Push-out testing of SiC monofilaments with a TiC based functionally gradedcoating

Metal matrix composites consisting of SiC monofilaments in Ti-based matrice s show great promise for aerospace applications. This work is on a novel gr aded coating system for SiC monofilaments used to reinforce Ti matrices. Si C Sigma monofilaments were coated with a functionally graded (FG) TiC-based coating(SiCf/C/(Ti,C)/Ti) using close field un-balanced magnetron sputteri ng. The coated fibres were incorporated into Ti matrices using hot isostati c pressing. The interfacial properties of the bulk composites were then eva luated using pushout testing of thin composite samples, in order to asses t he effect of the graded coating. The tests were repeated on the same sample s after heat treatment. The samples were subsequently analysed using scanni ng electron microscopy (SEM) equipped with both secondary and backscattered electron analysis modes to identify the region of failure. The test result s indicate that the FG coating offers an improvement on composite fracture toughness over the un-coated fibres by approximately 70% before heat treatm ent, approximately 35% after heat treatment. (C) 1999 Kluwer Academic Publi shers.