The surface microstructure of Ni-W alloy tapes, which are used as substrates to form films of high-temperature superconductors and photovoltaic devices, has been studied. Several samples of a Ni95W5 tape (Evico) annealed under different conditions were analyzed using scanning electron microscopy, energy-dispersive X-ray microanalysis, electron diffraction, and electron energy-loss spectroscopy. NiWO4 precipitates are found on the surface of annealed samples. The growth of precipitates at a temperature of 950 degrees C is accompanied by the formation of pores on the surface or under an oxide film. Depressions with a wedge-shaped profile are found at the grain boundaries. Annealing in a reducing atmosphere using a specially prepared chamber allows one to form a surface free of nickel tungstate precipitates.
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