ANODIC POLARIZATION BEHAVIOR OF COBALT-CHROMIUM ALLOYS IN SULFURIC ACID SOLUTIONS.

The anodic polarization behavior of annealed cobalt-chromium alloys in hydrogen saturated sulfuric acid solutions was investigated by using a potentiostatic technique. Polarization curves were obtained for eleven specimens, ranging from 100 cobalt to 100 chromium, in one normal, five normal, and ten normal sulfuric acid solutions at room temperature. The polarization curves for all specimens, except pure cobalt and the 95Co-5Cr alloy, exhibited active, passive, and transpassive behavior. Cathodic currents or loops were found in the passive region for all of the five specimens containing more than 30 chromium. Only the secondary active region was obtainable for five of the polarization curves, causing variation in the general trend of the polarization data. Increasing the acid concentration had the overall effect of shifting the polarization curves for each specimen in the noble direction. The general effect of increasing the chromium content was to shift the active region in the active direction without changing the transpassive region potential. Tafel behavior was observed in the transpassive region for all specimens containing more than 5 chromium. The Tafel slope varied from 0.168-0.239 for the high cobalt alloys to 0.038-0.048 for the high chromium alloys. As the chromium content of the specimens increased, the corrosion potential slowly became more active, except with six specimen-solution combinations where only secondary corrosion potentials were measurable. In all but two cases, the corrosion potential became more noble with an increase in pH. Author