Numerical Simulation Method Of The Martensitic Transformation In Ti-6Al-4V Alloy And Its Application In High Speed Machining

Titanium alloys are widely used in aerospace and automobile industries because of their excellent combination of low density, high strength, their exceptional resistance to corrosion and their good high temperature mechanical properties. The most widely used titanium alloy is Ti-6Al-4V. The titanium alloy undergoes non-diffusion martensitic phase transformation under transient high temperature, during which the crystalline structure evolves from hexagonal closed packed(HCP) α phase to body centered cubic(BCC) β phase. The macro-mechanical behavior of material will be significantly influenced by the phase transformation. So, it is necessary to study the phase transformation process of titanium alloys since it is helpful to find the titanium alloy response to thermo-mechanical coupling under high strain rate.In order to study the stress- and temperature-induced phase transformation of Ti-6Al-4V alloy, a three dimensional non-diffusional Phase Field Model is proposed. A temporal and spatial continuous scalar order parameter is employed to characterize the volume fraction of β phase in infinitesimal region. The time dependent Ginzburg-Landau equation which is used to describe microstructure evolution, and heat transfer equation in which phase transformation is taken into consideration are derived from Ginzburg-Landau potential. The phase field model is consistent with the second law of thermodynamics in the form of Clausius-Duhem inequality. To implement the differential equations into finite element procedure, discrete process of equations are derived. User defined element(UEL) subroutine of ABAQUS is developed in which large deformation, thermo-mechanical coupling and dynamic loading are considered. The capability of the proposed model to simulate stress- and temperature-induced phase transformation of Ti-6Al-4V alloy is verified by three sample problems: uniaxial tension, simple shear and adiabatic temperature rise.In order to simulate stress- and temperature-induced phase transformation in machining chip during High Speed Machining(HSM), cohesive zone elements are introduced into the Phase Field Model. The evolution of order parameter and temperature are simulated under different cutting speed. The simulation results show that: no phase transformation happens in cutting chip at initial stage of cutting because of instability, the influence of instability becomes smaller as the cutting speed increasing; when cutting speed increasing, the quantitative of new phase and temperature become larger and higher, respectively; it is logarithmic between the new phase, temperature and cutting speed.In this work, a three dimensional Phase Field Model is derived by Ginzburg-Landau potential to simulate stress- and temperature-induced phase transformation. Large deformation, thermo-mechanical coupling and dynamic loading are taken into accounted in the model. Uniaxial tension, simple shear and adiabatic temperature rise samples are used to simulate phase transformation in Ti-6Al-4V alloy. The accuracy and practicability of the model are evaluated and validated by those samples. The phase transformation and evolution of temperature are also simulated by the model and obtain some preliminary results. A solid foundation for Phase Field Model application in High Speed Machining is founded.