Effects of Corrosion-Resistant Elements on the Corrosion Resistance of Amorphous Bulk Ni-Cr-Mo-Ta-Nb-4P Alloys in Concentrated Hydrochloric Acids

摘要

Rod-shaped amorphous bulk Ni-Cr-Mo-Ta-Nb-P alloys resistant to concentrated hydrochloric acids were prepared by copper-mold casting. Most of them were spontaneously passive and immune to corrosion in 6 and 12 M HCl. Corrosion resistance was improved remarkably when both chromium and molybdenum were added to the alloy with sufficient tantalum contents. Spontaneous passivation was due to presence of stable air-formed films, in which chromium was particularly concentrated in addition to enrichment of tantalum. The angle resolved XPS revealed that chromium and molybdenum were rich in the inner part of the film. The high corrosion resistance was interpreted in terms of the high stability of the air-formed oxide film consisting of the outer double oxide of chromium and tantalum with a high stability in concentrated hydrochloric acids and the inner molybdenum oxide acting as the diffusion barrier.