Fiber-Matrix Compatibility in LZSA Glass-Ceramic Matrix Composites

Continuous fiber reinforced glass-ceramic (GC) matrix composites are potential candidates for thermomechanical applications at moderate temperatures (up to 1000°C) due to the combination of interesting properties such as high specific strength and toughness. Crack deflection into fiber-matrix interface, as well as subsequent fiber pullout and bridging are the respective toughening mechanisms. In this paper, the compatibility between LZSA glass-ceramic matrix and commercially available oxide alumina fibers (Nextel TM 610) is qualitatively examined. Toughening mechanisms such as crack deflection and fiber pullout are investigated by analyzing the path of Vickers-induced matrix cracks formed in the vicinity of the fibers and by investigating the crack surface of bending samples, respectively. GC matrix samples sintered and crystallized at different heat-treatment conditions have shown strong interfacial bonds between matrix and fibers, which leads to a brittle fracture without significant fiber pullout in all cases. This behavior indicates the requirement of using fiber coatings in this CMC system, to produce weak interfaces that enable toughening mechanisms to take place.