Development And Application Of EAM Potentials For Ti, Nb And Ti-Nb Alloys

Titanium alloys,as one of the most important structural metal materials,has high potential of development and broad prospect of application.Ti-Nb alloys have been widely used in aerospace,biomedical engineering,shipbuilding engineering,etc.fields.Because of long-term servicing in harsh working environment,where demand better performance for materials.In order to understand the failure mechanism of material at servicing process,it is very important to introduce atomic simulation of microstructure and defect performance,and the interatomic potential is the key to the atomic simulation.In recent years,although more achievements have been made in the development of the interatomic potentials,less can accurately simulate the properties of materials such as stacking fault energy and deformation behavior of materials.In this work,great efforts have been made to develop interatomic potentials that can improve the accuracy of molecular dynamics simulation for materials.In this paper,the interatomic potentials of Ti,Nb and Ti-Nb alloys are developed within the framework of EAM,and a new form of potential function and a new cut-off function are proposed.The parameters of the potential functions were determined by reproducing selected physical properties,e.g.,lattice constants,cohesive energies,elastic constants,unrelaxed vacancies,etc.,by the minimum mean square deviation method.In addition,the data of uniaxial tension or compression of alloys calculated by the first-principle were used to fit parameters of the potential for Ti-Nb alloys.The physical properties of Ti,Nb and Ti-Nb alloys are calculated by the first-principle,which provides reference data for interatomic potentials.The molecular dynamics software LAMMPS and ParaMD was used to simulate the properties of materials as the test and application of the interatomic potentials.Firstly,lattice constants,cohesion energies,vacancy formation,elastic constants,bulk modulus and shear modulus were calculated to test the accuracy of interatomic potentials.The results show that the interatomic potentials in this work can reproduce the mechanical properties of materials very well.The curves of interatomic potentials that conform to the interaction between atoms are smooth,which is conducive to molecular dynamics simulation.The structural stability of pure metals was tested by interatomic potentials.The results show that the most stable structures of Ti and Nb are HCP and BCC respectively,which shows that the structures of Ti and Nb can be well evaluated by the interatomic potentials in this paper.Secondly,molecular dynamics software LAMMPS was used to calculate the defect properties of materials,such as monovacancy and divacancy formation energy,self-interstitials formation energy,surface energy,stacking fault energy and planar fault energy,and the results can achieve highly accuracy.The performance of EAM potential of Ti developed in the past is unsatisfactory in stacking fault energy,which results in poor performance of material molecular dynamics simulation.In this paper,the stacking fault energy of Ti calculated by the interatomic potential can reach 107.54mJ/m~2,which is higher than that calculated by mostly EAM potentials as well.This result is very beneficial to molecular dynamics simulation.In calculating stacking fault energy,it is also found that if the demand for stacking fault properties of materials is too high,it will lead to a sharp decline in other properties.Therefore,Ti stacking fault energy in this work is not as good as the experimental value,but it should be the ultimate limit of this method.Planar fault energy indicates that the EAM potential in this work can well evaluate the deformation behavior of the materials.The physical properties of Ti-Nb alloy potentials,such as elastic modulus,lattice constant,cohesive energy,vacancy formation energy,etc.,were calculated and analyzed.The calculated results show that the physical properties of Ti-Nb alloys described by interatomic potential are in good agreement with the results of the first-principle.The change trend of cohesive energy of Ti-Nb alloys with different Nb content is in accordance with the trend of the first-principle calculation.The potential function curve of Ti-Nb alloys is smooth and can reproduce the physical properties of the material well.