Modelling of the β → α + β transformation in a metastable β Ti alloy based on the growth kinetics and the morphology of the a plates

摘要

The kinetics of the isothermal β → α + β transformation in a metastable β titanium alloy has been studied by dilatometry. Based on thermodynamic aspects, the volume diffusion of Mo in the titanium matrix ahead of the interface, the interface mobility, and the morphology of the primary a plates, a transformation model is developed, which incorporates mixed-mode behaviour of the transformation in the initial stage. Fraction curves are calculated based on the simulated growth of a typical a plate within the β phase having a volume determined from the nucleus density. For comparison, fraction curves are calculated using a three-dimensional model of the β grain in which a number of plates are simulated to grow with purely diffusion-controlled kinetics. It is shown that the calculated growth rate with the mixed-mode transformation model gives a better representation of the growth rate at the start of the transformation than the purely diffusion-controlled model.