Anharmonicity and Martensitic Phase Transition in β-Phase Alloys

Abstract

We obtain the third order elastic constants in the β₁ phases of Au–Cu–Zn and Cu–Al–Zn alloys by measuring the pressure dependence of the second order elastic constants under the uniaxial pressure. The β₁ phases are highly anharmonic. In any alloy, the free energy barrier to form the martensite is of the order of only meV/atom. We also calculate the pressure derivatives of the second order elastic constants as a function of the pressure directions. They are considerably anisotropic. Using the results, we consider the martensitic nucleation. The martensitic nucleation mechanism is originated from the anharmonic property of the β₁ phase.