M. Kazakevich

Nanohardness of copper in the vicinity of grain boundaries

The nanohardness in the vicinity of grain boundaries in high purity Cu was investigated. It was found that the nanohardness increases while approaching the grain boundary, the characteristic distance at which the grain boundary influences the nanohardness being in the range of few micrometers.

Downscaling Equal Channel Angular Pressing

ECAP (equal channel angular pressing) is a well-known severe plastic deformation method used to produce ultra-fine grained materials. The dimensions of ECAP specimens are usually in the centimeter range. For producing high strength wires or fibres with diameter in the micrometer/millimeter range, downscaling of the ECAP process may be a viable option. To achieve this, several experiments were carried out. For downscaling to the micrometer range, porous steel discs can be used as processing tools. In this case, a solid state infiltration method as a variant of the forcefill process can be used. Extremely large strain is introduced due to the material flow through the tortuous channels inside a porous pre-form leading to grain refinement depending on processing conditions. To obtain specimens with a typical dimension in the millimeter range, the forcefill approach was altered by using die channels produced by conventional drilling. The tool geometry used is equivalent to conventional ECAP, but with a multi-channel die. Microstructure investigations demonstrating significant grain refinement confirm the viability of this approach.

Combined scanning probe microscopy and electron microscopy study of microstructure evolution in copper processed by equal channel angular pressing

Abstract We produced submicrocrystalline Cu using the equal channel angular pressing technique with four passes. The as-deformed samples exhibited a high yield strength > 400 MPa and a poor elongation before failure < 20%. The majority of the grain boundaries after equal channel angular pressing were of the low-angle type. A series of heat treatments in the temperature range 220–300°C was performed and partly recrystallized microstructures with different fractions of recrystallized grains were obtained. The microstructures were analyzed by a combination of transmission electron microscopy, orientation image microscopy, light microscopy and scanning probe microscopy. The increase in ductility in partly recrystallized samples was accompanied by a decrease in the yield strength. It was suggested that to obtain a bulk nanocrystalline material which is both strong and ductile the majority of the grain boundaries should be of the high-angle type. It is shown that the scanning probe microscopy technique allows o...

New Applications of the SPD Concept: μSPD

Extreme grain refinement by severe plastic deformation (SPD) is an established processing approach broadly applied to bulk materials. The dimensions of specimens or workpieces used are typically in the centimeter range. We propose to adopt an analogue of equal channel angular pressing in the context of microforming. It is suggested that using sub-millimeter sized channels (“angular vias”) in a process similar to conventional forcefill technique, fibres or wires with ultrafine grain size can be manufactured. The cross-sectional dimensions of the channels can be in the micrometer range. An alternative technique that may lead to ultrafine grained fibres or wires is pressing of metals through porous “filters” with micrometer or submicrometer scale open porosity. First results demonstrate the viability of this approach which we refer to as μSPD.

Mechanical Behavior of the Patterned Copper Lines

The effect of geometrical confinement on mechanical response of the material was investigated. We used AFM technique (instrumented nanoindentation) for nanohardness (H) and Young’s modulus (E) measurements of the polycrystalline thin films of Cu (99.999%) film deposited on silicon substrate and patterned into 3-8 μm lines. The H and E values were calculated on the base of Oliver, Pharr’s procedure [1]. The H and E dependence on a distance from the line edge was studied. This approach allowed us to vary systematically only one of two line size limiting parameters, since the film thickness was constant. The load-displacement P(h) curves and corresponding indent images for different loads and different distances from the line edge were made with the DI Dimension 3100 and Hysitron Triboscope nanoindenter.