Effect of True Strains in Isothermal abc Pressing on Mechanical Properties of Ti49.8Ni50.2 Alloy
Round 1
Reviewer 1 Report
Please find herewith the review in attachment. Best regards
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 1 Comments and changes
Abstract
Point 1: Line 9: Please indicate that the microstructure was as well characterized.
Response 1: Corresponding changes were made to the text of the manuscript. (page 1, line 9).
Point 2: Line 10: In the sentence, it is written "up to", but the true strain is a value with a large range i.e. "0.29-8.44"
Response 2: Corresponding changes were made to the text of the manuscript. (page 1, lines 10).
Point 3: Lines 11-13: It is a long sentence. Please make two sentences. This would be helpful for a better understanding.
Response 3: Corresponding changes were made to the text of the manuscript. (page 1, lines 11-14).
Point 4: Line 16: The meaning of the abbreviation "< d >cr" should be given.
Response 4: Abbreviation ádñcr means critical average grain size, less than which begins a sharp increase in the ultimate tensile strength sUTS of the material (page 1, lines 16-17).
Point 5: Lines 16-17: Please give a short description of the possible mechanisms.
5.) Строки 16-17: пожалуйста, дайте краткое описание возможных механизмов.
Response 5: A description of a possible mechanism was added to the text of the manuscript, the main idea of which is that with an average grain size less than the critical one, a higher external stress is required for the nuckleation and propagation of the main crack (page 1, lines 15-21).
Introduction
Point 6: Lines 21-23: The sentence gives a list of references, i.e. [1] to [15]. It would better to have specific literature on the subject of TiNi-based alloys, rather than the list of manuscript or books dealing with shape memory alloys in general.
Response 6: A list of references [1] to [15] adjusted according to the reviewer's recommendation. Only works on the use of TiNi-based alloys are given. Corresponding changes were made to the text of the manuscript. (page 1, line 27, page 12, lines 347-452).
Point 7: Line 25: Please change "..for no change in their chemical composition." to "with no change of chemical composition.".
Response 7: Corresponding changes were made to the text of the manuscript. (page 1, line 29).
Point 8: Line 27: Please give adapted references for the techniques abc pressing, equal channel angular pressing,...
Response 8: Adapted references for the techniques abc pressing, equal channel angular pressing and high pressure torsion were added. (page 1, lines 31-32)
Point 9: Lines 37-39: Please give details for "...how this increase is contributed by grain size distributions".
Response 9: In many of the works cited above, it is shown that as a result of severe plastic deformation, a grain structure is formed in nickel-titanium based alloys, in which regions with different average grain sizes (coarse-grained, submicrocrystalline, nanocrystalline) coexist. The different volume fraction of such areas, i.e. the grain size distribution, as well as the uniformity of the distribution of such areas over the volume of the material can significantly affect its mechanical properties. The study of this influence is one of the tasks of this work. Corresponding changes were made to the text of the manuscript. (page 2, lines 43-48).
Point 10: Line 40: Please change "in relation to" to "in relation with".
Response 10: Corresponding changes were made to the text of the manuscript. (page 2, line 49).
Point 11: Lines 42-43: The sentence "Hereinafter the alloy composition is given in at%." can be given in the section "Experimental procedure".
Response 11: The sentence "Hereinafter the alloy composition is given in at%." repeattd in the section "2. Materials and Methods". (page 3, line 103).
Point 12: Lines 53-55: In order to explain the described observations, please give references on Ti2Ni type precipitates and their relation with shear deformation of martensitic transformation.
Response 12: Unfortunately, errors were made in the text of the manuscript. The corrected text is inserted in the text of the manuscript: “At e = 8.44, was reached after abc pressing at 723 K [14-16], the alloy was dominated by a submicrocrystalline structure with a noticeable nanograin fraction, residing mainly around coarse precipitation of the Ti2Ni type, and at this temperature (723 K), intensive recovery processes occurred.” (page 3, line 59-62). Ti2Ni type precipitates in TiNi-based alloys are always formed during the manufacture of these alloys (see Otsuka, Ren, Progress in Materials Science 50 (2005) 511-678). Depending on the purity of the initial components, the size and volume fraction of such particles may vary. As a rule, the volume fraction does not exceed 5 vol. %. In the cited works [14-16], the influence of Ti2Ni type precipitates on the shear deformation of the martensitic transformation is not discussed. The authors also did not conduct such studies. We consider it inappropriate to introduce such a discussion in this article.
