THE COBALT-NIOBIUM-NICKEL SYSTEM

An isothermal section of the Co-Nb-Ni system was studied at 1200 degre es C with alloys annealed for 288 h (12 days) using XRD and metallogra phy. Phase boundaries of several phase regions were determined through elemental analysis of phases in equilibrium using a scanning electron microscope. Niobium solubility in fee Co-Ni alloys was found to be si milar to 9 at.% Nb. A large extension of the Co2Nb phase region (from similar to 21 at.% Nb to similar to 36 at.% Nb and up to similar to 55 at.% Ni) was found. A continuous series of solid solutions exists for the mu phase. The mu-phase region appears to be narrow, similar to 6 at.% Nb wide. The NbNi3 and Co3Nb phase boundaries were not determined , but there are indications that they extend from the binaries by abou t 15 at.% Co and 10 at.% Ni, respectively, Existence of a phase or pha ses at similar to 67 at.% Nb was detected. However, inconsistency of p hase relations indicates that these phases may arise due to inability to attain proper phase equilibrium at this high Nb content.