Study On Calculation Method Of Alloy Phase Diagram

Ferrum-chromium-aluminum alloy has been a hot topic in nuclear cladding materials research in recent years.Various methods of alloy calculation have emerged during the last decades.This work starts from Chen-Mobius Inversion which uses the energy from the first-principles calculations by VASP,and then improves the precision of the potential with neural network fitting.This work introduces the idea of pseudo atom and then calculates the phonon spectrum and the vibrational density of states(VDOS)of the alloy under any composition with pair potentials in LAMMPS,analyzes the stability of the corresponding structure and the vibrational entropy is further obtained.In the end,we can get the free enery from the difference between the total energy and the product of entropy(the sum of the vibrational entropy and the configurational entropy)and temperature.Finally we can get the phase diagrams of ferrum-chromium-aluminum alloys by the minimum points of the free energy curves.The pseudo atom model is a new and creative atom potential model proposed by professor Chen Nianxian.The pseudo atom model not only contains the physical essence,but also greatly reduces the computational complexity compared to Monte Carlo simulations and other traditional methods for calculating solid solutions,this model provides a new idea for the calculation of alloys.In the sixth chapter of this work,Chen-Mobius inversion of quasilattice is performed based on the quasi-lattice coordinates from general dual method and the potentials of quasicrystals is obtained.These potentials can be used to do revelant analysis of quasicrystals.The quasi-crystal potential function has oscillation characteristics,so the nnet can be used to fit the scatter points obtained by the Chen-Mobius inversion.At present,there is no universal and accurate method for phonon calculation at for high temperatures and high pressures.Molecular dynamics simulation based on the pseudo atom model can calculate the temperature-component phase diagram and the pressure-component phase diagram of the multicomponent alloy.And such results need to be compared with the experiments to verify the reliability of the idea.The rationality of the pseudo atom model can be verified by existing alloy calculation software or Monte Carlo simulation of molecular dynamics.The potential functions obtained from the quasicrystal inversion also need to be compared with the relevant experimental results.For example,thermodynamic quantities calculated by the inversion potential functions can be compared with the experimental values.