| Ceramic/ceramic composites are attractive materials for high temperature structural applications. The interface between the fiber and matrix is critical in controlling mechanical properties.; In this study we have examined two types of Nicalon fiber reinforced Calcium Aluminosilicate, namely CAS II and IIA. The difference in these two matrix materials is the amount of As{dollar}sb2{dollar}O{dollar}sb3{dollar} added, i.e. 0.5 and 1 wt% respectively. Scanning and Transmission Electron Microscopes and Scanning Auger analysis have been employed to characterize the interface region. These techniques have been applied to fracture surfaces. The results show the chemical composition in the fiber/matrix interfacial region. The thickness of the carbon-rich layer that develops at the interface by chemical reaction during processing was determined to be 20-40nm and 50-80nm thick for Nicalon-CAS II and IIA composites respectively. This carbon rich layer is thought to enable fiber pull-out to occur during fracture and hence imparts a measure of toughness to the composite.; Indentation techniques using a Nano Indenter{dollar}sp{lcub}rm TM{rcub}{dollar}II and a Vickers Microindenter have been employed to analyze the micromechanical properties of the fiber/matrix interface.; Interfacial properties such as the friction stress ({dollar}tau{dollar}), friction coefficient ({dollar}mu{dollar}), residual stresses, and the interface fracture energy were determined for both CAS IIA and II composites by employing several different theoretical approaches.; The frictional stress and frictional coefficient at the fiber/matrix interface was found to be smaller for CAS IIA than for CAS II. This is consistent with the thickness of the carbon-rich layer in CAS IIA.; Shetty's theoretical approach was shown to predict the fiber sliding length very precisely for both types of CAS composites which have residual radial compression at the interface. |
