Effect of hydrogen concentration and cooling rate on hydride precipitation in α-zirconium

Reactor-grade zirconium specimens containing from 50 to 640 ppm hydrogen have been cooled from solution-treatment temperatures at different rates by water-quenching, oil-quenching, air-cooling and furnace-cooling. Optical and electron metallography have shown that the average size of the hydrides, the proportion of the hydrides located at grain boundaries, and the proportion of the equilibrium delta-hydride increased as the hydrogen concentration was increased and/or the rate of cooling was decreased. The precipitate distributions and relative amounts of the γ and delta hydrides observed can be explained in terms of nucleation theory. (Auth.)