The characterization of an oxide interfacial coating for ceramic matrix composites

This work focused on the use of metal organic chemical vapor deposition (MOCVD) to deposit a zinc oxide (ZnO) coating on ceramic fibers as an interfacial system for continuous fiber reinforced ceramic matrix composites (CFR-CMCs). ZnO coatings were deposited on ceramic grade (CG) Nicalon™, Hi-Nicalon™, and Hi-Nicalon™ Type S fabric by the thermal decomposition of zinc acetate dihydrate in a low pressure hot wall CVD reactor. A duplex SiO2 coating was also deposited in order to protect the ZnO layer from the reducing conditions during composite fabrication. Tow testing was used to evaluate the effect of the ZnO coating on the strength retention of the ceramic fabrics. Single strand unidirectional mini composites were fabricated by infiltrating SiC into the ZnO/SiO2 duplex coated tows in order to understand the interfacial properties of the ZnO coating. The mini composite utilizing Hi-Nicalon™ Type S produced the highest ultimate tensile strength (UTS) of 330 MPa. The coated fabrics and the mini composites were characterized using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and scanning Auger microscopy (SAM).