Point 13: Line 61: There is a high-dislocation density and annihilation can take place. Please explain or modify this "annihilation of highdensity dislocations" in order to have a correct description.
Response 13: We agree with the reviewer's comment. Corresponding changes were made to the text of the manuscript. (page 2, line 69).
Point 14: Line 82: Please change "dictated" by another more adapted synonym.
Response 14: Corresponding changes were made to the text of the manuscript. (page 3, line 91).
Point 15: Line 82: The description of the possible types of precipitate for this alloy is recommended. Please give as well adapted references.
Response 15: The authors did not find any articles devoted to the study of Ti3Ni4, Ti2Ni3, and TiNi3 phase precipitate in Ti49.8Ni50.2 alloy at the thermomechanical treatments. In our TEM studies, we did not observe the presence of these phases either in the material in the delivery state or after the thermomechanical treatments we used. In addition, when nickel-enriched phases are precipitated, the nickel concentration in the matrix changes, which leads to a shift in the temperature of martensitic transformations. In our experiments, as shown in figure 1, the temperatures of martensitic transformations practically did not change as a result of the thermomechanical treatments we used. These results allow us to say that the studied alloy does not contain the secondary phases Ti3Ni4, Ti2Ni3, and TiNi3.
Point 16: Line 90: Please indicate why it can be problematic.
Response 16: The authors had in mind that using abc pressing it is possible to obtain finished products by stamping, which may be problematic for other SPD methods. Apparently, this is not clearly written in the text, so the authors removed this part of the text. Corresponding changes were made to the text of the manuscript. (page 3, line 101)
Materials and Methods
Point 17: Line 95: Please give a description of the device that was used to carry out the deformation during abc pressing.
Response 17: A hydraulic press MIS-6000 K with a force of 600 tons was used to perform deformation during abc pressing. Corresponding changes were made to the text of the manuscript. (page 3, lines 107-109)
Point 18: Line 111: Please give a description of the dimensions of the tensile specimens. Were the sample manufactured according to a given norm?
Response 18: Specimens were shaped as a dumbbell with a gage area of 7´1´1 mm. The sample were manufactured according to a given norm. Corresponding changes were made to the text of the manuscript. (page 3, lines 124-125)
Point 19: Line 115: Please give the complete description of the strain rates.
Response 19: The speed of movement of the mobile gripper of testing machine was constant and was 0.007 mm/s. For a sample with a gage length of 7 mm, this corresponds to a relative strain rate of 10-3 s-1. Corresponding changes were made to the text of the manuscript. (page 4, lines 128-130)
Point 20: Line 119: Please add "light" before "optical microscopy".
Response 20: Corresponding changes were made to the text of the manuscript. (page 4, line 135)
Results
Point 21: Figure 1, lines 123-127: Please carefully describe in details the Figure 1. Indicate the meaning of abbreviations, the meaning of Ttest,...
Response 21: Corresponding additions were made to the text of the manuscript. (page 4, lines 149-154)
Point 22: Lines 129-132: Please give a specific subsection for the results of transmission electron microscopy (TEM). This subsection is proposed to be before the section "4. Discussion".
Response 22: Added subsection “3.2 Microstructure" (page 4, line 161) before subsection “3.3 Mechanical properties”. As a rule, the description of the microstructure of the material under study precedes the description of mechanical properties. We ask the reviewer not to insist on placing the "Microstructure" subsection before the section "4. Discussion".
Point 23: Lines 129-132: Please give literature referencing and describe the possible phases in the first section of the manuscript.
Response 23: Possible phases are described in the first section of the manuscript (page 3, lines 89-91).
