CORROSION-RESISTANCE OF CR-BASED AMORPHOUS METAL-ALLOYS

The corrosion resistance of Cr-based amorphous metal alloys at high temperature in concentrated acidic solutions of commercial interest was examined. Direct corrosion measurements and surface studies indicate that in binary, amorphous CrX alloys, their chemical stability is a strong function of the identity of the X component. The X = P, N, As and C samples are the most stable having excellent corrosion resistance to both oxidizing and reducing acidic solutions. Corrosion occurs in these materials at high temperature (> 90°C) in concentrated HCl solutions. The X = Si, Al and B samples are stable in mildly oxidizing solutions like H2SO4 and unstable in strongly reducing solutions like HF. Their chemical properties are dominated by the formation of a mixed oxide surface (Cr-silicate, Cr-aluminate, and Cr-borate) upon exposure to aqueous solutions. The X = Sb amorphous alloys did not passivate in any of the test solutions of this study. The nature of the passive layer and the passivation process is discussed for Cr-based amorphous alloys. At high temperatures, many of the CrX amorphous alloys exhibit a transition from a passive to an active corrosion state. Additions of Mo and Ta to the CrX amorphous alloys further improvement their corrosion resistance by increasing the temperature of this transition. © 1990.