Modeling of the precipitation kinetics and morphology evolution of lamellar α in Ti-alloys during non-isothermal treatments

Abstract

The non-isothermal diffusional phase transformation plays an important role in adjusting materials microstructure. In the modeling of non-isothermal transformation, actual temperature history has a remarkable effect on the precipitation kinetics of new phase. When morphology anisotropy effect is considered, taking actual temperature history effect into account is very difficult for guaranteeing the accuracy of kinetics prediction. In order to solve this problem, a new non-isothermal transformation model in combination with cellular automaton (CA) method with mixed-controlled mode was proposed. In this new model, actual temperature history effect was characterized by the effects of cooling path and additive isothermal path on the nucleation and growth of new phase. Firstly, the cooling path with the consideration of supercooling effect was introduced into the created isothermal transformation theory model. Secondly, the temperature-time path (i.e. additive isothermal path) in CA model was calibrated by using the solute concentration model from experiments. With the use of this new model, the precipitation kinetics and morphology evolution of the lamellar α for IMI834 titanium alloy during continuous cooling from single-phase region was predicted. The predicted results were in good agreement with experiments. It was also revealed that the dominant role of mixed-controlled mode for lamellar α precipitation was gradually changed from the diffusion control to the interface control with the increase of cooling rate.