Study of phase transition and local order in equiatomic and nonequiatomic mixtures of HfNbTaTi under uniaxial loading from molecular dynamics simulations

Abstract

We simulate an alloy of HfNbTaTi mixed in six different proportions and also of the equiatomic system under uniaxial tensile loading at 300 K. Molecular dynamics simulation trajectories are analyzed using radial distribution functions, OVITO, bond-orientational order parameters, and coordination numbers. Equiatomic and the two other alloys (Hf0.31Nb0.23Ta0.23Ti0.23 and Hf0.23Nb0.31Ta0.23Ti0.23) containing comparable fraction of elements deform similarly through the formation of an amorphous state. Two alloys rich in Nb (Hf0.17Nb0.50Ta0.16Ti0.17) and Ta (Hf0.17Nb0.16Ta0.50Ti0.17) deform similarly resulting in the formation of bcc atoms, which transform to fcc at higher loading. Finally, alloys rich in Hf (Hf0.50Nb0.16Ta0.17Ti0.17) and Ti (Hf0.17Nb0.16Ta0.17Ti0.50) deform resulting in high dislocation densities and hcp atoms. These two hcp-rich alloys also undergo strain hardening. In each mixture during loading, local orientational order of all the different elements changes similarly. Atoms prefer to pair with other atoms than to themselves during tensile loading.