Effect of deviation from stoichiometry and alloying on deformation of NiAl-based alloys in the hard orientation

The relatively simple crystal structure of B2 intermetallic compounds such as FeAl and NiAl belies the fact that they exhibit a wide range of mechanical properties. These diverse characteristics may arise upon deviation from stoichiometry, particularly in both NiAl and FeAl systems which have wide B2 phase fields, as well as the presence of low-level; impurities or ternary alloying additions. These compositional effects are often far more profound and complex than those anticipated from classical solute-dislocation interaction theories. In this presentation, we will discuss several examples of the dramatic effects of both stoichiometry and alloying on dislocation structure and deformation behavior in B2 compounds. As one example, we will contrast the behavior of Ni-50Al with Ni-44Al as a function of temperature - particularly for [001] oriented single crystals. The effect of alloying additions, such as Hf, on the dislocation structures and properties of NiAl-based alloys will also be discussed. As a third example, the (Fe,Ni)-Al pseudobinary system offers an opportunity to explore the effect of Fe/Ni ratio while remaining within the ordered B2 phase field. In this way, the properties of substitutional alloys bridging the behavior from FeAl to NiAl may be investigated. Single crystals with a wide range of compositions have been grown, and the results of experiments and microstructural analysis following compression testing of [001] oriented single crystals with a wide range of Fe/Ni ratios will be presented.