Effect of fiber coating on the mechanical properties of a Nextel-480-fiber-reinforced glass matrix composite

The effect of fiber coatings on the mechanical properties of glass matrix composites reinforced with Nextel 480 fiber was investigated. Two different fiber coatings, namely tin dioxide and boron nitride, were investigated. The presence of the coatings on the fiber led to an improvement in mechanical behavior. In particular, the boron nitride coating improved the total work of fracture of the composite without reducing the strength. A marked difference was observed in the fractographic features between the uncoated and tin-dioxide-coated samples as compared to the boron-nitride-coated samples. The uncoated and tin-dioxide-coated fiber composites failed in a brittle fashion, without any fiber pull-out, whereas the boron-nitride-coated fiber samples exhibited extensive fiber pull-out. This improvement in the toughness or energy absorbed during the fracture process was attributed to the relatively weak bonding between the fiber and matrix, induced as a result of the coating.