THE CORROSION BEHAVIOR OF SPUTTER-DEPOSITED AMORPHOUS MO-ZR ALLOYS IN12-M HCL

Amorphous Mo-Zr alloys were prepared in a wide composition range of 40 -80 at% zirconium by a magnetron sputtering method. The sputter-deposi ted Mo-Zr alloys exhibit lower corrosion rates than those of molybdenu m and zirconium in 12 M HCl solution open to air at 30 degrees C. The corrosion resistance of Mo-Zr alloys increases with increasing alloy z irconium content, but molybdenum and zirconium improve the corrosion r esistance synergistically. Mo-Zr alloys containing 60 at% or more zirc onium exhibit a passive region in a wide potential range without trans passive dissolution of molybdenum. The presence of zirconium suppresse s both the cathodic reaction for hydrogen evolution and the anodic red uction. The air-formed film is composed of a double oxyhydroxide of zi rconium and molybdenum. Spontaneously passivated films on the alloys c ontaining less than and more than 40 at% of zirconium are composed of molybdenum-enriched and zirconium-enriched oxyhydroxides, respectively . They seem to consist of a bilayer structure; the outer zirconium and inner molybdenum oxyhydroxides. Weak points in each layer in the bila yered passive film seem to be protected mutually by another layer. Thi s appears to be responsible for the high corrosion resistance of the M o-Zr alloys in comparison with alloy constituents.