日本金属学会誌

J. Japan Inst. Metals, Vol. 50, No. 6 (1986),
pp. 546-554

The Stress-induced Transformation of a Ti-Ni Alloy by the Pre-load Test Method

Tsunehiko Todoroki1 and Hirokazu Tamura2

1Air-conditioner Division, Matsushita Electric Industrial Co., Ltd., Kasatsu
2Central Research Lab., The Furukawa Electric Co., Ltd., Tokyo

Abstract:

In this study, the stress dependence of strain-and electrical resistance-temperature relations is investigated by thermal-cycling tests with tensile pre-load for Ti-Ni alloys (49.8 and 50.2 at%Ni) heat-treated at temperature between 743 K and 933 K. The resulting stress (σ )-transformation temperature (T) diagrams are, then, analyzed in detail. The results are summarized as follows.
(1)  The σ -T diagram in the present study shows similar aspects to that in the tensile test by Miyazaki et al. except for the low stress range in which an analysis with enough accuracy could not be made in tensile test.
(2)  The σ -T relation of the R → M transformation is not linear and is divided into three parts according to the stress level; (a) low-stress part with large dσ /dT, (b) middle-stress part with small dσ /dT and (c) high-stress part with relatively large dσ /dT. While the R-phase transformation strain increases as the stress becomes larger in the stress range of part (a), it remains constant in the stress range of parts (b) and (c). In the part (c), the R → M transformation takes place before the interaxial angle of the R-phase reaches a maximum. Furthermore, in the stress range of part (c), it is noted that stress dependence of the martensitic transformation strain becomes relatively small, that the residual strain becomes evident at Af point, and that the apparent heat of transformation evaluated from the Clausius-Clapeyron formula increases.
(3)  The electrical resistance at Mf point increases as stress becomes larger. As for the R → M transformation, the amount of the increase is found to be approximately twice as large as the value estimated from the elongation of the sample during transformation and the apparent increase in the specific resistance which brings residual resistance at Af point.


(Received 1986/1/20)

Keywords:

titanium-nickel alloy, shape-memory alloy, martensitic transformation, stress-induced transformation, pre-load test, Clausius-Clapeyron formula, R-phase transformation, electrical resistance


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