外文翻譯---碳結(jié)構(gòu)和固體顆粒侵蝕的保護(hù)高度多孔炭碳復(fù)合保溫材料的使用-材料科學(xué)(已修改)
2025-06-01 09:01 本頁(yè)面
【正文】 Microstructure and solid particle erosion of carbon based materials used for the protection of highly porous carboncarbon posite thermal insulation R. I. BAXTER, R. D. RAWLINGS Department of Materials, Imperial College of Science, Technology and Medicine, London SW7 2BP, UK Multiparticle erosion tests were performed on candidate coating (colloidal graphite paints) and cladding (dense carbonc— arbon posites and graphite foil) materials employed to protect porous carbon— carbon posite thermal insulation in vacuum and inertgas furnaces that utilize inert gas quenching. The dependence of the erosion rate on the angle of incidence of the erodent was examined and related to the microstructure and the mechanisms of material removal as observed by SEM. In addition, the effect of a thin chemical vapour deposited (CVD) carbon layer on top of a colloidal graphite paint coating and a graphite foil clad was investigated. The coating and cladding materials displayed a greater erosion resistance at all angles of incidence pared to the porous carbon— carbon posite. In general, the greatest erosion rate was found at an angle of incidence of 90176。, where the erodent stream is perpendicular to the erosion surface, and brittle fracture was the predominant mechanism of material removal. The exception was the graphite foil material which displayed maximum erosion at an angle of incidence of 60176。. For this material, two mechanisms were effective: disruption of the graphite ?akes, which are mainly held together by mechanical locking, and a ploughinglike mechanism. The addition of a thin CVD carbon layer to colloidal graphite paint improved performance, whereas the erosion resistance of the graphite foil was slightly degraded as the CVD layer was too thin to prevent the ploughinglike mechanism. 1. Introduction A class of highly porous carbon— carbon (C— C) posites, with low densities in the range — Mg m\3, are utilized as thermal insulation in vacuum and inertgas furnaces at temperatures up to2800 176。C. A consequence of the vacuummoulding process used in the production of the posite is that the discontinuous fibres are orientated into layers to form a twodimensional planar random structure. The vast majority of the volume of the posite consists of interconnected pores and the fibre work is bonded at the intersections of fibres by discrete regions of the carbon matrix as opposed to a continuous matrix. For this reason these posites are also known as carbon bonded carbon fibre (CBCF). As a result of the high porosity and the fibre orientation,the thermal conductivity perpendicular to the fibre layer planes is low, a typical value for a material with a nominal density of Mg m\3 is W m\1 K\1 at 2020 176。C in vacuum . Investigations into the microstructure [3, 4], mechanical properties [2, 5— 9] and thermal properties [10, 11] of these materials have been reported. ( 1997 Chapman amp。 Hall CBCF is used in furnaces employed in high technology applications such as singlecrystal growing (for example, silicon or gallium arsenide) or metal heat treatment. The heat treatment of metals, such as tool steels, is increasingly carried out in furnaces that utilize gas quenching (typically nitrogen is used) [12, 13]. The gas quench may be used to reduce
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