Outstanding strength and toughness in graphene reinforced Nb/Nb5Si3 composites with interfacial nano-phases

Graphene was first employed to improve the mechanical properties of Nb/Nb5Si3 composite, which is a critical candidate for the next-generation of high-temperature structural materials for aero-engines. Microstructures and mechanical properties of graphene reinforced Nb/Nb5Si3 composites with interfacial nano-Nb4C3 phase were systematically investigated. The graphene reinforced Nb/Nb5Si3 composite with outstanding room temperature fracture toughness and compressive strength was fabricated successfully via spark plasma sintering. The microstructure of this composite changes from laminated morphology to uniformly distributed equiaxed microstructure, with the increase of fabrication temperature from 1450 °C to 1550 °C. The high compressive strength of graphene reinforced Nb/Nb5Si3 composites is attributed to the load transfer of graphene, and this load transfer efficiency is strengthened due to the anchoring effect of the interfacial nano-scale Nb4C3 phase. The high fracture toughness of this composite is attributed to the pull-out of graphene, as well as the crack deflection and crack bridging induced by graphene. The laminated architecture is also beneficial to improve fracture toughness because it can promote the minor deflection of cracks. The superior combination of strength and toughness of graphene reinforced Nb/Nb5Si3 composites validates that our design strategy can successfully break through the strength-toughness trade-off. This study is expected to offer a new strategy and theoretical basis for the development of Nb/Nb5Si3 composites with outstanding mechanical properties.