Some aspects in designing passive alloys with an enhanced corrosion resistance

The technical and biomedical use of alloys containing reactive metals in aggressive environments is possible due to the spontaneous formation of a thin oxide barrier layers which slow down corrosion reactions by several orders of magnitude. Oxide films of several important technical metals like Cr and Cu are cation conductors with p-type semiconducting behaviour, and therefore they are electrochemically unstable and susceptible to anodic decomposition or localized corrosion. Alloying with elements that easily undergo oxidation and formation of highly charged cations can significantly stabilize the p-type oxide films by decreasing their ionic and increasing electronic conductivity. This method is an effective way how to design an alloy with significantly greater corrosion resistance in aggressive environments in comparison with its constitutive elements. The present paper describes several examples of alloying reactive metals to produce the alloys with improved corrosion resistance. Selected systems and the conditions under which the investigation was performed could be considered as the real conditions in which the alloys are used.