First Passage Times and Time-Temperature-Transformation curves for Martensites

Martensites are long-lived nonequilibrium structures produced following a quench across a solid state structural transition. In a recent paper (Phys. Rev. Lett. 78, 2168 (1997)), we had described a mode-coupling theory for the morphology and nucleation kinetics of the equilibrium ferrite phase and twinned martensites. Here we calculate nucleation rates within a first-passage time formalism, and derive the time-temperature-transformation (TTT) diagram of the ferrite-martensite system for athermal and isothermal martensites. Empirically obtained TTT curves are extensively used by metallurgists to design heat treatment cycles in real materials.