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The effect of solid solution supersaturation on the precipitation of γ' 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℃, 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 γ'. A transition from uniform to bimodal γ' 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 γ' precipitates. The microstructural observations were discussed in view of both kinetics and crystallographic considerations.