Development of process maps based on molten pool thermal history during laser cladding of Inconel 718/TiC metal matrix composite coatings

Abstract

In the present study, laser cladding of Inconel 718/TiC metal matrix composite coating on SS 304 was carried out using a 2 kW Yb-Fiber laser by preplaced and blown powder method. The molten pool thermal history during the deposition process was monitored using an IR pyrometer and correlated with the evolution of microstructure. The effect of various process parameters, viz. laser power ‘P’ (400 W – 1200 W), scanning speed ‘V’ (200 mm/min to 1400 mm/min) and powder feeding rate (8 g/min – 20 g/min) on the molten pool lifetime and cooling rate is investigated. Molten pool lifetime increased and cooling rate decreased with the decrease of scanning speed and increase of laser power. However, scanning speed had dominant effect on the molten pool lifetime and cooling rate compared to laser power. Moderate molten pool lifetime resulted in the formation of shell-core structure between Inconel 718 matrix and TiC particles. The longer molten pool lifetime (>0.45 s) resulted in complete decomposition of TiC particles rendering brittleness to the coating. The feasibility of detecting TiC particle decomposition in Inconel 718 matrix from the recorded thermal cycles based on multiple solidification shelfs is discussed. At the end, a process map based on a combined process parameter, PD/V2 (spot diameter D) and molten pool lifetime (τ) was developed. An optimum range of molten pool lifetime i.e. 0.25 s < τ ≤ 0.45 s was found to result in a good quality of coating with the formation of shell-core structure both in case of preplaced and blown powder laser cladding method.