Dissolution and precipitation behaviors of hydrides in N18, Zry-4 and M5 alloys

The terminal solid solubilities of hydrides dissolution (TSSD) during heatup and precipitation (TSSP) during cooldown for N18, Zry-4 and M5 alloys with hydrogen concentrations of 20–240 ppm were measured by differential scanning calorimetry (DSC) in the range of 50–500 °C. There is little difference in either TSSD or TSSP solvi among these alloys, and best-fit equations were derived from the two solvi. A significant hysteresis between the solvi of TSSD and TSSP occurred, resulting from the hydride–matrix volumetric misfit strain. Based on the widths of the DSC peaks obtained during cooldown, the average precipitation rates of zirconium hydrides from the super-saturated state were evaluated by best-fit equations. The hydride precipitation is rate-controlled by hydrogen diffusion, and the average rates increased with increasing temperature.