Determination of local strains in a monocrystalline turbine blade by microbeam X-ray diffraction with synchrotron radiation

X-ray peak profiles of the types {400} and {300} of monocrystalline nickel-based superalloy turbine blades were measured with a new microbeam synchrotron radiation X-ray diffraction technique. Under the coating of a turbine blade in the virgin state, a plastically deformed layer was found which is responsible for anomalous rafting. In a turbine blade subjected to an "accelerated mission test", the phases gamma and gamma' were found to be under elastic distortions arising from the superposition of counteracting internal stresses. It is concluded that the investigated section was under tensile creep load during service. In the regions near the surfaces, the lattice parameters of both gamma and gamma' increase. The reason for this increase is the diffusion of Al from the NiAl coating into the bulk of the blade. Finally, the differences between the peak profiles measured with the microfocus technique and with a conventional diffractometer are discussed. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.