Fracture of heterogeneous polycrystals based on dense modifications of boron nitride

The process of self-maintaining explosive fracture in the course of tests for compression of heterophase polycrystals on the basis of boron nitride high pressure phases is considered. Single-phase samples, consisting of sphalerite-like boron nitride, and two-phase samples, containing both sphalerite and wurtzite boron nitride modifications are investigated. Two-phase material is characterized by a high inner microstress level, and an explosive-type fracture occurs in it on reacing the critical value of compressing stresses. A conclusion is drawn, that the methods of the material crack resistance increasing, which are accompanied by inner microstress growth, do not lead to hardening because of the fracture mechanism change