Microstructural Evolution and Wear Resistance of Composite WC10%-Ni60AA Cermet Built by Laser Directed Energy Deposition

In this study, crack-free composite coatings with ratios of 40%, 50%, and 60% WC10%-Ni60AA cermet/Inconel 718 were successfully prepared using laser directed energy deposition. WC10%-Ni60AA cermet, as a reinforced particle, consists of 10% tungsten carbide (WC) particles and 90% nickel-based alloy. The bottom layers of the composite coatings were metallurgically well-bonded with substrates. The microstructures of the middle and top layers exhibited a novel eutectic precipitate skeleton structure (Cr23C6 phase), accompanied by an embedded nano-precipitate (MC (M: Nb, Mo) phase). The proportion of the eutectic precipitate skeleton structure increased with an increase in cermet content; in particular, the 60% cermet/Inconel 718 coating exhibited the largest proportion of the skeleton structure, with an area density of 86.15%. An increase in the cermet content improved the grain refinement in the composite coating. Fine equiaxed crystals were obtained in the 60% cermet/Inconel 718 coating, in which the proportion of high-angle grain boundaries (>15°) was 85.7% and the average grain size was 35.77 μm. Furthermore, the hardness and wear resistance of the composite coatings improved as the cermet content increased. The average hardness of the 60% cermet/Inconel 718 coating was 503 HV0.1 and wear loss was 107.9 mg, thereby exhibiting the best wear resistance owing to the synergistic effects of precipitation strengthening, grain refinement strengthening, and dispersion strengthening (unmelted and retained WC particle). Adhesive and abrasive wear were dominant wear mechanisms in the 40% cermet/Inconel 718 coating, whereas oxidative wear and abrasive wear were dominant in the 50% and 60% cermet/Inconel 718 coatings.