HIGH-TEMPERATURE STRENGTH OF COPPER-BASED CONDENSED MATERIALS

The temperature dependences of Vickers microhardness, ultimate strength, and offset yield point in the temperature range between 290 and 1070 K were determined for the transversal direction in copper-based composites Cu-Zr-Y-Mo, Cu-Cr, Cu-C, and Cu-W. The materials produced by electron-beam evaporation/condensation are used for the manufacture of current collectors which, when in operation, are subjected to intensive wear and electrical erosion as well as to mechanical loading at elevated temperatures. This production method provides composite materials with a special layered structure, where copper layers are interspersed with dispersed-particle layers of other metals. The paper describes the procedures of Vickers microhardness and tensile testing at high temperatures. A general thermodynamic activation analysis of the derived relationships of hardness and strength has been performed for various copper-based composite systems in the range of (0.2-0.8)T-melt of copper. A comparative analysis of the obtained values of the activation energy of plastic deformation of copper and copper-based composites as well as the theoretical and experimental data on deformation, internal friction, creep, and self-diffusion processes in copper has revealed that in a wide range of temperatures the activation energy of plastic deformation undergoes a significant change during a transition from one temperature region to another. This is indicative of a successive changeover of effective (governing) thermally activated mechanisms of plastic deformation, It is proved that a heat-induced change in the strength characteristics (hardness, ultimate strength, offset yield point) of the composites studied is controlled by the same plastic deformation mechanisms whose temperature regions coincide.