Geopolymer-Derived Aluminosilicate Matrix Composites Reinforced with Continuous Nickel-Coated Carbon Fibers: Tensile Properties and Thermo-Oxidative Behavior

This study aims to evaluate the feasibility of an aluminosilicate geopolymer composite reinforced with continuous nickel-coated carbon fibers and establish its baseline mechanical properties and thermo-oxidative behavior. Unidirectional and balanced cross-ply laminates were fabricated via slurry impregnation, drum winding, and autoclave consolidation. The as-fabricated laminates exhibited a bulk density of 1.94 ± 0.16 g/cm3 and an apparent porosity of 23.8 ± 2.5%. For the [0]8 laminates, the mean tensile strength was 827.0 MPa at room temperature, 832.1 MPa at 371 °C, 745.7 MPa at 427 °C, and 365.5 MPa at 538 °C. Temperature-dependent failure modes shifted from predominantly longitudinal splitting up to 371 °C, to mixed splitting and fiber-dominated tensile fracture within the gauge section at 427 °C, and finally to brittle, fiber-dominated tensile fracture with no apparent fiber pull-out at 538 °C. Thermo-oxidative studies showed that the net mass loss of the coupons remained below 0.4% after 1000 h at 316 °C but reached approximately 4.7% after 336 h at 371 °C. The sections examined after exposure at 371 °C showed non-uniform filament thinning. These results establish a baseline mechanical and thermo-oxidative characterization for the proposed material system and identify prolonged oxidation as a limitation requiring further evaluation.