Lytoshenko N. Regularities of influence of residual thermal microstresses and dispersion of carbide grains sizes on the deformation characteristics of WC-Co hardmetals.

The dissertation deals with the study of regularities of the influence of residual thermal stresses, which arise in phases of hardmetals at the stage of cooling after the sintering, and WC grain-size distribution on deformation characteristics of these alloys under tension and compression. In the work formulas for calculation of the average residual thermal stresses in phases of WC-Co hardmetals are suggested. It is established, that the residual stresses in volume of a sample exceed the stresses near a surface by a factor of 2. The dependence of the carbide phase contiguity on the dispersion of the phase grain sizes in alloys WC-Co is revealed. This has allowed us to take into account coefficient of variation of WC grain sizes when determining deformation characteristics of WC-Co hardmetals. A theoretical method of construction of the deformation diagrams of WC-Co under tension and compression is developed. It takes into account volume fraction, elastic modules and coefficients of thermal expansion of the phases, residual thermal microstresses, deformation characteristics of the phases on the regions of strengthening, mean sizes of Co layers and WC grains, dispersion of carbide grain sizes and their contiguity. The comparison with experiment testifies to adequacy of the developed theoretical model to real processes of deformation in WC-Co alloys provided that damages of the microstructure are absent. The essential influence of residual thermal stresses on conditional yield points under tension and compression is revealed. The increase of a level of residual thermal stresses results in an increase of conditional yield points under tension and a decrease of their values under compression. The increase of the coefficient of variation of WC grain sizes insignificantly increases conditio-nal yield points under tension and essentially reduces them under compression.