Formation and Dissolution of γ’ Precipitates in IN792 Superalloy at Elevated Temperatures
Precipitation of γ’ phase in nickel-base superalloy IN792-5A was studied using in-situ Small Angle Neutron Scattering (SANS). It was found that additional precipitates are formed after reheating above 600 °C when the material is previously fast cooled (100 K/min) from 900 °C. The size distribution and volume fraction of the additional γ’ precipitates as well as of the already present medium-size precipitates in dependence on temperature were evaluated. The small precipitates can influence mechanical properties of the alloy, which exhibits an anomaly in the temperature dependence of the yield stress. Volume fraction of all precipitate populations above 900 °C was estimated as well.
Characterization of γ′ Precipitates in Cast Ni-Based Superalloy and Their Behaviour at High-Homologous Temperatures Studied by TEM and in Situ XRD
In situ X-ray diffraction and transmission electron microscopy has been used to investigate René 108 Ni-based superalloy after short-term annealing at high-homologous temperatures. Current work is focused on characterisation of γ′ precipitates, their volume fraction, evolution of the lattice parameter of γ and γ′ phases and misfit parameter of γ′ in the matrix. Material in the initial condition is characterised by a high-volume fraction (over 63%) of γ′ precipitates. Irregular distribution of alloying elements was observed. Matrix channels were strongly enriched in Cr, Co, W and Mo, whereas precipitates contain large amount of Al, Ti, Ta and Hf. Exposure to high-homologous temperatures in the range 1100–1250 °C led to the dissolution of the precipitates, which influenced the change of lattice parameter of both γ and γ′ phases. The lattice parameter of the matrix continuously grew during holding at high temperatures, which had a dominant influence on the more negative misfit coefficient.
Specificity of glucose oxidase.
Abstract The specificity of glucose oxidase for catalyzing the oxidation of β- d -glucose in contrast to α- d -glucose, other hexoses, and pentoses was investigated. The enzyme appears to catalyze the oxidation of the beta form only, and the mutarotation of the alpha form is rate limiting. d -Galactose, d -mannose, and d -xylose are slowly oxidized in the presence of glucose oxidase, but approximately 300 times as much enzyme is required to give a rate of oxidation equal to that for glucose. Galactose and mannose are oxidized directly to the corresponding aldonic acids without a prior conversion to glucose. Thirtyfold purification of the enzyme does not increase the ratio of glucose to galactose oxidation. d -Arabinose, which itself is not oxidized, inhibits glucose oxidase in catalyzing the oxidation of glucose. The clinical implications of these specificity studies are discussed.