【正文】
f 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。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。 for metals, and material removal is thought to occur by a micromachining mechanism with a contribution of deformation wear at higher angles. On the other hand, for brittle materials, maximum erosion is found where the erodent stream is perpendicular to the erosion surface, and material removal typically results from the formation of Hertzian or lateral cracks . Although it is a convenient approach to idealize materials erosion behaviour in this manner, it is an oversimplification, because erosion is found to depend on other factors, including the erosion conditions, such as erodent par ticle size and shape, as well as the details of the microstructure of the target material . This paper is concerned with the examination of the microstructure and the efectiveness in improving the erosion resistance of several candidate coatings and claddings. The results presented involve the steady state erosion rate as a function of impingement angle under defined conditions. The overall aim of this work is to relate the microstructure to the erosion data by means of a mechanistic approach .materials included the Fiber Materials Inc. C3 posite], which is resin impregnated, and the Toyo Tanso G3470 . In addition, a highdensity carbon— carbon posite was produced by employing CVD over a period of 800 h to infiltrate a 5 mm thick section of the CBCF substrate to a density of 1 Mg m\3. The CVD process used natural gas as the carbon precursor and nitrogen as the carrier gas. The densification was carried out at approximately 1100 176。 Mg m\3) used as cladding pressure of 5 kPa. (Note that the CVD of carbon in the interior of a porous medium is sometimes termed chemical vapour infiltration, CVI.) Another cladding material was graphite foil which was produced by Toyo Tanso by pressing exfoliated graphite ?akes in a rolling operation [23]. The foil is ?exible in nature and is predominantly held together by mechanical locking, as no binder is used. Further samples were produced by subjecting the Calcoat coating and the graphite foil to a CVD treatment (samples designatedCVD in Table I) for a period of 75 h under the conditions described above. A more extensive descrip tion of the materials will be forthing in the dis cussion on the microstructures. . Erosion testing Multiparticle erosion tests were performed on a gas blast type rig, as described by Carter et al. [24]. In this apparatus the erodent particles enter the rig via an aperture in the base of an