REGULARITIES OF PHASE TRANSFORMATIONS AND PLASTIC STRAINING OF MATERIALS IN COMPRESSION AND SHEAR ON DIAMOND ANVILS: EXPERIMENTS AND THEORY

Regularities of phase transformations (PT) and plastic straining of materials in compression and shear in a shear high-pressure apparatus with diamond anvil cells (SDAC) have been experimentally studied and an analytical model of material phase transformations in straining between diamond anvils has been developed. Based on a higher yield stress of a new phase and an additional plastic flow of the specimen material from the center to its periphery, we have offered a new explanation of the pressure self-multiplication phenomenon occurring in phase transformations. The rotation of the anvil contributes to the production of fundamentally new materials that cannot be produced by compression without rotation. If two materials which differ only in the yield stress form due to phase transformations, then a material having a lower yield stress forms in compression without rotation, while a harder phase forms in compression with rotation. Therefore, the method based on the material compression with rotation is of particular importance for producing highstrength materials. Phase transformations in elastoplastic materials are one of the most abundant phenomena in the nature, physical experiments and modern technologies. They are widely used in metallurgy, thermomechanical processing of materials, and in the production of new materials with predetermined properties, e.g., in synthesis of superhard materials. Various factors like temperature, high pressures, impurities, large plastic compression and shear deformations, etc. affect essentially the PT proceeding and the formation of the required microstructure of the material with predetermined physico-mechanical properties, thus considerably decreasing, for instance, the transformation pressure. In this case, the formation of new structures that cannot be produced without an additional plastic straining is a possibility. The majority of these phenomena have a purely qualitative explanation and their applications in technological processes are based on purely empirical regularities. The mechanics of materials under these conditions is not adequately developed. Therefore, more comprehensive studies of the effect of stresses, deformations, temperatures and high pressures on the PT proceeding should result in the development of experimentally justified theories and computer-aided models allowing for possible variations in the structure and phase states of real materials as well as in new processes and materials.