Microstructural development in complex nickel-aluminum bronzes

The development of microstructure in complex nickel-aluminum bronzes of nominal composition Cu-10 wt pet Al-5 wt pct Ni-5 wt pct Fe, during continuous cooling from temperatures approaching the solidus, has been investigated using optical and electron microscopic techniques. At high temperatures the alloy consists of bccβ phase, and as the temperature is lowered the fcc copper-rich α phase is precipitated with a Widmanstätten morphology. As the temperature continues to decrease, Fe₃Al precipitates form in theβ phase and this is followed by the formation of Fe₃Al precipitates in the a phase. On further cooling theβ phase decomposes eutectoidally into ga+ NiAl; the eutectoid reaction initiates at thea/β interface and grows into theβ regions. Under normal cooling conditions the decomposition ofβ into α+ NiAl does not reach completion and the remnantβ phase transforms to martensite.