We study the martensitic transformation with a phase field model, where we consider the Bain transformation path in a small strain setting. For the order parameter, interpolating between an austenitic parent phase and martensitic phases, we use a Ginzburg-Landau evolution equation, assuming a constant mobility. In [1], a temperature dependent separation potential is introduced. We use this potential to extend the model in [2], by considering a transient temperature field, where the temperature is introduced as an additional degree of freedom. This leads to a coupling of both the evolution equation of the order parameter and the mechanical field equations (in terms of thermal expansion) with the heat equation. The model is implemented in FEAP as a 4-node element with bi-linear shape functions. Numerical examples are given to illustrate the influence of the temperature on the evolution of the martensitic phase. A phase field model is used to study the martensitic transformation (MT). We couple the phase field with the heat equation. The order parameter φ scales between the austenitic parent phase (fcc, φ = 0) and one martensitic orientation variant (bcc, φ = 1). The total free energy readswhere we introduce the temperature dependency by the phase separation potential ψ sep [1] and the coupling with the mechanics by the elastic energy W in terms of eigenstrain [3]. The gradient energy density ψ grad accounts for the surface energy.Here, G and L are related to the characteristic interface energy density and the length of the transiton zone as shown in [4]. The total strain is additively split up:considering linear elastic small strain, transformational eigenstrain and thermal expansion, respectively. The coefficient of thermal expansion α and the eigenstrain ε 0 bcc are assumed to be constant. This leads to a time dependent Ginzburg-Landau equation, the equilibrium balance and the heat equation as set of field equations:The mobility M , the density ρ, the heat capacity c and the thermal conductivity k are held constant. Therefore, the change of the order parameter in timeφ is proportional to the variational derivative of the total free energy E with respect to the order parameter φ itself.
Temperature DependencyTemperature dependency is introduced on the one hand by thermal expansion, on the other hand by a temperature dependent separation potential. As given in (2) the phase separation potential is proportional to a Landau polynomial. Using the conditions that the local and global minima are at φ = 0 and φ = 1, the initially four paramaters of the Landau polynomial f can be reduced to two independent parameters [5]: