Enhanced strength of dual-phase Ti6242 alloy via a heterogeneous microstructure

Abstract

In α + β titanium alloys, increasing the amount of α/β phase boundaries via conventional heat treatment usually improves the strength but significantly deteriorates the alloy’s ductility. Instead of homogeneous β transformation microstructure (βt) in conventional equiaxed microstructure (EM), two types of microstructures with heterogeneous βt are obtained via insufficient diffusion of alloying elements induced by rapid heat treatment (RHT), forming a unique semi-equiaxed structure (S-ES) in the Ti6242 alloy. Such microstructural characteristics, including the Type Ⅰ microstructure characterized by a wavy interface between primary α phase (αp) and heterogeneous βt, and the Type Ⅱ microstructure, featuring heterogeneous βt embedded in the surrounding homogeneous βt structures, exhibit an enhanced strength with an insignificant loss of ductility. The enhanced strength is attributed to the increased fraction of α/β phase boundaries and precipitated residual β (βr) nanoparticles, whereas good ductility is obtained due to the soft αp, coherent β nanoparticles, and deformable β lamellae in the heterogeneous βt. However, the excessive presence of the Type Ⅱ microstructure can deteriorate ductility to some extent. This work provides a novel approach to achieving high-performance dual-phase titanium alloys and being potentially applicable to other α + β titanium alloys.