A new dynamic module for in-situ nanomechanical testing at high strain rate

In-situ nanomechanical testing is commonly used to probe surface mechanical properties of bulk materials or thin films, like hardness, Young’s modulus, Yield stress…Actually most of the instruments can measure these properties only statically, i.e. a low frequency, leading to property measurement only at low strain rate (usually 10-1s-1 by nanoindentation). This is mainly caused by the low resonance frequency of the system, preventing making tests at higher speed. Performing high dynamic measurements could bring new information on materials properties like deformation mechanism at high strain rate, or high dynamic fatigue properties. A new high dynamic module usable for in-situ mechanical testing has been developed. It is composed of a small piezotube attached directly behind the tip. Because of the small dimensions of the module, his resonance frequency is very high (higher than 50kHz) in comparison to classical nanomechanical testers, permitting to perform and measure precisely the signals at very high frequency. Moreover, it can be used as a sensor and as an actuator, in x, y and z directions which gives to this module a very large range of measurements. Firstly, the characteristics, the performances and the limits of the new high dynamic module will be presented. Secondly some indentations experiments performed at high strain rate on nanocrystalline nickel with the in-situ nanomechanical tester (Alemnis Gmbh) equipped with the high dynamic will be presented and discussed (Fig. 1). Finally, some micropillar compression at high strain rate on the same material will be described and discussed

Some recent advances in nanomechanical testing: High strain rates, variable temperatures, fatigue and stress relaxation, combinatorial experimentation

In the first part of the talk, I will present two recently developed platforms for high temperature nanomechanical testing. The first platform allows for variable temperature and variable strain rate testing of micropillars in situ in the scanning electron microscope. By utilizing an intrinsically displacement-controlled micro-compression setup, which applies displacement using a miniaturized piezo-actuator, we’ve recently extended the attainable range of strain rates to up to~ 103 s−1, and enabled cyclic loading up to 107 cycles and load relaxation tests. Stable, variable temperature indentation/micro-compression in the range of -45°C to 600°C is achieved through independent heating and temperature monitoring of both the indenter tip and sample and by cooling the instrument frame. A second system allows for measurements at lower loads ex-situ in a dedicated vacuum chamber in the range of -150 °C to 700 °C. The cryo temperature is achieved by means of a liquid nitrogen line, while the high temperature is generated by three independent heat sources for the sample and the two tips of the differential displacement measurement system, establishing an infrared bath in the measurement area. In the second part several case studies will be presented. Using these new capabilities, we examine the plasticity of electrodeposited nanocrystalline Nickel, of combinatorial thin film libraries, of hard nanocrystalline ceramic thin films. Activation parameters such as activation volume and activation energy were determined and discussed in view of the most probable deformation mechanism. High strain rates and cyclic fatigue tests were performed on nanocrystalline Ni. The strain rate sensitivity seems to increase for strain rates higher than 10 s-1 suggesting a change in deformation mechanism with increasing strain rate. Cyclic fatigue tests up to 1 million cycles were performed on nanocrystalline Ni microbeams and compared with existing data from literature. Combinatorial libraries of bulk metallic glasses were synthesized by a combination of gradient sputtering and evaporation. Hardness and Young’s modulus was mapped as a function of temperate, strain rate and composition. The results are discussed in the light of shear band kinetics. Finally, a wide range of chromium nitride-based hard coatings was investigated using in situ micro-cantilever bending and compression testing. This allowed the first direct measurement of the high temperature compressive strength and fracture toughness

The Femtoprint project

The Femtoprint project, a European project, aims at demonstrating the use of low-energy laser pulses (i.e. below the ablation threshold) to manufacture monolithically integrated devices including optofluidic, optomechanical and photonic devices. The longer-term objective is the implementation of a versatile table-top machining center. This paper summarizes the project progress to date and demonstrates the potential of this approach through various illustrative examples