•Submerged micro-abrasive waterjet peening is proposed to improve the metal surface integrity and fatigue performance.•The surface integrity state of TA19 titanium alloy after the SMA-WJP is ...systematically analyzed.•The high-cycle fatigue life of TA19 titanium alloy treated by SMA-WJP is increased by a maximum of 2.72 times.•The improved fatigue life is attributed to the plastic deformation layer and large CRS induced by SMA-WJP.
Waterjet peening has become a critical surface treatment technology due to its great potential for improving the surface integrity and fatigue performance of metallic materials. The present study aims to investigate the influence of submerged micro-abrasive waterjet peening (SMA-WJP) on the surface integrity and fatigue properties of TA19 titanium alloy. First, the SMA-WJP with different water pressure (P = 70, 100, and 130 MPa) was conducted on the TA19 specimen. The surface integrity of the specimen before and after SMA-WJP treatment was studied, including the microstructure, surface roughness, microscopic morphology, microhardness, and residual stress. Results showed that the SMA-WJP treated specimen with different water pressure formed a plastic deformation layer with a depth of 24–44 μm, the minimum surface roughness of Ra = 0.363 μm and Sa = 0.95 μm. The depth of the work-hardened layer and compressive residual stress (CRS) layer was approximately 100–150 μm and 160–290 μm. The microstructure evolution on the top surface and sub-surface of the as-received and SMA-WJP treated specimens were characterized by transmission electron microscopy (TEM), which showed that nanocrystals with an average size of 12 nm and high density of dislocations formed on the top surface of the SMA-WJP treated specimen. Finally, stress-controlled high-cycle fatigue (HCF) tests were carried out to study the fatigue behavior of the TA19 titanium alloy before and after SMA-WJP treatment. The HCF life of the specimen is increased by a maximum of 2.72 times. The fatigue fracture surface was examined with scanning electron microscopy (SEM), which revealed that the existence of the plastic deformation layer and large CRS induced by SMA-WJP could effectively inhibit the initiation and propagation of cracks. This work enriches the waterjet peening process by investigating submerged abrasive waterjet peening and brings a new solution for improving the surface integrity and fatigue performance of TA19 titanium alloy.
•A crystal plasticity-based approach is implemented to predict creep-fatigue life.•Creep and fatigue indicator parameters are introduced to describe damage evolution.•A potential methodology for ...conservative creep-fatigue life evaluation was provided.
A numerical process based on crystal plasticity finite element (CPFE) was implemented to predict creep-fatigue crack initiation life. CPFE-based model can describe the macroscopic cyclic deformation and reveal grain-level damage mechanism. A new life prediction approach was then constructed by introducing fatigue and creep indicator parameters. Furthermore, a series of strain-controlled creep-fatigue tests in GH4169 superalloy at 650℃ were used to validate predicted accuracy of this model, where most of the data points lied within ±1.5 error band. Finally, a potential methodology for conservative creep-fatigue life evaluation was provided by flexible creep-fatigue damage summation rule in engineering applications.
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•The work aims to provide theoretical bases for engineering damage evaluation method.•LCF test is interrupted to study damage evolution and mechanical property of GH4169.•Strength ...degradation is due to shearing of γ″ precipitate and de-twinning behavior.•Formation of LAGB and slip band leads to decrease in elongation after 50 % lifetime.•A mapping model from micro-damage to macro-property is developed using average KAM.
Mechanical properties of metallic materials gradually degrade under high-temperature low cycle fatigue (HTLCF) loading, which is a manifestation of fatigue damage accumulation. In this study, a mapping modeling is developed to determine the relationship between micro-scale HTLCF damage and macro-scale mechanical property degradation. Strain-controlled HTLCF tests in GH4169 superalloy are carried out at 650 °C and interrupted at various lifetime fractions for subsequent microscopic characterizations and high-temperature tensile tests. Quantitative analysis of electron backscatter diffraction indicates a three-stage increase in kernel average misorientation and geometrically necessary dislocation throughout the cyclic process, along with variations in the fraction of different grain boundaries. Simultaneously, the evolutions of shearing precipitate and de-twinning are characterized using transmission electron microscope. Furthermore, the mechanical properties of GH4169 superalloy, such as yield strength, ultimate tensile strength, elongation and work-hardening rate, demonstrate different degradation characteristics after exposure to HTLCF damage. Based on these results, the mechanism of HTLCF-induced mechanical property degradation is clarified and the mapping modeling is established using tensile plastic strain energy density and kernel average misorientation. Finally, a damage level evaluation method for engineering components is developed after the generality and flexibility of model is verified in different high-temperature materials.
