Micro- and submicrocrystalline structure of cooper: processing and low temperature mehanical behaviour
Multi-scale and/or multi-disciplinary approach to process-product innovation
Nanotechnology & Nanomanufacturing (T3-1P)
Keywords: cooper, structure, low temperature plasticity
Micro-, submicro- and nanostructured materials, which possess unusual mechanical and other physical properties, have been attracting growing interest among researchers. The copper (99.5% pure) polycrystals was investigated on samples of three types (A, B, C) of microcrystalline structure. The TEM analysis showed that samples A contained slightly misoriented grains (~1 mm) with high densities of dislocations coils and low-angle boundaries. Samples B had a bimodal structure: about 30% of the volume was taken by elongated grains with the spacing of ~0.5-1mm between the nearest boundaries that were characterized by high-degree misorientation and high density of dislocation; the rest of the volume (~70%) was occupied by large dislocation-free variable-size (1-10 mm) grains that contained abundant twins of different systems. The C-type microstructure consisted of large (several tens of microne) recrystallized grains with numerous long twins. The x-ray examination shows that the structures investigated also differ in the coherent scattering area, microdeformation and the average shift of the atoms from the sites of the FCC lattice. The high structural inhomogeneity of the samples was particularly evident in the experiments on microindentation. According to their structural features, the samples are intermediate between ordinary polycrystals with the grain size over 100 mm and ultrafine-grained materials with grains smaller then 1 mm.
Tensile deformation was performed at T=295, 77.3, 4.2 and 0.5K; the Vickers hardness was measured in the interval 295-77.3K. At all the temperatures of the experiment, the yield point increases with the decreasing grain size (C-B-A) following the empirical Hall-Petch Law. A qualitatively similar regularity was also observed in microhardness. Plasticity decreases considerably with the grain size. When the temperature is lowered, the plasticity of all types of the samples increases.
Presented Tuesday 18, 13:30 to 15:00, in session Nanotechnology & Nanomanufacturing (T3-1P).
