The smallest earthquakes ever detected in metals at the micron scale

When studying the deformation of metals at the micrometre scale, the regular and continuous behaviour usually observed macroscopically gives way to a jerky behaviour due to the localisation of so-called plastic events. This is explained by the intermittent and complex redistribution of dislocations—linear defects responsible for the irreversible deformation of crystalline materials—induced by mechanical loading. These defects cause the formation of surface “stair steps”.

To study this phenomenon in greater detail, research groups from Eötvös Loránd University in Budapest, Charles University in Prague, and Mines Saint-Étienne (Georges Friedel Laboratory, UMR 5307 CNRS) developed an ultra-sensitive micromechanical testing platform enabling the detection of weak elastic waves emitted during the deformation of micron-scale pillars. Compression experiments performed on such single-crystal zinc micropillars in a scanning electron microscope confirmed the correlation between these so-called acoustic signals and the jerky evolution of deformation in the form of “bursts”. This experiment enabled us, for the first time, to hear the “noise of dislocations”.