Sunday, June 28, 2020
In recent years, nanoindentation systems have been developed which can operate at ever higher temperatures in order to characterize the local mechanical properties and thermally activated mechanisms of high temperature materials such as nickel-based superalloys at their operating temperature. In this work a new ultra-high temperature nanoindentation system for testing at up to 1100 °C will be presented. The system is capable to perform indents from small scale up to large indentation depths due to the combination of a 1 N actuator and a high frame stiffness of > 106 N/m even at 1100 °C. Dynamic testing allows a continuous determination of the contact stiffness which is essential for determining the depth dependent material properties, like hardness and modulus. Low drift rates can be achieved by an independent tip and sample heating, the active actuator cooling ensures that the machine properties will not change during ultra-high temperature or long term testing. Operating the nanoindenter inside a scanning electron microscope equipped with a high temperature backscattered electron detector opens the possibility of in-situ observations, as high vacuum prevents oxidation effects.
Tests were performed on fused silica, molybdenum and single crystalline nickel using a constant strain rate, strain rate jump as well as a step-load and hold creep method to show the capability of the system at high temperatures.
