Ripening of L12Ni3Ti precipitates in the framework of the trans-interface diffusion-controlled theory of particle coarsening

Abstract

Abstract Data are presented on the kinetics of coarsening of γ′-type Ni3Ti precipitates (L12 crystal structure) in three binary Ni–Ti alloys containing 10.31, 11.84, and 13.72at.% Ti aged at 720°C for times up to 64 h. Data on the distributions of particle sizes (PSDs) are also presented. These data, as well as previously published data, are analyzed in light of a new theory of coarsening in which diffusion is controlled by transport through the non-sharp interface between the matrix and precipitate phases. The new theory, called the trans-interface diffusion-controlled (TIDC) theory of coarsening, predicts time (t)-dependent behavior of the type 〈r〉n ∝ t for the growth of precipitates of average radius 〈r〉 and XTi ∝ t−1/n for the depletion of the solute concentration of the matrix, XTi. The exponent n is intimately related to the width of the interface between the precipitate and matrix phases, δ, which is assumed to depend on the particle radius as δ ∝ m, where n = m + 2. The shape of the scaled distrib...