Papers by Keyword: Reaction-Bonded Silicon Carbide

Abstract: This work was focused on improving machining performance of reaction-bonded silicon carbide (RB-SiC) ceramic material using an electrical discharge machine (EDM) with the aid of surfactant. The changes of material removal rate, electrode wear ratio and surface roughness were investigated under two different surfactants, namely Span 20 and Span 80. The surfactant was mixed with carbon nanofiber (CNF) and EDM oil prior to the experiment. Then, the mixture was homogenized in an ultrasonic homogenizer for 35 minutes. In order to investigate the effect of surfactant, different weight percentages which is 0.4wt%, 0.6wt% and 0.8wt% of surfactant were used. The experimental results show that with the addition of Span 20 and Span 80, the electrode wear ratio was decreased with the increased of surfactants weight percentage. Surface finish also can be improved by adding surfactant in the dielectric fluid. The lowest surface roughness was achieved at a surfactant weight percentage of 0.4wt%. The optimum weight percentage for obtaining the highest material removal rate (MRR) was 0.6wt% for both surfactants. In comparison, CNF added with surfactant Span 80 was more effective to improve the machining efficiency of RB-SiC compared to surfactant Span 20, at the optimum weight percentage 0.6wt%.

Abstract: Experiments were carried out to join reaction-bonded silicon carbide (RBSC) ceramic in green body. SiC green bodies were fabricated by gel-casting method. The slurries for joint were prepared by different grain size of SiC. The results indicate the solid loading and the grain size of SiC influence the strength of welding. There is no clear welding interface between the two substrates in an appropriate solid volume loading and grain size. The average bending strength of welding after sintering can reach 300MPa. SEM was used to observe the cross-section morphology and microstructure of binding sites. The test result shows that its microstructure is similar to the RB-SiC ceramic. The mechanical properties of binding sites were tested. The result shows a desirable mechanical property.

Abstract: This paper represents a technique to produce the large size optical aspherical mirror by using reaction-bonded silicon carbide to meet the material requirements of the space used mirrors, based on the characters comparison of all types mirror material. Techniques are described in this paper, including the bonding procedure of silicon carbide to form a mirror shape, the CCOM technology for aspheric grinding, polishing on a home-developed tool –FSGJ-2, and the aspheric profilometry. A specialized Offner Null lens is also developed to measure the aspherical mirror with laser interferometer. With the technology depicted in the paper, a 502mm x 298 mm off-axis SiC aspherical mirror is successfully made with a surface accuracy better than 1/50λrms, the final result meets the design requirement.

Abstract: Reaction-bonded silicon carbide (RB-SiC) is a recently developed ceramic material with many merits such as low manufacturing temperature, dense structure, high purity and low cost. In the present paper, the precision machinability of RB-SiC was studied by microindentation and single-point diamond turning (SPDT) tests. The influence of depth of cut and tool feed rate on surface roughness and cutting force was investigated. Results showed that there was no clear ductile-brittle transition in machining behavior. The material removal mechanism involves falling of the SiC grains and intergranular microfractures of the bonding silicon, which prevents from large-scale cleavage fractures. The minimum surface roughness depends on the initial material microstructure in terms of sizes of the SiC grains and micro pores. This work preliminarily indicates that SPDT can be used as a high-efficiency machining process for RB-SiC.