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

In a + 13 titanium alloys, increasing the amount of a/13 phase boundaries via conventional heat treatment usually improves the strength but significantly deteriorates the alloy's ductility. Instead of homogeneous 13 transformation microstructure (13t) in conventional equiaxed microstructure (EM), two types of microstructures with heterogeneous 13t 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 a phase (ap) and heterogeneous 13t, and the Type II microstructure, featuring heterogeneous 13t embedded in the surrounding homogeneous 13t structures, exhibit an enhanced strength with an insignificant loss of ductility. The enhanced strength is attributed to the increased fraction of a/13 phase boundaries and precipitated residual 13 (13r) nanoparticles, whereas good ductility is obtained due to the soft ap, coherent 13 nanoparticles, and deformable 13 lamellae in the heterogeneous 13t. However, the excessive presence of the Type II microstructure can deteriorate ductility to some extent. This work pro -vides a novel approach to achieving high-performance dual-phase titanium alloys and being potentially applicable to other a + 13 titanium alloys. & COPY; 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Increasing the amount of a/13 phase boundaries through conventional heat treatment in titanium alloys improves strength but reduces ductility. However, a unique semi-equiaxed structure is formed in the Ti6242 alloy through rapid heat treatment, resulting in two types of microstructures with heterogeneous 13 transformation. These microstructures exhibit enhanced strength and good ductility due to the increased fraction of phase boundaries and precipitated nanoparticles, as well as the presence of soft ap, coherent nanoparticles, and deformable lamellae in the heterogeneous 13 transformation. Excessive Type II microstructure can deteriorate ductility to some extent. This work provides a novel approach for high-performance dual-phase titanium alloys.