New flat-punch indentation creep testing approach for characterizing the local creep properties at high temperatures

Highlights: • New indentation creep testing method based on flat punch indentation inside a thermo mechanical analyzer at high temperatures. • Conversion parameters allow transformation of indentation creep data of single crystals into uniaxial data. • Creep tests on Ni single crystals with 2 at. % Ta, Re, W show that Ta is the most effective strengthening element at 650°C. -- Abstract: An indentation creep testing approach has been developed which allows measuring creep properties at high temperatures. In contrast to existing indentation or impression creep experiments, the approach described here allows to achieve a quite high spatial resolution, as flat punch indenters with a diameter of only 20 μm are used. First indentation creep tests have been performed on single crystalline nickel and nickel binary solid solution alloys with Re, Ta or W as alloying elements, respectively. The indentation creep tests have been carried out at a temperature of 650 °C and stress levels in the range of 85 to 400 MPa. Using crystal plasticity finite element modeling, the indentation creep response is converted into equivalent uniaxial creep properties. It is shown that the conversion parameters, evaluated for differently oriented single crystals, can be chosen independently of the creep rate exponent in the power law creep regime. It is found that the indentation creep results agree well with conventional uniaxial creep tests. Furthermore, the results show that Ta is the most effective solid solution strengthener of all tested solid-solution strengtheners at 650 °C because of the large atomic size mismatch, followed by W and Re.