K. Máthis

In-situ neutron diffraction and acoustic emission investigation of twinning activity in magnesium

The neutron diffraction and acoustic emission (AE) techniques have been used for in-situ investigation of deformation twinning activity in cast polycrystalline magnesium at room temperature. The combination of these two techniques results in obtaining complementary information about the twinning mechanism during the straining. It is shown that loading mode significantly influences the twin nucleation and the twin size. In tension, the twin nucleation is observed during the entire test, while in compression only at the beginning of the plastic deformation. Nevertheless, the overall twinned volume does not differ. The optical micrographs support the above mentioned conclusions.

Micron-scale deformation: a coupled in-situ study of strain bursts and acoustic emission

Plastic deformation of micron-scale crystalline materials differs considerably from bulk samples as it is characterized by stochastic strain bursts. To obtain a detailed picture of the intermittent deformation phenomena, numerous micron-sized specimens must be fabricated and tested. An improved focused ion beam fabrication method is proposed to prepare non-tapered micropillars with excellent control over their shape. Moreover, the fabrication time is less compared with other methods. The in situ compression device developed in our laboratory allows high-accuracy sample positioning and force/displacement measurements with high data sampling rates. The collective avalanche-like motion of the dislocations is observed as stress decreases on the stress-strain curves. An acoustic emission (AE) technique was employed for the first time to study the deformation behavior of micropillars. The AE technique provides important additional in situ information about the underlying processes during plastic deformation and is especially sensitive to the collective avalanche-like motion of the dislocations observed as the stress decreases on the deformation curves.

Comparison of the microstructure and the mechanical properties of AX41 magnesium alloy processed by EX-ECAP via three different routes A, Bc and C

This work is devoted to the creep-resistant AX41 magnesium alloy (Mg-4 wt.% Al-1 wt.% Ca), processed by extrusion and consecutive Equal Channel Angular Pressing (EX- ECAP) up to total of eight passes, via route A, Bc and C at 220 °C. Beyond the deformation behavior the change of the microstructures was studied by electron back-scattering and X-ray diffraction methods. Significant grain refinement was found for all processing routes (grain sizes decreased below 1 pm after 8 passes). The X-ray line profile analysis performed by Convolutional Multiple Whole Profile (CMWP) fitting method has not revealed differences between the particular dislocation structures. Route A was found to be the most effective processing route from the point of view of grain size refinement and the room temperature strength. The influence of the texture and the dislocation structure on the plastic deformation processes is discussed in detail.