Corrosion Behavior

There has been a growing interest in the corrosion behavior of bulk metallic glasses (BMGs). The enhanced glass formability of these amorphous alloys has made the fabrication of bulk size components easier and thereby improving their prospects for engineering applications. The corrosion behavior of BMGs is particularly pertinent when considering biomedical applications and is also relevant for other applications, e.g., watches and electronic casings. The corrosion resistance is also a critical factor for the consideration of their use in hostile or chemical environments.

The corrosion properties of an amorphous alloy are expected to be superior to those of its crystalline counterpart due to its chemical homogeneity and lack of microstructure. Amorphous alloys lack grain boundaries, dislocations, and other defects that are commonly the culprits behind the localized corrosion observed in crystalline alloys. The rapid cooling rates required to produce amorphous alloys are believed to promote chemical homogeneity since there is no time for appreciable solid-state diffusion. The short time available for significant diffusion suggests that amorphous alloys should lack second phases, precipitates, and segregates. However, this assertion has been shown not to always be true for BMGs. It should be noted that the second phases (crystalline inclusions) observed in some BMGs are a result of heterogeneous nucleation often caused by impurities in the melt.