Tempering of cast nickel–aluminium bronze

Microstructural changes associated with the tempering at 675°C of cast nickel–aluminium bronze, of nominal composition (wt-%) Cu–10Al–5Ni–5Fe, have been investigated using optical, electron optical, and microprobe analysis techniques. The tempering treatment resulted in the elimination of the non-equilibrium martensitic (‘retained β’) phase, precipitation with the α grains, and a coarsening of the as-cast structure. On heating to 675°C the martensite phase, which contained a high density of NiAl precipitates, reconstituted to form the high temperature bcc β phase and, after extended times at 675°C, this phase progressively decomposed into NiAl and α. The precipitates which formed in α grains were based on NiAl and had the B2 structure. These precipitates nucleated as laths either in the α matrix or on the pre-existing particles of Fe3Al; the two morphologies exhibited the Kurdjumov–Sachs and the Nishiyama–Wasserman orientation relationships, respectively, with α.