Mechanical and Magnetic Properties of Porous Ni50Mn28Ga22 Shape Memory Alloy
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The present manuscript reports the influence of porous structure on SMA, SE, and MCE effects of Ni-Mn-Ga SMAs. The topic is scientifically and technologically important in the SMA fields, and their approach is well documented and leads to meaningful results. However, there are some omissions in description. Therefore, the manuscript needs to improve results and discussion with more clear description.
Comment:
1. P.1, line 28: In the introduction, authors mentioned that “By reducing the dimension, the number of grain boundaries can be decreased, and the constraint of martensitic transformation can be effectively weakened. However, stress-induced martensitic transformation in polycrystalline Ni-Mn-Ga alloy is impeded by grain boundaries, resulting in low macro-superelasticity.”. To reinforce this introduction about the influence of grain boundaries and grain size effects on martensitic transformation behavior, authors use some of literatures like [Appl. Mater. Today 22 (2021) 100961].
2. P.1, lines 32-40: Generally, the martensitic transformation in SMAs can be influenced by number of grain boundaries in unit volume (grain boundary density), which strongly relates to grain size. However, an introduction of pores into the bulk alloy does not significantly influence the grain boundary density. The formation of large number of coarse grains by heat treatment is more effective to modulate the martensitic transformation.
3. There are some errors in wording. So, authors should check the whole sentences.
For examples:
P.1, line 32: alloy grain boundaries à grain boundaries
P.1, line 23 and P.2, line 55: Authors used same abbreviations of MCE for both “magnetocaloric effect” and “magnetic cooling effect”, which cause the misunderstanding from the readers. Please use different abbreviations.
P.2, line 59: alloy ingots were prepared by arc-melting (with or using) high purity elements of Ni (99.99%), Mn (99.7%) and Ga (99.99%)
4.P.1, line 42: authors introduced an abbreviation of “martensite transformation” (MT) in this line. The wording “martensitic transformation” is used in P.1, line 24, line 28 and P.2, line 81, etc.. Did the “martensite transformation” and “martensitic transformation” use in different meaning in this manuscript? If these wording used in same meaning, please use identical wording.
5. P.2, line 61: In experimental procedures, authors should provide the method to fabricate powder from the ingot.
6. A strong discussion is missing for Fig. 3(a). The transformation heat required for phase transformation on SMAs is very important for scientific discussion about phase transformation behavior (please refers JALCOM 692 (2017) 77-85). The porous alloys have same composition, and heat flow unit of DSC curves is mW per unit weight. Nevertheless, the alloys with different pore size exhibited different height of endothermic and exothermic peaks with identical base line condition, which can be considered that the alloys have different transformation heat for austenitic and martensitic transformations during thermal cycle. Therefore, authors should provide the values of transformation heat (ΔH) for the austenitic and martensitic transformations and discuss the reason why the alloys require or show difference heat values for phase transformation.
In addition, the label of Y-axis in Fig. 3(a) is wrong. Please change to “Heat flow”.
Comments on the Quality of English Language
Minor editing of English language required.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
In the current manuscript, authors give a characterisation of porous NiMnGa alloy. The topic is interesting for broad community and potentialy might give a big impact into the field. The material show predicted porosity, nevertheless, authors do not discuss a nature of such porosity. From the Fig. 2 and from the text is not clear if pores are closed or open, as well as authors give an estimation of porosity using density. Is it possible to measure porosity directly using sorbtion techniques or alternative methods?
Table 1 is not really clear, I would suggest to give more explanation in the capture and in the text (authors do not refere to table 1 in the text).
Figure 2b. Authors do not give any reference XRD data (material seems to be fcc), I would also suggest to refine cell parameters and cristallite size for all samples.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors
see the file attached
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for Authors
Authors addressed all issues mentioned
Reviewer 3 Report
Comments and Suggestions for Authors
After the corrections made I propose to accept the paper in the present form
