A novel method of pulsed laser-cladding for effective control of melting of WC particulates in NiCr-WC composite coatings

In Cermet coatings such as WC reinforced NiCr metal matrix, distribution of WC particles with effective bonding at particle-matrix interface plays an important role in retention of high hardness and toughness. Formation of secondary carbide phases are found to be detrimental in reducing hardness and there by rendering low wear and erosion resistance of the coating. Although, Laser cladding in continuous-wave (CW) energy mode can be utilized to control heat input to reduce melting of WC particles in NiCr matrix as compared to other conventional methods, the problem of melting of these particles still persists. A method of laser-cladding under pulsed mode was found to provide a better alternative to effectively control heat input leading to controlled melting of WC in NiCr matrix with reduction in formation of deleterious secondary carbides. In the present work, laser cladding of NiCr with 25% WC addition on SS310 steel substrate has been carried out using a 6kW diode laser and an off-axis powder feeding nozzle under argon atmosphere. Coatings were produced in both pulsed and CW modes at similar average laser powers. Coatings were characterized for microstructure, hardness and also analysed for erosive wear resistance. Clads produced under pulsed-mode of processing showed relatively higher amount of unmelted WC particles in γ-Ni+Ni₃B eutectic matrix as compared to CW mode of processing. Relatively higher amounts of secondary carbides and other meta-stable phases were observed in CW mode as compared to Pulsed counterpart. A 30% improvement in clad hardness and 35% improvement in erosive wear resistance have been obtained in pulsed-clad coating than CW clad one.