Formation mechanism of Si3N4 in reaction-bonded Si3N4-SiC composites |
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| Affiliation: | 1. Department of Materials Science and Engineering, Graduate school of Engineering and Resource Science, Akita University, 1-1 Tegata-Gakuencho, Akita 010-0852, Japan;2. Akita Prefectural Research and Development Center, 4-11 Sanuki, Araya, Akita 010-1623, Japan;1. National Engineering Research Center of Near-net-shape Forming Technology for Metallic Materials, South China University of Technology, Guangzhou 510640, China;2. School of Engineering Technology, Beijing Normal University, Zhuhai, Zhuhai 519087, China |
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| Abstract: | The formation mechanism and thermodynamics of Si3N4 in reaction-bonded Si3N4-SiC materials were analyzed. There are two kinds of Si3N4, fibroid α-Si3N4 and columnar β-Si3N4, which are formed by different processes in Si3N4-SiC materials. Silicon reacts with oxygen, forming gaseous SiO and reducing oxygen partial pressure. SiO(g) diffuses from central to peripheral sections of blocks and reacts with nitrogen, thus forming Si3N4, mainly in peripheral sections. The reaction between silicon and oxygen causes the consumption of oxygen and leads to low oxygen partial pressure in the sintering system, which allows silicon to react with nitrogen directly generating Si3N4in situ. SiO(g) reacts with nitrogen forming Si3N4 at both central and peripheral sections of block. The non-uniform distribution of Si3N4 and uneven microstructure is caused by the generation process, indicating that it is unavoidable in Si3N4-SiC composites. |
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| Keywords: | Silicon nitridation Formation mechanism Thermodynamics SiO(g) |
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