Transformation behavior of shock-compressed Ni₄₈Ti₅₂

T. Kurita, H. Matsumoto ., K. Sakamoto, Hiroshi ABE

Department of Materials Science and Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686

Journal of Alloys and Compounds 400 (2005) 92.

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Abstract

The transformation behavior on shock-loaded Ni₄₈Ti₅₂ has been studied by employing a differential scanning calorimeter in order to reveal residual effects of shock treatment in the thermoelastic martensitic transformation of Ni₄₈Ti₅₂, exhibiting a shape memory effect between a high temperature phase and a low temperature phase. The shock treatment of Ni₄₈Ti₅₂ was performed by a flyer plate impact method with the flyer velocity of 1.2 km s.1. The height of the exothermic and endothermic peaks due to the transformation of shock-treated Ni₄₈Ti₅₂ become small and their temperature regions are expanded. Although the increase of the number of the thermal cycles induces no intermediate phase on Ni₄₈Ti₅₂ before the shock treatment to result in a one-step transformation, a three-step transformation is observed after annealing at an appropriate temperature on the shock-treated Ni₄₈Ti₅₂, which correspond to the appearance of two intermediate phases. The shock treatment increases non-chemical free energy such as strain energy and interfacial energy of a phase boundary, which is attributable to the microstructure of shock-induced dislocations and an increase of the disorder in the lattice of ordered Ni₄₈Ti₅₂, resulting in the three-step transformation. Therefore, it is thought that the shock treatment can make it possible to achieve a new state on NiTi.

Keywords: Shock compression; Powder gun; DSC; Phase transformation

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ab@nda.ac.jp

Department of Materials Science and Engineering
National Defense Academy

Last Modified: April 1, 2009