Point 24: Figure 2: Please describe in details the Figure. Indicate in the experimental procedure how the B2 and R phases are determined using SADP. The authors may provide the necessary crystallographic data, which allowed the phase identification using SADP.
Response 24: Description of figure 2 were made to the text of the manuscript (page 5, lines 161-168). The presence of phases in the samples was determined by microdiffraction patterns according to standard method. The distance from the central reflex to selected reflex was measured and the interplane distances were calculated. The results were compared with the database ASTM.
Point 25: Line 151: What is the meaning of "average"?
Response 25: The word "average" in this sentence is incorrect. Replaced with “typical” in the text (page 6, line 184).
Point 26: Line 151-160: Please indicate how the stages I, II, and III were determined.
Response 26: There are four stages of the strain –stress curve (as in Ref. [Pushin]), the length of which was determined graphically. The initial stage I corresponds to quasi-elastic strain, stage II- pseudo-yield plateau, stage III - quasi-linear stage of strain hardening, ending with a yield stress, stage IV corresponds to parabolic hardening up to the ultimate tensile strength. There is some transition area between the stages. The definition of stages is added to the text of the manuscript (page 6, lines 185-189).
Point 27: Lines 183-185: The description of the experiments are not sufficiently supporting these mentioned findings.
Response 27: The word "hardly" has been replaced with "weakly». (page 7, line 222)
Point 28: Figures 6 and 7: The figures and explanations would be better suited in the section of "Results".
Response 28: Figures 6 and 7 use the results of the studies shown in figure 5 in the "Results" section, rearranged in other coordinates for ease of analysis. Figure 7 also uses the results of other authors. Figures 6 and 7 in the manuscript illustrate the analysis of the experimental results obtained. Therefore, the authors consider it impractical to move figures 6 and 7 to the "Results" section and ask the reviewer not to insist on this.
Author Response File: Author Response.pdf
Reviewer 2 Report
Dear Editor,
The main aim of the manuscript is studying the effect of isothermal abc pressing on the grain size of Ti49.8Ni50.2 alloy at different true strains and the effect of grain structure on mechanical properties under uniaxial tension at room temperature. The work is extensive and contains a lot of interesting data. I recommend publishing this manuscript after minor corrections given below:
1) Please correct the content of Ti 49.0 on 49.9 according to the Ref. [35] (line 42).
2) Please write what the abbreviations Md (line 84), Af, Tr, As (Fig. 1) mean when they are presented in the first time. Providing also an information what the phases B2, R and B19’ mean (line 126), makes the work more understandable to the reader.
3) In the section of Materials and Methods, please write the name of the equipment for measuring the temperatures of phase transformations, with the help of which the data presented in the Fig.1 were obtained. How the samples were prepared for SEM and TEM microstructure studying?
4) I am sure that the Fig. 2d is a SEM image, not TEM image (lines 132-133). Please check it. I think, that the Fig. 2d describes well the microstructure containing twinned B19′ domains (according to the text of manuscript written between lines 138-140), not B2 and R phases. Please correct it (line 133).
5) The Fig. 3b has a very bad resolution (diffraction points are almost invisible). Please improve the picture quality.
6) The Authors written, that “The data exemplify that the bulk of all specimens is occupied by B19ʹ martensite (Figures 2c and 3b) with a small (5–10 vol. %) amount of R and B2 phases (Figures 2f and 3b) which fail to transform to B19ʹ on cooling to room temperature.” (line 135-137). However the Fig. 3b does not provide the R phase. How was the volume fraction of the phases measured? Do I understand correctly that the volume fraction of the R and B2 phases before and after abc pressing remained the same?
7) How the size of grains and its volume fraction were calculated? (lines 145-149)
8) The curves 5 and 3 are difficult to distinguish in Fig. 4. If it possible, mark them with a different color or type of curve, please.
9) The word "yield" is written incorrectly (line 173).
Author Response
Response to Reviewer 2 Comments
Point 1: Please correct the content of Ti 49.0 on 49.9 according to the Ref. [35] (line 42).
