Phase stability and defect structure of the C15 phase in the Hf-V-Nb system

摘要

The phase stability and defect structure in the C15 HfV2-based Laves phase were studied by a combined experimental and theoretical investigation. It was found that C15 HfV2 can be alloyed with a large amount of Nb (about 20 at.%), where the Nb atoms occupy both I-If and V sites, and the lattice parameters of the ternary C15 phases containing the same Nb content decrease with increasing V to Hf ratio. The extended defects observed in the ternary C15 phase are extrinsic {111} stacking faults, {111}[112] annealing twins, and faceted Sigma = 3 ([111], 70.53 degrees) grain boundaries. Examination of the extrinsic {111} stacking faults revealed that synchroshear may occur in this C15 phase. The total and l-projected density of electronic states of C15 HfV2 were obtained by first-principles total energy and electronic structure calculations. The phase stability, Nb site occupancy and compositional dependence of the lattice parameter of the C15 phase in the Hf-V-Nb system are qualitatively explained by geometric and electronic structure considerations. [References: 39]