Microstructure–Based Analysis of Deformation and Fracture in Coated Equiatomic Polycrystalline Titanium Nickelide

Abstract The coupled processes of stress–induced phase transformation, elastic–plastic deformation, and fracture during tensile loading and subsequent unloading of a polycrystalline TiNi alloy coated with an inner–outer layer system are investigated numerically, with the polycrystalline microstructure of Ti4Ni2O–TiO coating used as a representative example. The coating is synthesized from a Ti / Ni / Ti trilayer laminate deposited on a TiNi substrate. The microstructure of the coated polycrystalline composite is characterized experimentally using electron backscatter diffraction (EBSD). Based on the measured grain orientations and phase distribution, a finite element microstructure model of the coated material is constructed. Dynamic boundary value problems describing the deformation of the composite are solved using ABAQUS / Explicit. The constitutive model accounts for anisotropic elasticity, crystal plasticity, brittle and ductile fracture of the coating layers, and stress–induced phase transformation in the TiNi substrate. Numerical simulations are performed for several combinations of the mechanical behavior of the coating layers to investigate the coupled evolution of deformation and fracture. Particular attention is devoted to the influence of plastic deformation and cracking within the coating on the formation of residual martensite in the TiNi substrate after the composite unloading.