Correlations between microstructure evolution and mechanical behavior of a nickel-based single crystal superalloy with long-term aging effects

The microstructure evolution and mechanical property degradation are investigated for a nickel-based single crystal superalloy during 1000 similar to 1100 degrees C thermal exposure for up to 1000 h. Microstructure analyses are aimed at the coarsening of gamma ' precipitates and the formation of rafted structure. The morphology of gamma/gamma ' phase is described by the coarsening parameter lambda ' and the degree of rafting xi depending on aging time and temperature. The non-monotonic change in the volume fraction of gamma ' phase, caused by aging, is also considered. Multi-directional observations reveal that the aged superalloy displays cubic anisotropy with layered rafting structure blocks. The compression experiment results show that elastic modulus is independent of the aging process, but the yield strength degraded exponentially and drops close to 30% after 500 h aging. Relationships among microstructure evolution, aging time/temperature, and macroscopic mechanical property are discussed and proposed. It is confirmed that the material degradation is not only related to the morphology of gamma/gamma ' phase, but also depends on the precipitation of harmful phases, such as the TCP phase from thermal exposure. The material strength of the aged single crystal superalloy is expressed as a function of microstructure characteristics.