Mechanical Properties and Deformation Mechanisms of an A1 2 O 3 Fiber-Reinforced Nial Matrix Composite
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MECHANICAL PROPERTIES AND DEFORMATION MECHANISMS OF AN A120 3 FIBER-REINFORCED NiAl MATRIX COMPOSITE S. M. Jeng*, J.-M. Yang* and R. A. Amato** * Department of Materials Science and Engineering, University of California, Los Angeles, CA 90024-1595 **GE Aircraft Engines, Cincinnati, OH 45215 ABSTRACT The mechanical behavior of a continuous Al2 0 3 fiber-reinforced NiAl matrix composite was investigated. The interfacial mechanical properties were measured at room temperature using a fiber pushout test. Tensile test was conducted at room and elevated temperatures. Four-point bending creep test was also conducted at 700 *C. The key microstructural parameters controlling the mechanical behavior and fracture processes were identified. The effect of fiber surface coating on the interfacial properties and mechanical behavior of the composite was also studied. INTRODUCTION Ordered intermetallic compounds have emerged as a new class of materials for advanced structural applications. NiAl-based intermetallics, in particular, has been recognized as one of the most promising candidate materials for high temperature applications. It possess several attractive properties including low density ( - 6 g/cm 3), high melting point (1638 *C), high modulus (189 GPa) and excellent oxidation resistance up to 1300 *C. The polycrystalline NiAl exhibits a brittle-to-ductile transition at temperatures ranging from 300 to 600 °C, the exact temperature depends on the stoichiometry and grain size. However, to make the NiAl as a viable material, it is necessary to overcome some of its inherent problems. These include low ductility and fracture toughness at ambient temperatures, and inadequate strength at elevated-temperatures. Accordingly, a significant effort has centered on enhancing the mechanical properties of the NiAl through grain refinement, micro- and macro-alloying as well as incorporating second phase reinforcements[1-4]. Recent studies indicated that the interfacial requirements in the intermetallic matrix composites are more complicated than those in a typical metal or ceramic matrix composite [5]. At ambient temperatures, the intermetallics are brittle as a ceramic exhibiting a catastrophic fracture behavior. Therefore, a weak bond is required to activate the toughening mechanisms such as crack defection, fiber bridging and fiber pullout. However, at elevatedtemperatures, the intermetallics behave more like a metal exhibiting plastic yielding behavior. A strong bond is needed to effectively transfer the load from the weak, ductile matrix to the strong, stiff reinforcing fibers. The optimum interfacial properties for a NiAI matrix composite with a combination of room-temperature toughness and high-temperature strength have not been determined yet. This work is conducted to study the mechanical behavior of an A12 0 3 fiber-reinforced NiAI matrix composite at room- and elevated- temperatures. The single-crystal aluminum oxide fiber has been shown as the most promising reinforcements for several intermetallic matrix composites. Both coat
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