A modified constitutive model coupled with microstructure evolution incremental model for machining of titanium alloy Ti–6Al–4V

Abstract

• A modified constitutive model that considers work hardening, dynamic recovery and dynamic recrystallization mechanism is proposed. • The constitutive model provides an interface to response of flow stress on microstructure evolution. • Incremental formulation of the JMAK model is proposed to capture microstructure evolution during cutting process. The altered microstructure during machining process had an inverse influence on materials behavior, machining forces and surface integrity. Thus, a constitutive model which builds the response of flow stress on microstructure evolution is gaining rising interest. Based on Johnson-Cook model, a modified constitutive model coupled with microstructure evolution incremental model for machining of Ti-6Al-4V is proposed. The competing effect of work hardening and dynamic recovery mechanism on flow stress is accentuated in the constitutive model. And a new softening term is introduced to describe material softening behavior caused by dynamic recrystallization. In addition, the modified constitutive model builds the response of flow stress on microstructure evolution by introducing the dynamic recrystallization volume fraction as an internal state variable. Considering the complex and variable loading conditions during the cutting process, the incremental formulation of the Johnson-Mehl-Avrami-Kolmogorov model is proposed to capture microstructure evolution during cutting process. Subsequently, orthogonal cutting experiments and simulations of Ti-6Al-4V have been carried out to evaluate the effectiveness of the proposed model. Simulation results show that the modified constitutive model has accurate predictions of the cutting and thrust forces and illustrates that DRX is the inducement of serrated chip formation. In addition, the modified model is able to simulate the microstructure evolution during Ti-6Al-4V cutting process, which is attractive for surface integrity research of cutting operations.