TY - THES

T1 - Cryogenic nanoindentation of single crystalline Copper, Chromium and Tungsten

AU - Esterl, Raphael

N1 - embargoed until null

PY - 2015

Y1 - 2015

N2 - The increasing digitalization and rising number of electronic devices is accompanied by a decreasing size of microelectronic components. This development requires the knowledge of mechanical properties of materials at small scales. Nanoindentation profiles itself as technique to investigate the behavior at these dimensions. Two phenomenona protrude in this context. One the one hand side an increasing hardness with decreasing indentation depths, the so-called Indentation Size Effect is observed. Furthermore, the transition from elastic to plastic behavior manifests itself as discontinuity in the typical load-displacement curve. To investigate the size effect and the onset of plasticity, the so-called pop-in event, and especially their temperature dependence, single crystalline materials, namely Copper as representative of face centered cubic metals, as well as Chromium and Tungsten as body centered cubic metals, were analyzed at room temperature as well as at -150°C. The major challenge for investigating the size effect at cryogenic temperature consisted in controlling thermal drift, which can be associated to a temperature difference between sample and indenter tip. However, the examinations delivered an increasing size effect with decreasing temperature for Copper. This behavior is in accordance to several scientific investigations of face centered cubic metals at elevated temperatures. Chromium showed the opposite trend as the size effect decreased with reduced temperatures. This phenomenon correlates as well to first scientific investigations that body centered cubic metals posses a decreasing size effect below a material specific critical temperature. Furthermore, we showed that the specific force necessary for the initiation of plasticity increases with decreasing temperature. This underlines the importance of thermally activated processes on the nucleation of dislocations.

AB - The increasing digitalization and rising number of electronic devices is accompanied by a decreasing size of microelectronic components. This development requires the knowledge of mechanical properties of materials at small scales. Nanoindentation profiles itself as technique to investigate the behavior at these dimensions. Two phenomenona protrude in this context. One the one hand side an increasing hardness with decreasing indentation depths, the so-called Indentation Size Effect is observed. Furthermore, the transition from elastic to plastic behavior manifests itself as discontinuity in the typical load-displacement curve. To investigate the size effect and the onset of plasticity, the so-called pop-in event, and especially their temperature dependence, single crystalline materials, namely Copper as representative of face centered cubic metals, as well as Chromium and Tungsten as body centered cubic metals, were analyzed at room temperature as well as at -150°C. The major challenge for investigating the size effect at cryogenic temperature consisted in controlling thermal drift, which can be associated to a temperature difference between sample and indenter tip. However, the examinations delivered an increasing size effect with decreasing temperature for Copper. This behavior is in accordance to several scientific investigations of face centered cubic metals at elevated temperatures. Chromium showed the opposite trend as the size effect decreased with reduced temperatures. This phenomenon correlates as well to first scientific investigations that body centered cubic metals posses a decreasing size effect below a material specific critical temperature. Furthermore, we showed that the specific force necessary for the initiation of plasticity increases with decreasing temperature. This underlines the importance of thermally activated processes on the nucleation of dislocations.

KW - nanoindentation

KW - single crystals

KW - cryogenic temperatures

KW - indentation size effect

KW - tungsten

KW - copper

KW - chromium

KW - Nanoindentierung

KW - Einkristalle

KW - Eindringgrößeneffekt

KW - Tieftemperatur

KW - Wolfram

KW - Kupfer

KW - Chrom

M3 - Diploma Thesis

ER -