Microstructural and lattice parameter study of as-cast and rapidly solidified NiAl intermetallic alloys with Cu additions

In the current paper, the effect of Cu additions to the NiAl intermetallic compound on the microstructure and lattice parameter of the β-Ni(Al,Cu) and γ′-(Ni,Cu)3Al phases was investigated. As-cast and rapidly solidified specimens were characterized using X-ray diffractometry, scanning and transmission electron microscopy techniques. Biphasic microstructures composed of the B2 β-Ni(Al,Cu) and L12 γ′-(Ni,Cu)3Al phases were observed in both cases, except in the alloy with 50 at.% Ni, 30 at.% Al, and 20 at.% Cu, which exhibits a martensitic microstructure composed of needles of γ′-(Ni,Cu)3Al with L10 tetragonal structure in the as-rapidly solidified condition. Generally γ′-Ni3Al is reported as an L12 cubic phase and there are many documents concerning such a phase, however, there are few publications with regard to γ′-(Ni,Cu)3Al with tetragonal structure. In addition, the present experimental data confirm the Bozzolo's model on site occupancy of ternary additions to the B2 NiAl intermetallic compound.