Place: MSE 2012, Darmstadt, Germany
Reza Darvishi Kamachali
The formation of coherent particles in austenite or in supersaturated ferrite during thermomechanical processing is the main source of precipitation hardening in microalloyed steels. The nucleation and growth of these precipitates occur due to diffusion under stress gradient caused by misfit between the particle and corresponding matrix. The resulting mechanical potential contributes to the diffusion potential changing the composition fluxes resulting from the concentration gradient. This issue has been already outlined by Larche and Cahn  dividing it in two contributions, the first being the compositional dependency of the lattice parameters (Vegard's law) and the second being the composition dependent elastic coefficients. But they neglected the later effect. In this study, we investigate the effect of compositional dependency of elastic constants which vary under such diffusion condition and may play an important role on the precipitation process. We employ the phase field modeling and simulation to study the effect of concentration and stress fields on the formation of precipitate. This model predicts the existence of stress stabilized solutal gradient around the precipitates which influences future ripening of the particles. In contrast to the other state of art methods, this effect can give an explanation for systems, where the precipitate's size is only temperature dependent.
 F.C. Larche J.W. Cahn. The effect of self-stress on diffusion in solids. Acta metall, 30:1835?1845, 1982.