During the first scientific period, the main focus of the ERC NanoHighSpeed project was on the development of a high-strain rate nanoindenter prototype. The system was designed around fast piezoelectric transducers. Piezoceramics are materials that instantaneously expand upon applying an electrical voltage. In our setup, they are used as fast actuators to indent the samples with a tiny diamond tip. Conversely, when placed under mechanical compression, piezoceramics instantaneously deliver an electrical voltage. This effect is used in our setup to measure fast force transients. In addition to fast transducers, our prototype relies on an ultrafast electronic controller, which allow measurements at 1 MHz, i.e. every microsecond. After overcoming several technical challenges related to the integration of the different components, we engaged in a careful characterization of the dynamic behavior of the instrument and developed a model to correct for machine artefacts. We also optimized the protocols used for controlling the experiments and ruled out a possible hysteresis effect (unwanted dependence of the hardness measurement on the loading path). While we are still in the process of optimizing our high-speed nanoindenter prototype, we have already reached a critical milestone by producing sustained strain rates of 20 000/s. This is 200 times higher than our proof of concept, and sufficient for investigating the high strain rate deformation resulting from a collision.
In parallel to the hardware developments, we started investigating technologically important materials, such as intermetallic compounds. These materials account for the high temperature strength of the turbine blades used in aircraft engines. The underlying physical mechanism, called “strength anomaly”, has been known since the 1970s. However, it had not yet been experimentally probed whether this positive effect persists under the high-speed deformation conditions of a bird strike, which would be a safety concern. The reason is that intermetallic compounds are tiny components found inside a larger superalloy, which generally cannot be produced in sufficient volume for classical characterization methods. Teaming up with Prof. G.M. Pharr (Texas A&M), we carried out high-speed, high-temperature nanoindentations and reached conclusive evidence ruling out the safety concern.
