Computational thermodynamics and the kinetics of martensitic transformation

To assist the science-based design of alloys with martensitic microstructur e, a multicomponent database kMART (kinetics of MARtensitic Transformation) encompassing the components Al, C, Co, Cr, Cu, Fe, Mn, Mo, N, Nb, Ni, Pd, Re, Si, Ti, V,and W has been developed to calculate the driving force for m artensitic transformation. Built upon the SSOL database of the Thermo-Gale software system, a large number of interaction parameters of the SSOL datab ase have been modified, and many new interaction parameters, both binary an d ternary, have been introduced to account for the heat of transformation, T, temperatures, and the composition dependence of magnetic properties. The critical driving force for face-centered cubic (fcc) --> body-centered cub ic (bcc) heterogeneous martensitic nucleation in multicomponent alloys is m odeled as the sum of a strain energy term, a defect-size-dependent interfac ial energy term, and a composition-dependent interfacial work term. Using p ur multicomponent thermodynamic database, a model for barrierless heterogen eous martensitic nucleation, a model far the composition and temperature de pendence of the shear modulus, and a set of unique interfacial kinetic para meters, we have demonstrated the efficacy of predicting the fcc --> bcc mar tensitic start temperature (M-s) in multicomponent alloys with an accuracy of +/- 40 K over a very wide composition range.