Modeling of the effect of the b phase deformation on the a phase precipitation in near-b titanium alloys

A model has been developed in order to describe the influence of a prior plastic deformation of the b phase above the transus on the precipitation of the a phase occurring during subsequent cooling. The model relies on the calculation of the nucleation and growth rates of the a precipitates at the grain boundaries, based on a model presented formerly. Two major modifications have been made: first, the geometrical representation of the b microstructure accounts for subgrains resulting from the deformation process; second, the calculation of the nucleation rate is dependent on the conditions of the plastic deformation. A careful analysis of the main parameters of the model has led to a distinction between several assumptions: Widmanstaetten colonies are likely to cross the subgrains during their growth; and the critical width of the transition from allotriomorphs to Widmanstaetten plates is likely to decrease when the misorientation angle of the grain boundary decreases. Calculations performed to assess the influence of the strain and strain rate on the transformation kinetics are in good agreement with previous measurements.