The evolution of the lattice parameter mismatch of a nickel-based superalloy during a high-temperature creep test

We report in-situ measurement of both ( 200) and ( 002) diffraction profiles ( parallel and perpendicular to the tensile axis) and of the lattice mismatch of the AM1 superalloy during a tensile creep experiment ( 150 MPa; 1080 degreesC). The measurements were made by high-resolution high-energy X-ray diffraction at the ID 15A beam line of the European Synchrotron Radiation Facility. Peak shape and lattice mismatch have well-defined non-monotonic behaviours clearly related to the evolution of the microstructure ( rafting, ripening and encapsulation of the gamma phase) and the different stages of the creep curve. Modelling of the raft microstructure as a multilayer gives a good description of the experimental parameters ( peak shape and lattice mismatch) during stage II, and a qualitative explanation of their behaviour during stage III.