Transformation-induced plasticity in the heterogeneous microstructured Ti-Zr-Nb-Sn alloy via in-situ alloying with directed energy deposition

Abstract

Adjusting the phase transformation behavior in metallic alloys is important for controlling both the strengthening capability and the shape memory effect in a specific area. Because phase transformation usually occurs in high interfacial energy regions, heterogeneous microstructures with inclusions may induce a unique phase transformation during plastic deformation or temperature changes. In this study, transformation-induced plasticity in a heterogeneous microstructured Ti-Zr-Nb-Sn alloy was investigated. To design a heterogeneous microstructure, in situ alloying with directed energy deposition and elemental powders was conducted, and unmelted Nb particles were distributed in the beta-Ti matrix. The high interfacial energy between the unmelted Nb particles and the beta-Ti matrix supports the initiation of deformation-induced alpha '' martensite, while no phase transformation occurs at the grain boundaries. Moreover, the heterogeneous microstructure and transformation-induced plasticity of the in-situ alloyed Ti-Nb-Zr-Sn alloy contribute to their high strength (700.8 MPa) by accumulating geometrically necessary dislocations and absorbing plastic deformation energy, respectively. This result indicates that the heterogeneous microstructure design with laser-based additive manufacturing is helpful for manipulating phase transformation in specific regions, which allows the adjustment of the local shape memory effect and plastic deformation in complex-shaped parts.