Laser Cladding Highly Corrosion-Resistant Nano/Submicron Ultrafine-Grained Fe-Based Composite Layers

Carbide reinforced Fe-based cladding layers usually exhibit relatively poor corrosion resistance owing to galvanic corrosion. In this study, highly corrosion-resistant cladding layers comprising in-situ nano vanadium carbides embedded into a submicron Fe-based matrix were obtained using graded particle-size alloy powders, and adjusting the energy density of a pulsed laser. The resulting microstructure of the ultrafine-grained layer was lath martensite with granular V6C5. The average sizes of the V(6)C(5 )and the layer matrix grains were 53 nm and 0.90 kmi, respectively. The nanocrystallization of vanadium carbides was affected by the pulsed laser and graded particle-size alloy powders. The refining effect caused by the pulsed laser on the layer matrix was about 12.20%, and the submicron ultrafine crystallization mainly occurred because of the nanovanadium carbides. The hardness of the ultrafine-grained layer was 600 HV0.2 higher than that of low carbon steel and, more importantly, the corrosion resistance was 21.60 times greater. The initial immersed corrosion products of the cladding layer were Fe2O3 and Fe3O4; after 8 h, they turned into a dense film of Fe2O3. The high-temperature oxidative weight gain of the ultrafine-grained layer was greater than that of low carbon steel in the early stages, which increased slowly owing to the gradual formation of a dense oxidative-product film.