Novel CMCs based on B4C-TiB2 blends and carbon fibres

Lightweight carbon fibre reinforced B 4 C/TiB 2 composites with varying B 4 C contents and fibre gradients were produced by slurry infiltration and sintering for the first time. Tuning the B 4 C content allowed to adjust the fibre/matrix interfacial strength, leading to different fracture behaviours: for a B 4 C content of 75%, the fibre/matrix interface was relatively weak and the composite had significantly high fracture toughness, whereas higher TiB 2 contents led to a denser matrix, stronger interface and low degree of delamination. Even though the fracture toughness was considerably high, the addition of Carbon fibres lowered the hardness down to ≈ 4 GPa. Therefore, an additional composite with a fibre gradient was fabricated to demonstrate the feasibility of combining a high fibre content in the inner layer with a harder layer on the outside, reaching hardness values of ≈ 27 GPa. • Carbon fibre-reinforced TiB 2 /B 4 C composites with fibre contents > 40 vol% were successfully manufactured for the first time via slurry infiltration and sintering techniques, incorporating both long and short fibres. • Adjusting the B4C/TiB2/fibre ratio allows fine-tuning of the fibre/matrix interfacial strength, promoting extensive fibre pull-out and enhancing fracture toughness. • Long fibre-reinforced composites exhibited a flexural strength of approximately 300 MPa, comparable to ZrB 2 -based materials of similar composition. • Short fibre-reinforced composites displayed a flexural strength of around 150 MPa and a fracture toughness of 5.5 MPa·m⁰·⁵, due to the random distribution of fibres. • A graded composite (density of 2.5 g/cm³) with a fibre content gradient—approximately 50% short fibres in the core and a fibre-free outer shell—achieved an excellent combination of properties, including high hardness (~27 GPa) in the outer layer and improved fracture toughness (5.5 MPa·m⁰·⁵) in the core.