Microstructural influences on fatigue crack initiation and early propagation in Ni-based superalloy

Effects of microstructures on fatigue crack initiation and short crack propagation at room temperature in an advanced disc superalloy

Characterisation of strain localisation processes during fatigue crack initiation and early crack propagation by SEM-DIC in an advanced disc alloy

Mechanisms of fatigue crack initiation and early propagation in cyclically strained nickel superalloy

Fatigue tests have been conducted on an advanced disc Ni-based superalloy [low solvus, high refractory (LSHR) alloy] at 650 °C in air under three-point bend loading to investigate the role of orientation-dependent grain boundary (GB) oxidation in crack initiation and early propagation. It is found that crack initiation occurs mainly from bulged GB oxides, and cracks then predominantly propagate along the oxidised grain boundaries. These bulged oxides are extremely enriched in Co and preferentially form at the boundaries between high and low Schmid factor grains which are inclined normal to the applied tensile stress direction. Meanwhile, relatively flat/thin Ni/Ti/Al-rich oxide complexes also form at other grain boundaries, but they appear to be much less detrimental in fatigue crack initiation and propagation compared with the bulged GB Co-rich oxide complexes.

Strain localization and fatigue crack initiation in ultrafine-grained copper in high- and giga-cycle region

Fatigue crack propagation initiated at artificially made small defect in two different HAZ microstructures

High-temperature ultra-high cycle fatigue damage of notched single crystal superalloys at high mean stresses

Microstructural influence on small fatigue cracks in a ferritic–martensitic steel

Small crack initiation and early propagation in an as-extruded Mg-10Gd-3Y-0.5Zr alloy in high cycle fatigue regime

The etching susceptibility of dislocations in 3% silicon iron is used to study the initiation and early propagation of small fatigue cracks in smooth specimens subjected to completely reversed cyclic bending. The condition for crack initiation along grain boundaries, which is the dominant mode of crack initiation, is derived from the crystallographic relationship of adjacent grains relative to the stress axis and grain boundary. The propagation behavior of small cracks was compared with that of long through-cracks. Most of the small cracks begin to decelerate, departing from the relation between the rate and the effective stress intensity range for long cracks when the growth path changes from the grain boundary or slip band to the noncrystallographic or transitional path. Some cracks become nonpropagating, while others accelerate again in accordance with the relation between the rate and the stress intensity range for long cracks. Since the crack growth rate is expressed as a unique power function of the size of the highly strained region near the crack, except for slip band cracks, it is concluded that the crack closure is primarily responsible for the anomalous growth behavior of small cracks. Some discussion is given on the influence of the grain size on the fatigue process of the smooth specimen.

This paper reviews fatigue strength, fatigue crack initiation and fatigue crack propagation behavior of protium treated ultra-fine grained Ti-6Al-4V alloy in air and in 3% NaCl aqueous solution. First the protium treatment procedure for Ti-6Al-4V alloy and characteristics of ultra- fine grained Ti-6Al-4V alloy such as microstructure and mechanical properties is briefly summarized. Then the fatigue and corrosion fatigue strength of ultra-fine grained Ti-6Al-4V alloy are described mainly on the basis of the authors’ recent experimental findings. The emphasis is placed upon fatigue crack initiation and propagation behavior of ultra-fine grained Ti-6Al-4V alloy in air and in 3% NaCl aqueous solution. Finally a replica method expected to reveal crack initiation and early crack propagation mechanism in ultra-fine grained Ti-6Al-4V alloy is described by demonstrating a couple of recent findings on conventional Ti-6Al-4V alloy.

Fatigue behaviour of bare and pre-corroded magnesium alloy AZ31

Effects of microstructure on room temperature fatigue crack initiation and short crack propagation in Udimet 720Li Ni-base superalloy

Effect of microstructure on the crack initiation and early propagation mechanism in the very high cycle fatigue (VHCF) regime was studied in 316L stainless steel (316L SS) by atomic force microscope (AFM) and electron back scattered diffraction (EBSD). The results show that small fatigue cracks initiate from the slip band near the grain boundaries (GBs) or the twin boundaries (TBs). Early crack propagation along or cross the slip band is strongly influenced by the local microstructure such as grain size, orientation, and boundary. Besides, the gathered slip bands (SBs) are presented side by side with the damage grains of the run-out specimen. Finally, it is found that dislocations can either pass through the TBs, or be arrested at the TBs.

Effect of microstructure on slip-induced crack initiation and early propagation of martensitic steel during high cycle fatigue