Effect of Stress-Induced Martensite Stabilization on Acoustic Emission Characteristics and the Entropy of Martensitic Transformation in Shape Memory Ni51Fe18Ga27Co4 Single Crystal
, Yury Chumlyakov 2, Nikita Surikov 2 and Dezső László Beke 1,*Round 1
Reviewer 1 Report
The paper reports on the martensitic transformation of a Ni51Fe18Ga27Co4 single crystal comparing the stress induced martensite with the one quenched from high temperature, using calorimetry and acoustic emission. Stress induced martensite is associated with clearly larger transformation temperatures and sharper transitions, with a much smaller variation in entropy during the transformation. In general the paper is well written.
I have two main concerns linked to each other:
- the introduction seems to be disconnected with the rest of the paper. Whereas the purpose seems to investigating SIM aging is general, reporting examples of different systems in the introduction, the paper discusses one single material, Ni51Fe18Ga27Co4, which is not even mentioned in the introduction.
- Why Ni51Fe18Ga27Co4 ? The paper assumes that the reader is expert on the system, while it shouldn’t be the case. The main characteristics of structure and MT of the Ni51Fe18Ga27Co4 system should be defined in the introduction.
Therefore I recommend to modify the introduction to provide information about the investigated system. Also, if the authors plan to keep a general discussion in the introduction about SIM aging, they should discuss whether the same conclusions should apply to other shape memory alloys. Would different martensite transformations lead to the same results?
Minor points:
line 109: I am not sure figure 4d is the proper reference
line 172, “. .”
line 259: whitespace
fig 10b: what is the solid line?
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors! I have reviewed your manuscript "Effect of stress-induced martensite stabilization on acoustic emission characteristics and the entropy of martensitic transformation in shape memory
Ni51Fe18Ga27Co4 single crystal ". I think that this article is not ready for the publication in its present shape and it needs the revision. My main concerns are:
- The subject of the study is related with shape memory effects in alloys, what is am impacting field. On the other hand, the choice of the object of investigation is not justified. Your massively cite and discuss your own previous publications devoted to the Ni-Fe-Ga-Co alloys. That leaves the impression that this particular alloy is of unique interest to your group only. Please, improve.
- I found almost no microstructural information and you do not discuss structural aspects of acoustic effects (and you openly admit this). This makes the discussion of the experimental results (generally good, in my opinion) very shallow. I found few mentions of twins and movements of austenite-martensite interfaces. Is there any chance to discuss the energy of these events, what are their characteristic frequencies. Please, improve.
- I have very serious question - the most interesting SIM-aged sample was MUCH smaller (the mass is 20 times less) than quenched counterpart. And exactly SIM-aged sample has shown very specific effects, that one may ascribe to the influence of scale effects - martensitic particles (lamellae) during the growth may interact with outer surface much more often giving rise to specific effects. Please, describe why the sample for SIM-aging was cut (and how) and what was the cooling rate after SIM-aging. Please, discuss possible influence of surface energy, inhomogeneity and defects of crystalline lattice introduced by SIM-aging on the entropy.
- How many samples were studied for each state of the alloy?
- Steel waveguide. Steel grade? Cross-section.
- Even not being a native English writer I point on some bad phrasing and give my recommendations:
15-17 "Simultaneous differential scanning calorimetry, DSC, and acoustic emission, AE, measurements were carried out for single crystals of quenched and stress-induced martensite stabilized (SIM-aged) shape memory Ni51Fe18Ga27Co4 alloy. "
21-23 "For quenched and SIM-aged alloys at heating, in accordance
with the sharper (burst-like) transition observed in the DSC run, few high energy solitary hits were observed, and these hits did not fit to the energy distribution function fitted for smaller energies. "
27 "... entropy was for about 36 % smaller after SIM-aging of quenched sample and entropy was ..."
39 "..., in order to reach ... "
51 "...crystals carried out using differential ..."
69 " ... undergoes to a ..."
72 "The sample was undergone to ..."
84 " ... DSC curves [24]."
108 "... during cooling at temperatures higher Ms ..."
145 " ...which it originates ..."
157 " ... the number of hits .."
167 " ... as the values for ..."
199 " ... shows the σcr and εtr as the function of T ..."
250 " ... transformation entropy was within the limits of the experimental error ..."
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The present paper has described on the comparative investigations of the martensitic transformation in SIM-aged and quenched single crystalline shape memory Ni51Fe18Ga27Co4 crystals by DSC and AE measurements. However, the clear purpose and detailed discussion in this study are insufficient. Please reconsider the following comments. The reviewer judges that the paper is acceptable after some major revision.
1. One of authors already presented some experimental results using the same Ni51Fe18Ga27Co4 single crystals in papers [12, 13]. The changes of transformation temperatures and hysteresis has been clarified so far. What are the novel results and interesting discussions of this paper? What is the novel discussion for martensitic transformation based on the AE results?
2. Explain the reason why the DSC curves of SIM-aged sample split into separate peaks?
3. Authors cite the following discussion: “The energies of the individual acoustic events are directly related to the relaxation of the energy of elastic waves emitted during an individual jump of the moving austenite/martensite interface [20,28,30,32]”. Describe the physical meaning and origin of “high sudden jumps” in the phase transition during heating in conclusion.
4. How much change is the long-range order by heat treatment in this study? Why is the transformation entropy unchanged after austenite stabilization?
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Dear Authors! The manuscript of "Effect of stress-induced martensite stabilization on acoustic emission characteristics and the entropy of martensitic transformation in shape memory Ni51Fe18Ga27Co4 single crystal" has been improved. However, I detect some minor imperfections to be fixed. Your insert hereinafter "It is one of the reasons why the mass of the SIM-aged sample was about twenty times smaller: this helped us to fix the sample. The second reason was that, after few thermal cycles, the sample was broken into small pieces, because of the very large local stresses during transformation. On the smaller samples no cracking was observed even after many cycles. Of course, the DSC and AE measurements were carried out on the same piece of sample. This size, we believe, did not introduce disturbing scale effects: according to [27] decreasing the size of the sample resulted only in a split of the DSC peaks, at the same cooling/heating rates, but e.g. the energy distribution of AE events did not essentially change. This was also confirmed by measuring AE on another piece of the broken sample (with a mass of about three times larger (i.e. with m=47 mg) and, besides the increased AE activity, the same characteristic features were obtained. " raised few remarks:
- Si - should be changed for silicone (that is a polymer grease, not hard matter), I guess.
- Please, provide the results for 47 mg piece somewhere in the Figure 4 and 8 as well.
- The cracking of the sample due to the high internal stress releases the energy embedded in the material. This energy contributes to entropy. Please, estimate and discuss this term.
Author Response
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Reviewer 3 Report
The present paper has revised for the comments of refree. Therefore, this paper is acceptable for publication.
Author Response
No changes were requested by this reviewer.
