Low Density High Strength Intermetallic Matrix Composites By Xd Trademark Synthesis

There is an increasing need for lightweight high performance materials in today's aerospace arena. High temperature engine designs, for example, require engine materials with elevated temperature strength, creep resistance, damage tolerance, oxidation resistance, and low density. Ordered intermetallics are considered potential alternatives to superalloys because they exhibit many of these properties. A major problem with most ordered alloys is their tendency toward inherently low ductility. The reasons can be quite varied depending on the alloy system, and include poor grain-boundary cohesion, an insufficient number of available slip systems (primarily in non-cubic alloys), limited cross slip, and impurity locking of dislocations. However, intermetallics of high symmetry, such as the L12 structure, have a number of slip systems, which can provide some plasticity, at least at intermediate temperatures, thus enabling the matrix to accommodate some of the strain associated with the thermal stresses.

A feasibility study was conducted to evaluate the potential of particulate composites based on low-density, L1(sub 2) trialuminide matrices for high-temperature applications. The compounds evaluated included Al22Fe3Ti8 (as a multiphase matrix), Al67Ti25Cr8, and Al66Ti25Mn9. The reinforcement consisted of TiB2 particulates. The TiB2 composites were processed by ingot and powder metallurgy techniques. Microstructural characterization and mechanical testing were performed in the hot-pressed and hot-isostatic-pressed condition. The casting were sectioned and isothermally forged into pancakes. All the materials were tested in compression as a function of temperature, and at high temperatures as a function of strain rate. The test results are discussed. Kumar, K. S. and Dipietro, M. S. and Brown, S. A. and Whittenberger, J. D. Glenn Research Center...

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