Al₂O₃ 복합 세라믹스의 균열치유재 강도와 탄성파 특성

Abstract

Alumina(Al₂O₃) is the most cost effective and widely used material in the family of engineering ceramics. However, it has weak points that are the bending strength, the fracture toughness and the heat-resistance limit temperature for strength. These weak points restrict the application for structural components. This study aims to overcome these weaknesses by inducing a self crack healing ability. First of all in this study, Al₂O₃/SiC Composite Ceramics were sintered to evaluate the bending strength and elastic wave characteristics. The three-point bending test was carried out under room temperature. The elastic wave detected by fracture wave detector. The crack healing behavior was investigated from 1100 ℃ to 1450 ℃. The bending strength of Al₂O₃/SiC composite by nanocomposite is higher than that of Al₂O₃ monolithic. Crack-healing behavior was depended on an amount of additive powder Y₂O₃. In Al₂O₃/SiC composite ceramics with 3 wt.% Y₂O₃ for additive powder, the bending strength at 1300 ℃ is about 100% increase than that of the smooth specimens. From the result of wavelet analysis of elastic wave signal, the smooth specimen and heat treated specimen of Al₂O₃ monolithic and Al₂O₃/SiC composite ceramics showed characteristics of frequency about 58 kHz. The strength of Al₂O₃/SiC composite ceramics was a little higher than those of Al₂O₃ monolithic. The dominant frequencies were high with increasing of Y₂O₃ for additive powder. The dominant frequencies had direct connection with the bending strength. Second, we are preparing tree kinds of Al₂O₃ composite ceramics, including Y₂O₃ 1, 3, 5 wt.%(for sintering additive powder) and SiC in other to examine High-temperature bending strength and Crack-Healing Behavior. We studied the basic crack-healing strengths function of crack-healing temperature and the effect of crack-healing treatment according to an amount of sintering additive powder Y₂O₃. The specimens were produced in order to evaluate three-point bending strength with a Surface Crack length of 80~120㎛, which was made with a Vickers Indentation. The crack-healing behavior was observed for 1 hour of heat treatment temperature from 1100 ℃ to 1300 ℃ in the air. The three-point bending test was carried out under room temperature. Three main conclusions were drawn from the results of this study. 1) In-Situ Observation, the surface crack length of the heat treated specimen of Y₂O₃ 3 wt. % showed a better crack-healing ability than the addition of Y₂O₃ 1, 5 wt.%. 2) The additive powder Y₂O₃ 5 wt.% has about half the smooth specimen strength of Y₂O₃ 1, 3 wt.%. 3) The additive powder Y₂O₃ 1, 3, 5 wt.% showed strength recovery under heat-treatment, and Y₂O₃ 3wt. % in particular has an excellent crack-healing ability.