Microstructure evolution and wear resistance of laser cladded 316L stainless steel reinforced with in-situ VC-Cr7C3

Laser cladding (LC) has been applied to enhance the wear resistance of 316L coatings by depositing in-situ VCCr7C3 metal matrix composites (MMCs) coating on structural steel substrate using pre-mixed powder consisting of vanadium, carbon, and 316L stainless steel. The effects of different process parameters, varied V and C contents on the phase constituents, microstructure, and the mechanical properties of 316L LC coatings were investigated systematically. The related microstructure evolution and the mechanical properties were comprehensively studied. The results indicated that under the selected laser irradiance of 80 W/mm2, scanning rate of 4 mm/s, and powder feeding rate of 10 g/min, by increasing V and C content from 0 wt % to 14 wt %, VC, Cr7C3, and Cr23C6 would be progressively precipitated at grain boundaries, and the austenite grains tended to be refined. Consequently, the microhardness of reinforced 316L coatings significantly increased from 207 HV1 to 467.8 HV1. Wear tests showed that the wear resistance improved some 8 times compared to the pure 316L layer under the dry sliding condition, and the dominating wear mechanism for the cladding transferred from adhesive wear to abrasive wear. Further microstructure characterization revealed that besides precipitation strengthening and fine-grain strengthening, the strengthening effect was also originated from the interfacial structure between the precipitated carbides, including a coherent interface for gamma/Cr7C3, semi-coherent interfaces for gamma/VC, and VC/ Cr7C3. Based on the results of thermodynamic calculation and Fe-Cr-C ternary phase diagram, the spherical VC acted as the nucleation sites for the dispersed carbide reinforcement and the austenite grains, and the inhibition against austenite matrix growth by ceramic precipitations dispersedly distributed along the grain boundaries.