On the Microstructure and High-Temperature Stability of Nano-Grained Zircaloy-4

A nano-grained microstructure of an α-Zr alloy (Zircaloy-4) was produced by high-pressure torsion, which shows evidence of a metastable ω-Zr phase, rather than β-Zr, determined by combining synchrotron X-ray diffraction and detailed electron microscopy observations. The ω-Zr phase is retained at ambient conditions and shows a new orientation relationship of [-1011] α // [-1100] ω and (-101-1) α // (-1-120) ω with the α-Zr matrix but is thermally unstable, fully reverting back to α-Zr phase upon heating above 350 °C