THE CORROSION BEHAVIOR OF SPUTTER-DEPOSITED AMORPHOUS COPPER NIOBIUM ALLOYS IN 12 N-HCL

Binary Cu-Nb alloys were prepared by magnetron sputtering. The alloys containing 36-66 at% Nb became amorphous. These amorphous alloys were spontaneously passive in 12 N HCl and showed lower corrosion rates than niobium metal. The Cu-89Nb alloy, in which the Nb content responsible for high corrosion resistance was too high to form the amorphous structure, had higher corrosion resistance than the sputter-deposited niobium metal. This alloy was composed of about 20 nm large grains showing an intense reflection close to the 110 reflection of BCC Nb in the X-ray diffraction pattern. The atomic ordering inside the grains was not well established, and this degree of homogeneity based on the disordered structure was high enough to provide higher corrosion resistance than the niobium metal having well developed crystallinity. The Cu-21Nb alloy had a further disordered structure but was not completely amorphous and did not passivate spontaneously, because the alloy Nb content is insufficient. An XPS analysis revealed that the high corrosion resistance of these alloys was due to the formation of the passive film composed mainly of Nb2O5. This passive film also contained some cuprous and cupric chlorides.