Preparation And Properties Of Tectum On Reacation-Bonded SiC

The reaction-bonded silicon carbide (RB-SiC) is a kind of mirror material withexcellent comprehensive properties. RB-SiC is composed of two kinds of materi-als with different hardness, and it is hard or impossible to obtain very high surfacesmoothness for normal machining. The deposition of tectum was used to improvethe surface smoothness of RB-SiC in present research. In order to reduce cost andimprove the pertinence of experiments, the computer simulations were used to get theoptimized parameter of deposition. The simulation methods include the Monte Carlofor deposition process, the Molecular dynamics simulation for interaction energy andthe Finite Element Analysis method for simulation of stress state. The deposition ofthe tectum is prepared by magnetron sputtering based on the optimized parameters,and then, the properties of the tectum were studied. It could be known that the adhe-sion of the tectum to substrate and the density of the tectum were all improved whenthe deposition temperature increased. Besides which, the results of molecular dynam-ics simulation indicated that the interactive energy between the tectum and substrateincreased with the increasing deposition temperature. However, the results of FEAshowed that the higher deposition temperature led to higher stress, which is in directproportion with the difference between the deposition and room temperature, in thetectum-substrate system. And the higher stress will do harm to the stability of thetectum-substrate system. At the same time, the effect of the deposition temperatureon the adhesion of the tectum to substrate is weak, as indicated by the morphology ofintercross section. Therefore, the deposition temperature was set as 200℃in orderto reduce the stress in the tectum-substrate system.Furthermore, the higher surface roughens of substrate could result in lower adhe-sion of the tectum to substrate and the weaker density of the tectum as indicated by thedeposition simulation of the tectum. Therefore, the surface roughness of the substrateshould be reduced as low as possible before the deposition process. Besides which,the study on the tectum on substrates with different surface roughness shown that thestress level increased with the increasing surface roughness of substrate, and the de-lamination will appear when the specimen were put in air at room temperature. As a result of which, the tectum should be deposited on the substrate with lower surfaceroughness.The effects of the tectum thickness on the properties, such as the value and dis-tribution, of the stress in the tectum-substrate system were studied. As indicted bythe FEA results, the stress in the tectum decreased at a rate slowing down with theincreasing tectum thickness. And the conclusion agrees well with the results providedby literatures, and the results of our experiments shown that the tectum with thicknessequal to 12μm had a excellent comprehensive properties.The crystal structure could affect the surface roughness of polished tectum, andthe surface roughness of tectum prepared at 200 ?C could reach a higher level if thecontent of a-Si is higher. It could be found that content of a-Si is the highest amongthe specimen prepared at different temperature. The surface roughness of the polishedtectum prepared at 200?C was the lowest among that prepared at other temperatures.The properties of the silicon tectum prepared by electron beam physical vapordeposition, plasma enhanced chemical vapor deposition and the silicon carbide tectumprepared by chemical vapor deposition were studied. And the comparison betweenthose methods and magnetron sputtering has been made, and the result of comparisonindicated that the magnetron sputtering is most suitable method among four methods.