Mullite whisker felt and its application in composites

The Naval Surface Warfare Center has developed a process for the in situ preparation of 80% porous mullite whisker felt which consists of randomly oriented whiskers mutually intergrown, forming a rigid structure. The felt can be used as pre-forms for the preparation of metal and ceramic matrix composites. The patented process involves mixing and shaping the powdered precursors followed by firing to form in situ the mullite whisker felt. The powders can be shaped by any conventional process. An advantage of the process is the elimination of health hazards associated with loose respirable whiskers. The low dimensional changes of the final felt compared with the green shapes are a valuable feature for the preparation of near-net shape composite preforms. Methods for infiltration of the felt with cast aluminum alloy A356 and properties of the composites will be discussed.