BEGIN:VCALENDAR VERSION:2.0 PRODID:icalendar-ruby CALSCALE:GREGORIAN METHOD:PUBLISH BEGIN:VEVENT DTSTAMP:20260825T180540Z UID:https://www.mpie.de/events/20262/3755656 DTSTART:20190924T113000Z DTEND:20190924T123000Z CLASS:PUBLIC CREATED:20190906T141203Z DESCRIPTION: Materials at small scale behave differently from their bulk co unterparts. This deviation originates from the abundance of interfaces at small scale. Quantifying the properties and revealing the underlying mecha nisms requires experiments with small samples in situ in analytical chambe rs. However\, small size poses the challenge of sample handling\, but offe rs the opportunity of in situ inspection of mechanism during testing in an alytical chambers. In order to overcome the challenge and take advantage o f the opportunity\, we developed a MEMS based micro scale testing stage wh ere the sample and the stage are co-fabricated. The stage suppresses any m isalignment error in loading by five orders of magnitude. The stage allows in situ inspection of samples during testing in SEM and TEM. We employed the stage in two scenarios. (1) Exploring the effect of microstructural he terogeneity\, such as grain size and orientation\, on the deformation mech anisms in nano grained polycrystalline metals. Here the test specimens are free standing thin films subjected to uniaxial tension. We found that het erogeneity introduces two apparently dissimilar\, but fundamentally linked \, anomalous behaviors. The samples undergo plastic deformation during unl oading\, i.e.\, exhibit Bauschinger type phenomenon. Upon unloading\, they recover a significant part of plastic deformation with time. The underlyi ng mechanism\, verified by in situ TEM inspection\, is as follows: during loading\, the relatively larger grains undergo plastic deformation and rel ax by employing dislocations\, while the smaller grains remain elastically deformed. During unloading\, the smaller grains apply reverse stress on t he larger grains causing reverse plasticity resulting in a deviation from linear stress-strain response. Upon complete unloading\, the residual stre ss of the elastically strained small grains continue to apply reverse stre ss on the larger grains resulting in biased jumps of dislocation in the la rger grains and strain recovery. (2) Exploring the effect of size on britt le to ductile transition (BDT) temperature (540C) in single crystal silico n. Here the sample is a micro scale single crystal silicon beam subjected to bending which limits the high stress region to a small volume in the sa mple\, and minimizes the probability of premature failure from random flaw s. We found that silicon indeed deforms plastically at small scale at temp eratures much lower than 540C. Ductility is achieved through a competition between fracture stress and the stress needed to nucleate dislocations fr om the surface. Our combined SEM\, TEM and AFM analysis reveals that as a threshold stress is approached\, multiple dislocation nucleation sites app ear simultaneously from the high stressed surface of the beam with a unifo rm spacing of about 200 nm between them. Dislocations then emanate from th ese sites with time lowering the stress while bending the beam plastically . This process continues until the effective shear stress drops and disloc ation activities stop. A simple mechanistic model is presented to relate d islocation nucleation with plasticity in silicon.\nSpeaker: Prof. Taher Sa if LAST-MODIFIED:20190909T093444Z LOCATION:Max-Planck-Institut für Eisenforschung GmbH\, Room: Large Confere nce Room No. 203 ORGANIZER;CN=Prof. Gerhard Dehm :mailto: SUMMARY:Lessons learned from nano scale specimens tested by MEMS based appa ratus: Lessons learned from nano scale specimens tested by MEMS based apparatus URL;VALUE=URI:https://www.mpie.de/events/20262/3755656 END:VEVENT END:VCALENDAR