3D Diffuse Scattering and Displacement Short-Range Ordering in Pre-martensitic State: A Computational Study

Abstract

A quasi-spin Ising model of ferroelastic phase transition is developed and employed to perform atomic-scale Monte Carlo simulation of thermoelastic martensitic transformation. The quasi-spin variable associated with the lattice sites characterizes the local unit cells of the orientation variants of the ground-state martensite phase, which interact with each other through long-range elastic interactions. The simulation study focuses on the intrinsic behaviors of a defect-free crystal that undergoes cubic-to-tetragonal martensitic transformation. It is shown that the diffuse scattering in the pre-martensitic austenite state results from the spatial correlation of the atomic-scale heterogeneous lattice displacements and manifests the displacement short-range ordering. The effects of temperature, elastic anisotropy, and shear modulus softening on the diffuse scattering and displacement short-range ordering are investigated. It is found that the shear modulus softening promotes 〈110〉|〈11¯0〉 displacement plane waves that stabilize the cubic austenite phase through increased entropy, decreasing the martensitic transformation temperature. The simulated diffuse scattering is compared and agrees with the complementary synchrotron X-ray single-crystal diffuse scattering experiment.