Fabrication and Evaluation of Low Cost Alumina Fiber Reinforced Metal Matrices.

The fibers investigated to date on this program are all in multifilament yarn form and are highly flexible and easily handled. The fibers are alumina fiber FP, a mixed oxide fiber AB 312, and a mixed oxide fiber. All composite matrices were aluminum alloys whose compositions were selected on the basis of melt surface tension and reactivity with the reinforcing fibers. The fabrication process chosen was vacuum infiltration casting. Fiber properties important for achieving a strong composite were measured. Principles by which matrix composition should be chosen for successful infiltration were deomonstrated. Composite fabrication techniques were developed and refined. Composite specimens for evaluation were produced and shown to exhibit high levels of mechanical properties predictable from fiber test data. The fibers tested exhibited marked differences in surface chemsitry, surface topography, mechanical properties and fracture modes. Individual filament tensile strengths of up to nearly 4000 MPa were measured with average strengths of up to 2000 MPa. Aluminum alloy matrices containing significant alloying additions of Li, Bi and Mg either individually or in combination were all shown to infiltrate fiber filled molds. Composite fabrication procedures included the use of both fluxed melt surfaces and melting under argon, and also a comparison between the use of preevacuated fiber filled molds and molds containing fibers and air. Composites with axial tensile strengths of up to 620 MPa were produced through the use of the FP alumina fiber.