Prior Β-phase Research Articles

Nanoindentation of zirconium oxide films prepared near the α/β transformation temperature

Zirconium oxidized above the α/β transformation temperature and quenched to room temperature, had a needle-like prior-β phase. As prior-β zirconium was known to influence the mechanical properties of the cladding tube during a loss-of-coolant accident (LOCA), the nanochemical properties of prior-β zirconium were studied by nanoindentation tests at room temperature. The nanohardness and the oxygen distribution of prior-β phase have wave undulations whose wavelengths are almost the same as the grain size in the prior-β phase. A grain in the prior-β phase has nanohardness distribution caused by the difference in oxygen concentration.

1161. ジルコニウム-酸素-水素3元系計算状態図

In the present study, the phase diagrams for zirconium-oxygen-hydrogen ternary system were assessed between 573.15K and 1, 473.15K by means of CALPHAD technique. The calculated ternary isothermal section of zirconiumoxygen-hydrogen system at 973.15K was in good agreement with the experimental diagram. The calculated and experimental Sieverts' constants also accorded well. Isothermal sections of the other temperatures were also obtained, and drastic shifts of phase boundaries were prospected. From the zirconium (with hydrogen)-oxygen pseudo binary phase diagrams, it was predicted that dissolved hydrogen let the oxygen content for prior-β phase increase, and that the zirconium based fuel cladding became less ductile by the addition of hydrogen.

Carbides precipitated from the melt in a Zr-2.5Nb alloy

Abstract An experimental method is presented which leads to the formation of carbides similar in size (3 to 8 μm) and composition to those observed in pressure tubes of CANDU-type reactors. The method is based on melting of the Zr-2.5Nb alloy in a graphite crucible, where isothermal C diffusion in the Zr-Nb melt took place. As a result of the diffusion couple liquid Zr-2.5Nb/solid graphite, a carbide layer, up to 100 μm thick, grew attached to the crucible wall, together with carbide particles whose size was in the micrometer range. The smallest particles were arranged in rows determined by the prior β-phase grains. The main carbide phase detected was the cubic MC1−x; hexagonal M2C was also detected (M stands for metal). In some experiments that involved quenching from the β-phase, the ω-phase was detected. Its occurrence was ascribed to the interstitial atoms (C, O, N) present in the samples.

The variation of stacking order and structure-symmetry in copper-base martensites

The influence of ordering on the structure of copper-base martensites has been studied. The ordering, occurring during quenching in the prior β-phase is responsible for the orthorhombic distortion. This orthorhombic distortion varies with composition and determines the variation of the total stacking shift density. The stacking fault density may be smaller, equal, or larger than 1 3 ; the stacking sequence observed in the martensite is then ABCBCACAB + ABC, ABCBCACAB and ABCBCACAB + AB.