Study of Electrolytic Hydrogen Charging Process and Microstructure Evolution of Zirconium Alloy

The cladding tubes of a newly designed SZA-4 zirconium alloy of Zr-Sn-Nb system were hydrided using electrolytic hydrogen charging technique. The effect of electrolytic hydrogen charging time on the hydrogen absorption amount and the type and distribution of hydrides, as well as the effect of homogenization annealing time on the type and distribution of hydrides in SZA-4 zirconium alloy were investigated. The results show that the hydrogen absorption amount of samples increases with the increase of hydrogen charging time, and a parabola relationship between hydrogen absorption amount and hydrogen charging time was found. Microstructure analysis shows that the hydride layers form on the surface of the samples after electrolytic hydrogen charging, while the inner part remains the zirconium alloy matrix. And the thickness of the hydride layers increases with the increase of hydrogen charging time. The phase structure analysis shows that the hydride layer is merely composed of delta-ZrH1.66 at the beginning and increases with hydrogen charging time. When hydrogen charging time reaches 24 h, the hydride layer is composed of epsilon-ZrH1.801 and delta-ZrH1.66 phase. After 400 degrees C/6 h homogenization annealing, the thickness of the hydride layer of hydriding samples further increases, and platelet-like hydrides precipitate within the tubes along the circumferential direction. The phase structures analysis of the homogenization annealing of hydriding samples shows that epsilon-ZrH1.801 disappears and the original delta-ZrH1.66 hydride transforms into delta-ZrH1.5 hydride in hydride layers. And after 400 degrees C/96 h homogenization annealing treatment, all of hydride layers disappear, and thin platelet-like hydrides evenly distribute in the samples.