High temperature impact testing of a thin hard coating using a novel high-frequency in situ micromechanical device

High-impact applications such as forging, punching or fine blanking often utilise hard-coating systems to improve wear and lifetime performance. For rational design of such systems, evaluation after repeated impacts at the application temperature is critical. However, such investigations are time-consuming and costly to perform in-line on an industrial scale. Small-scale impact testing allows for rapid and inexpensive investigation of attractive thin coating designs, which can be performed over a range of controlled temperatures. Here, a novel in situ nanoindentation device was developed, able to perform precise displacement cycles to 1 kHz at temperatures up to 500 °C within a scanning electron microscope. The system is based on a piezoelectric driving tip containing four discrete piezo devices, allowing for the collection of load-displacement data for each individual cycle. Operation of the device at 500 Hz was demonstrated on arc-PVD chromium nitride coated nitrided steel with a diamond flat-punch counter-body, and the effects of temperature and impact number on fatigue deformation studied using electron microscopy techniques. It was found that as the impact number increased as did the residual plastic damage from the impact force. Additionally, the deformation of the tooling was highly dependent on the temperature, which became more strongly apparent with an increased number of impacts. Such testing will be useful for evaluating the lifetime and fatigue properties of potential new thin films and coatings for high-impact operations, where understanding the influence of temperature is crucial.