Magnetic circular dichroism in EELS: Towards 10 nm resolution

We describe a new experimental setup for the detection of magnetic circular dichroism with fast electrons (EMCD). As compared to earlier findings the signal is an order of magnitude higher, while the probed area could be significantly reduced, allowing a spatial resolution of the order of 30 nm. A simplified analysis of the experimental results is based on the decomposition of the Mixed Dynamic Form Factor S(q,q',E) into a real part related to the scalar product and an imaginary part related to the vector product of the scattering vectors q and q'. Following the recent detection of chiral electronic transitions in the electron microscope the present experiment is a crucial demonstration of the potential of EMCD for nanoscale investigations.Comment: 12 pages, 6 figures, submitted to Ultramicroscop

Study of the microstructure, tensile properties and hardness of AZ61 magnesium alloy subjected to severe plastic deformation

Hot extruded (EX) AZ61 magnesium alloy was processed by the twist channel angular pressing (TCAP) method, which combines equal channel angular pressing (ECAP) and twist extrusion (TE) processes and significantly improves the efficiency of the grain refinement process. Both the initial hot extruded AZ61 alloy and the alloy after completion of TCAP processing were examined by using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) and their corresponding micro-tensile testing (M-TT) and hardness testing at room temperature. The results showed that the microstructure of hot extruded alloy was refined well by TCAP due to dynamic recrystallization (DRX) caused by TCAP. The tensile properties, investigated by micro-tensile testing (M-TT), of the AZ61 alloy were significantly improved due to refined microstructure. The highest tensile properties including YS of 240.8 MPa, UTS of 343.6 MPa and elongation of 21.4% of the fine-grained alloy with average grain size below 1.5 mu m was obtained after the third TCAP pass at 200 degrees C using the processing route B-c.Web of Science810art. no. 77

Využití numerických simulací při optimalizaci technologických procesů objemového tváření za studena

The paper deals with numerical and physical modelling aimed at optimisation of production technology and designing of manufacturing tools with use of finite-element method. For the topic of cold bulk forming a manufacture of pressed insert, used in industry as a component for damping system for passenger cars, was simulated. It is a rotationally symmetric component, which is subjected to high axial load, and strength and fatigue characteristics of which depend substantially on service life and reliability of the whole damping system. This component was subjected to analysis of distribution of flow stress and deformation intensity at combined extrusion from the viewpoint of their load with use of simulating software Simufact.Forming 10.0. The simulation process ran smoothly, without sudden changes of the shape leading to formation of possible internal defects.Práce se zabývá numerickým a fyzikálním modelováním za účelem optimalizace výrobní technologie a konstrukce výrobních nástrojů s využitím metody konečných prvků. Pro danou problematiku objemového tváření zastudena byla provedena simulace výroby zálisku využívaného v praxi jako součást tlumícího systému osobních vozů. Jedná se o rotačně symetrickou součást, která je vysoce namáhaná axiálním zatížením a jejíž pevnostní a únavové charakteristiky závisí podstatnou měrou na životnosti a spolehlivosti celého tlumícího systému. U dané součásti byla provedena analýza rozložení deformačního napětí a intenzity deformace při kombinovaném protlačování z hlediska jejich namáhání za pomoci simulačního programu Simufact.Forming 10.0. Vlastní proces simulace probíhal plynule, bez náhlých změn tvaru vedoucích ke vzniku možných vnitřních vad