Fail-Safe Joints between Copper Alloy (C18150) and Nickel-Based Superalloy (GH4169) Made by Transient Liquid Phase (TLP) Bonding and Using Boron-Nickel (BNi-2) Interlayer

Round 1

Reviewer 1 Report

Since the thickness of filler metal interlayer is quite thin, 30 um, surface roughness and flatness values for both alloys after polishing should be shown in section 2. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Thank you for submitting this work to "Metals" - it is an excellent fit, I am from industry and it makes me actually quite happy to see such applied and relevant work.
Here some suggestions to further improve the quality of your work:

-I think the alloy names are the Chinese description C181150, etc. - consider listing the AISI, EU, etc. equivalent as well to attract a larger audience
-CuCRZr is particularly relevant for nuclear fusion - not sure about its application in nuclear power plants
-you could provide an overview of the analysis methods you used in the abstract, hardness testing, tensile testing, etc. - you mention the results so indirectly it is there - I find it great to know from the start what the authors did since we consider some testing methods more relevant than others...
-I also suggest mentioning in the abstract already that you investigated different bonding times and kept the temperature constant - it is always interesting to see what you optimized for

-You mentioned past studies and cite your own work - this is absolutely fine with me - it was a specific research paper though - I suggest mentioning this review paper published in metals (https://doi.org/10.3390/met10050613). The authors also looked into diffusion bonding of CuCrZr to structural material (stainless steel), a relevant topic that you mention in your introduction as well and generally provide a good overview of diffusion bonding and TLP bonding I find. 

-I like it that you lost the melting points of the material - this is really helpful
-You provide the heating rate - maybe provide the cooling rate - or at least an estimate of it - I know this is more difficult
-Please provide more information on the "purpose-built steel fixture" - what material is this - are you actually applying pressure through different thermal expansion coefficients?
-How many samples did you do in total? how many tensile tests were done?

-line 105-107 - if it is well established there should be a reference for this
-The results are generally very well presented. Interestingly you get the highest tensile strength diffusion bonding it for 60 min - nonetheless isothermal solidifcation was obtained after 90 min as you show in Fig. 7 - I guess they just all fail in the Cu and this is within the experimental error

-The conclusions are fine with me - very short but I like it concise anyway

-Maybe you want to provide a little bit of an outlook as well. I think two things could be interesting for readers: (1) how can this be applied on industrial level, you use rather complicated chemical treatments for the preparation of the bonding surfaces, could this be simplified (2) could this be further optimized. You use one bonding temperature - would a higher temperature yield better results, why yes/no? would it be possible to achieve similar results using a loer temperature and say for instance apply a temperature gradient as previously proposed by Shirzadi?
Looking forward to you responses and another great paper on TLP bonding

Author Response

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Reviewer 3 Report

It is a good paper devoted to the very important method, namely the transient liquid phase (TLP) bonding of copper alloy (C18150) and nickel-based superalloy (GH4169). The copper guideway is the most component of the electromagnetic. The combination of heat conducting materials (i.e. copper alloys) and high-temperature structural materials (i.e. stainless steel or nickel-based superalloys) is of great interest to the manufacturers of nuclear power plants and liquid propellant launch vehicles. The paper could be published after major revisions. In particular, it is good visible in the micrograph in Fig. 4 that the grains of the matrix phase appearing light-grey are completely or partially separated from each other by the layers of the phase appearing dark-grey. Such behaviour is intimately connected with the so-called complete and incomplete wetting of grain boundaries by the liquid or second solid phase (see for example J Mater Sci 50 (2015) 4762 or J. Mater. Sci. 58 (2021) 7840). The morphology of integranular phase strongly influences the overall mechanical properties of a polycrystalline composite. In particular it can lead to the strong embrittlement (see for example Scripta mater. 37 (1997) 729). The grain boundary wetting transitions can definitely influence the phenomena observed by the authors. I 

Author Response

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Round 2

Reviewer 2 Report

Excellent - you did a good job responding to my comments. This manuscript can now be accepted for publication

Reviewer 3 Report

After revision the paper is acceptable for publication as it is