Impact of high temperature pre-exposure on creep damage behaviors and life of NiCoCrAlYHf coated DD6 single crystal superalloys

In the pursuit of safeguarding aircraft engine turbine blades from oxidation and erosion, the application of NiCoCrAlYHf coatings is a standard practice. During long-term high-temperature service, chemical differences between the coating and substrate, thermo-mechanical effects, and interdiffusion cause microstructural degradation and performance loss. High-temperature pre-exposure effectively simulates this process, enabling a more accurate assessment of long-term material performance. Despite the critical importance of understanding these effects, existing studies have primarily examined the independent roles of coatings or pre-exposure, without systematically investigating their synergistic influence on creep behavior under combined thermal and mechanical conditions. This study addresses this gap by systematically evaluating the interplay between NiCoCrAlYHf coatings, pre-exposure conditions (time/temperature), and applied stress on the creep life of DD6 single-crystal superalloys. Through a combination of experiments and detailed analyses using scanning electron microscopy and energy-dispersive spectroscopy, the research reveals that pre-exposure duration increases oxide layer thickness, while IDZ thickness and TCP phase quantity remain stable. In contrast, higher pre-exposure temperatures significantly promote TCP phase formation and IDZ growth. Creep life comparison under 300 MPa and 240 MPa stress shows that oxide layer thickness is the dominant factor influencing the variation in creep life between different stress levels. To evaluate the impact of pre-exposure conditions, an empirical life prediction model is introduced, yielding results with prediction accuracy within twice the scatter band of the experimental findings.