The effects of alloying additions on the mechanical properties of the B2 intermetallic NiAl have been investigated in both the melt-spun ribbon and consolidated, bulk form. The study is based on a matrix of NiAl-based alloys with up to 20 a/o Co and Fe additions and with reduced Al levels in the range of 30 – 40 a/o. Characterization of the melt-spun ribbon by optical and scanning electron microscopy indicates a range of microstructures: single phase β γ, necklace phase surrounding either martensitic or β grains, and a mixture of equiaxed martensitic and γ grains. Bend ductility is present in melt-spun and annealed ribbons exhibiting the γ necklace structure and in a single phase β material containing 20 a/o Fe.

The analysis of compressive flow behavior on consolidated, bulk specimens indicates that the single phase γ alloys exhibit a continuous decrease in yield stress with increasing temperature and profuse microcracking at grain boundaries. In contrast, multiphase (γ + either martensite or β) alloys tend to display a peak in flow stress between 600 and 800K with little or no signs of microcracking. In general, heat treatments which convert the martensitic grains to β + γ result in improved strength at temperatures above 600K and better resistance to crack initiation. These results are discussed in terms of the effects of β, martensite and γ on the yield stress and flow behavior of NiAl-based alloys.