Abstract
Equiatomic CuZr alloy undergoes a martensitic transformation from the B2 parent phase to martensitic phases (P21/m and Cm) below 150 °C. We clarified the effect of the thermal cycling on the morphology and crystallography of martensite in equiatomic CuZr alloy using a transmission electron microscopy. The 10th cycled specimens consisted of different multiple structures at the maximum temperature of differential scanning calorimetry (DSC) measurement −400 °C and 500 °C, respectively. At the maximum temperature 400 °C of DSC measurement, it is composed of the fine plate-like variants, and a lamellar eutectoid structure consisting of Cu10Zr7 and CuZr2 phases on the martensitic variant. Concerning the maximum temperature of 500 °C of DSC measurement, it is observed the martensitic structure and the lamellar structure in which the martensitic phase was completely eutectoid transformed. The formation of this lamellar eutectoid structure, due to thermal cycling leads to the shift of forward and reverse transformation peaks to low and high temperature side. In addition, new forward and reverse transformation peaks indicating a new transformation appeared by thermal cycling, and the peaks remained around −20 °C. This new martensitic transformation behavior is also discussed.
Highlights
Near equiatomic Ti-Ni alloys are widely used as a shape memory alloy in the industrial and the medical fields
This alloy shows a martensitic transformation from the B2 matrix to the two martensitic phases at about 150 ◦ C, and its reverse transformation temperature is around 265 ◦ C [3,4,5]
The analysis by Reference intensity ratio method [13] using the results of X-ray diffraction (XRD) measurement showed that the volume fraction of each phase in water-quenched equiatomic CuZr alloy is CuZr: 84% (Cm: 64%, P21 /m: 20%), Cu10 Zr7 : 8%, CuZr2 : 1%, and Cu2 Zr4 O: 7%
Summary
Near equiatomic Ti-Ni alloys are widely used as a shape memory alloy in the industrial and the medical fields. Equiatomic CuZr alloy is expected as a high temperature shape memory material, since it undergoes martensitic transformation point over 100 ◦ C [1,2,3,4,5,6,7,8,9,10,11]. This alloy shows a martensitic transformation from the B2 matrix (space group: Pm3m) to the two martensitic phases (space group: P21 /m and Cm) at about 150 ◦ C, and its reverse transformation temperature is around 265 ◦ C [3,4,5].
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