Atomistic simulations of alloying additions to NiAl

Alloying additions of Ti to NiAl are of technological interest since NiAl+Ti alloys are extremely creep resistant. Also, Cr additions are of interest due to its low solubility and the potential for precipitating α-Cr, which at higher volume fractions acts as a ductile phase toughening component. However, very little is known about the structure of the corresponding ternary alloys besides the formation of Ni–Al–Ti Heusler precipitates or the phase separation of Cr in the NiAl+Cr alloys. Consequently, an atomistic analysis of NiAl+X (X=Ti, Cr) alloys using the method of Bozzolo, Ferrante and Smith (BFS) for alloys, along with complementary TEM analysis, was performed. The results include the determination of the corresponding solubility limits for each alloying addition, site preference and the formation of ordered structures within the B2 NiAl matrix. Analytical results as well as temperature dependent Monte Carlo numerical simulations are presented, highlighting the formation of Ni2AlTi Heusler precipitates and the α-Cr phase separation, in excellent agreement with experiment.