Response 1: Corrected in accordance with the reviewer's recommendation (line 51)
Point 2: Please write what the abbreviations Md (line 84), Af, Tr, As (Fig. 1) mean when they are presented in the first time. Providing also an information what the phases B2, R and B19’ mean (line 126), makes the work more understandable to the reader.
Response 2: Md is the maximum temperature at which a martensitic transformation of B2(R)®B19¢ induced by an external applied stress is possible; B2 is the high – temperature BCC phase, R is the intermediate martensitic phase with a rhombohedral crystal lattice, and B19¢ is the martensitic phase with a monoclinic crystal lattice. MS and Mf are the start and finish temperatures of the direct martensitic transformation B2(R)®B19¢ at cooling, respectively; AS and Af are the start and finish temperatures of the reverse martensitic transformation at heating, respectively; TR is the start temperature of the martensitic transformation B2®R at cooling; Ttest is the tensile test temperature. The corresponding additions were made to the text of the manuscript. (Page 3, lines 94-96, Page 3, line 89-91, Page 4, line 149-154)
Point 3: In the section of Materials and Methods, please write the name of the equipment for measuring the temperatures of phase transformations, with the help of which the data presented in the Fig.1 were obtained. How the samples were prepared for SEM and TEM microstructure studying?
Response 3: Temperature of phase transformations were determined by an experimental setup (direct current, four-point potential method) manufactured at the ISPMS SB RAS, Tomsk, Russia. The measurement method is described in detail in [15].
The specimens for optical and SEM microstructure studying were cut using an electric discharge machine along the plane passing though the specimen center and parallel to any two arbitrary opposite edges of the specimen. Such cross section provided analysis of the specimen microstructure in its overall bulk. After cutting, the specimen surfaces were mechanically polished using a Saphir 350 (ATM GmbH, Germany) grinder, and then they were chemically etched and electrolytically polished.
TEM microstructure studying was performed using thin foils. Thin plates with a thickness of 0.2 mm were cut from the blanks obtained after abc pressing in the selected section using an electric discharge machine, which were then thinned electrolytically.
The corresponding additions were made to the text of the manuscript. (Page 4, lines 132-134, lines 138-146).
Point 4: I am sure that the Fig. 2d is a SEM image, not TEM image (lines 132-133). Please check it. I think, that the Fig. 2d describes well the microstructure containing twinned B19′ domains (according to the text of manuscript written between lines 138-140), not B2 and R phases. Please correct it (line 133).
Response 4: Indeed, the description of Fig. 2d is incorrect. Fig. 2d shows optical image in DIC (Differential Interference Contrast) mode, which clearly shows structures that can be visually identified as twinned domains of the B19ʹ martensitic phase. It is, of course, impossible to identify the B2 and R phases in figure 2d. The presence of the B2 and R phases were determined by the microdiffraction patterns (Fig. 2f). The corresponding corrections were made to the text of the manuscript (Page 5, lines 162-169).
Point 5: The Fig. 3b has a very bad resolution (diffraction points are almost invisible). Please improve the picture quality.
Response 5: Image quality of Fig. 3b improved in accordance with the reviewer's recommendation.
Point 6: The Authors written, that “The data exemplify that the bulk of all specimens is occupied by B19ʹ martensite (Figures 2c and 3b) with a small (5–10 vol. %) amount of R and B2 phases (Figures 2f and 3b) which fail to transform to B19ʹ on cooling to room temperature.” (line 135-137). However the Fig. 3b does not provide the R phase. How was the volume fraction of the phases measured? Do I understand correctly that the volume fraction of the R and B2 phases before and after abc pressing remained the same?
Response 6: Indeed, on Fig. 3b only phase reflexes B2 and B19¢ are identified. The data exemplify that the bulk of all specimens is occupied by B19ʹ martensite (Figures 2c and 3b) with a small (5–10 vol. %) amount of R (Figures 2c) and B2 phases (Figures 2f and 3b) which fail to transform to B19ʹ on cooling to room temperature.
The volume fraction of the phase was evaluated visually by the occupied area on light-field and dark-field in the corresponding diffraction reflexes TEM images. However, there was no significant difference in the volume fraction of B2 and R phases before and after abc pressing. The corresponding corrections were made to the text of the manuscript. (Page 5, lines 162-169).
