Experiment of double grits scribing 2D SiCf/SiC composite

ObjectivesTo improve the grinding quality and efficiency, reveal the material removal mechanism of SiCf/SiC composites, and determine the coupling effect among abrasives during grinding.MethodsFirstly, uniaxial tensile, shearing, and bending experiments of SiC fiber bundles are conducted to observe damage modes. Secondly, double-abrasive scratching experiments are carried out on the woven surface (WS) and stacking surface (SS) of 2D SiCf/SiC composites along the 0°, 45°, and 90° fiber directions, respectively. The scratch surface topographies are observed and the scratch force is measured to reveal the material removal mechanism and abrasive coupling effect.ResultsThe tensile-fractured SiC fiber shows a 45° bevel fracture surface at the tip. The shear-fractured SiC fiber tip surface is perpendicular to the axis of the SiC fiber. The bending-fractured SiC fiber shows a hybrid of bevel and perpendicular surfaces, indicating both tensile and shear fracture characteristics. In the longitudinal fiber cut-in direction on WS0, the matrix shows a large area of ductile removal scratching. The fiber shows tensile fracture, and the broken fiber is peeled off from the matrix, with some fiber tips showing tensile fractures. Bending fracture also occurs in the cutting direction of WS0 longitudinal fibers, and a large number of fiber peel-off marks are observed on the surface. At the same time, ductile removal marks of the matrix and some large-sized fibers appears on the surface. The transverse fibers on WS0 show the characteristics of tensile fracture, bending fracture, and shear fracture simultaneously. There are tensile fractures, bending fractures, and shear fractures on the surface of WS45 fiber. The ductile removal and fiber peeling also appear on the fiber. A shear fracture occurs on the SS0 fiber and bending fracture occurs at the boundary of the woven structure. The removal modes of SS0 longitudinal fibers are mainly tensile and shear fractures, accompanied by secondary scratches formed by fiber exposure. SS90 fibers show shear and bending fractures at the boundary. The transverse fibers show tensile, shear, and bending fractures while the matrix shows strong brittle removal. The scratching force varies significantly with fiber orientations. The order of scratching force is FSS0 > FWS45 > FSS90 > FWS0. Under the same scratching depth, the normal scratching force of the double abrasives is much smaller than that of a single abrasive.Conclusions(1) In scratching of 2D SiCf/SiC, the transverse fibers undergo shear, tensile, and bending fractures. The fiber is removed by shearing, with a small amount of bending removal occuring at the woven boundary. The longitudinal fibers mainly exhibit tensile (cut-in) and bending (cut-out) fractures, accompanied by a large number of fiber peeling. The removal forms of the matrix include crack propagation, ductile scratching, powder removal, and brittle peeling. (2) 2D SiCf/SiC shows strong anisotropy. The order of scratching force obtained under different surfaces and scratching directions is FSS0 > FWS45 > FSS90 > FWS0. The material removal energy consumed in the WS0 direction is the lowest while SS0 consumes the most. At this time, a large number of matrices are powdery. The normal scratching force of the double abrasives is much smaller than that of the single abrasive. For the same volume of material removed, the first abrasive causes more surface damage after scratching, reducing the scratching force of the second abrasive. This indicates a strong coupling relationship between the abrasives, which can effectively reduce the normal scratching force when processing 2D SiCf/SiC composites.