Nucleation and Growth of β'-SiAlON |
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Authors: | Shyh-Lung Hwang I-Wei Chen |
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Affiliation: | Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109–2136 |
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Abstract: | Elongated β'-SiAlON grains grown from several finegrained Ym/3Si12(m+n)Alm+nOnN16–r compositions with α-Si3N4, AlN, Al2O3, and Y2O3 starting materials have been examined. These grains have large aspect ratios and are oriented along the 0001] axis. TEM structural and chemical analysis suggests that they are nucleated from various seed crystals, which can be α-Si3N4, β-Si3N4, or other β'-SiAlON. The β'-SiAlON seed and the initial precipitation on β-Si3N4 show a higher content of Al and O, indicating that a large transient supersaturation of Al and O in the liquid is instrumental for β'-SiAlON formation, whereas subsequent growth proceeds under a much lower driving force. The misfit between phases is accommodated by interfacial dislocations ( c -type and a -type). Fully grown β'-SiAlON grains usually contain several variants independently nucleated from the same seed. In particular, the two alternative α/β phase-matching possibilities result in two 0001] growth habits separated by a twin boundary. |
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