PRECIPITATION BEHAVIOR OF Co PHASES IN B2-ORDERED(Ni,Co)Al COMPOUND

The precipitation behavior of Co phases in B2-ordered (Ni,Co)Al has been investigated in terms of transmission electron microscopy. Fine precipitation of fcc-Co occurs in (Ni,Co)Al by aging at temperature over 973K. The orientation relationship between the fee-Co precipitates and the B2-(Ni,Co)Al matrix follows the Kurdjumow-Sachs (K-S) orientation relation. But when the aging temperature is under 873K the Co precipitates have a hcp crystal structure. The orientation relationship between the hep-Co precipitates and the B2-(Ni,Co)Al matrix follows the Burgers orientation relation. (Ni,Co)Al is hardened appreciably by the fine precipitation of both the fee-Co and hep-Co phases. The temperature dependence of the yield strength of precipitate-containing BS-ordered (Ni, Co)Al was investigated by compression tests over the range of 298-1273K. The fine precipitation of Co phases enhances greatly the low and intermediate temperature yield strength. When the deformation temperature was over 87SK, the strength of precipitate-containing (Ni, Co)Al is comparable to ternary dual-phase (Ni,Co)Al Ni3Al alloy.