Point 7: How the size of grains and its volume fraction were calculated? (lines 145-149)
Response 7: The size of individual grains was determined by secant-based microphotography obtained by optical microscopy and TEM. To determine the volume fraction of regions with different grain structure (coarse-grained, submicrocrystalline, nanocrystalline), which are quite clearly visualized in the studied samples, microphotographs were used to calculate the area occupied by the region with the studied structure. We used at least 10 fields of view from 3 samples from this batch.
Point 8: The curves 5 and 3 are difficult to distinguish in Fig. 4. If it possible, mark them with a different colour or type of curve, please.
Response 8: The curves in Fig. 4 were marked with a different color in accordance with the reviewer's recommendation.
Point 9: The word "yield" is written incorrectly (line 173).
Response 9: Corrected in accordance with the reviewer's recommendation. (Page 7, line 211)
Author Response File: Author Response.pdf
Reviewer 3 Report
The work is well organized and conducted even if the investigation of the results could be improved.
I indicate only some suggestion and I have one important question:
the authors wrote: "The choice of Ti49.8Ni50.2 is dictated by its non-aging, which excludes the formation of secondary
Ti3Ni4, Ti2Ni3, and TiNi3 phases during thermomechanical treatments and their influence on the properties of the alloy."
I'm not so sure that it is true, see Otuska, Ren, Progress in Materials Science 50 (2005) 511–678
The presence of precipitates starts also during and after the melting production. Please the authors add explain and demonstration that during the thermal treatment at 723K there is no formation of precipitates.
Moreover it is better to insert a scheme or figure or image of the experimental procedure and also of the tensile test, the dumbbell is obtained from which part of the sample?
there is a control more precise of the distribution of the grain size in the section of the die?
Author Response
Response to Reviewer 3 Comments
Point 1: the authors wrote: "The choice of Ti49.8Ni50.2 is dictated by its non-aging, which excludes the formation of secondary Ti3Ni4, Ti2Ni3, and TiNi3 phases during thermomechanical treatments and their influence on the properties of the alloy."
I'm not so sure that it is true, see Otuska, Ren, Progress in Materials Science 50 (2005) 511–678. The presence of precipitates starts also during and after the melting production. Please the authors add explain and demonstration that during the thermal treatment at 723K there is no formation of precipitates.
Response 1: The precipitation of Ti3Ni4, Ti2Ni3, and TiNi3 phase particles in nickel-titanium based alloys near the equiatomic composition during thermomechanical processing is still a subject of discussion. In Otuska (2005), there is no direct indication that the alloy Ti49.8Ni50.2 there will necessarily be a release of such particles, as occurs in alloys with a higher nickel content. In our opinion, the nickel concentration is 50.2 at. % is the boundary for this process. In our TEM studies, we did not observe the presence of these phases either in the material in as received state or after the thermomechanical treatments we used. In addition, when Nickel-enriched phases are precipitated, the nickel concentration in the matrix changes, which leads to a shift in the temperature of martensitic transformations. In our experiments, as shown in figure 1, the temperatures of martensitic transformations practically did not change as a result of the thermomechanical treatments. These results allow us to say that the studied alloy does not contain the secondary phases Ti3Ni4, Ti2Ni3, and TiNi3.
Point 2: Moreover it is better to insert a scheme or figure or image of the experimental procedure and also of the tensile test, the dumbbell is obtained from which part of the sample?
Response 2: Of course, the drawing or diagram is more visual, but the used procedures are not original and are described in many articles. The working part of the samples for mechanical testing was cut from the central part of the cubic samples obtained after abc pressing, parallel to the two opposite faces, retreating 2 mm from their surface. This provided a small variation in the mechanical properties of samples with the same true strain.
Point 3: there is a control more precise of the distribution of the grain size in the section of the die?
