In-process detection of microstructural changes in laser cladding of in-situ Inconel 718/TiC metal matrix composite coating

Highlights: • Thermal history in laser cladding of Inconel 718+ in-situ TiC was studied. • Changes in microstructure were identified from the recorded thermo-cycle. • Influence of microstructure on mechanical properties was studied. • Excess dilution was identified by the shift in solidification shelf location. • Effect of laser pulsing on microstructure was also studied. Online monitoring of thermal history during laser cladding of Inconel 718/TiC metal matrix composite (MMC) produced by in-situ process was carried out. Effects of weight percentage of Ti+C and process parameters on the thermal history, and its correlation with the evolution of microstructure were studied. Further, changes in the evolution of microstructure and excessive dilution were identified online by monitoring various features of the thermo-cycle profile, i.e. occurrence of undercooling with change in microstructure from dispersed fine particles to dendritic structure caused by assembling of floating TiC particles at slow cooling, molten pool lifetime and shift in solidification shelf location because of compositional changes caused by excessive dilution. Coating with dispersed fine TiC particles exhibited high hardness and good wear characteristics compared to the one with dendritic structure. Further, dendritic growth of TiC particles resulted in embrittlement of the coating. Cladding was also carried out in laser power modulated mode to enhance the cooling rate, thereby refining the microstructure. Identification of optimum parameters through real-time monitoring of molten pool thermal history and its physical state (liquid/solid) during laser power modulation to ensure refinement of microstructure was studied. SEM and XRD analyses were carried out for analysing the microstructure and phases.