INTERATOMIC POTENTIALS FOR TI-AL WITH AND WITHOUT ANGULAR FORCES

Interatomic potentials of the embedded atom and embedded defect types were derived for the Ti-Al system by empirical fitting to the properties of the L1(0) TiAl tetragonal phase. Consideration was also given to properties of the D0(19) Ti3Al and the D0(22) TiAl3 phases. The embedded atom potentials reproduce most of the properties needed, except that L1(0) TiAl presents one negative Cauchy pressure, meaning that the elastic constants cannot be fit exactly using the embedded atom method. The embedded defect technique for angular forces was used in order to fit the elastic constants correctly. Keeping the same effective pair interaction of the embedded atom potential, the effects of angular forces were studied using the embedded defect technique. The strongest effects of the angular forces are seen in the values of the elastic constants. Planar fault energies change by about 5%. The potentials were tested for the lattice properties of other stable and metastable phases of interest in the binary system. It was found that the addition of angular forces has little effect on phase stability, and c/a ratios of the tetragonal and hexagonal structures. The present potentials are adequate for simulation of defects in various phases of the Ti-Al system.