Transactions of the Japan Institute of Metals
Online ISSN : 2432-4701
Print ISSN : 0021-4434
ISSN-L : 0021-4434
Pseudoelasticity due to Consecutive β1\ ightleftarrowsβ1′\ ightleftarrowsα1′ Transformations and Thermodynamics of the Transformation in a Cu–14.4Al–3.6Ni Alloy
Hidekazu SakamotoKen’ichi Shimizu
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1987 Volume 28 Issue 9 Pages 715-722

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Abstract

One-stage pseudoelasticity associated with the consecutive β1\ ightleftarrowsβ1′\ ightleftarrowsα1′ transformations in a Cu-14.4Al-3.6Ni (mass%) alloy has been examined in detail by tensile testing and metallographically observing single crystals with near ⟨001⟩ orientations. On the basis of the experimental results, the occurrence of the consecutive transformations was thermodynamically analyzed by taking into account the stress hysteresis of each transformation. As a result, the following points are clarified: The α1′ martensite forms in crossed regions of two variants of the β1′ martensite stress-induced from the β1 parent phase as in the case of Cu–Zn–Al alloys. The consecutive transformations are observed to occur in a temperature range between two critical temperatures, where the critical stress for β1→β1′ transformation becomes equal to that for the β1′→α1′ transformation and where the critical stress for the α1′→β1′ transformation becomes equal to that for the α1′→β1′ transformation, respectively. Temperature dependence of the equilibrium stress for the β1\ ightleftarrowsα1′ transformations has been calculated on the basis of the Clausius-Clapeyron equation, by using observed temperature dependencies of the equilibrium stresses and calculated transformation elongations for the β1\ ightleftarrowsβ1′ and β1′\ ightleftarrowsα1′ transformations. It is thus concluded that the direct β1→α1′ transformation is difficult to experimentally observe in Cu–Al–Ni alloys, being different from the case of Cu–Zn–Al alloys.

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