Indentation at elevated temperatures for determination of material properties of fusion relevant materials

For structural materials assigned for future fusion application, the characterization of their mechanical behavior at their operating conditions is a very important part of the fusion research. In this context, the instrumented indentation is a useful technique of testing even small neutron­ irradiated samples. For this purpose, a high-temperature indentation device was developed to investigate materials at temperatures up to 650°C under remote-handling conditions at KIT. First results have shown the functionality of the different parts of the indentation device, e.g. a sufficient resolution of the optical displacement measurement and the thermal stability of the system. Sapphire and diamond are used as indenter tip materials for spherical and Vickers indenter. The differences in the elastic behavior of the materials with increasing temperature and the changes in the tip shape over time are not negligible and have to be taken into account for an accurate interpretation of the results. Hence, frequent inspections of the tips are necessary for a reliable performance of the device. In this study, a routine is presented to ensure a constant quality of the used indentation tips with respect to the restrictions of a future operation in a Hot Cell of the Fusion Material Laboratory. ... mehrThe characterization of the reduced-activation ferritic-martensitic steel EUROFER is the core of this study. Samples with different heat treatments are investigated at testing temperatures up to 500°C. The results show a temperature dependency with respect to the hardness of the tested material which can be correlated to results of corresponding tensile tests. In addition to conventional hardness testing, the identification of material parameters with respect to plastic deformation and creep behavior based on a neural network method has been applied for indentation tests with multiple loading-unloading cycles with hold periods at increasing force levels. The requirement for a reliable application of the neural network method is a high quality of the load-depth-time data of the indentation tests which is reached with continuous improvements of the device, e.g. minimizing the fluctuations of the cooling system. Finally, it will be outlined that the temperature-dependent indentation data can be used towards determining the ductile-to-brittle transition of irradiated materials making a highly efficient use of irradiated sample materials.