Journal
MATERIALS CHARACTERIZATION
Volume 149, Issue -, Pages 41-51Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.matchar.2019.01.007
Keywords
NiTi shape memory alloys (SMAs); Electroplastic rolling; Hot tensile tests; Stress-induced martensite transformation; Serrated plastic flow
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Funding
- Department of Science and Technology, Government of India [DST/INT/RFBR/IDIR/P-04/2016]
- National Research Nuclear University MEPhI (Moscow Engineering Physics Institute)
- Ministry of Education and Science of the Russian Federation [02.A03.21.0005]
- RFBR of Russia [16-58-48001]
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Ni50.7Ti49.3 alloy of coarse grained (CG) and ultrafine grained (UFG) microstructures were subjected to tensile tests at different strain rates of 10(-1) s(-1), 10(-2) s(-1), 10(-3) s(-1) and temperatures of 25 degrees C, 50 degrees C and 200 degrees C. The CG state was attained by quenching and the UFG state by electroplastic rolling (EPR). Transmission electron microscopy of the UFG Ni50.7Ti49.3 alloy revealed the presence of shear bands and sub -grains. The microstructure after tensile testing revealed the presence of grains and twin planes of the B19' martensite phase, which indicates that twinning also plays a role in the deformation of the alloy, in addition to crystallographic slip. The effects of grain size, strain rate and temperature on the stress-induced martensite transformation present during the tensile tests are discussed. Serrated flow was observed intermittently in the stress-strain curves of both CG and UFG Ni50.7Ti49.3 alloy for some specific combinations of strain rate and temperature. Serrations observed were not limited to the stress plateau region, which is typically seen in the stress-strain curves of NiTi alloys as a result of phase transformation, but were noticed rather randomly through the entire strain range. This unsteady flow behaviour is also discussed.
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