Hot Isostatic Pressing of Silicon Nitride with Boron Nitride, Boron Carbide, and Carbon Additions |
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Authors: | Diane M. Mieskowski William A. Sanders |
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Affiliation: | Lewis Research Center, National Aeronautics and Space Administration, Cleveland, Ohio 44135 |
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Abstract: | Si3 N4 test bars containing additions of BN, B4C, and C, were hot isostatically pressed in Ta cladding at 1900° and 2050°C to 98.9% to 99.5% theoretical density. Room-temperature strength data on specimens containing 2 wt% BN and 0.5 wt% C were comparable to data obtained for Si3 N4 sintered with Y2O3, Y2O3 and Al2O3, or ZrO2. The 1370°C strengths were less than those obtained for additions of Y2O3 or ZrO2 but greater than those obtained from a combination of Y2O3 and Al2O3. Scanning electron microscope fractography indicated that, as with other types of Si3N4, roomtemperature strength was controlled by processing flaws. The decrease in strength at 1370°C was typical of Si3N4 having an amorphous grainboundary phase. The primary advantage of non-oxide additions appears to be in facilitating specimen removal from the Ta cladding. |
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Keywords: | silicon nitride isostatic pressing boron carbon mechanical properties tantalum |
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