Potential of High Compressive Ductility of Ultrafine Grained Copper Fabricated by Severe Plastic Deformation
, Tatsuya Tanaka 1, Can Erdogan 2 and Tuncay Yalçinkaya 2Round 1
Reviewer 1 Report
The present manuscript is an exhaustive work on deformation behavior of copper after severe plastic deformation by equal channel angular pressing. The strong part of the work is detailed investigation of work hardening and plasticity of copper using different methods. Conclusions are well written and well describe the objective and main results obtained and here reported. The minor comments to which the authors should address their replies are listed hereafter.
1. There are some typos, for examples, at page 3 line 91.
2. A specific source of information about Young's modulus and Poisson's ratio should be indicated.
3. It should be indicated whence specimens for microstructure investigation after ECAP were cut and how orientation image maps were built.
4. It should be indicated low-angle and high-angle boundaries on orientation image maps.
5. Perhaps the term «saturation of microstructure» could be replaced.
6. It is not clear how the discussion on page 6 lines 187-192 linked to previous results. In addition, this reasoning about grain (subgrain) size and HAB fraction can be confirmed by EBSD analysis.
7. It is not clear whence specimens after ECAP and compression test for microstructure investigation were cut and how this fact could effect on results.
8. In my opinion, the analysis of deformation curves indirectly testifies to the mechanisms of deformation and therefore it is impossible to assert about the implementation of one or another deformation mechanism. These data should be additionally confirmed by other experiments.
Author Response
Dear Reviewer
We all appreciate the reviewer valuable comments. We revised the paper according to your comments as follows,
There are some typos, for examples, at page 3 line 91.
Revised.
A specific source of information about Young's modulus and Poisson's ratio should be indicated.
We have taken E as 120 GPa since there was a problem with identification from the stress strain relation. In the books it is given about 110-130 GPa and we took an average value. And for Poission’s ratio they were giving around 0.33-0.34. Source of the data is cited in the text.
It should be indicated whence specimens for microstructure investigation after ECAPwere cut and how orientation image maps were built.
Observation was carried out on the plane perpendicular to the transverse direction which is normal to both extrusion and intrusion direction of ECAP. This is described in the text.
It should be indicated low-angle and high-angle boundaries on orientation image maps.
In the initial discussion, void nucleation was considered limited to high-angle grain boundaries (HAGBs). However, as shown below, void may nucleate at low-angle GBs too, regardless of misorientation of grain boundaries. Thus, distinction between HAGB and LAGBs become less important, and misorientation maps are not described.
Perhaps the term «saturation of microstructure» could be replaced.
As the reviewers comment, the term “Saturation of microstructure” is not appropriate since it is NOT quantitative value. Thus the “saturation” is replaced with “steady-state” of microstructure
It is not clear how the discussion on page 6 lines 187-192 linked to previous results. In addition, this reasoning about grain (subgrain) size and HABfraction can be confirmed by EBSDanalysis.
Discussion is confusing. Void nucleation may occur by dislocation pile-up and resulting local high stress concentration at grain boundaries, and not necessarily be limited to high angle grain boundaries (HAGB). Thus, in the text, HAGB was replaced to (just) grain boundaries.
It is not clear whence specimens after ECAPand compression test for microstructure investigation were cut and how this fact could effecton results.
Microstructure observation was carried out on the plane perpendicular to the transverse direction so that the microstructure with regard to the macroscopic shear direction can be observed. The sample of compression tests were cut parallel to extrusion direction. Effect of loading direction on stress-strain curve of compression test can be expected to some degrees especially for 1 to 2 passes where microstructure was anisotropic (not uniaxial).
In my opinion, the analysis of deformation curves indirectly testifies to the mechanisms of deformation and therefore it is impossible to assert about the implementation of one or another deformation mechanism. These data should be additionally confirmed by other experiments.
The deformation of deformation mechanism of UFG materials fabricated by SPD is NOT discussed solely on the data obtained in the present experiments, but discussed being supported by other papers well recognized in SPD community. Especially, grain boundaries mediated plasticity where grain boundaries play a role as dislocation source/sink accompanying grain boundary sliding, is well accepted by SPD community. Our observation on microstructures before and after compression tests does not contradict with these deformation mechanism, and our discussion is NOT over-speculation.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Very interesting and original work.
The presented results are new and develop modern concepts of the physics of plasticity of ultrafine-grained materials.
The only remark is an insufficiently detailed review of works in the field of compression tests for UFG materials.
Author Response
Dear Reviewer
Thank you for valuable comments, and we revised the paper according to your comments as follows,
The presented results are new and develop modern concepts of the physics of plasticity of ultrafine-grained materials.
The only remark is an insufficiently detailed review of works in the field of compression tests for UFG materials.
