THE STABILITY OF PASSIVE STATE OF MELT-SPUN AMORPHOUS CHROMIUM-BASE ALLOYS

The CrNi alloy was vitrifiable by the addition of about 15 at% phosphorus. The melt-spun alloys containing over 15 at% phosphorus exhibit a very low corrosion rate of the order of 10-4 mm/y in 6 M HCl solution at 30°C. They passivate spontaneously and show no passivity breakdown by immersion or cathodic polarization. The alloys containing 14.9-15.0 at% phosphorus are amorphous by X-ray diffraction and passivate spontaneously, but are activated by prolonged immersion or cathodic polarization. Accordingly, the latter alloys show about four orders of magnitude higher corrosion rate than the former alloys. XPS analysis revealed that the passive film on melt-spun amorphous CrNiP alloys consists exclusively of hydrated chromium oxyhydroxide, regardless of the fact whether activation occurs or not by prolonged immersion or cathodic polarization. © 1990.