Micro-texture and Stress Evolution Under Monotonic Tension in an Additively Manufactured Near-α Titanium Alloy

Abstract

The yield strength (σ_y.s.) of directed energy deposited near-α Ti-6Al-2Sn-4Zr-2Mo alloy exceeds 1000 MPa while possessing very low ductility of less than 10%. The possibility of enhancing the ductility without a significant decrease in the σ_y.s. is via judicious heat treatment which transforms the as-built martensitic α′ into an α/β phase mixture, which has been examined in conjunction with the numerical investigation on the correlation between microstructure and mechanical properties. The resulting alloy deforms in a heterogeneous manner with stress and strain, partitioning in the α and β phases. Deformation heterogeneity at the micron scale plays a vital role in the damage initiation and, consequently, the fracture process. Crystal plasticity based on fast-Fourier transform (CPFFT) simulations were carried out to study the evolution of spatially heterogeneous stress and strain in the two phases and to identify the correlation between the spatial strain–stress heterogeneity and the global mechanical response. Simulation results show the evolution of higher von Mises stress in the hcp α phase than the bcc β phase. Plastic heterogeneity of the two phases leads to strain incompatibility at the α–β interfaces, leading to microcrack initiation. Simulations capture the effect of crystallographic orientation on the evolution of localized equivalent von Mises stress and strain.