Computer Simulation of the Early Stage of Precipitation of L12-Ni3(Al,V) Using Microscopic Phase Field Method

Based on the phase field theory, the long-range order (LRO) parameter related interatomic potentials equations were utilized to calculate the interatomic potentials of L10-Ni3(Al,V), L12-Ni3Al and L12-Ni3(Al,V) phases varying with temperature and concentrations. Using these potentials, the simulated microstructure evolution and the order parameter with the time of Ni75Al20V5 ternary alloy are simulated at temperature 1000K during the early stage of the precipitation process in this research. Results testify that the precipitation sequence during the early stage of Ni75Al20V5 alloy is the disordered phase →L10 pre-precipitation phase →L12 equilibrium phase. Firstly, the nonstoichiometric L10 pre-precipitation phase formed by congruent ordering precipitation mechanism; secondly, the nonstoichiometric L12 phase formed by transforming from L10 phase; thirdly, the stoichiometric equilibrium L12 phase formed by spinodal decomposition precipitation mechanism. It is discovered that the precipitation mechanism (congruent ordering+ spinodal decomposition) process was closely related to free energy and interatomic potentials: L10 pre-precipitation phase’s free energies are higher and interatomic potentials are smaller than those of L12 equilibrium phase.