About the choice of Tungsten carbide indenter to determine mechanical properties of superalloys by using high-temperature microhardness tester

Abstract

In the aeronautical field, materials are used in severe environmental conditions (temperature, atmosphere), particularly in engine applications. In order to qualify mechanical properties of new composition Ni-based superalloys, ONERA performs Vickers hardness tests from room temperature up to 750 °C close to operating conditions. This method consists in applying a pyramidal tip onto the specimen to characterize hardness and mechanical resistance of the material. This simple method appears to be faster than other methods using classical hot tensile or bending tests.
Nevertheless, the choice of the indenter tip for high-temperature experiments is crucial. Tungsten carbide tip is used for characterizing Ni-based superalloys. Electron microscopy and X-ray analysis are presented and discussed on new and used tungsten carbide tips. A simple experimental method to control the evolution of the indenter before and after using it in the high-temperature hardness test is explained.
Evolution of hardness and mechanical resistance versus temperature by using Tabor relationship on a Nickel-based superalloy sample is compared to evolution of mechanical resistance values determined by classical high temperature tensile tests. A good agreement is found between these two methods with WC indenter. These hardness measurements could be carried out up to 1 000 °C if indenter is still available to characterize layers, coatings, composite materials, additive manufacturing materials or gradient properties materials.