Corrosion and mechanical behavior of amorphous-nanocrystalline NiCrMo coatings

Abstract

To develop a high-performance coating for marine engineering equipment, we successfully designed amorphous-nanocrystalline NiCr0.25Mox (x = 0, 0.02, 0.05, 0.1, 0.2, 0.4) alloy coatings via direct current (DC) magnetron sputtering. The compositional, microstructural, corrosion and mechanical properties, specifically the relationship between the coating structure and performance were discussed in detail. The results showed that the amorphous phase sharply alleviated grain boundary corrosion, and the addition of Cr and Mo was beneficial to improve repassivation ability with the formation of a dense passive film. In the nanoindentation and micro-scratch tests, the nanohardness and adhesion strength of the coatings first increased remarkably with Mo content and then declined due to the formation of an amorphous phase. The enhancement of strength was caused by nanocrystals hindering the formation of shear banding, while the addition of Mo improved the tendency of amorphous formation due to the difference in atomic size and lattice distortion. Most importantly, the NiCr0.25Mo0.1 coating exhibited excellent corrosion performance and mechanical behavior through the formation of a dense passivation film composed of Cr2O3 and Cr(OH)3. These ductile solid solution crystalline phases promoted homogeneous plastic deformation and decelerated crack propagation during the scratching process.