Reinforcement/matrix interaction in Al < inf> 2 O < inf> 3 and Al < inf> 2 O < inf> 3 -ZrO < inf> 2 fiber-reinforced Ni < inf> 3 Al matrix composites

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The interfacial reaction characteristics of fibers with nickel aluminide (Ni3Al) matrices have been investigated after consolidation by hot isostatic pressing (HIPing) and after post-consolidation heat treatment. Two matrix alloys have been studied: Ni3Al alloyed with 0.6 wt.% Zr-(IC-50) and Ni3Al alloyed with 8 wt.% Cr, 2.8 wt.% Mo and 0.6 wt.% Zr (IC-396). Pure alumina (FP) and alumina-zirconia (PRD-166) reinforcements, in the form of discontinuous fibers, were added to the Ni3Al alloys. Elemental compositions across the reaction zone have been analyzed quantitatively using scanning electron microscopy (SEM), electron microprobe analysis (EMPA) and Auger electron spectroscopy (AES). The results show that all composites HIPed at 900°C have residual porosity, but no chemical interactions between matrix and reinforcements were detected. At the other extreme, while full density was achieved at 1200°C, significant formation of zirconium rich precipitates was observed at the fiber/matrix. The extent of fiber/matrix reaction varied significantly among the various fiber/matrix combinations. At intermediate temperatures (1050°C), non observable porosity was detected by optical microscopy and precipitation of zirconium rich phases was reduced or eliminated, depending on the fiber/matrix combination. Fiber clustering, fiber breakage and fiber/matrix debonding occurred during HIPing processes. Solid-state reactions between fibers and matrices were studied after heat treating (vacuum annealing) the HIPed composites at 950°C, 1050°C and 1150°C for times ranging from 1 to 100 hours. The reaction zone, i.e. precipitation at the fiber matrix interface, increased with time and temperature. Nickel and zirconium (and, when present, chromium and molybdenum) diffused from the matrix toward the reaction zone. Aluminum diffused outward from the reaction zone. The thickness of the reaction zone varied from 1 to 10 μm according to composition and experimental conditions. Zirconium is believed to be responsible for the strong chemical reaction between fiber and matrix. © 1997 Acta Metallurgica Inc.

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Acta Materialia