The Effect of Crystal Orientation on Thermal Shock-induced Fracture and Properties of Ion Implated Sapphire

Ion beam modification of thermal shock resistance of sapphire single crystals with various crystallographic faces is experimentally investigated. The temperature threshold of fracture is determined in both implanted and unimplanted crystals by measuring the fragment contraction on cooling from fracture temperature. Optical and SEM microscopy are used to analyse fracture morphology and thermal shock behaviour on the (0 0 0 1), (1 1̄ 0 2) and (1 1 2̄ 0) faces in sapphire crystals implanted with 70 keV Si- ions and then subjected to thermal stress testing using pulsed plasma. The most stable crystal faces in terms of stress resistance are established. Ion implantation is shown to reduce the temperature threshold of fracture for all faces tested. The (1 1̄ 0 2) face proved to be the most stable for both implanted and unimplanted crystals. The results are discussed on the basis of fracture mechanics principles and the implantation-induced crack nucleation process