Finite element modelling of the effect of a functionally graded protectivecoating for SiC monofilaments on Ti-based composite behaviour

Metal matrix composites consisting of Ti-based alloys reinforced with SiC m onofilaments show great promise for aerospace applications. This work is on a novel functionally graded (FG) coating system for SiC monofilaments, use d as improved reinforcements for Ti-based matrices. The system is abbreviat ed as [SiCf/C/(Ti,C)/Ti]. A finite element analysis was carried out to inve stigate the effect of the coating on thermal residual stresses generated at the fibre/matrix interface due to differences in the thermal expansion coe fficient (CTE mismatch) between the various materials within the coating sy stem. These residual stresses are known to affect fracture behaviour of the composite. The aim of the study was to compare a graded system [SiCf/C/(Ti ,C)/Ti], and a non-graded multi-layer system [SiCf/C/TiC/Ti]. The role of t he carbon layer within the FG coating system and the effect of layer thickn ess were also investigated. The FG coating was seen to reduce residual stre sses generated due to CTE mismatch. In addition correct choice of the coati ng material was seen to allow tailoring of the residual stress-state at the fibre/matrix interface. (C) 2000 Elsevier Science S.A. All rights reserved .