Transient deformation behavior during rate-jump nanoindentation testing of glassesThursday (27.09.2018) 10:30 - 10:45 S1/01 - A03 Part of:
Over the past years, nanoindentation testing has become a routinely applied technique for probing the time-dependent deformation, also termed as creep. Benefitting from the high flexibility of the testing conditions, a variety of advanced indentation protocols beyond the classical constant load and hold creep test have been developed. Among them, the nanoindentation strain-rate jump test, as introduced by Lucas and Oliver , has recently attracted a growing attention for evaluating the creep exponent and activation volume of metals, glasses as well as ceramics [2, 3].
In a typical strain-rate jump test, the material is initially indented at a constant strain-rate until a depth-independent hardness value is achieved. Subsequently, with the further load increase, the strain-rate is suddenly changed while the materials response, i.e., rate-dependent hardness alterations, is continuously monitored. Lowering the strain-rate usually results in a sudden drop of the hardness. In most cases, such a hardness reduction occurs gradually over a short transient period. However, a marked deviation from this regular transient deformation behavior, which is characterized by an initial decrease of the hardness at the beginning of the down-jump interval followed by a slight re-increase of the hardness towards a constant value at larger indentation depths, has recently been reported for glasses  as well as high-entropy-alloys .
To reveal the underlying mechanisms governing this unique effect, the transient deformation behavior of selected oxide, chalcogenide and bulk metallic glasses was studied in a nanoindentation strain-rate jump test. Depending on the creep characteristics of the glasses tested as well as the height of the corresponding strain-rate jumps, distinct variations in the transient deformation behavior have been observed and based on these findings, a first mechanistic description for this phenomenon has been proposed.
 B. N. Lucas, W. C. Oliver, Metall. Mater. Trans. A 30 (1999) 601-610.
 V. Maier-Kiener, K. Durst, JOM (2017). doi.org/10.1007/s11837-017-2536-y
 P. Sudharshan Phani, W. C. Oliver, G. M. Pharr, JOM (2017). doi.org/10.1007/s11837-017-2535-z
 R. Limbach, B. P. Rodrigues, L. Wondraczek, J. Non-Cryst. Solids 404 (2014) 124-134.