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Evaluation of the Oxidation Response and Fiber-Matrix Compatibility in Aluminum-Rich Intermetallic Composites.
Final rept. Oct 89-Sep 93,
NAVAL AIR WARFARE CENTER AIRCRAFT DIV WARMINSTER PA AIR VEHICLE AND CREW SYST EMS TECHNOLOGY DEPT
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The present study was undertaken in order to elucidate the role of fiber-matrix interactions on the oxidation response of Al3Ti-based metal matrix composites. The fibers examined in this work were SCS-6, TiB2, and Saphikon. Since these trialuminides have very high melting points, a solid state powder processing fabrication route was chosen in order to minimize fiber degradation. The matrix alloy was rapidly solidified by melt spinning in order to insure compositional homogeneity. A hammer mill was used to comminute the alloy ribbon into -40 mesh powder. The powder and fibers were then encapsulated in titanium cans, hot vacuum degassed, and hot isostatically pressed. Preliminary investigations indicated that Al3Tis narrow range of compositional stability could present difficulties excess aluminum could melt and vigorously attack fibers at the HIP consolidation temperatures. viz., 1100 deg C and 1200 deg C. Niobium additions were used to expand the phase field of Al3Ti and reduce the alloys propensity to partition aluminum during melt processing. HIP consolidated composites all exhibited some matrix cracking making them unsuitable for oxidation studies. However. the oxidation response of the monolithic matrix alloys was investigated. The extent of fiber-matrix reaction owing to the HIP consolidation procedure was also pursued. The SCS-6 fibers reacted severely with the matrix materials. The TiB2 fibers did not experience significant chemical degradation although significant diffusion and cracking was observed. Saphikon was the least affected by the consolidation process. The fiber does not react chemically with the matrix materials however, differences in the thermal expansivities of the fiber and matrix materials are believed responsible for extensive cracking. jg
APPROVED FOR PUBLIC RELEASE