Laser powder bed fusion of Inconel 718-based composites: Effect of TiB2 content on microstructure and mechanical performance

The laser powder bed fusion (LPBF) additive manufacturing process has been extensively used to manufacture various nickel-based metal components because it offers the capability of manufacturing three-dimensional structures with complex shapes directly from raw materials. Although LPBF-fabricated Inconel 718 (IN718) superalloys have been successfully applied in the aerospace field, IN718-based composites can offer an alternative pathway to further enhance high-temperature performance. This systematic study examined the effect of various TiB2 contents on the microstructure and mechanical performance of IN718 fabricated by LPBF. Pure IN718 (IN718-P), IN718-1 wt% TiB2 (IN718-1) and IN718-2 wt% TiB2 (IN718-2) composites were nearly fully dense, with relative densities of 99.71%, 99.34% and 99.67% respectively, when fabricated under the optimal process parameters. The degree of grain size refinement was greater for IN718-2 than for IN718-1, and the IN718-1 grains were mainly refined in the width direction, while the IN718-2 grains were refined in both the width and length directions. The proportion of low-angle grain boundaries was significantly higher for the composites than for IN718-P, and it increased with increasing proportions of TiB2. Compared with the IN718-P sample, the microhardness, yield strength and ultimate tensile strength of IN718-2 at room temperature were increased by 19.93%, 24.83% and 11.07%, respectively, while the yield strength and ultimate tensile strength of IN718-2 at a high temperature of 650 °C were increased by 31.76% and 17.62%, respectively. This indicated that the enhancement of mechanical performance was more noticeable at high temperature than at room temperature. By contrast, less improvement in mechanical properties was achieved by adding 1 wt% TiB2 particles than by adding 2 wt% TiB2 particles. These findings indicate an alternative way to manufacture IN718 superalloys with improved mechanical properties through the synthesis of composite materials.