Modelling, Simulations and Monitoring of Lamella Structure Formation in Titanium Alloys Controlled by Diffusion Redistribution

Abstract

A mathematical model and computer programs are developed for simulation and monitoring of the processes of nucleation and growth of the α phase Widmanstatten plates during the course of the β ⇒ α phase transformation in titanium alloys. Based on integration of thermodynamic modelling and finite element simulations, the α phase appearance at the grain boundary of β phase is described by a numerical procedure for random nucleation as a function of the alloy composition and the temperature. The rate at which an interface moves depends both on the intrinsic mobility and on the rate at which diffusion can remove the excess of β stabilising atoms ahead of the interface. This process is controlled by diffusion redistribution of the alloying elements between the α and β phases that are different for different titanium alloys. The finite element method was used for solving the diffusion equation on the domain occupied by β phase. The models and program packages developed are used to simulate the morphology of the microstructure evolution (Fig. 1) in different titanium alloys during variety of heat treatment processings and can be used in the real processing route.