Heterogeneous precipitate microstructure in titanium alloys for simultaneous improvement of strength and ductility

Abstract

• We propose a step-aging method to improve the comprehensive mechanical properties of titanium alloys by designing heterogeneous microstructures through simulations and experiments. • The formation of heterogeneous microstructure can be attributed to the integration of conventional nucleation and growth, and non-conventional pseudospinodal decomposition mechanisms. • Ti-1023 (Ti-10V-2Fe-3Al) alloy with heterogeneous microstructure has shown enhanced ductility by ∼50% and strength by ∼10% comparing with that of homogeneous microstructure. • Both deformation twin and dislocation slip for heterogeneous microstructure have been activated and contributed to the enhanced mechanical properties. The design of alloys with simultaneous high strength and high ductility is still a difficult challenge. Here, we propose a new approach to designing multi-phase alloys with a synergistic combination of strength and ductility by engineering heterogeneous precipitate microstructures through the activation of different transformation mechanisms. Using a two-phase titanium alloy as an example, phase field simulations are carried out firstly to design heat treatment schedules that involve both conventional nucleation and growth and non-conventional pseudospinodal decomposition mechanisms, and the calculated microstructures have been evaluated by crystal plasticity finite element modeling. According to simulations, we then set a two-step heat treatment to produce bimodal α + β microstructure in Ti-10V-2Fe-3Al. Further mechanical testing shows that the ductility of the alloy is increased by ∼50% and the strength is increased by ∼10% as compared to its unimodal counterpart. Our work may provide a general way to improve the mechanical properties of alloys through multiscale microstructure design.