Effect of refractory alloying additions on mechanical properties of near-stoichiometric NiAl

Alloying effects have been investigated in near-stoichiometric NiAl for the purpose of improving it mechanical properties. NiAl alloys containing up to 3% of Mo, W, Nb, Ta, Zr and Hf were prepared by are melting and drop casting, followed by hot extrusion at temperatures to 1000 °C. The mechanical properties of the NiAl alloys were characterized by tensile and creep testing at temperatures to 1000 °C. Among the alloying elements, Mo is found to be most effective in improving the room temperature ductility of NiAl alloys in stress-relieved conditions. Alloying with 1.0 ± 0.6% Mo almost doubles the room temperature tensile ductility of NiAl and triples its yield strength at 1000 °C. The creep properties of Mo-modified NiAl alloys can be further improved by alloying with up to 1% Nb, Ta and Zr. Alloying with 1% MoZr reduced the creep rate and extended the rupture life of NiAl by more than 5 orders of magnitude. Transmission electron microscope and electron microprobe studies show that the solubility of Mo, Nb and Zr is low, less than 0.1 at.%. Both coarse and fine precipitates enriched with refractory elements are observed, with fine particles about (0.1 μm) distributed within grains. The mechanical properties of these NiAl alloys are discussed in terms of both particle strengthening and solid solution hardening.