Influence of Y2O3 reinforcement particles during heat treatment of IN718 composite produced by laser powder bed fusion

A metal matrix composite with Inconel 718 as the base metal and yttrium oxide (Y2O3) as the reinforcement particles was fabricated by the laser powder bed fusion technology. This paper presents a comprehensive study on the influence of the Y2O3 reinforcement particles on the microstructures and mechanical properties of the heat-treated printed composite. Complex precipitates formation between the Y2O3 nanoparticles and the carbonitride precipitates were shown. The complex precipitates separated into individual Y2O3 and titanium nitride (TiN) nanoparticles after heat treatment. Nano-sized Y-Ti-O precipitates were observed after solutionization due to the release of supersaturated Y in the metal matrix. Grain refinement was also observed in the heat-treated composites due to the high number of nano-sized precipitates. After solutionizing and aging, the grain size of the Y2O3-reinforced sample is 28.2% and 33.9% smaller, respectively, than that of the monolithic Inconel 718 sample. This effectively reduced the segregation of Nbat the grain boundaries and thus, γ′ and γ′′ precipitates were distributed in the metal matrix more homogeneously. Combined with the increased Orowan strengthening from a significantly higher number of nano-sized precipitates and grain boundary strengthening, the composite achieved higher yield strength, and ultimate tensile strength (1099.3 MPa and 1385.5 MPa, respectively) than those of the monolithic Inconel 718 (1015.5 MPa and 1284.3 MPa, respectively).