THE EFFECTS OF CHROMIUM ON NIAL INTERMETALLIC ALLOYS .1. MICROSTRUCTURES AND MECHANICAL-PROPERTIES

The effects of Cr on the microstructure and mechanical properties of NiAl have been characterized. It is shown that Cr is an efficient solid solution strengthener in NiAl, effectively tripling the 0.2% yield strength at the 1 at. % level; this is also its maximum solubility. The presence of Cr also increases the BDTT of NiAl by approximately 150K and reduces the already limited ductility to essentially zero. Larger alloying additions produce fine alpha-Cr precipitation. However, the associated hardening contribution due to precipitation is relatively minor compared with solid solution effects. Independently of Cr content, stoichiometric deviation was observed to produce significant increases in strength and BDTT. It is shown that hardening due to both intrinsic and extrinsic substitutional defects is ultimately a function of the solubility, site preference, and alloying strategy (e.g., a particular Ni/Al ratio, or Cr substituted solely for either Ni or Al) of the Cr addition.