To investigate the value of artificial intelligence (AI) assisted quantification on initial chest CT for prediction of disease progression and clinical outcome in patients with coronavirus disease ...2019 (COVID-19). Patients with confirmed COVID-19 infection and initially of non-severe type were retrospectively included. The initial CT scan on admission was used for imaging analysis. The presence of ground glass opacity (GGO), consolidation and other findings were visually evaluated. CT severity score was calculated according to the extent of lesion involvement. In addition, AI based quantification of GGO and consolidation volume were also performed. 123 patients (mean age: 64.43 ± 14.02; 62 males) were included. GGO + consolidation was more frequently revealed in progress-to-severe group whereas pure GGO was more likely to be found in non-severe group. Compared to non-severe group, patients in progress-to-severe group had larger GGO volume (167.33 ± 167.88 cm
versus 101.12 ± 127 cm
, p = 0.013) as well as consolidation volume (40.85 ± 60.4 cm
versus 6.63 ± 14.91 cm
, p < 0.001). Among imaging parameters, consolidation volume had the largest area under curve (AUC) in discriminating non-severe from progress-to-severe group (AUC = 0.796, p < 0.001) and patients with or without critical events (AUC = 0.754, p < 0.001). According to multivariate regression, consolidation volume and age were two strongest predictors for disease progression (hazard ratio: 1.053 and 1.071, p: 0.006 and 0.008) whereas age and diabetes were predictors for unfavorable outcome. Consolidation volume quantified on initial chest CT was the strongest predictor for disease severity progression and larger consolidation volume was associated with unfavorable clinical outcome.
•A modeling approach by combining crystal plasticity with creep cavity model is developed.•Transition mechanism from transgranular to intergranular crack with increasing hold time is ...revealed.•Predicted crack initiation life agrees with the experimental data within an error band of ±2.
In this study, a dual-scale numerical procedure is developed to reveal the creep-fatigue damage mechanisms and estimate the crack initiation life for notched structures made of Inconel 718 superalloy at 650 °C. The macro-scale simulation solves the creep-fatigue deformation behavior with viscoplastic constitutive models, and the local deformation histories are supplied to the micro-scale simulation as boundary conditions. In the micro-scale simulation, the local damage evolutions are solved based on crystal plasticity combined with grain boundary cavity model. The creep damage is calculated by a special formulation in the form of cavity nucleation, growth and coalescence. The fatigue damage is represented by accumulated energy dissipation originated from crystal plasticity finite element simulation. Experimentally, the creep-fatigue tests of notched structures are carried out for Inconel 718 superalloy at 650 °C to validate the feasibility and robustness of the proposed numerical procedure. Moreover, the crack initiation behavior, including transgranular cracks under fatigue loading and intergranular cracks under creep-fatigue loading, is explained through different types of microstructure observations together with a dual-scale numerical procedure. In detail, the crack initiation sites transferred from the grain interior at notched surface to the grain boundaries at notched subsurface with an increase in hold times can be well predicted by the proposed numerical procedure. In addition, the simulated life based on the developed life prediction approach agrees well with the experimental data within an error band of ±2. Parametric studies show that the creep damage is more sensitive to grain boundary diffusion than to the external conditions of strain level and hold time.
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In this study, the microstructural evolutions are systematically investigated in the IN718 alloy that has been in-service for eight years. Correspondingly, the effect of in-service process on ...mechanical properties are explored in terms of tensile properties, fatigue performance and crack growth behavior. Results show that the grain sizes at different sampling locations vary from 9.8 to 15.5 μm, exhibiting the inhomogeneous microstructures for the in-service IN718 alloy. The volume fraction of δ phase and kernel average misorientation (KAM) at outermost layer are the maximum ones, followed by the middle and innermost layers. In addition, the high magnitude of δ phase is caused by the transformation from strengthening phase γ′′. From the perspective of mechanical properties, the in-service IN718 alloy can maintain excellent yield strength and elongation at the high temperature of 650 °C, while the tensile performance is degenerated at room temperature (RT) compared with those of new IN718 alloy. The fatigue life at 650 °C is similar to that at RT under the stress levels lower than 600 MPa. As the stress level increases to 800 MPa, an obvious decrease in fatigue life at 650 °C compared with that at RT. This special fatigue performance is revealed based on the fractography examinations under different loading conditions. Moreover, the investigation of fatigue crack growth for the in-service IN718 alloy is carried out under different stress ratio and temperatures.
