Ion beam modification of thermal stress resistance of MgO single crystals with different crystallographic faces

Ion beam modification of thermal shock stress resistance of MgO single crys tals with various crystallographic faces is investigated. The most stable c rystal faces in terms of stress and damage resistance are established. Ion implantation is shown to reduce the temperature threshold of fracture for a ll crystal faces tested. The (1 1 1) face is demonstrated to be of highest stability compared to (1 1 0) and (1 0 0) faces in both implanted and unimp lanted crystals. At the same time ion implantation substantially increases the microcrack density for all the faces tested and reduces the degree of f racture damage following thermal shock. The theoretical resistance paramete rs for various crystal faces are calculated using the continuum mechanics a pproach, The results are discussed on the basis of fracture mechanics princ iples and the effect of the implantation-induced lattice damage on crack nu cleation. (C) 2001 Elsevier Science B.V. All rights reserved.