Interior long-life-fatigue cracking behavior and life prediction of a selective laser melted GH4169 superalloy at different temperatures and stress ratios

The axial fatigue tests at elevated (650°C) temperature with stress ratios of 0.1 and −1 were conducted under the loading cycle range of 10⁴–10⁸ cycles to investigate interior cracking mechanism at elevated temperature of one selective laser melted GH4169 superalloy. Results showed that the interior fatigue crack nucleation was the main failure mode with both stress ratios at 650°C in the long-life regime. The interior crack nucleation region consisting of many facets was formed under shear stress and strain according to the 3D morphology restructure of the fracture surface. Combined with the evaluation of the threshold stress intensity factor, the transition lengths from a small crack to a long crack for interior failure at both stress ratios were evaluated. Based on the above analysis, the microstructure-related interior failure mechanism was summarized. Finally, crack nucleation and propagation lives were predicted to obtain the total fatigue life, which showed that the prediction and experimental data scattered between the factor-of-three boundaries.