Fatigue and fracture properties of Al2618 + TiB2-reinforced metal matrix composite produced by Laser-powder bed fusion

Metal Matrix Composites (MMCs) represent a class of materials where a reinforcement phase is added to a metallic alloy to enhance specific functional and mechanical properties. Initially developed for aerospace applications in the mid-twentieth century, MMCs have recently received renewed interest thanks to the possibility of being processed by additive manufacturing processes. This study aims to investigate the fatigue and fracture properties of the Al2618 alloy reinforced by 7.1 wt% TiB2 particles, produced via the Powder Bed Fusion Laser Beam (PBF-LB) process. The original gas-atomized Al2618 powder was initially pre-alloyed by 1.30 wt% of TiB2; successively, the target 7.10 wt% TiB2 content was achieved by high-energy mechanical mixing with additional TiB2 powder. The resulting MMC exhibited increased elastic modulus and tensile strength compared to the unreinforced Al2618 alloy. In the second part of the study, a comprehensive characterization of the fatigue and fracture properties was carried out, further demonstrating the promising structural properties of the present MMC. Fracture toughness (KIC) tests were performed with the crack plane along three different orientations. Fatigue crack growth properties were instead assessed in the primary vertical orientation; these data were used to interpret the fatigue experiments conducted on net-shape specimens. Detailed fracture surface analyses, supported by computed tomography scans, enabled extensive characterization of the defects generated in this MMC pointing to the complexity of manufacturing this material. Overall, this work provides a comprehensive characterization of the structural performance of Al-based MMCs produced by PBF-LB , establishing a reference framework for researcher and industry to approach damage-tolerance-based assessment on this class of materials.