Thank you for valuable comments. We added the important literature in the field of compression tests of UFG materials by severe plastic deformation. Compression tests mainly has been employed because we can examine the deformation behavior at higher strain range compared with tensile tests. Thus, we can obtain microstructural evolution during compression, and we can examine the effect of strain rate, strain-hardening behavior.
[1] B. Talebanpour, R. Ebrahimi, K. Janghorban, Microstructural and mechanical properties of commercially pure aluminum subjected to Dual Equal Channel Lateral Extrusion, Materials Science and Engineering: A 527(1) (2009) 141-145.
[2] I. Sabirov, M.R. Barnett, Y. Estrin, P.D. Hodgson, The effect of strain rate on the deformation mechanisms and the strain rate sensitivity of an ultra-fine-grained Al alloy, Scripta Materialia 61(2) (2009) 181-184.
[3] E.A. El-Danaf, M.S. Soliman, A.A. Almajid, M.M. El-Rayes, Enhancement of mechanical properties and grain size refinement of commercial purity aluminum 1050 processed by ECAP, Materials Science and Engineering: A 458(1) (2007) 226-234.
[4] W. Blum, Y.J. Li, Y. Zhang, J.T. Wang, Deformation resistance in the transition from coarse-grained to ultrafine-grained Cu by severe plastic deformation up to 24 passes of ECAP, Materials Science and Engineering: A 528(29) (2011) 8621-8627.
[5] E.A. El-Danaf, Mechanical properties and microstructure evolution of 1050 aluminum severely deformed by ECAP to 16 passes, Materials Science and Engineering A 487(1–2) (2008) 189-200.
[6] M. Hockauf, L.W. Meyer, Work-hardening stages of AA1070 and AA6060 after severe plastic deformation, Journal of Materials Science 45(17) (2010) 4778-4789.
[7] J. May, H.W. Hoppel, M. Goken, Strain rate sensitivity of ultrafine-grained aluminum processed by severe plastic deformation, Scripta Materialia 53(2) (2005) 189-194.
[8] R.Z. Valiev, E.V. Kozlov, Y.F. Ivanov, J. Lian, A.A. Nazarov, B. Baudelet, Deformation behaviour of ultra-fine-grained copper, Acta Metallurgica et Materialia 42 (1994) 2467-2475.
[1] B.Q. Han, F.A. Mohamed, E.J. Lavernia, Mechanical properties of iron processed by severe plastic deformation, Metallurgical and Materials Transactions A 34(1) (2003) 71-83.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear authors,
The aim of the paper, i.e. description of deformation by ECAP technique is interesting and important for other researchers. The compression test between two rollers is also interesting aspect. It was written in a clear but simplified manner. I recommend the following amendments:
41 – According to Considere’s criterion … - it is necessary to recall the relevant literature.
56 - … by ECAP … - no explanation of the acronym.
68-71 – The paper is organized … - this is self-evident and can be omitted. At this point, it would be advisable to include what is novelty in the presented article.
79 - … the tensile test sample and its gauge part is small (2×2×10mm) … - reference should be made here to the standard or test procedure for samples of this shape.
88 – the PRBC test - this is not a standard research procedure, so it should be discussed much more or there should be a reference to relevant articles it described!
91 - … where to is … - should be “to”
102 - This amount to about 8000 kN … - you can't write like this, specifically "what amount"?
Fig. 5 - What does "as" mean in the picture?
Fig. 7 - Remove annotations from the microscope operating program leaving only the marker and its description.
198 – Fig. 9 … - no description of where in the sample these observations came from.
210 - Strain rate sensitivity, m … - no literature reference.
210-212 - sentence is unclear, too long. It is also wrong to say that “for m > 0.3 we have a superplastic strain”. “0.3” is the limit for hard deformable alloys such as Fe-Al alloys (see R. Łyszkowski, J. Bystrzycki: Influence of temperature and strain rate on the microstructure and flow stress of iron aluminides, Archives of Metallurgy and Materials, 52/2 (2007) 347-350 or newer DOI: 10.1016/j.matchar.2014.07.004). However, for pure metals such as Cu, this value is above 0.5.
Fig. 10 - The results presented in the graph come from only 3 measuring points. For this reason, they are not very reliable and are subject to a large error. Such points must not be connected with a continuous but a dashed line (probable course). Since the values of (lnε.) go from -7 to -4.5, the line must not be drawn to -2.5, as this suggests research in this regard as well, which is not true. The caption does not mention that the presented results refer to "8 x ECAP". Suggestion: regarding the determination of the "m" parameter, I recommend that you read the above-mentioned articles once again. There, these matters are treated more broadly.
Fig. 12 - For clarity of drawing, complete the axis marking: T (σm/σeq) and Die displacement - from what? Add an arrow indicating the direction of compression of the sample. Why is the sample 3 mm thick in the drawing, when in reality it was 4 mm?
