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 d2 ∝ 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 transition 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 d3 ∝ t with increasing t in the mixed stage and the coarsening stage.