  The presence of thermal gradients in alloys often leads to non-uniformity in
concentration profiles, which can induce the thermomigration of microstructural
features such as precipitates. To investigate such microstructural changes, we
present a phase-field model that incorporates coupling between concentration
and thermal gradients. First, we simulated the evolution of non-uniform
concentration profiles in the single-phase regions of Fe-C and Fe-N alloy
systems due to imposed thermal gradients. To validate our model with the
classical experiments performed by Darken and Oriani, we studied the evolution
of spatially varying concentration profiles where thermal gradients encompass
single-phase and two-phase regions. We developed a parameterized thermodynamic
description of the two-phase region of a binary alloy to systematically study
the effect of interactions between chemically-driven and thermal
gradient-driven diffusion of solute on the evolution of precipitates. Our
simulations show how thermal gradient, precipitate size, and interparticle
distance influence the migration and associated morphological changes of
precipitates. The composition profiles and migration rates obtained from
single-particle simulations show an exact match with our analytical model. We
use twoparticle simulations to show conditions under which thermomigration
induces the growth of the smaller particle and shrinkage of the larger one in
contrast to the isothermal Ostwald ripening behavior. Our multiparticle
simulations show similar behavior during coarsening. Moreover, in the presence
of a thermal gradient, there is a shift in the center of mass of the
precipitates towards the high-temperature region. Thus, our study offers new
insights into the phenomena of microstructure evolution in the presence of
thermal gradient.
