AbstractThe as—extruded microstructures of two alloys in the two phase field consisting of Ni3Al and NiAl in the Ni—Al phase diagram exhibit fibrous morphologyand consist of Ll2 Ni3Al and B2 NiAl. These as—extruded microstructures can be modified dramatically by suitable heat treatments. Martensite plus NiAl or martensite plus Ni3Al microstructures are obtained upon quenching from1523 K. Aging of martensite at 873 K results in the recently identified phase Ni5Al3 whereas aging at 1123 K reverts the microstructures to Ni Al plui NAl. The microstructures with predominantly martensite or Ni5Al3 phases are brittle in tension at room temperature. The latter microstructure does not deformplastically even in compression at room temperature. However, some promise of room temperature tensile ductility is indicated by the Ni3Al plus NiAl phase mixtures.