of metal/TiB2 composites and how controlling reaction parameters might regulate Ti and B in situ reaction and affect composite mechanical and electrical performances. However, the knowledge gap that the authors are trying to fill in with their current study is unclear. The authors are to provide more information after line 69 - on what is missing in literature that their study tries to address. And therefore, bring out the novelty of their approach.
(c) In Line 65 - the authors very briefly refer to their previous work [ref. 19]. But the context is missing. In [19], the authors had dealt with the effect of rare earths on the microstructure and performances of TiB2p + TiBw/Cu composites. The authors are to (in the introduction section) explain the main findings of this work and then state that the current work extends the previous study in terms of analyzing the effects of reaction temperature and time.
Relatedly, in [19] - best tensile performances were achieved with Ce. In the current study, La has been chosen. The authors are to justify why La (not Ce) was chosen - in the introduction section.
(3) Materials and Methods
(a) Please add details in the text on the sample sizes used for tensile and conductivity tests. Also, please add information on the number of samples tested to present (presumably) the average values.
(b) Please add the image processing protocol (and software) used for obtaining the size of reinforcements (presented in figures 1 and 5). What is the definition of "size of reinforcement". In whiskers, for instance, was “size of reinforcement” the length or the diameter/thickness? How many particles were measured to obtain the average values? Please add these details in the text.
(4) Results and discussion
(a) Please provide error bars for the average size of reinforcements - figure 1 (d) and figure 5 (d). In table 1 and 2 - average conductivity values are presented with errors. But there are no error values for tensile strengths. Please include this data.
(b) The inset in Figure 1(a) needs to have a clear boundary. The inset appears merged with the low-mag image in Fig. 1(a). The red font description TiB2 and TiB are not clearly visible. Please change the font color to say, yellow to make it more visible. Also, please label as TiB2p and TiBw. The scale and scale bar of the inset is not clear. Please enlarge and please provide in the caption the scale bar size.
(c) A key reason that the authors state for changes in composite performances vs. reaction temperature and time (section 3.12 and 3.2.2) is change in residual solute (Ti) amount. However, the authors provide hardly any evidence for this.
(The authors provide indirect evidence on change in viscosity with temperature for Cu-Ti and Cu-B. But even the indirect evidence is lacking for reaction time.)
Can the authors quantify residual solute amount vs. temperature and time – to provide an estimate of how much the reaction proceeds and how much residual solute is left? If not experimentally, some theoretical estimates (based on diffusion and kinetics) would greatly help with providing evidence for author claims on how residual solute (Ti) changes with reaction time/temperature.
(d) Regarding the reinforcement refining observed in Figure 1(d) vs. reaction temperature: the authors are to explain in the manuscript how this grain refinement affects tensile strength and conductivity in combination with changes in residual solute.
(e) In the experimental section, the wt% of TiB2p + TiBw is estimated to be 3 wt%. How was this determined? This is to be explained in the manuscript. Also, the authors are to explain if there are any changes in the wt% of TiB2p + TiBw with reaction time and temperature.
(f) In Line 218: The authors state that there is “recrystallization coarsening” of Cu matrix with heat treatment time. The authors are to provide SEM/TEM evidence for this as supplementary material.
(g) The authors are to compare their conductivity and tensile strengths with other values stated in literature and bring out the novelty of the results and approach of this study. This is to be included both in the results and discussion as well as in the conclusions section.
Author Response
Thank you very much for your valuable comments from the reviewers about our manuscript submitted to "Metals" (metals-1648410). We have point-by-point responded to the comments and revised the whole paper carefully. Please see the attachment for detailed response.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
- Summary, strengths, weaknesses, overall contribution
Summary: In the paper the Authors studied the effects of reaction temperature and heat treatment time on the electrical conductivity and tensile strength of (TiB2p+TiBw)/Cu composites prepared by in situ reaction casting. The Authors discuss their results and present also microstructure investigation. They try to explain the observed phenomena on the microstructural basis.
General strengths: Rather interesting results, which may be of some interest for the community.
General weaknesses: The experimental part is not detailed enough. The measurement error analysis is not presented. The discussion of the results may be deeper.
- Major comments
The paper may be accepted if the authors will refer to the following remarks and do the necessary corrections, which would significantly improve the paper:
- the introduction should be significantly improved in order to show the novelty of the presented idea. In the discussion part it would be worth to refer to other papers in which Cu/ceramic composites were produced and to describe in more detail the novelty and significance of the achieved results. Relatively quick literature research provides a lot of such papers.
- The Authors do not discuss the influence of the interfacial bonding on the obtained results. And certainly it is significant. Is it possible to show more SEM images of the samples after tensile tests? What is the debonding mechanism? How the crack propagates (through the reinforcement or rather along the interface?). Is the interface porous or not? The Authors may also refer to the following papers: ; 10.1016/j.compstruct.2018.06.071; 10.1515/amm-2017-0200;
- what was the measurement error for all the presented values. How many tests were performed? What was the shape of the specimen for the tensile test? Are the stress and strain indicated on the curves engineering or true?
- the Authors claim that the tensile strength may have been reduced due to the grains coarsening during heating. Is it possible to provide any XRD or EBSD measurements of the grain size for every state of the samples?
- Minor comments
- the images are of poor quality and are extremely small. It is difficult to see any interesting especially at SEM images.
Author Response
Thank you very much for your valuable comments from the reviewers about our manuscript submitted to "Metals" (metals-1648410). We have point-by-point responded to the comments and revised the whole paper carefully. Please see the attachment for detailed response.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have made appropriate changes to the manuscript taking suggestions from the review-report. The manuscript can be accepted for publication pending minor revisions -
[a]As a minor revision, the authors are to include figures S1 and S2 in the supplementary material and refer to these figures in the text.
In addition, R10 is important information for the readers. The authors are to include this text within the manuscript (altered appropriately to fit in the flow).
[b] There are minor issues with English language here and there, which can be looked into at the proof stages.
Author Response
Thank you very much for your comments about our manuscript submitted to "Metals" (metals-1648410). We have point-by-point responded to the comments and revised the whole paper carefully. Please see the attachment for detailed response.
Author Response File: Author Response.pdf
Reviewer 2 Report
The Authors have addressed all the issues rised by the reviewer. In my opinion the paper can be accepted in the current form.
Author Response
The Authors have addressed all the issues raised by the reviewer. In my opinion the paper can be accepted in the current form. Thank you very much for the recognition of our work.
