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Microstructural evolution of a nickel-base single-crystal superalloy during homogenisation at ultra-high temperature has been investigated using scanning electron microscope and electron probe microanalyzer. The results show that incipient melting occurs and all γ/γ′ eutectics are re-melted into liquid after 1 h homogenisation at 1350°C. The volume fraction of IM decreases gradually with increasing homogenisation time. The IM disappears totally after 14 h homogenisation. Moreover, the formation of the TCP phase is suppressed during long-term thermal exposure at 1100°C for the reduction of element segregation, especially the segregation of refractory element Re was reduced during ultra-high-temperature homogenisation. The microstructure evolution of IM was discussed based on the element diffusion during homogenisation.

Metallic Ag films were observed to be layer-by-layer oxidized by reactive-sputtering deposition of TiO2, leaving a layer of Ag2O with hexagonal structure (h-Ag2O), which is rarely reported in literature. The oxidation of Ag film behaved rather abnormally because it was not until the Ag film was completely oxidized that amorphous TiO2 (a-TiO2) could form on the h-Ag2O layer, thus providing an effective method for fabrication of h-Ag2O films and a-TiO2/h-Ag2O heterostructures. O atoms in the plasma were proved to be responsible for the oxidation of Ag film, and the formation of TiO2 on the film that was not completely oxidized was disenabled, probably due to the formation of a new kind of oxide, (TiAg)­O2. The optical properties of h-Ag2O films were studied for the first time, and the photocatalysis was found to be better than that of TiO2 films. The a-TiO2/h-Ag2O heterostructures exhibited excellent photocatalytic activity under ultraviolet and visible-light irradiation, much better than that of the a-TiO2 and the h-Ag2O single-layer films. The photocatalysis was discussed using the special electronic structure built in the a-TiO2/h-Ag2O heterostructures. In addition, decomposition of Ag2O was suggested to play an important role in the photocatalysis.

Reactive sputtering deposition of metal oxides onto Ag films for fabrication of hierarchically structured silver oxide films with rich porosity.

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