The Monte Carlo simulation of the ordering kinetics of fcc to Ll2 structure in NiAlX ternary alloys

The Monte Carlo method was applied to the simulation of temporal evolutions of atomic arrangement in Ni-base ternary alloys. The ordering process is controlled by randomly selecting a single atom with one of its neighbouring atoms. The evaluation of the order parameter for Ni—22at.%Al—3at.%Ti, Ni—23.5%Al—3at.%Cr and Ni—25at.%Al—3at.%Co ternary alloys and Ni—25at.%Al binary alloy shows that no significant effects of Ti and Co on the ordering kinetics is observed. However, ordering kinetics are retarded by the addition of Cr. The formation rate of the γ′ phase in the Ni—17at.%Al—3at.%X (X = Ti, Cr and Co) alloy is highest in the NiAlCo alloy and lowest in the NiAlTi alloy. The variations of average volume in the NiAlCo alloys is very small. On the other hand, the average volume increases proportionally with time and approaches a constant value in the NiAlTi alloy. The variation of the partition coefficient of Ti indicates the enrichment of Ti in the γ phase. Both Co and Cr are enriched in the γ′ phase. With the increase of bulk Al content the concentrations of Cr and Ti decreases. In NiAlTi ternary alloys, all Ti atoms substitute for Al atoms in the Al sublattice in the γ′ phase. The simulation results are cosistent with those obtained using cluster variation analysis.