Analysis of high-temperature creep deformation in a polycrystalline nickel-base superalloy

A new quantitative method has been developed for the analysis of the high-temperature creep deformation of polycrystalline nickel-base superalloys. Local deformation was measured by means of microextensometry using ceramic square grids deposited on flat specimens thanks to an electron lithography technique. The efficiency of this method has been proved for tensile creep tests performed under vacuum at 750°C and 525MPa on the NR6 superalloy and for a wide range of creep strains. This study revealed localization of deformation at grain boundaries and slip bands within the grains. A specific analysis method based on image correlation was developed to quantify the local strain fields. Electron back-scatter diffraction analysis showed that grain boundary sliding is mainly concentrated at general grain boundaries.