Danylenko V. Hardening peculiarities of bcc and hcp metals during developed stages of deformation.

The work is dedicated to studying of effect of temperature, deformation scheme and grain size on hardening peculiarities of severe deformed bcc and hcp materials. Original methodology for determination of hardening parameters for severe deformed materials has developed with a use of compressive tests. Temperature dependence of linear coefficients of hardening was analyzed. It is shown that temperature sensitivity of hardening curve is determined by thermoactivated processes that are responsible for yield stress temperature sensitivity. Hardening parameters for bcc metals are investigated in a wide range of deformation levels and grain sizes. Dependence on grain size correspondent to a change of hardening mechanism is determined. Effect of degradation of linear hardening coefficient under increase of preliminary deformation by rolling is determined in first time. This effect is related to reorientation of slip planes in direction the most favorable according to rolling conditions. In the severe deformed materials, the degradation of hardening does not occur. These materials have high coefficient of linear hardening, which is much higher than yield stress and, according to Consider criterion, leads to potential ability of these materials to store a big amount of deformation in nanostructured state.