Abstract
Abstract The effect of high temperature predeformation on deformation characteristics of ductile LiF and brittle BaF2 crystals was investigated. The same predeformation, as has been shown previously, leads to the increasing of the limited plastic deformation of MgO crystals by one order of magnitude. It was found that in both investigated crystals, as in the case of MgO crystals, at the test temperature T2 ≅ 0.1 Tm limited plastic deformation before fracture obviously increases if the specimen was prestrained up to εp ≦ 1% at T1 = 0.5 Tm. This increase is as higher as the plasticity of crystal is lower. In BaF2 crystals it reaches a factor of 20 and more. The effect is connected with the creation of mobile dislocations during the high temperature predeformation and dislocaton sources for subsequent deformation at lower temperatures and with the homogeneity of the process of plastic deformation. These conditions prevent the appearance of dangerous places in which the fracture can begin.