The effect of heat treatments on martensitic transformations in monocrystalline Cu–14.1Al–4.2Ni (mass%) (alloy 1) and Cu–14.7Al–4.2Ni (mass%) (alloy 2) shape memory alloys has been investigated by means of differential scanning calorimetry measurements, optical microscopy and tensile tests of martensitic specimens. As a result, it was found in alloy 1 that not only transformation temperatures shifted but also thermally formed martensite changed from β
1' to γ
1' with heat treatment. Meanwhile, in alloy 2, the γ
1' martensite was thermally formed regardless of heat treatment. To clarify the reason for the change of thermally formed martensite, equilibrium temperatures,
To, for the β
1_??_γ
1' and β
1_??_β
1' transformations and their variation within heat treatment were estimated by utilizing previous data on stress-induced martensitic transformations and associated pseudoelasticity of the alloys (
Trans. Jpn. Inst. Met., 28 (1987), 264). Consequently, by taking into consideration the variation of To temperatures and, in addition, supercooling neccessary for the nucleation of the γ
1' and β
1' martensites, the origin was successfully elucidated in terms of a simple scheme that the martensite phase with the highest
MS temperature changed from the β
1' to the γ
1' with heat treatment. Applicability of this scheme was discussed on similar phenomena occurred in other alloy systems in which martensite phases changed with chemical composition.
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