Shut O. Regularities of polycrystals hardening at the transition from micro- to nanostructured states

The generalized expression of the yield strength, hardness dependencies upon the grain size at the transition from micro- to nanostructured states and these values rationed onto Young's modulus were obtained with the use of S-functions and averaging integrals. The existence of the two critical grain sizes, which correspond to the change of the deformation mechanism and corresponding change of the sigma(d) dependence, was taken into account. The structural dependence of hardness and its value rationed onto Young's modulus at the transition from micro- to nanostructured states for the chromium and titanium based thin film materials obtained with the help of magnetron sputtering at the controlled change of the partial pressure of oxygen has been experimentally studied. Significant differences in the experimental dependencies for chromium and titanium properties, which are caused by the difference in solubility of interstitial impurities in the crystal lattice, were found. Because of the enrichment of the interfaces by "useful" impurities it was possible to ensure the increase in hardness in the chromium case up to 19 GPa and in the case of titanium - up to 11,5 GPa. With the use of the obtained generalized expression sigma(d) the construction of the limiting curves for different characteristics of the interfaces and of the solid solution was proposed. The analysis of the experimental data in these conditions allows to estimate real changes of state for the interfaces and solid solution at the change in grain size. In the frame of the composite model the achieved interface strength for the Cr-37,2 wt.%Ni alloy was estimated at the level of E/50 and for chromium thin films - at the level of E/30, which is approaching the maximal (theoretical) strength for the given material.