Corrosion behavior of Zr-based metallic glasses and composite alloys

(Korrosionsverhalten Zr-basierter metallischer Gläser und Kompositlegierungen)

Fundamental corrosion studies on bulk glassy alloys of compositional types (Zr,Ti,Nb)-(Cu,Ni,Co,Fe)-(Al,Be,Ag,Pd) revealed excellent passivity in halide-free electrolytes within a wide pH value range at room temperature. This is mainly due to their high concentration of valve-metals which form thin barrier-type oxide films on the alloy surfaces. However, chloride-induced local corrosion (pitting) related with severe pit growth and poor re-passivation ability is very typical. Comparative studies with prominent glass-formers revealed that the corrosion susceptibility correlates with the Cu content of the alloys. Moreover, the surface finishing state of a glass, e.g. mechanically ground, fine polished or shot peened, determines surface passivation and corrosion initiation. In particular, structural heterogeneities like crystalline inclusions (cast defects) are critical corrosion initiation sites. In consequence, for glass-matrix composites with significant structural and compositional differences between the constituent phases the corrosion behaviour has to be carefully assessed.    

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