Tensile behavior of AI 2 O 3 /FeAI + B and AI 2 O 3 /FeCrAIY composites
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I.
INTRODUCTION
FIBER-reinforced intermetallic and superalloy matrix composites have potential applications in advanced gas turbine engine component applications. FeA1 + B (Fe-40A10.JB, at. pct) and FeCrA1Y (Fe-24Cr-8A1-0.06Y, at. pct) were selected as potential matrix materials. FeA1 + B was chosen as a potential matrix due to its ductility, low density, and excellent oxidation resistance. While FeCrA1Y also has excellent oxidation resistance, its advantages over FeA1 + B include a lower coefficient of thermal expansion (CTE) and higher ductility. Both FeA1 + B and FeCrA1Y are weak at elevated temperature. Therefore, the elevated-temperature strength of composites containing these matrices will depend largely on the strength of the fiber. Few fibers are commercially available that are both strong and compatible with intermetallics and superalloys from both chemical and thermal expansion standpoints. Single-crystal A1203 fibers were chosen for this study due to their availability, chemical compatibility, relatively high CTE, high-temperature strength, low density, and excellent creep resistance. The objective of this research was to assess the feasibility of A1203/FeA1 + B and A1203/FeCrA1Y composite systems for high-temperature applications. The fiber-matrix chemical compatibility and interfacial bond strength in the two systems were investigated. Since fiber strength is crucial to the strength of the composite, A1203 fiber strengths were determined both prior to and after processing. The tensile responses of the FeA1 + B and FeCrA1Y matrices, as well as the composites, were characterized. The experimentally
S.L. DRAPER and J.I. ELDRIDGE, Materials Research Engineers, are with the Materials Division, NASA Lewis Research Center, Cleveland, OH 44135. B.J.M. AIK1N, Research Associate, is with the Department of Materials Science & Engineering, Case Western Reserve University, Cleveland, OH 44106. Manuscript submitted October 19, 1994.
METALLURGICAL AND MATERIALS TRANSACTIONS A
measured composite tensile properties were compared to predicted values. Acoustic emission (AE) instrumentation was used during room-temperature tensile tests to aid in determining the failure mechanisms of the composites. Stress waves, which are emitted during plastic deformation or crack growth, are processed by the AE equipment into AE parameters. Interpretation of the AE parameters can only be done in general terms, but some correlation of AE parameters to damage modes has been establishedY ,2] AE signals associated with fiber fractures typically have high amplitudes, in excess of 90 dB, It,2J whereas those due to matrix cracks and debonding have lower amplitudes. Results of the acoustic emission testing and microstructural analyses of the composites after tensile testing were related to possible failure mechanisms. II.
EXPERIMENTAL PROCEDURE
Prealloyed powders with nominal compositions Fe-40A10.5B and Fe-24Cr-8A1-0.06Y (at. pct) were used to fabricate matrix-only and composite plates. The composites were reinforced with three plies o
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