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• RE-Mg enriched with LPSO structure or SFs. • SFs-enriched Mg shows outstanding fatigue strength. • Solute strengthening improves the fatigue resistance of Mg nanolayers. Both solute-segregated long-period stacking ordered (LPSO) structure and stacking faults (SFs) are essential in strengthening rare-earth (RE) Mg alloys. Herein, LPSO-enriched Mg and SFs-enriched Mg are fabricated and comparably investigated for fatigue performances. During fatigue, the Mg nanolayers between LPSO lamellae or SFs act as the gliding channels of dislocations. However, SFs-enriched Mg exhibits outstanding fatigue strength due to solute strengthening within Mg nanolayers. Solute strengthening is assumed to contribute to the local accumulation of basal dislocations and the activation of non-basal dislocations. Dislocations are restricted locally and cannot glide long distances to specimen surfaces, which mitigates fatigue-induced extrusions and slip markings, ultimately leading to an increase in fatigue strength. These findings guide the development of RE-Mg alloys towards a synergy between high tensile and high fatigue performances. [Display omitted] [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties, and high/very‐high cycle fatigue behaviors of 9Cr3W3Co turbine rotor steel and its welded joint were investigated. The welded nugget zone (WNZ) exhibited the highest microhardness value, followed by the heat‐affected zone (HAZ), while the base material (BM) showed the lowest hardness value. The WNZ exhibited a higher yield strength compared to the BM with reduced elongation, while maintaining similar ultimate tensile strength. The fatigue strength of the BM at 5 × 107 cycles is roughly 53.7% of the yield strength, whereas that of the WNZ increases to approximately 55.0%. In comparison to the fatigue strength of the BM at 5 × 107 cycles, the WNZ exhibits a notable increase of 10.5%. Smaller grain size and higher dislocation density were observed in the WNZ, which contributed to improved microhardness, yield strength, and fatigue resistance through grain boundary strengthening and dislocation hardening. Highlights: Microstructure and mechanical properties of 9Cr3W3Co steel welded joints were studied.Microhardness values of various zones are non‐uniform and the maximum value in WNZ.Dislocation and grain boundary strengthening contributed to strengthening in WNZ. [ABSTRACT FROM AUTHOR]

Ultrasonic fatigue tests were performed on Ti60 titanium alloy up to a very high cycle fatigue (VHCF) regime at various stress ratios to investigate the characteristics. The S-N curves showed continuous declining trends with fatigue limits of 400, 144 and 130 MPa at 109 cycles corresponding to stress ratios of R = −1, 0.1 and 0.3, respectively. Fatigue cracks found to be initiated from the subsurface of the specimens in the VHCF regime, especially at high stress ratios. Two modified fatigue life prediction models based on fatigue crack initiation mechanisms for Ti60 titanium alloy in the VHCF regime were developed which showed good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The study aimed to investigate the high and very-high fatigue properties of 9Cr3W3Co turbine rotor steel at room temperature (RT) and 650 °C. The resulting S–N curves demonstrated a continuous downward trend, without exhibiting a conventional fatigue limit. The fatigue strength corresponding to 5 × 107 cycles is approximately 53.9% of yield strength at RT, increasing to around 55.4% at 650 °C. Meanwhile, compared to the fatigue strength at 5 × 107 cycles at RT, it at 650 °C decreased by 53.3%. Surface crack initiation was found to be the main fatigue fracture failure model, observed at both RT and 650 °C. Microscopic analysis revealed that severe dislocation motion and grain deformation occurred within the material matrix during the cyclic loading process at both RT and 650 °C, resulting in the formation of abundant low-angle grain boundaries, dislocation lines and sub-grains. At RT, the presence of the M 23 C 6 precipitated phase imposed a strong pinning effect, while the MX phase within the martensite laths effectively impeded the movement of dislocation lines, thereby enhancing fatigue properties. However, at 650 °C, the emergence of newly precipitated Cu-rich phases was observed, which can reduce the free path of dislocations, hinder slip motion of dislocations, and thus compensate for the negative effect caused by high-temperature microstructural degeneration. [ABSTRACT FROM AUTHOR]

Corrosion pits preferentially initiate in the bainitic regions of Q420qNH steel against the simulated marine atmospheric environment, where a high initial dislocation density is present. This occurs in addition to the initiation sites associated with nonmetallic inclusions that exhibit significant lattice distortion. The formation of corrosion the corrosion-induced non elastic buckling exacerbates the cyclic softening effect and significantly reduces fatigue strength. At a strain amplitude of 0.4 %, the fatigue life decreases by 73.2 % after 60 days of pre-corrosion treatment. Layered segregation of Cr and Cu alloying elements could develop the formation of dense rust layer to inhibit further surface degradation. • Corrosion pits of ferrite-bainite weathering steel predominantly occur in the bainite regions with high initial dislocation density upon cyclic salt spray corrosion environment. • Hierarchical non-metallic inclusions enclosed by a significantly distorted lattice shell tend to be preferential initiation sites for corrosion. • Surface degradation caused by corrosion pits, coupled with the cyclic softening, could result in inelastic buckling upon low cycle fatigue loading, leading to fatigue strength degradation. [ABSTRACT FROM AUTHOR]

This work investigated the fatigue behaviors of Mg 96.32 Gd 2.5 Zn 1 Zr 0.18 alloy under both solution and aging conditions. The main microstructural difference between the two conditions is characterized by the dense β′ nano-precipitates under aging condition. The fatigue strengths are comparable under both conditions, whereas the fatigue lives at medium stress levels tend to be improved apparently under aging condition. The improved fatigue lives under aging condition are attributed to the dense β′ nano-precipitates, which delay the processes of crack initiation and early propagation. Under solution condition, fatigue damage exhibits a continuous pattern along the damage bands. However, under aging condition, fatigue damage shows a scattered pattern along the damage bands due to the pinning effect of β′ nano-precipitates and their inhomogeneous distribution. • Dense β′ nano-precipitates delaying the crack initiation and early propagation process. • Inhomogeneous distribution of β′ nano-precipitates influence the damage accumulation. • Fatigue damage showing a high concentration of oxygen. [ABSTRACT FROM AUTHOR]