Nano-precipitation in hot-pressed silicon carbide |
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| Authors: | X F Zhang M E Sixta D Chen and L C De Jonghe |
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| Affiliation: | (1) Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720;(2) Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA, 94720;(3) University of California, Berkeley, CA, 94720 |
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| Abstract: | Heat treatments at 1300°C, 1400°C, 1500°C, and 1600°C in Ar were found to produce nanoscale precipitates in hot-pressed silicon carbide containing aluminum, boron, and carbon sintering additives (ABC-SiC). The precipitates were studied by transmission electron microscopy (TEM) and nano-probe energy-dispersive X-ray spectroscopy (nEDS). The precipitates were plate-like in shape, with a thickness, length and separation of only a few nanometers, and their size coarsened with increasing annealing temperature, accompanied by reduced number density. The distribution of the precipitates was uniform inside the SiC grains, but depleted zones were observed in the vicinity of the SiC grain boundaries. A coherent orientation relationship between the precipitates and the SiC matrix was found. Combined high-resolution electron microscopy, computer simulation, and nEDS identified an Al4C3-based structure and composition for the nano-precipitates. Most Al ions in SiC lattice exsolved as precipitates during the annealing at 1400 to 1500°C. Formation mechanism and possible influences of the nanoscale precipitates on mechanical properties are discussed. |
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