کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1448770 | 988683 | 2009 | 11 صفحه PDF | دانلود رایگان |
The fatigue behavior of a polycrystalline nickel-based superalloy René 88DT was examined in the lifetime regime of 105–109 cycles at 593 °C in air using an ultrasonic fatigue apparatus operating at frequencies close to 20 kHz. Three experimental techniques were combined to obtain new insights into the crack initiation process: serial sectioning, electron backscatter diffraction and quantitative fractographic analysis. Most fatigue failures initiated from internal microstructural sites comprised of large grains. Large crystallographic facets formed at crack initiation sites due to cyclic strain localization on {1 1 1} slip planes in the region close to Σ3 twin boundaries in large grains having high Schmid factors. The micromechanical mechanism of crystallographic fatigue crack initiation was analyzed in terms of both resolved shear stress and elastic incompatibility stresses in regions close to Σ3 twin boundaries. The influence of critical microstructure features on fatigue crack initiation and fatigue life variability is discussed.
Journal: Acta Materialia - Volume 57, Issue 20, December 2009, Pages 5964–5974