Crack self-healing behavior in silicon carbide composite ceramics

Abstract

The structural integrity of ceramic component may be seriously affected since the structural ceramics are brittle and sensitive to cracks. However some engineering ceramics have the ability to healing the crack that is considerable advantages can be expected. In this work, crack-healing behavior and mechanism was investigated in different silicon carbide based materials; alumina, mullite, silicon nitride, aluminum nitride, and zirconium diboride. To find self-healing conditions in economical way for commercial structural ceramics, self-healing parameters were reviewed based on silicon carbide composite ceramics; healing temperature, testing temperature, healing atmosphere, crack size, SiC volume fraction, applied healing and testing stress, threshold stress for crack-healing, and fatigue stress. Enhancing the self-crack-healing ability is valuable way to expand the usage of SiC ceramics such as engineering parts in extremely hard conditions and advanced semiconductor parts for higher density of circuit. CVD grown silicon carbide is ideal performance material for silicon wafer processing. Crack- healing ability of CVD SiC ceramics is a very useful technology for higher structural integrity and for reducing the machining and non-destructive inspection costs. This study focuses on CVD SiC ceramic performance and its crack-healing behaviors were investigated as a function of crack-healing temperature, time, size, and temperature dependence of the resultant bending strength. Three-point bending specimens were made and a semi-elliptical crack was introduced on the specimen by a Vickers indenter. Pre-cracked specimens were healed at various temperature conditions. The main conclusions were: (1) CVD grown SiC has cubic β structure, it offers isotropic characteristics. (2) Optimized crack-healing condition is; temperature: 1500℃, 1hr in air. (3) The bending strength is increased as testing temperature increased, means the material can be safely used up to a temperature of 1500℃ with a good retention of thermal and mechanical properties. In addition, the YAG single crystal growth will follow the same path as the semiconductor industry with cost becoming the main driver. Thus, it become imperative that models be developed that can be used for scaling purposes for the design of large YAG crystal growth systems. Analysis of thermal phenomena in the crystal growing by induction heating hot zone and resistance heating carbon hot zone has been addressed. To grow a good quality, productivity improvement, and large size of YAG crystal growing is shortfalls of current induction heating Czochralski method. The simulation includes the temperature gradient in melt and melt-crystal interface, growing zone. Resistance heating has stable temperature gradient in melt and higher gradient in melt-crystal interface which can be controlled by hot zone design change. Power consumption also improved by using lower thermal conductivity carbon insulation materials.