As an electrical contact material that is compatible with the recent trend of miniaturization of electronic devices and components, the authors have been investigating electrodeposited amorphous gold alloys with properties that are unaffected by their crystal-grain size, unlike conventional electroplated hard gold. Amorphous alloys in general, however, are known to suffer from high electrical resistivity because of the short mean free path of electrons in such alloys. To resolve this problem, we developed a process of electroplating Au-Ni alloy films with a mixture of nanocrystalline and amorphous phases and investigated the films' physical characteristics. Results show that those Au-Ni films with mixed phases possess low electrical resistivity, retaining corrosion resistance in a range of practical tolerances. The microstructure of the new material of nanocrystalline-amorphous Au-Ni alloy excels in mechanical strength while retaining the properties of Au. Moreover, it is thermally stable at temperatures up to 300°C. Consequently, this new material is expected to be useful as a material for electrical contact surfaces. Furthermore, this study revealed that the electroplated Au-Ni alloy film microstructure is controllable by selecting suitable bath compositions and plating conditions.
The galvannealing behaviors of Ti-IF steel and P-added steel are affected by the application of sulfur before annealing. For this study of those effects, the amounts of sulfur on the steel surface were 5-500 mg/m2. In each steel, application of 500 mg/m2 of sulfur increased the number of ζ crystals, which were densely and randomly distributed. Furthermore, the galvannealing rate of each steel was higher than in steels without sulfur application. The ferrite grains of the annealed surface with 500 mg/m2 of sulfur were finer than those with less than 50 mg/m2 of sulfur. Moreover, small (Fe,Mn) S particles formed along the fine grain boundaries. The thickness of the area consisting of those fine grains, which were as large as 2 μm, was approximately 0.8 μm. The (Fe,Mn) S particles were formed as the steel was annealed after application of sulfur on the surface. The recrystallized ferrite grains on the surface were fine because the particles suppressed the grain growth. In galvannealing of the steel, the fine ferrite grain boundaries are the outburst reaction sites: they increased galvannealing sites and raised the galvannealing rate. Results show that the galvannealing rates of steels with added Ti-IF and P were almost equal.