Silicon Carbide Platelet/Silicon Carbide Composites (original) (raw)
Related papers
Anisotropic Properties in Hot Pressed Silicon Nitride—Silicon Carbide Platelet Reinforced Composites
Journal of the European Ceramic Society, 1999
The anisotropic properties (microstructure, mechanical properties) of a hot-pressed platelet reinforced silicon nitride composite were compared with those of the monolithic material. The platelets appeared to be orientated with their basal plane in the compressive plane, and to be embedded in a silicon nitride matrix consisting of interlocked elongated b-Si 3 N 4 grains with their c axis orientated in this plane. TEM analysis showed an interface, consisting of glassy phase and graphite at the platelet±matrix grain boundary. Moreover the interfacial tensile stresses are in favour of a crack de¯ection mechanism. It was shown by TEM analysis that crack de¯ection occurs not only at the silicon nitride±platelet interface, but also at silicon nitride±silicon nitride grain boundaries. The eciency of this reinforcing mechanism is highly orientation dependent. Because of their two dimensional geometry compared to the one-dimensional b-Si 3 N 4 grains, platelets increase the toughness in two dimensions. #
Silicon carbide platelet-reinforced silicon nitride composites
Journal of Materials Science, 1993
Different grades of high aspect ratio SiC platelets were used to reinforce Si3N 4. Dispersion of additives (4 wt % Y203 and 3 wt % AI203) was achieved by ball milling in ethanol using alumina balls, while dispersion of platelets was done by ball milling using plastic balls. Consolidation of the composites was carried out by uniaxial hot pressing. A slight decrease in flexural strength was measured, while significant increases in elastic properties, fracture toughness and Weibull modulus were noted. Microstructure and crack-propagation studies as well as reinforcement mechanisms are presented.
Mechanical properties of silicon nitride-SiC platelet composites
Journal of the European Ceramic Society, 1991
Silicon nitride and SiC platelet-silicon nitride composites have been prepared by hot-pressing and by pressureless sintering. As-received, large SiC platelets behave as critical flaws and were separated into two narrow size fractionsjor the production of composites.
R-Curve Behavior of Silicon Nitride Ceramic Reinforced with Silicon Carbide Platelets
Journal of the American Ceramic Society, 2005
Si 3 N 4 ceramics reinforced with SiC platelets were fabricated by hot pressing at 1800°C. The microstructure of the Si 3 N 4 matrix itself was the same with or without the addition of the SiC platelets. However, the mechanical properties of the Si 3 N 4 were changed remarkably by the SiC addition. The fracture toughness and the crack resistance with crack propagation (R-curve behavior) were improved while the fracture strength was decreased slightly by the platelets. Improvement in crack resistance was attributed to the extensive interaction of cracks with the platelets. The reduction in strength, on the other hand, is believed to be due to cracks associated with weak platelet-matrix interfaces.
1996
Silicon carbide composites were fabricated through the incorporation of alumina-coated SiC platelets into a SiC matrix. Mechanical properties were evaluated in direct comparison with a commercial Hexoloy SiC. The fracture toughness of the composite, with a fine grained 13-SiC matrix, was twice that of the commercial material. The alumina-coating on the platelets provided a weak interface to promote crack deflection and platelet bridging, as well as easing densification of the composites. On the other hand, a threefold increase in fracture toughness (9.1 MPa-Jm) of an in situ toughened monolithic SiC was achieved by processing at higher temperatures, promoting the 13-to-a phase transformation and forming a microstructure containing high-aspect-ration plateshaped grains. Efforts were made to combine the effects of coated-platelets reinforcement and in situ toughening in the matrix. Moderate high toughness (8 MPa-Jm) was achieved by coupled toughening. The contribution of matrix-grain-bridging, however, was limited by the processing temperature at which the oxide coating was stable.
Processing and characterization of SiC platelet/SiC composites
This document was prepared as an account of work sponsored by the United States Government. Neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, produck, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California and shall not be used for advertisiig or product endorsement purposes.
Journal of materials …, 2001
Several analytical and numerical models proposed to predict the effective fracture toughness (K IC ) of dispersion reinforced brittle matrix composites require the knowledge of the in situ fracture toughness of the included phase . These values are usually unavailable and they may differ significantly from data obtained on bulk materials. Ceramic platelets (e.g. Al 2 O 3 and SiC platelets) have a high potential to be used as reinforcement in ceramic and glass matrices . In order to be able to predict the effective toughness of platelet-reinforced composites it is necessary to know the value of the platelets' intrinsic toughness. However, the data are not easily available.
Acta Materialia, 2015
Freeze casting has proven to be a versatile processing route to fabricate bioinspired ("nacre-like") hybrid composites that exhibit unique combinations of strength and toughness (damage-tolerance). To date, however, the effects of small changes in the architecture of such composites on their mechanical properties have been poorly investigated. Here we examine the influence of microstructural features such as ceramic/polymer ratio, layers thickness, and presence of bridges between ceramic lamellae, on the mechanical performance of the resulting composites. To this end, we compare the flexural strength and resistance to failure of a suite of silicon carbide/polymethyl methacrylate (SiC/PMMA) layered composites made by polymer infiltration of freeze-cast SiC scaffolds with various architectures. Our composite structures all show an increasing fracture resistance with crack extension (rising Rcurve behavior) due to extrinsic toughening mechanisms such as uncracked-ligament bridging, inelastic deformation of ductile layers, lamellae pull out and ceramic bridge fracture. We show that a fine tuning of the composite architecture can lead to SiC/PMMA samples with a dendritic morphology, which exhibit the best strength and toughness. Specifically, the presence of ceramic bridges connecting the lamellae is seen to provide a strengthening effect similar to the mineral bridges between aragonite platelets in nacre, where they prevent debonding and limit platelet sliding; additionally, the fracture of these bridges between lamellae during crack extension is a potent toughening mechanism, thereby conferring optimal damage tolerance to the material.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 1993
A colioidal-chemistry-based technique was developed for interface modification of s&on carbide platelets (SiCp) by coating with alumina particles. The coating process utilizes electrostatic and/or electrosteric interactions between the particles to promote heterocoagulation. Since an understanding of the chemical interface between the SiCp and alumina is important for improving the coating process, the powders were characterized by the measurement of the electrokinetic sonic amplitude (ESA). The major factors studied were particle size, type of alumina, presence of polyacrylate surfactant, and concentration of alumina in the coating slip. The surface coverage and morphology of the alumina coating on SiCp was determined quantitatively by scanning electron microscopy (SEM). The results indicate that around pH 5.8, the surface charge difference between SiCp and alumina was the largest and the coating of alumina on SiCp was feasible. The SEM data showed that surface coverage was uniform, and the highest surface coverage on SiCp was 66% when the surface area ratio of alumina to SiCp was 250% in the suspensjon. No significant improvement of the coating rate was observed by the addition of a polyacrylate for dispersion of SiCp. The concentration of alumina in the slip exhibited a strong influence on the amount of surface coverage on SiCp.