Dresden 2014 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 2: Topical Session: Nanomechanics of nanostructured materials and systems I - Grain size effects

MM 2.3: Talk

Monday, March 31, 2014, 11:00–11:15, BAR 205

Small scale deformation of Chromium - Influence of Microstructure & Temperature — •Verena Maier, Megan J. Cordill, and Daniel Kiener — Department Materials Physics, Montanuniversität Leoben, Jahnstr.12, A-8700 Leoben

Time-dependent mechanical behavior, expressed by a materials strain-rate sensitivity, is an important indication for thermally activated processes during deformation. The ongoing miniaturization of components and material phases requires studying these effects on the local scale. In this work, the influence of microstructure and temperature on the strain-rate sensitivity of body-centered cubic Cr was studied by nanoindentation strain-rate jump tests at ambient and elevated temperatures. It was observed that Cr in the single crystal condition exhibits a more pronounced strain-rate sensitivity than ultrafine-grained Cr. This is due to the effects of the high lattice friction of bcc-metals at low temperatures, where the motion of the screw dislocations are dominating the deformation behavior, causing there an enhanced strain-rate sensitivity. Increasing the temperature over a material-dependent critical temperature Tc, it is demonstrated that the deformation behavior clearly changes. The thermally activated strength contribution diminishes and thus the strain-rate sensitivity is significantly reduced. However, for the ufg-state an increase of the strain-rate sensitivity with increasing temperature can be observed. This might be correlated to thermally activated motion and annihilation of dislocations at grain boundaries, as previously seen in ultrafine grained face centered cubic materials such as Al and Cu.