Effects of Active Oxidation on the Flexural Strength of α-Silicon Carbide |
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Authors: | Hyoun-Ee Kim Arthur J. Moorhead |
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Affiliation: | Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6069 |
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Abstract: | The effects of oxygen partial pressure ( P o2) on the oxidation behavior and room-temperature flexural strength of sintered α-SiC were investigated. Groups of flexure bars were exposed at 1400°C to flowing Ar containing various levels of oxygen ( P o2 ranging from 7.5 × 10−7 to 1.5 × 10−4 MPa). The changes in weight, flexural strength, and surface morphology of the samples were strongly influenced by the P o2 level. When the P o2 was higher than 3 × 10−5 MPa, SiO2 was formed on the surface (i.e., passive oxidation occurred) and the strengths of the samples were not significantly affected. However, when the P o2 was lower than 2 × 10−5 MPa, material loss occurred (active oxidation), decreasing the weight and strength of the samples. Both the reduction in strength and the weight loss resulting from active oxidation were proportional to the P o2. An approximately 50% reduction in strength was observed in the SiC after oxidation for 20 h at a P o2 of 1.5 × 10−5 MPa, a level that is slightly lower than the P o2 at which the transition from active to passive oxidation occurs. Large pits formed during exposure were responsible for the reduction in strength. |
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Keywords: | silicon carbide oxidation strength oxygen partial pressure morphology |
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