Thermal Stresses and Cracks During the Growth of Large-sized Sapphire with SAPMAC Method |
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Authors: | Xu Chenghai Meng Songhe Zhang Mingfu Zuo Hongbo Wang Guigen |
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Affiliation: | Center for Composite Structure, Harbin Institute of Technology, Harbin 150080, China |
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Abstract: | The finite-element method has been used to study the thermal stress distribution in large-sized sapphire crystals grown with the sapphire growth technique with micro-pulling and shoulder-expanding at cooled center (SAPMAC) method. A critical defect model has been established to explain the growth and propagation of cracks during the sapphire growing process. It is demonstrated that the stress field depends on the growth rate, the ambient temperature and the crystallizing direction. High stresses always exist near the growth interfaces, at the shoulder-expanding locations, the tailing locations and the sites where the diameters undergo sharp changes. The maximum stresses always occur at the interface of seeds and crystals. Cracks often form in the critical defect region and spread in the m-planes and a-planes under applied tensile stresses during crystal growth. The experimental results have verified that with the improved system of crystal growth and well-controlled techniques, the large-sized sapphire crystals of high quality can be grown due to absence of cracks. |
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Keywords: | thermal stress crack sapphire SAPMAC method Method Sapphire the Growth During Cracks Stresses high quality experimental results improved system techniques form region spread tensile crystal growth maximum interface seeds |
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