Novel ultra nanoindentation method with extremely low thermal drift: Principle and experimental results

Despite active development over the past 15 years, contemporary nanoindentation methods still suffer serious drawbacks, particularly long thermal stabilization and thermal drift, which limit the duration of the measurements to only a short period of time. The presented work introduces a novel ultra nanoindentation method that uses loads from the μN range up to 50 mN, is capable of performing long-term stable measurements, and has negligible frame compliance. The method is based on a novel patented design, which uses an active top referencing system. Several materials were used to demonstrate the performance of the method. The measurements with hold at maximum load confirm extremely low levels of instrument thermal drift. The presented Ultra Nanoindentation Tester opens new possibilities for testing thin films and long-term testing, including creep of polymers at high resolution without the need of long thermal stabilizatio

Pushing the envelope for high temperature nanoindentation measurements

One of the primary motivations for development of instrumented indentation was to measure the mechanical properties of thin films and individual phases/grains. Characterization of thin film mechanical properties as a function of temperature is of immense industrial and scientific interest. The major bottlenecks in elevated temperature measurements have been thermal drift, signal stability (noise) and oxidation of the surfaces. Thermal drift is a measurement artifact that arises due to thermal expansion/contraction of indenter tip and loading column. This gets superimposed on the mechanical behavior data precluding accurate extraction of mechanical properties of the sample at elevated temperatures. Vacuum is essential to prevent sample/tip oxidation and to push the envelope for high temperature testing. This poster will present the high temperature vacuum nanoindenter designed at Anton Paar that can perform reliable load-displacement measurements over a wide temperature ranges (up to 700 °C). This system is based on the Ultra Nanoindentation Tester (UNHT) that utilizes an active surface referencing technique comprising of two independent axes, one for surface referencing and another for indentation. The differential depth measurement technology results in negligible compliance of the system due to symmetric architecture and very low thermal drift rates at high temperatures as the thermal drift is actively compensated by the surface referencing technology. The sample, indenter and reference tip are heated separately and the surface temperatures matched to obtain drift rates as low as 10 nm/min at 700 °C on copper Test results on standard calibration materials like fused silica and oxygen free high conductive copper, used for validating the system, will be presented. The developed experimental protocol for minimizing thermal drift and the challenges associated with high temperature testing will be discussed

Variable temperature ultra-nanoindentation system: Elevated and cryogenic temperature measurements

One of the primary motivations for development of instrumented indentation was to measure the mechanical properties of thin films. Characterization of thin film mechanical properties as a function of temperature is of immense industrial and scientific interest. The major bottlenecks in variable temperature measurements have been thermal drift, signal stability (noise) and oxidation of/condensation on the surface. Thermal drift is a measurement artifact that arises due to thermal expansion/contraction of indenter tip and loading column. This gets superimposed on the mechanical behavior data precluding accurate extraction of mechanical properties of the sample at elevated/cryogenic temperatures [1]. Reliable load-displacement measurements up to 700 °C have additional technical requirements including a differential displacement measurement system, independent tip and sample heating and active thermal management of the system as well as answers to scientific questions like the temperature in the contact area or the tip wear. It is then mandatory to have a suitable device for exploring such scientific limits to technical goals and understanding nanoscale high temperature deformation and fracture. Such a device must be able to maintain the thermal drift below 0.1 nm/sec, and should be implemented in a robust system which minimizes noise (electrical, vibrational, thermal, etc..), with a continuous correction based on active top- referencing. A novel vacuum nanoindentation system that can perform reliable load-displacement measurements over a wide temperature range (-150 to 700 °C) will be presented. This system is based on the Ultra Nanoindentation Tester (UNHT [2], [3]) that utilizes an active surface referencing technique comprising of two independent axes, one for surface referencing and another for indentation. This results in negligible compliance of the system and very low thermal drift rates. Vacuum is essential to prevent sample/tip oxidation at elevated temperatures and condensation at cryogenic temperatures. The sample, indenter and reference tip are heated separately and the surface temperatures matched establishing an Infrared bath to obtain drift rates as low as 5nm/min at 700 °C. Instrumentation development, system characterization, experimental protocol, operational refinements and thermal drift characteristics at various temperatures will be presented. The system was validated by performing extensive testing on calibration materials like fused silica and single crystal aluminum. Case studies on elevated temperature properties of P91 and 316L steels and low temperature properties of nanocrystalline nickel and copper will be presented. Finally, the current status and future roadmap for variable temperature nanoindentation testing will be discussed

Correlation between processing parameters and mechanical properties as a function of substrate polarisation and depth in a nitrided 316 L stainless steel using nanoindentation and scanning force microscopy

The effects of substrate polarisation in a nitrided 316L stainless steel have been investigated in an attempt to accurately correlate processing parameters with surface mechanical properties. Nanoindentation allows the Vickers hardness to be measured at precise depths, meaning that the variation in properties with nitriding depth can be evaluated and correlated with the process parameters. By combining such measurements with surface imaging techniques (scanning force microscopy and scanning electron microscopy) and electron probe micro-analysis, it is possible to explain both the mechanical property and microstructural variations of such layers, having been produced in a low pressure arc plasma discharge at 680 K with a mixed Ar-N2 gas. In this study the nanoindentation technique is presented as a new and valid method for the characterisation of nitrided layers, shown by hardness measurements on four nitrided layers produced with different substrate polarisation potentials. The net advantages of such an approach over conventional methods (e.g. microhardness testing) and the possibility of analysing microstructural phases previously not well detected by X-ray diffraction, make nanoindentation an attractive tool for a more complete understanding of the nitriding process