DUCTILITY ENHANCEMENT IN NIAL (B2)-BASE ALLOYS BY MICROSTRUCTURAL CONTROL

An attempt to improve ductility of NiAl (B2)-base alloys has been made by the addition of alloying elements and the control of microstructure. It has been found that a small amount of fcc gamma phase formed by the addition of Fe, Co, and Cr has a drastic effect not only on the hot workability but also on the tensile ductility at room temperature. The enhancement in ductility is mainly due to the modification of beta-phase grains by the coexistence of gamma-phase. The effect of alloying elements on the hot forming ability is strongly related to the phase equilibria and partition behavior among gamma, gamma' (L1(2) structure), and beta-phases in the Ni-Al-X alloy systems. The ductility-enhancement method shows promise for expanding the practical application of nickel aluminide.