질화규소(Si3N4)복합세라믹스의 굽힘강도와 균열치유거동에 미치는 SiO2의 영향

Abstract

The ceramics are classified into the functional ceramics and structural ceramics. Recently various components are being developed using structural ceramics, which are based on unique properties like lightness, heat resistance, corrosion resistance, abrasion resistance and rub resistance. Also the structural ceramics are being actively researched for the automobile components, but these components are pointed out the deficiency of mechanical characteristics which are demand on the working condition, and lack of reliability due to the brittle failure and economical efficiency so on. Generally the structural ceramics can be cracked during on machining, production and service, and furthermore the possibility of material destruction is highly increased when stress effect the defected area. Therefore it can bring about serious problem to material soundness. As mentioned above, if the crack which occured during machining, production and in use is healed and the enough strength is recovered, we can secure the safety and improve the material reliability. In this study the crack-healing and bending stress characteristic of Si3N4 ceramics have been evaluated as follows. (a) The effect of SiO2 Nano colloid level on bending strength of Si3N4/SiC compound ceramics and crack-healing behavior was investigated. The crack-healing behavior was investigated to smooth specimen, heat treated smooth specimen and cracked specimen. And also the bending strength of specimen healed at various temperature were checked. All crack healing process was examined through in-situ observation. (b)The bending strength of Si3N4/SiC compound showed the maximum strength when 1.3 wt.% SiO2 colloid was added. So we evaluated the surface morphology of 1.3 wt% SiO2 colloid. (c) And then the solidity characteristic of high temperature according to Nano SiO2 colloid additive contents was investigated. This study have investigated bending strength accordance with SiO2 colloid contents and surface coating of Si3N4 compound ceramics. We checked bending strength of heat treated specimen at room temperature and bending strength of crack healed specimen at high temperature. (d) To find out the crack-healing behavior of single indentation crack which is made by Vickers indentation and multi indentation crack according to the weight of limit length, we looked into the strength recovery. The bending test was done at room temperature after the surface was coated with SiO2 colloid and heat-treated. (f) To detect the crack healing characteristic of multi indentation crack, we used three kinds of SiO2 colloid coating methods with heat treatment and investigated the recovery of bending strength at room temperature.