첨가제 SiO2 나노 콜로이달에 의한 SiC 세라믹스의 균열치유 특성

Abstract

Because of its good mechanical properties, radioactivity, and corrosion resistance, silicon carbide (SiC) constitutes a leading candidate material for high temperature structural applications such as future generation gas turbines and the inner containment of nuclear fusion reactors. However, it is saddled with low fracture toughness, which results in the rapid and easy propagation of cracks once an initial crack has been introduced. As a result, the structural integrity of a ceramic component may be seriously affected, and this low reliability has limited their application. To overcome this, many studies have attempted to achieve the following: (a) non-destructive inspection with very high ability to detect micro cracks (b) increase fracture toughness through fiber-reinforcement,while also decreasing sensitivity to cracks; (c) introduce crack-healing properties. The introduction of crack-healing properties to the structural components used in engineering can be expected to yield significant results such as: (1) increased reliability, (2) decreased machining costs, (3) decreased maintenance costs, and (4) prolongation of the relevant item’s lifetime. Crack-healing has been observed in ceramics such as Si3N4, Al2O3-SiC composites, mullite-SiC composites, and Si3N4-SiC composites. In this regard, while SiC is a ceramic that has a high potential for crack-healing, very few studies have been conducted on its crack-healing behavior. This study focuses on the crack-healing behavior and bending strength of SiC ceramics to which sintering additives have been added (Al2O3 + Y2O3 = 10 and 12 wt.% (Al2O3:Y2O3=60:40) and SiO2 = 0 and 3 wt.%). Both SiO2 additives feature nano-powder and nano-colloidal. The crack-healing behavior and bending strength of SiC ceramics were systematically examined, as the functions of crack-healing temperature, crack size, surface condition, the SiO2 additive and the bending strength of the crack-healed sample from room temperature to 1300 ℃ were investigated. Three-point bending specimens were created and a Vickers indenter was used to introduce semi-elliptical cracks on the specimens. Pre-cracked specimens were healed at various conditions. All fracture tests were performed on a three-point loading system with a 16mm bending span. The specimen surfaces were analyzed by electron probe microanalysis (EPMA), EDX line analysis by FESEM and X-ray diffraction to investigate crack-healing material. The main conclusions obtained were the following: (1) The optimized crack-healing condition was found to be one hour at an atmospheric level of 1100 ℃ (2) The maximum crack size that can be healed at the optimized condition was a semi-elliptical surface crack of 450 μm in diameter. (3) Strength could be recovered by healing at optimum temperature regardless of surface roughness. However, oxide evaporation and formation of gas were found to harmful to the crack-healing ability. (4) Limiting temperature for bending strength of a crack-healed zone was about 1000 ∼ 1100 ℃. (5) Amorphous silica was revealed to be the principle material involved in crack-healing.