Study on Precipitation Phenomena in Thin Films of Supersaturated Gold-Nickel Alloy

Abstract

Structure changes of supersaturated gold-nickel alloy after successive agings were studied by means of electron diffraction and electron microscopy. Specimens were prepared by vacuum evaporation and subsequent quenching (Y. Fukano and S. Ogawa, J. Phys. Soc. Japan 14 (1959) 1671). After aging at temperatures lower than 165°C, side maxima appear beside the main spots from the matrix. The side maxima disappear after aging at 250–300°C, indicating that they correspond to pre-precipitations. The side maxima were interpreted by assuming a modulated structure similar to that found in Au-Pt alloy by Tiedema et al. (T.J. Tiedema, J. Bouman and W.G. Burgers, Acta Metallurgica 5 (1957) 310). This implies that gold-nickel alloy at the pre-precipitation stage contains a modulated structure similar to that in Au-Pt alloy. After aging at temperatures higher than 300°C, two stable phases with parallel lattices appear. In this state, Widmanstätten structure was found in electron micrographs.