“Order–order” kinetics in Ni 3Al 1− xFe x. Monte Carlo simulation of the effect of iron

Abstract

The influence of Fe alloying on the long-range ordering (LRO) kinetics in Ni 3Al 1− x Fe x has been studied in atomistic scale by means of Monte Carlo (MC) simulations of “order–order” relaxations in a model system A 3B 1− x C x showing, similarly to Ni 3Al 1− X Fe x , destabilization of the L1 2-ordered phase upon admixing a ternary element C. The relaxations were simulated within Glauber dynamics implemented with vacancy mechanism of atomic jumps. The two-time-scale structure of the relaxations known from the case of Ni 3Al was still observed in the quasi-binary A 3B 1− x C x . Detailed analysis of the elementary atomic-jump statistics revealed, however, a dominance of the C-atom jumps in the creation/elimination of minority (B and C) antisite defects, as well as in the migration of B- and C-antisite within the majority sublattice. The origin of the enhanced role of the C atoms in the process has been explained by analysing the vacancy availability in the first coordination shell of the C atoms and the energetics of particular atomic jumps. The results elucidate the experimentally observed equality of the activation energies for “order–order” kinetics in Ni 3Al 1− x Fe x and for Fe diffusion in Ni 3Al.