単結晶超合金の熱機械疲労微小き裂進展におけるクリープ疲労相互作用の影響

抄録

This study conducted in-phase TMF loading on single crystal Ni-based superalloys to investigate the small crack propagation behavior of naturally generated cracks on the specimen surface. In addition, the effect of creep-fatigue interaction on small crack propagation was investigated by implementing the conditions of temperature and stress holding at the maximum temperature during in-phase TMF loading. The experimental results indicated that the elastic deformation was dominant in the cyclic deformation behavior, and the hysteresis loops contained almost plastic strain under all loading conditions. However, slight creep deformation occurred during the high-temperature tensile holding in each cycle. The naturally initiated small cracks propagated perpendicular to the loading direction macroscopically. However, the microscopic SEM analysis could not reveal the crystallographic crack propagation path due to the Al-rich-oxide (Al₂O₃) formed around the crack tip and surface. The crack growth rates under the in-phase TMF loading were significantly higher than those under the out-of-phase one at the same stress intensity factor range or the same fatigue J-integral range. In addition, the introduction of the high-temperature tensile holding in the in-phase TMF loading cycle accelerated the crack growth rates. The small-scale creep stress field at the crack tip might dominate the small crack propagation behavior under the in-phase TMF loading with high-temperature holding as the creep-fatigue interaction.