Si3N4와 SiCf/SiC 복합재료의 트라이볼러지 및 탄성파 특성

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 economic 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 occurred during machining, production and in use is healed and the enough strength is recovered, we can secure the safety and improve the material reliability. Wear test was investigated on Si3N4 ceramics with SiO2 nano-colloid added various amounts of the crack healing agent. Also, In view of using of high temperature, the mirror polished specimen with SiO2 nano-colloid coating heat treated at the temperature of 1273 K for one hour in air. These specimens heat treated at the temperature of 1073, 1273 and 1573 K for 10 minute in air, respectively, and wear test carried out. We also made SiC specimen and SiCf/SiC composite specimen, and then investigated the property of the wear and the acoustic waves the according to the direction of the fiber orientation when occurs wear and abrasion. The room temperature result of Si3N4 ceramics has a friction coefficient about 1.0 and wear loss about 0.02 mm. Among these specimens, the test specimen added 1.3 wt% SiO2 nano-colloid indicates the best wear resistance because of its lowest friction coefficient and the smallest wear loss. In addition, this specimen shows the highest vickers hardness and bending strength. The friction coefficient has inverse proportion relation to the hardness and bending strength. Si3N4 ceramics annealed at the 1073 ∼ 1573 K high temperature represented the behavior of abrasive wear, and the friction coefficient was proportional to wear loss. Smooth specimens without SiO2 nano-colloid have been showed the high bending strength, vickers hardness, and best wear resistance due to the lower friction coefficient. According to the SiO2 nano-colloid content and the temperature of heat treatment, hardness and high bending strength of Si3N4 ceramics was inverse proportion with the friction coefficient. SiC specimen showed abrasive wear and SiCf/SiC composites was different in wear resistance according to the direction of the fiber orientation, and the friction coefficient and wear loss of perpendicular to the fiber direction showed the smallest value. The wear loss and wear coefficient was directly proportional. The results of the WT and frequency analysis showed that dominant frequencies by using acoustic emission test were 19.5, 39 and 58.6 kHz in SiC specimen and 117.2 and 136.7 kHz in SiCf/SiC composite, respectively.