Fabrication of CMCs and MMCs using novel processes

Lanxide Corporation, a Newark, Delaware, based company, has an exceptionally broad technology portfolio in ceramic matrix and metal matrix composites. This publication gives an overview of Nicalon(TM) or Hi-Nicalon(TM) fiber-reinforced CMCs and silicon carbide or alumina particle-reinforced MMCs. Fabrication methods are explained, properties summarized, and examples of applications given. One technique for fabricating fiber-reinforced CMCs is the DIMOX(TM) directed metal oxidation process in which a molten metal reacts with an oxidant to form a ceramic matrix which ''grows'' into ceramic preforms. For example, the reaction of a molten aluminum alloy with oxygen in ambient air forms an alumina reaction product which grows into the spaces between individual fibers and fiber tows of a fiber preform. A method for fabricating fiber-reinforced SiC matrix composites is the repeated infiltration and pyrolysis of a fiber preform with a preceramic polymer. Such composites have been fabricated using Lanxide's CERASET(TM) preceramic polymer, a low viscosity, thermosettable polysilazane with excellent stability in ambient air. The second group of materials which are described here are aluminum MMCs which contain either SiC or Al2O3 particles as the reinforcement. These MMCs are fabricated using the PRIMEX(TM) pressureless metal infiltration process in which a molten aluminum alloy wicks into a preform without the application of any pressure. The simplicity of this process allows for the economic fabrication of components with vastly different geometries, ranging from automotive brake rotors to actively cooled heat sinks with complex internal structures for electronic applications. Alternatively, billets of Al-MMC can be fabricated by pressureless metal infiltration, using various amounts of molten aluminum alloy to obtain upon stirring of the melt a castable alloy composition containing up to 40 vol% particles. This technology is known as the PRIMEX CAST(TM) foundry process Examples of products which are being manufactured by casting are brake discs for automobiles and trains, electronic constraining cores, and components used in semiconductor processing equipment.