CORROSION RESEARCH ROUND‐UP

GERMANY. Oxidation of refractory carbide alloys (hard metals). The effect of additions of tungsten, chromium and tantalum‐niobium on the oxidation rate and structure of the oxide layers was studied on samples of titanium carbide/cobalt bonded, and annealed at 800 to 1,100°C. for 75 hr. If these contain sufficient tungsten carbide to dissolve completely in titanium dioxide (rutile), the tungsten trioxide formed in oxidation, the rate of this latter decreases strongly owing to reduced ion diffusion. If, owing to the higher tungsten carbide content, the proportion of WO3 in the oxide layer becomes so high that the solubility limit for WO3 in TiO2 is exceeded, then CoTiO2, Co2TiO4 and C0WO4 occur in the oxide layer in addition to CoO and TiO2. This decreases oxidation velocity still more.