Construction Of The Bond Order Potential Of Fe-Bi System And Study Of Phase Stability Of Fe-Bi Solid Solution

Iron and bismuth are thermodynamically immiscible binary systems,but in recent years,studies in the literature have found that iron and bismuth will form solid solutions and affect the mechanical properties of materials.However,there are few reports on the structure and stability of iron-bismuth solid solution in the whole composition range.The mechanism of how bismuth affects the binding and mechanical properties of iron bismuth solid solution are not clear,and there is also a lack of research on the possible order-disorder transition of iron bismuth-solid solution.There is no potential function that can accurately describe the ground state structure of bismuth and the solid phase of iron-bismuth in the literature.Therefore,in view of the above problems,molecular dynamics simulation method（MD）was used to studies the stability of iron bismuth solid solution.The main results are as follows:（1）Based on the first principle calculation data and experimental data,the Fe-Bi bond order potential was constructed.After verification,the new bond level potential can reliably simulate the solid phase of iron bismuth system,and is the potential that can accurately simulate the ground state structure of bismuth for the first time.Its prediction result is better than several potential functions in the literature.（2）Based on the new Fe-Bi bond order potential,the structural stability of Fe_100-xBi_x is predicted by molecular dynamics simulation.The results show that when the content of Bi is 0≤x<10,10≤x<26,26≤x<70,70≤x<86 and 86≤x≤100,the BCC,BCC+amorphous,amorphous,a7+amorphous and A7 of Fe_100-xBi_x are more favorable and stable in energy respectively.At the same time,it is also found that the addition of Bi can significantly reduce the tensile strength and plasticity of Fe in BCC structure.（3）Monte Carlo simulation and molecular dynamics simulation are used to predict the order-disorder transition of BCC Fe₁₅Bi₁ solid solution.It is found that ordering can reduce the lattice constant of solid solution and improve the structural stability and mechanical properties of solid solution.In Fe-rich BCC Fe-Bi solid solution,the negative bond energy of Bi-Bi bond is the intrinsic reason for the order-disorder transition.The Gibbs free energy difference between the ordered and disordered solid solutions is the driving force of the ordered-disordered transition.Enthalpy and entropy play a major role in the ordered-disordered transition below and above the phase transition temperature,respectively.