Ultra-high temperature ceramic (HfC) reinforcement of laser powder-directed energy deposited inconel 718: Microstructural evolution and tensile properties at room and high temperatures

Abstract

This study explores the influence of ultra-high-temperature ceramic (UHTC) hafnium carbide (HfC) reinforcement on the microstructural evolution and mechanical properties of Inconel 718 produced by laser powder directed energy deposition (LP-DED). Inconel 718 powder was uniformly coated with HfC particles (HfCp) via the surface modification and reinforcement transplantation (SMART) process. The introduction of HfCp, which accumulated at the melt pool surface during LP-DED, significantly enhanced the laser beam absorptivity, inducing localized heating that resulted in the dissolution of HfC and the formation of secondary phases, such as Ni₅Hf, (Hf,Nb,Ti)C, and Hf-enriched Laves phases. These secondary phases, causing Nb depletion, contributed to grain refinement, stabilized the microstructure, and promoted the formation of γ′/γ′′ co-precipitates. Mechanical testing revealed that at 650 °C, Inconel 718 samples reinforced with 1.5 vol% and 3.0 vol% HfC demonstrated superior tensile strength and elongation compared to the unreinforced sample, with no observed serration behavior. The secondary phases enhanced the dislocation density and strain-hardening behavior, while acting as diffusion barriers to prevent oxidation-induced intergranular cracking, whereas Hf and C specifically stabilized the grain boundaries, further enhancing the oxidation resistance at elevated temperatures. These results emphasize the importance of reinforcing the laser beam absorptivity during the fabrication of high-performance composites by LP-DED and confirm that HfC-reinforced Inconel 718 has great potential for high-temperature applications.