Comparison of shape memory characteristics of a Ti-50.9 At. Pct Ni alloy aged at 473 and 673 K |
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Authors: | Jae Il Kim Shuichi Miyazaki |
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Affiliation: | (1) the Department of Mechanical Engineering, Texas A&M University, 77843-3123 College Station, TX;(2) the Institute of Materials Science, Tsukuba University, 305-8503 Ibaraki, Japan |
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Abstract: | The effect of aging on transformation and deformation behavior, i.e., the transformation temperatures, shape memory behavior, and multistage martensitic and R-phase transformations, was investigated
for a Ti-50.9 at. pct Ni alloy aged at a low temperature (<600 K) rarely used for practical applications and at a high temperature
(>600 K) conventionally used for practical applications. It was found that there are many differences between aging at 473
and 673 K. The martensitic and R-phase transformation temperatures significantly varied depending on aging time and temperature.
It is found that two-stage R-phase and multistage martensitic transformations appear in both the specimens aged at 473 and
673 K, respectively. The two-stage R-phase transformation appeared by aging at 473 K over 36 ks, while the multistage martensitic
transformation (MSMT) appeared by aging at 673 K in the range of aging times between 1.2 and 36 ks. It is found that the critical
stress for slip increases with increasing aging time in specimens aged at 473 K, while that of specimens aged at 673 K increases
with increasing aging time until reaching a maximum, then it decreases with a further increase in aging time. It is also found
that the critical stress for slip is superior for specimens aged at 473 K than that for specimens aged at 673 K. It was confirmed
that dense and fine lenticular precipitates of about 10 nm in length were formed through aging, resulting in superior shape
memory characteristics. |
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