In-situ interfacial design via reactive sintering aids for short carbon fiber-reinforced SiC composites

This study proposes an in-situ interfacial design strategy for short carbon fiber-reinforced SiC composites (C sf /SiC) as a simplified alternative to complex CVD coating by utilizing controlled reactions between sintering aids and carbon fibers. Three additive systems—Al 2 O 3 -Y 2 O 3 , Al 4 C 3 -B 4 C-C, and Al-B-C—were employed to fabricate composites via spark plasma sintering at 1700 °C, 1750 °C, and 1800 °C. 1750 °C was identified as the optimum temperature, achieving high densification (>92% relative density) while avoiding excessive fiber erosion. Comprehensive characterizations revealed distinct interfacial reaction mechanisms and their effects on composite performance. The Al 2 O 3 -Y 2 O 3 system triggered severe carbothermal reduction, forming a porous yttrium aluminum garnet (YAG)-rich reaction layer, resulting in an interfacial strength of 162 MPa, moderate flexural strength (232 ± 35 MPa) and fracture toughness (4.5 ± 0.2 MPa·m 1/2 ), yet high porosity (6.48%) and poor ablation resistance (mass ablation rate R m = 0.30 mg/s under oxyacetylene flame at 2.1 MW/m 2 for 60 s). The Al 4 C 3 -B 4 C-C system preserved a clean interface with strong bonding (575 MPa), leading to brittle fracture, the lowest mechanical properties (flexural strength: 199 ± 38 MPa; fracture toughness: 3.9 ± 0.2 MPa·m 1/2 ), and limited ablation improvement ( R m = 0.16 mg/s). In contrast, the Al-B-C system promoted a uniform ∼1 μm Al 2 O 3 -rich interphase, achieving an optimally weakened interface (119 MPa) due to thermal expansion mismatch and partial fiber graphitization. This delivered the best mechanical performance (flexural strength: 353 ± 9 MPa; fracture toughness: 4.8 ± 0.2 MPa·m 1/2 ) and superior ablation resistance ( R m = 0.12 mg/s), as the dense, uniform interphase effectively shielded carbon fibers from oxidation. The results demonstrate that in-situ tailored interphases, enabled by strategic additive selection, can concurrently enhance the mechanical and ablation performance of C sf /SiC composites.