Effect of thermal history on the terminal solid solubility of hydrogen in Zircaloy-4

• The TSS of H in Zry-4 for heat-up and cool-down showed a significant hysteresis.
• The TSSP was significantly affected by previous thermal history.
• The TSSP2 of H in Zry-4 was measured.
• A solubility path during thermal cycling was proposed.

The terminal solid solubility (TSS) of hydrogen in zirconium alloys has a hysteresis. The TSS of hydrogen in Zircaloy-4 during cooling and heating were studied using differential scanning calorimetry (DSC) with a hydrogen content of 40–731 wppm. A significant hysteresis gap was observed between the TSS for dissolution (TSSD) and precipitation (TSSP). It was confirmed that the hydrogen dissolution temperature was unaffected by the previous thermal history in comparison with the hydride precipitation temperature. The TSSP temperature increased with a decrease in the maximum temperature, but a significant temperature gap remained even when the maximum temperature was equal to the TSSD temperature. The terminal solid solubility of hydrogen in Zircaloy-4 can be represented by the following equations.TSSD: C = 2.255 × 105 exp (−39101/RT).TSSP: C = 4.722 × 104 exp (−26843/RT).TSSP2: C = 8.612 × 105 exp (−30583/RT).Based on the experimental results hydrogen solubility path depending on the previous thermal history was proposed.