A combination of Al diffusion and surface nanocrystallization of carbon steel for enhanced corrosion resistance

Surface nanocrystallization is beneficial to the corrosion resistance of passive alloys, but generally has a negative effect on the corrosion behavior of non-passive alloys due to the enhanced surface reactivity. In this study, a combination of Al diffusion treatment and surface nanocrystallization was applied to carbon steel with the aim of exploring an alternative approach to improve the corrosion resistance of non-passive carbon steel. The surface nanocrystallization was achieved by sandblasting and subsequent recovery treatment. The former resulted in severe plastic deformation, while the latter turned high-density dislocation cells into nano-sized grains. The present study demonstrates that the combined Al diffusion and nanocrystallization generated a nanocrystalline Al-containing surface layer on the carbon steel with its surface grain diameter in the range of 10-300 nm. The corrosion resistance of the treated steel was evaluated. It is demonstrated that treated specimens possess increased resistance to corrosion with higher surface electron stability. Surface microstructure of the treated specimens was examined using SEM, AFM, and EDS in order to elucidate the mechanism responsible for the improved corrosion resistance.