Diffusion Phase Transition Of Binary Alloys Under Temperature Gradient

The phase transition of metals and alloys is the focus of the interdisciplinary study of mechanics,materials science and physics.The numerical simulation of phase transition evolution process by mathematical modeling is an efficient and practical method,which avoids the conditions of experimental method.By introducing the phase field variable,the phase field method avoids the real-time tracking of the two-phase interface when describing the complex evolution of the interface in non-equilibrium state,and can directly simulate the entire phase transition process.Then,by means of appropriate numerical method,the whole phase field model is solved on the computer,and satisfactory simulation results can be obtained.In this paper,based on the classical WBM model and KKS model,phase field models for pure metal solidification process and solid phase transition of binary alloy are established respectively.Considering the influence of temperature field,solute concentration field and elastic field on the phase field,the finite element method is adopted to solve the phase field model,and the simulation of the whole phase transition evolution process is realized on the finite element software FreeFem++.For the phase transition of pure metal solidification,the relationship between the morphology of single grain growth and temperature field was studied.The effects of interface dynamics coefficient,interface thickness coefficient,interface anisotropy modulus and strength on the dendrite morphology and temperature field were analyzed quantitatively.Finally,the temperature gradient condition was added to observe the change of solidification phase transition process.The solute concentration field and elastic field are introduced into the phase field model,and the effect of elastic field on other fields is simplified.By adjusting the initial solute concentration condition,the solute distribution of diffusion-controlled growth and interfacial controlled growth of single grain was compared.The distribution of elastic field during solid state phase transition is simulated by means of equivalent strain.Finally,the external field of temperature gradient was artificially added to observe the changes of grain morphology,elastic strain field and temperature field.