Simulation of paraequilibrium growth in multicomponent systems

A methodology to simulate paraequilibrium (PE) growth in multicomponent sys tems using the DICTRA (Diffusion-Controlled Transformation) software is pre sented. For any given multicomponent system containing substitutional and i nterstitial elements, the basic approach is to define a hypothetical elemen t Z, whose thermodynamic and mobility parameters are expressed in terms of the weighted average (with respect to site fraction) of the thermodynamic p arameters and mobilities of the substitutional alloying elements. This proc edure facilitates the calculation of PE phase diagrams and the PE growth si mulations directly in the Thermo-Gale and DICTRA software, respectively. Th e results of two distinct case studies in multicomponent alloys are present ed. In the first example, we simulate the isothermal growth of PE cementite in an Fe-C-Co-Cr-Mo-Ni secondary hardening steel during tempering. This is of practical importance in modeling the carbide precipitation kinetics dur ing secondary hardening. In the second example, we have presented the resul ts of PE ferrite growth during continuous cooling from an intercritical tem perature in an Fe-Al-C-Mn-Si low-alloy steel. This is of importance to the design of triple-phase steels containing an austenite that has optimum stab ility, to facilitate stress-induced transformation under dynamic loading. T he results of both simulations are in good accord with experimental results . The model calculations do not consider any resistive or dissipative force s, such as the interfacial energy, strain energy, or solute drag, and, as a result, the interface velocities represent an upper limit under the availa ble chemical driving force.