Nickel-based superalloys are used where things get hot, like in turbine blades for power plants or aircrafts. The higher the temperature, the better the efficiency and the lower the pollutant emission. Therefore, the maximum temperature with which components can be strained is constantly being driven up. To achieve this, improved coatings for turbine blades must be developed, which protect blades from chemical corrosion and oxidation. Due to the relatively small layer thickness of the functional coatings, it is very difficult to determine the mechanical properties by using traditional mechanical testing methods. In conventional hardness tests, a comparatively large volume is tested, where the properties of the thin coating superimpose those of the substrate.
A good method to avoid this effect is nanoindentation. An indenter with a certain geometry is driven into the surface of a material under an applied load. (Here you can find a detailed introduction to this technique on our homepage.) Nanoindentation is widely used. For example, to determine mechanical properties such as hardness, indentation modulus and creep resistance of thin films; either in the form of hard coatings or modified surface layers. Vacuum operation prevents harmful oxidation of the sample or indenter tip.
The literature contains reports on the successful application of high-temperature nanoindentation in the investigation of permalloy materials and their bonding layers. CMSX-4 was characterized at up to 400 °C and René N4 at up to 800 °C. Both studies on high-temperature nanoindentation also illustrate the experimental difficulties due to creep, especially in the measurement of the modulus of elasticity.