Effects of initial microstructure on the aging behavior and subsequent mechanical properties of Ti-Nb-O titanium alloy

Metastable beta-type Ti-38Nb-0.2O alloy was subjected to cold rolling (CR) and solution treatment (ST), and the effects of initial microstructure on the aging behavior and subsequent mechanical properties were investigated. High density of dislocations and grain refinement were introduced by CR, which suppressed the omega phase and promoted the alpha phase in the subsequent aging process. Upon aging at 573 K, the CR specimen consisted of alpha + beta phase and high density of dislocations, while the ST specimen showed homogeneous precipitation of omega phase. Upon aging at 773 K, the CR specimen exhibited ultrafine equiaxed alpha phase without obvious beta grain boundary, while the ST specimen contained acicular alpha precipitates nonuniformly distributed in the internal grain and grain boundary, and precipitate-free zone near grain boundaries were observed. The different initial microstructures led to large difference in strength and Young's modulus between the aged specimens.