Investigation of Stresses in Superalloys by Analysis of γ/γ'-Microstructure

The response of the structural parameters to applied stress was investigated in a conic single-crystal specimen of nickel-base superalloy CMSX-4 crept at 1100°C for 300 hours. The investigation was performed by Fourier analysis of scanning electron microscope images and by X-ray diffraction. Measurement of the period of the y/y'-microstructure (total thickness of the γ- and γ'-rafts) and the γ/γ'-misfit along the specimen axis showed clear correlations of these parameters with the change of applied stress along the specimen axis. At stress levels > 40 MPa the measured change of misfit was described by a model proposed by the authors earlier. It is intended to continue the investigation to develop a method for the estimation of stresses acting in turbine blades during operation at high temperatures.