Precipitation of string-shaped morphologies consisting of aligned α phase in a metastable β titanium alloy

Abstract

String-shaped morphologies consisting of preferentially aligned lath-shaped α precipitates were observed in the metastable β Ti-6Cr-5Mo-5V-4Al alloy after deformations at high strain rates and elevated temperatures. The morphology and 3-dimentional arrangement of this feature have been elaborated based on the characterizations via a combination of transmission electron microscopy, transmission kikuchi diffraction and atom probe tomography. The 2D projected morphology of the coalescent α laths observed in the etched samples by SEM depends on the metallographic section. All the microstructural observations indicate that dislocation structures are most likely the nucleation sites for the aligned α laths. In addition, an appropriate testing temperature, which can ensure a relatively high diffusion rate of solutes without inducing strong recovery of dislocation structures, is necessary for the occurrence of the string-shaped morphologies.