Effect of substrate preheating on the microstructure and bending behavior of WC-Inconel 718 composite coating synthesized via laser directed energy deposition

In this study, a substrate is reinforced with WC/Inconel 718 composite coating via directed energy deposition (DED). During the DED, the substrate was preheated to 300 °C and 500 °C. The microstructural characteristics of the matrix, fusion area, and area around the WC particles were systematically investigated. The results showed that the depth of the transition zone at the interface of the deposited layer and substrate for preheating to 500 °C increased, enhancing the metallurgical bonding between the deposited layer and the substrate. Additionally, three different types of WC particle diffusion mechanisms were exhibited: (i) slight dissolution diffusion for non-preheating sample, (ii) dissolution-diffusion fragmentation for 300 °C-preheating sample, and (iii) disintegration and diffusion for 500 °C-preheating sample. In contrast, the effects of dispersion and solid solution strengthening are more pronounced than that of the microstructure coarsening caused by preheating, resulting in a higher hardness value of 384.0 HV 0.1 (preheating at 300 °C) and 381.3 HV 0.1 (preheating at 500 °C) compared to that of the non-preheated sample (358.9 HV 0.1 ). Furthermore, the bending fracture of the WC/Inconel 718 composite layer exhibited typical pseudo-ductile behavior with premature fracture. Consequently, the highest bending strength occurred at preheating 500 °C, in which the maximum bending load and the displacement at the initial crack increased by 9.15% and 39.69%, respectively, compared with the non-preheated sample. Additionally, the fracture mechanism exhibited mainly intergranular fracture and less transgranular fracture.