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[Display omitted] • Fatigue lives with interior failure are longer at 750 °C and shorter at 1000 °C. • Interior crystallographic plane cracking behavior belong to Mode I & Ⅱ cracking. • Climbing, bypassing and shearing mechanisms are remarkable at elevated temperature. • Threshold value and transition crack size are lower at 1000 °C. • A crystallographic version of FIP controlled crack initiation life is proposed. Asymmetric load tests with stress ratio of 0.1 at 25 °C, 750 °C and 1000 °C were performed to investigate the high-cycle and very-high-cycle fatigue properties of Inconel-713C Ni-based superalloy. Results show that the life at 750 °C is longer than that at 25 °C, but shortens as temperature keeps rising to 1000 °C. Relevant crack initiation and growth belong to the mixed Modes I & Ⅱ cracking along the maximum shear stress. Moreover, due to the effects of temperature and vacuum environment, threshold values for small and long cracks, and the transition crack size decreases as the temperature increases. Moreover, further analysis of dislocation structures such as tangled dislocations, dislocation loops and finer stacking faults shows that the deformation mechanism with faceting cracking at 750 °C should be the interaction of bypassing and shearing mechanisms, especially under stress concentration effect of crack. Based on these, a crystallographic version of fatigue index parameter model for crack nucleation life is proposed and the predicted results are within a factor of two with respect to experimental data. The present model can be applied to predict the fatigue life based on the microstructure attributes and load conditions at different temperatures, which can effectively improve operational safety and reliability of structural components in reality. [ABSTRACT FROM AUTHOR]

• The crack-front plastic zone evolution of three aluminum alloys under the single overload with two overload ratios was traced using DIC technique. • Crack closure phenomenon was directly observed by using in-situ SEM testing. • The crack closure effect based on Paris-type bi-linear relation can well interpret the post-overload crack growth behavior. The dominant role of crack-front plasticity on crack growth retardation is verified. • A modified Willenborg model considering plastic zone shape effect and residual stress distribution was proposed. Fatigue crack growth behaviors of three aluminum alloys under single overload are investigated by in-situ optical microscopy testing and in-situ SEM testing. The results show that the shape effect of overload-induced plastic zone leads to a larger crack growth retardation range than that assumed in Willenborg model. Besides, the crack closure effect based on general form of Paris law cannot correlate the post-overload crack growth, but a bi-linear form fit the measured effective stress intensity factor behavior well. Moreover, the crack-front plasticity effected range can match the retardation extent. A modified Willenborg model is proposed to predict crack growth retardation. [ABSTRACT FROM AUTHOR]

• The near-tip plasticity and crack tip opening level are traced under four typical variable amplitude loading. • The crack tip deformation process is directly observed under fatigue loading by in-situ SEM testing. • The governing role of near-tip plasticity in controlling fatigue crack growth is verified. • A modified Wheeler model is proposed to predict the fatigue crack growth under variable amplitude loading. Fatigue crack propagation behavior of Al7075-T6 and Al2024-T3 under four typical variable amplitude loading (VAL) patterns are investigated by using in-situ testing. The near-tip strain fields and crack opening level are measured combining in-situ optical microscopy testing and digital image correlation (DIC) technique. The crack tip deformation process is directly observed by in-situ scanning electron microscope (SEM). The results show that both the crack propagation behaviors and the crack-tip strain distributions are greatly influenced by the VAL patterns. The shape effect of the overload-induced plastic zone may prolong the crack growth retardation. The crack-front plasticity plays a dominant role in controlling fatigue crack growth. The crack-front plasticity supplies a link between crack closure and crack growth. The crack tip resharpening caused by the underload applied immediately after the overload may reduce the retardation extent. Finally, a modified retardation model is proposed and gives reasonable prediction results of the crack growth rate under VAL. [ABSTRACT FROM AUTHOR]

The structure-property of a Ni-based superalloy fabricated by selective laser melting (SLM) was investigated under very high cycle fatigue (VHCF), and the subsurface cracking with fisheye pattern becomes a remarkable failure mode. Due to the presence of subsurface failure, the descending S–N curve property is represented. Based on 2D & 3D microscopic observation, a rough region with facets and inclusions, named as "multi-inclusion assisted facetted cracking zone (MAFCZ)", is present within the fisheye. By combining electron backscatter diffraction analysis, the subsurface failure is related to grain size & orientation, microtexture and crystal defects. The crack is nucleated from the large grain slip with the highest Schmid factor under the assistance of the inclusions. The rough surface morphology with crack deflection reveals ultra-slow crack growth behavior within MAFCZ. Combined with failure modeling and fracture mechanics analysis, the subsurface failure mechanisms of SLM Ni-based superalloy under the VHCF are elucidated. Image, graphical abstract [ABSTRACT FROM AUTHOR]