Influence of stress-induced α’’ phase transformation on mechanical properties in metastable β type Ti-5Al-2.5Cr-5Mo-1Sn alloy

Abstract

The stress-induced α’’ phase transformation in titanium alloys has received extensive attention due to its significant effect on mechanical properties. In this work, by adjusting the heat treatment process, the stress-induced α’’ phase transformation is activated in Ti-5Al-2.5Cr-5Mo-1Sn. The quasi-static tensile mechanical properties of the alloy under air-cooled and as-quenched states have been compared. Further, the morphology and orientation of the stress-induced α’’ phase and its interaction with dislocations are investigated by X-ray diffraction (XRD), optical microscope (OM), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM) experiments. The value of average misorientation at the stress-induced α’’ bands region is larger than that in the β matrix, which indicates that the degree of plastic deformation in the stress-induced phase transformation region is higher. Therefore, the stress-induced α’’ phase exhibits a strong strain partitioning effect during the stretching process and improves the ductility of the material. The β/α’’ interface has a weak effect to hinder the dislocations, which results in low tensile strength of the alloy. This work can provide insight into the influence of stress-induced α’’ phase transformation on the mechanical properties of transformation induced plasticity (TRIP) type titanium alloys. • The Ti-5Al-2.5Cr-5Mo-1Sn alloy is elaborately regulated to produce TRIP effect. • Average misorientation of α’’ band region is generally larger than that of β matrix. • α’’ phase exhibits a strong strain partitioning effect to increase alloy ductility. • The β/α’’ interface is semi-coherent and has a weak effect to hinder dislocations.