Growth Process of ω-precipitates in a Ti-20 mass% Mo Alloy

Abstract

The growth process of ω ︲ precipitates was studied for a Ti ︲ 20 mass ％ Mo alloy aged at 673 K. Investigations of the aging time t dependences of precipitate size, precipitate volume fraction, and precipitate number density revealed that the growth process was divided into three stages: the first stage of diffusion ︲ controlled growth, the second mixed stage of growth and coarsening, and the third stage of coarsening. In the first stage, the precipitate size d increased as d 2 ∝ t with increasing t , and then the precipitate growth became very slow after a value of d =14 nm was reached at the beginning of the second mixed stage. This is ascribed to the transi - tion from the growth stage to the mixed stage of growth and coarsening, and the collision of neighboring ω ︲ precipitates. After the neighboring ω ︲ precipitates of the same variant collided and then coalesced, the precipitate size increased as d 3 ∝ t with increasing t in the mixed stage and the coarsening stage. ［ doi:10 . 2320 / jinstmet.J2016049 ］