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•A small creep-fatigue crack growth model is established based on the combination of CPFEM and XFEM.•The criterion for creep-fatigue crack growth is proposed based on accumulated ...energy dissipation and shear strain.•Effects of grain orientation and constraint on creep-fatigue crack growth behavior is investigated.
The multifarious nature of small crack growth at the micro-scale necessitates the use of advanced modeling methods. In this work, small creep-fatigue crack growth behavior is investigated based on the combination of crystal plasticity finite element method (CPFEM) and extended finite element method (XFEM). A creep-fatigue crack growth indicator parameter (CFCGIP) is developed to predict creep-fatigue crack path and growth rate with the aid of total accumulated energy dissipation and accumulated shear strain. Results show that the small creep-fatigue crack growth rate can be predicted accurately by comparing experimental data. Moreover, the combined effects of constraint condition and grain orientation on the small creep-fatigue crack growth behavior are studied by adopting the developed CFCGIP. Under low constraint conditions, the creep-fatigue crack growth rate is dominated by the grain orientation, accompanying with significant fluctuation. With the increase in constraint condition, the dominated role of the creep-fatigue crack growth rate is identified as constraint condition.
•Damage mechanisms under creep-fatigue combined with high-low cycle were revealed.•Damage evolution under various cyclic loadings was described by energy dissipation.•Multi-damage model was ...established by using crystal plasticity finite element.
Many high-temperature rotating components are always subjected to complex loading waveforms, arising the concerns for multi-damage driving crack initiation. In this paper, a series of strain-controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests as well as the novel creep-fatigue combined with high-low cycle (CF-HL) tests were performed in a nickel-based superalloy at 650 ℃. Then, post-test microstructure observations were carried out to reveal the damage mechanisms under the multi-damaged CF-HL loading based on the EBSD-TEM combinative characterizations. In this aspect, the single-slip-dominated deformation mechanism under CFI loadings transformed to double-slip-dominated one under CF-HL loading was revealed. Computationally, a numerical procedure with a combination of crystal plasticity theory and finite element implementation was constructed for predicting the CF-HL crack initiation life and quantifying the crack initiation mechanisms. With the help of the developed fatigue and creep indicator parameters represented by accumulated energy dissipation, good agreements between experimental data and simulated results were achieved within a scatter band of ± 2 on life prediction. In addition, the simulation results indicate that the combined effects of grain orientation and multiple slip system activation showed great influence on the CF-HL crack initiation.
•The sample with smaller thickness and larger aspect ratio of lamellar grains could achieve strength-ductility synergy.•More grain rotation caused by larger aspect ratio of lamellar grains is ...responsible for the improved ductility.•Longer high angle grain boundaries (GBs) and more coincidence site lattice GBs contribute to enhancing ductility.
In order to overcome the trade-off between strength and ductility in traditional metallic materials, the gradient lamellar structure was fabricated through an ultrasound-aided deep rolling technique in pure Ni with high stacking fault energy after heat treatment. The gradient lamellar Ni was successively divided into three regions. In-situ micro-tensile tests were performed in different regions to reveal the corresponding microscopic mechanical behaviors. Microscopic characterization techniques were adopted to explore the effects of microstructural parameters and defects on mechanical properties. This work demonstrates that the micro-tensile sample with small lamellar thickness and large aspect ratio possesses excellent strength and ductility when the loading direction is parallel to the long side of lamellar grain boundaries. The finding is helpful to the design of metallic material microstructure with superior comprehensive properties. On one hand, the reason for high strength is that the strength increases with the decrease of lamellar thickness according to the Hall-Petch effect. Besides, initial dislocation density also participates in the strengthening mechanism. On the other hand, the deformation mechanisms include dislocation slip, grain rotation, and the effects of grain boundaries on dislocations, jointly contributing to good ductility.
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