Konevskyi P. The strength of sapphire under extreme loads

The thesis is aimed at study of the influence of anisotropy of crystal lattice, parameters of growth and after-growth treatment on physical and mechanical parameters of sapphire under extreme loads. The anisotropy of sapphire hardness at loads on indenter up to 1000 N was first measured. It is shown that the sapphire plane (0001) which is the hardest at low loads (up to 1 N) at high loads (from 100 N to 1000 N) shows a hardness of 50% less than the plane (10-10) and 30 % less than the plane (11-20). The optimum crystallographic plane (10-10) for products from sapphire in stock multilayer transparent security that provides the same ballistic strength as a multi-protection glass 3 times greater in thickness and weight was discovered. On the basis of the research results the modules of transparent protection layers of sapphire of crystallographic orientation which have the necessary ballistic survivability (3 hits with 7.62 mm WC projectile without penetration protection in 150x150 mm2) were produced and successfully tested. The sapphire shock resistance and dependency of resistance on the oxidation-reduction potential of the chemical environment of annealing was determined with the help of the method of the impact fragmentation. The sapphire annealed in a hydrogen medium for 4 hours at 1750oC has the maximum impact resistance. It was shown that during the growing of variable cross-section sapphire crystals (sapphire crucibles) the number of blocks and gas bubbles generated in the zone of cross-section changes depends on the shouldering angle. The optimum shouldering angle is ~ 50°, than there are no gas bubbles and the number of blocks is corresponding to the block structure of the crucible seed.