  The microstructure evolution due to thermomechanical treatment of metals can
largely be described by viscoplastic deformation, nucleation and grain growth.
These processes take place over different length and time scales which present
significant challenges when formulating simulation models. In particular, no
overall unified field framework exists to model concurrent viscoplastic
deformation and recrystallization and grain growth in metal polycrystals. In
this work a thermodynamically consistent diffuse interface framework
incorporating crystal viscoplasticity and grain boundary migration is
elaborated. The Kobayashi--Warren--Carter (KWC) phase field model is extended
to incorporate the full mechanical coupling with material and lattice rotations
and evolution of dislocation densities. The Cosserat crystal plasticity theory
is shown to be the appropriate framework to formulate the coupling between
phase field and mechanics with proper distinction between bulk and grain
boundary behaviour.