Finally, I must say that the article is interesting, but the literature review on the effects of processing (Cu) by the SPD method is modest. As you are discussing the ECAP method, you may be interested in the article about the similar CCE technique (DOI: 10.3390/ma12233995) as very similar in subject. I recommend. You may also find it useful: DOI 10.1007/s10853-017-1814-y.
Good luck.
Author Response
Dear Reviewer
Thank you for the valuable comments. We revised the paper according to your comments as follows,
41 – According to Considere’s criterion … - it is necessary to recall the relevant literature.
Revised. The following paper is cited in the text.
- Considere, Ann. Ponts. Chaussees, ser.6 (1885) 574.
56 - … by ECAP … - no explanation of the acronym.
Revised. This “equal channel angular pressing”
68-71 – The paper is organized … - this is self-evident and can be omitted. At this point, it would be advisable to include what is novelty in the presented article.
Revised. This sentence is deleted, and new results were described shortly.
79 - … the tensile test sample and its gauge part is small (2×2×10mm) … - reference should be made here to the standard or test procedure for samples of this shape.
Revised. Sample was small because of the limited size of ECAP billet. Strain was measured by digital image correlation.
88 – the PRBC test - this is not a standard research procedure, so it should be discussed much more or there should be a reference to relevant articles it described!
PRBC may not be a standard test to evaluate compressive ductility. Usually, compression test (upsetting test) has been employed to evaluate it for low to medium ductile materials. However, as shown in the text, for high ductile materials, the conventional upsetting tests does not meet this purpose for high ductile materials because the maximum load become very high abruptly when the materials become very thin. On other hand, cold rolling is often employed to show high compressive ductility (compressive extensibility) (for example, L. Lu, M.L. Sui, K. Lu, Superplastic extensibility of nanocrystalline copper at room temperature, Science 287 (2000) 1463-1465). PRBC test is a kind of cold rolling, where mode of rolls is more simple than cold rolling.
91 - … where to is … - should be “to”
Revised.
102 - This amount to about 8000 kN … - you can't write like this, specifically "what amount"?
The description was revised to become clearer. “The maximum load reaches to about 8000 kN when yield stress is 400 MPa “,
Fig. 5 - What does "as" mean in the picture?
As-annealed means that the sample was annealed and no ECAP. In the caption, as-annealed was changed to annealed samples.
Fig. 7 - Remove annotations from the microscope operating program leaving only the marker and its description.
Revised.
198 – Fig. 9 … - no description of where in the sample these observations came from.
Revised
210 - Strain rate sensitivity, m … - no literature reference.
Strain rete sensitivity, m is a common materials propertiy when effect of strain rate, and degree of viscous nature of deformation is discussed.
210-212 - sentence is unclear, too long. It is also wrong to say that “for m > 0.3 we have a superplastic strain”. “0.3” is the limit for hard deformable alloys such as Fe-Al alloys (see R. Łyszkowski, J. Bystrzycki: Influence of temperature and strain rate on the microstructure and flow stress of iron aluminides, Archives of Metallurgy and Materials, 52/2 (2007) 347-350 or newer DOI: 10.1016/j.matchar.2014.07.004). However, for pure metals such as Cu, this value is above 0.5.
Thank you for valuable comments. We modified the sentence and change from 0.3 to 0.5. and the following papers. [1] T.G. Nieh, J. Wadsworth, O.D. Sherby, Superplasticity in metals and ceramics, Cambridge university press1996.
Fig. 10 - The results presented in the graph come from only 3 measuring points. For this reason, they are not very reliable and are subject to a large error. Such points must not be connected with a continuous but a dashed line (probable course). Since the values of (lnε.) go from -7 to -4.5, the line must not be drawn to -2.5, as this suggests research in this regard as well, which is not true. The caption does not mention that the presented results refer to "8 x ECAP". Suggestion: regarding the determination of the "m" parameter, I recommend that you read the above-mentioned articles once again. There, these matters are treated more broadly.
Figure 10 was revised according to the comments.
Fig. 12 - For clarity of drawing, complete the axis marking: T (σm/σeq) and Die displacement - from what? Add an arrow indicating the direction of compression of the sample. Why is the sample 3 mm thick in the drawing, when in reality it was 4 mm?
Figure 12 was revised according to the comments.
Finally, I must say that the article is interesting, but the literature review on the effects of processing (Cu) by the SPD method is modest. As you are discussing the ECAP method, you may be interested in the article about the similar CCE technique (DOI: 10.3390/ma12233995) as very similar in subject. I recommend. You may also find it useful: DOI 10.1007/s10853-017-1814-y.
Good luck.
Thank you for valuable comments. We strengthened the literature reviews and added the recommended papers, which is very useful for us.
Author Response File: Author Response.pdf
