A metallographic study of the terminal solubility of hydrogen in zirconium at low hydrogen concentrations

The terminal solid solubility of hydrogen in alpha zirconium has been investigated using optical metallographic techniques. Hydrogen concentrations from 4 to 230 mg/kg were studied and good agreement found with previous determinations at concentrations above 25 mg/kg. Based on electron microscopic analysis of the hydrides, the solvus measured at hydrogen concentrations less than 25 mg/kg was determined to be that for the gamma hydride phase. From a least-squares fit of the data, the terminal solid solubility of this phase is given by the expression 3.43 × 10 4 exp(−32200/ RD) mg/kg.