Response 3: The TEM method is the most informative for studying the grain structure. For each true strain, the sample structure contains regions with different grain structure (coarse-grained, submicrocrystalline, nanocrystalline), which are uniformly distributed over the cross-section of the cubic samples, except sones of 2 mm near surface. In samples with different true strain, these regions have different average grain size and volume fraction. This determines the average grain size over the entire volume of the sample. Due to the small variation in the mechanical properties of samples with the same true strain, it can be assumed that the volume of the working part of the samples for mechanical testing is a representative volume for the microstructure of the obtained samples, the characteristic of which is the average grain size.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Please find herewith the review.
Best regards
Comments for author File: Comments.pdf
Author Response
Response to Reviewer 1 Comments and Changes
Abstract
Point 1: Lines 9-21: The changes were made according to the review #1. The abstract allows a better for understanding. The meaning of the abbreviations is available.
Response 1: Thank you for your review. Yours comments allowed us to better to present results obtained in the work.
Introduction
Point 2: Lines 25-40: The changes were made according to the review. There are still minor English improvements, which can be made.
Response 2: Thank you for your review. Yours comments allowed us to better to present results obtained in the work.
Point 3: Line 69: The annihiliation of dislocation is possible, but the measurement of dislocation density is something else. Please change to annihilation of dislocation. It is possible to explain the change of dislocation density in the next sentence.
Response 3: Here we cite the results obtained in Shamsolhodaei et al. (2017) (reference [10] in our manuscript). In [10] it is written: "In addition, by increasing the amount of equivalent strain.. the recovered regions through rearrangement and annihilation of dislocations of high density are intensifying". In this context, the word "annihilation" means a lowering in the high density dislocations due to their rearrangement, but not annihilation as a result of the interaction of dislocations of different signs. We are probably not quoting correctly. We made the following changes in the text of the manuscript: It was reported that the abc pressing temperature 673 K provided a dynamic recovery in the alloy by rearrangement and lowering of high density dislocations, the formation of dislocation-free recrystallized grains with a random grain size distribution, whose pattern was not given. (page 2, lines 67-70).
Point 4: Lines 70-90: The changes were made according to the review.
Response 4: Thank you for your review. Yours comments allowed us to better to present results obtained in the work.
Point 5: Line 91: Please add a space before ”phase”.
Response 5: Corresponding changes were made to the text of the manuscript. (page 3, lines 91).
Experimental procedure and results
Point 6: The changes were made according to the review.
Response 6: Thank you for your review. Yours comments allowed us to better to present results obtained in the work.
Point 7: The description of the parameters used for tensile testing were added to the section ”Experimental Procedure”.
Response 7: Thank you for your review. Yours comments allowed us to better to present results obtained in the work.
Point 8: English can be improved.
Response 8: The translation of our manuscript into English was performed by a certified specialist who translates scientific publications in Russian journals into English for publication in English-language journals. Of course, English can be improved. However, we believe that the main content of our work is quite clear. We ask the reviewer not to insist on improving the English language.
Author Response File: Author Response.pdf
Reviewer 3 Report
Concerning the presence of precipitates, it is true that the composition chosen by the authors are in the limit zone of the composition to have aging process, but I consider a presence of precipitates which is sufficient to induce (together with the residual cold work) the intermediate rombohedral phase and it is not so high to have change in average chemical composition and shift of martensitic temperature transition. In my opinion is better to consider negligible presence of precipitates, no total absence.
The answers and the other comments are ok.
Author Response
Response to Reviewer 3 Comments
Point 1: Concerning the presence of precipitates, it is true that the composition chosen by the authors are in the limit zone of the composition to have aging process, but I consider a presence of precipitates which is sufficient to induce (together with the residual cold work) the intermediate rombohedral phase and it is not so high to have change in average chemical composition and shift of martensitic temperature transition. In my opinion is better to consider negligible presence of precipitates, no total absence.
Response 1: The authors agree with the reviewer's comment. We do not know of any studies that have experimental confirmation of the precipitates Ti3Ni4, Ti2Ni3, and TiNi3 presence in the Ti49.8Ni50.2 alloy. However, the formation of such precipitates in this alloy is not excluded.
The text of the manuscript has been corrected accordingly. (Page 3, line 92-94).
Author Response File: Author Response.pdf
