The precipitation behaviour of Co–Ni–Cr-base alloys containing various amounts of Nb has been studied. The main strengthening phase in 5·0 and 8·0% Nb alloys was found to be orthorhombic β-Ni3Nb. This phase precipitates on {111} matrix planes and has a plate-like shape. In 3·0 and 5·0% alloys carbon, present as an impurity element, gave rise to NbC precipitates that were responsible for the minor peaks in the hardness/ageing curves. Precipitation of NbC in 5·0% Nb alloy occurred in association with stacking faults, which also appear to provide nucleation sites for the precipitation of β-Ni3Nb phase. Nucleation of β-Ni3Nb also occurs in the stacking-fault-free areas of the matrix.
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