INVESTIGATION OF FATIGUE MESOSCOPIC MECHANICAL PROPERTIES OF A NICKEL-BASED SUPERALLOY BY INSTRUMENTED MICROINDENTATION MEASUREMENTS

摘要

The characteristic parameters of indentation were determined from the measured indentation load-depth curves for both virgin and fatigue fractured specimens of GH4145/SQ superalloy. The fatigue mesoscopic mechanical properties of the superalloy were estimated using Dao et al's approach [17], combined with the indentation characteristic parameters, and their distribution characteristics were further verified in a statistical sense. It was shown that as the imposed strain amplitude increased, the yield stress exhibits increase almost linearly, while Young's modulus and strain hardening exponent display liner decreasing characters. Microstructure observations using OM and TEM reveal that, with increasing strain amplitudes, the density of slip bands tends to increase, while the precipitate morphology becomes more irregular in the form throughout the grains. The dependence of the microstructures on the applied strain amplitude is thus responsible for the change characteristics of the mesoscopic mechanical properties of the superalloy subjected to high-temperature low-cycle fatigue loading.