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 [ 1 ¯ 011 ] α // [ 1 ¯ 100 ] ω and (1 ¯ 01 1 ¯) α // (1 ¯ 1 ¯ 20) ω with the α-Zr matrix but is thermally unstable, fully reverting back to α-Zr phase upon heating above 350 °C. [Display omitted] [ABSTRACT FROM AUTHOR]