Abstract:

NiAl based two phase (β+γ) alloy Ni 30Al 1Hf was prepared by a directionally solidified method. It was found that the microstructure of the alloy was composed of β NiAl dendrites surrounded by interdendritic γ phases, There is an orientation relationship between β and γ phases in the as cast state. Homogenization at 1280℃/6h followed by air cooling or oil quenching resulted in the β NiAl phases in the two alloys mostly transformed to NiAl martensites . In the meantime, the volume percent of the γ Ni3Al phases decreased with increased cooling rate. After tensile testing at 900℃, all of the martensites disappeared, while γ precipitates were formed in the β NiAl phases.

Key words: NiAl, two-phase alloys, micr ostr uctur e, phase transformations