Effect of Grain Size on Corrosion: A Review

Grain refinement is known to lead to improvements in strength and wear resistance. Inherent processing involved in grain refinement alter both the bulk and the surface of a material, leading to changes in grain boundary density, orientation, and residual stress. Ultimately, these surface changes can have an impact on electrochemical behavior and, consequently, corrosion susceptibility as evidenced by the large number of studies on the effect of grain size on corrosion, which span a range of materials and test environments. However, there has been limited work on developing a fundamental understanding of how grain refinement and more generally how grain size affects the corrosion resistance of an alloy. Existing literature is often contradictory, even within the same alloy class, and a coherent understanding of how grain size influences corrosion response is largely lacking. A survey of previous work related to the relationship between grain size and corrosion resistance for a number of light metals (Mg, Al, and Ti) and transition metals (Fe/steel, Co, Ni, Cu, and Zn) will be presented in this manuscript. A holistic examination of current literature will allow for the identification of a number of critical factors, such as environment, texture, residual stress, and impurity segregation, that need consideration to assess whether or how grain size variation will affect a specific alloy's electrochemical behavior in a specific environment.