Monitoring and assessment of tungsten carbide wettability in laser cladded metal matrix composite coating using an IR pyrometer

Laser cladding technique was applied to deposit a metal matrix composite coating of Inconel 718 with 30 wt% WC as a ceramic phase. One of the major problems associated with obtaining fully dense MMC coating is the poor wetting/bonding between the ceramic particles and the metal matrix. Further, a large number of process parameters involved in the laser cladding process makes it more complex to optimise the process window. Therefore, the current study focuses on the monitoring of molten pool thermal history which is an outcome of the combination of all process parameters, and identifies the molten pool lifetime and cooling rates that are favourable for the formation of interfacial layer improving the wetting characteristics. The thermal history of molten pool was recorded using an IR pyrometer. The molten pool lifetime, solidification shelf time and cooling rates were assessed from the data acquired and effect of these on wetting characteristics and formation of interfacial layer between WC particles and metal matrix was analysed using SEM analysis. Molten pool lifetime greater than 0.68 s exhibited proper wetting of WC particles with the matrix. Fractured surface of coatings that experienced relatively fast cooling revealed the delaminating of ceramic particles from the metal matrix under the tensile load, whereas in one with slow cooling particles found to stay intact with the metal matrix improving the wear properties of the coating. However, too slow cooling resulted in settlement of WC particles at the bottom of molten pool reducing the wear resistance of the coating.