Effect of Solid Solution Supersaturation on Precipitation of γ′ in Rapidly Quenched Ni-Al Binary Alloys

The effect of solid solution supersaturation on the precipitation of gamma' in rapidly quenched Ni-Al binary alloys containing 11.6, 14.2 and 16.5 at. pct Al was investigated. The samples were solutioned at 1250 degrees C, quenched in iced brine, and then analyzed by electron microscopy and XRD (X-ray diffraction) techniques. In Ni-11.6 at. pct Al alloy, ordering and phase separation took place simultaneously, resulting in a uniform distribution of gamma'. A transition from uniform to bimodal gamma' phase distribution occurred in the composition range between 14.2 and 16.5 at. pct Al. This transition was accompanied by changes in the morphology of gamma' precipitates. The microstructural observations were discussed in view of both kinetics and crystallographic considerations.