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The simultaneous increase in strength and plasticity of aluminum and its alloys at cryogenic temperatures has been shown in previous research, but the deformation mechanism was still unclear. Therefore, the purpose of this investigation was to reveal the relationship between slip behavior and mechanical response at low temperatures. A quasi-in situ scanning electron microscope was used to observe the evolution of slip bands in the selected aluminum single crystals with two typical orientations at 25 °C, −100 °C, and −180 °C. The results showed that irrespective of orientation, the density of the slip plane was increased with the decline in temperature, which inhibited slip localization and significantly improved plasticity and work hardening. In detail, at RT, the slip bands were widening until the micro-cracks were generated, causing early failure during deformation. When the temperature was decreased to −180 °C, the slip plane density was increased, and the deformation was more homogenous. Moreover, the slip mode was influenced by orientation and temperature. In particular, a single slip system was activated in the sample with the [112] orientation at all the temperatures investigated. Multiple slip systems were found to activate at 25 °C and −100 °C, and only the primary slip system was activated in the sample with [114] orientation at −180 °C. These findings deepen the understanding of slip behavior at cryogenic temperatures, providing new insights into the deformation mechanism of aluminum and its alloys. [ABSTRACT FROM AUTHOR]

In situ Transmission Electron Microscopy (in situ TEM) tensile tests of single crystal nickel were performed in order to correlate direct observations of nanostructural changes resulting from applied mechanical and electrical stimuli in an effort to provide clarity on the mechanisms of electroplasticity (EP). A dual-tensile geometry was tested with an electrical push-to-pull device (EPTP) and digital image correlation (DIC) was used to track the location of dislocation nucleation along the sample surface. By analyzing the change in sample geometry precisely we are able to directly track individual dislocation motion as a result of the combined electromechanical actuation. From our observations, the pulsed electrical current leads to a more uniform deformation as compared to purely mechanically triggered plasticity. When the sample is undergoing stable plastic deformation, the pulsed current delays the formation of a stress concentration and distributes the deformation more uniformly. Our analysis finds that enhancement of surface nucleation from the electron wind force is more likely than Joule heating to be the origin of the more uniform plasticity observed during electrical pulsing.

The simultaneous increase in strength and plasticity of aluminum and its alloys at cryogenic temperatures has been shown in previous research, but the deformation mechanism was still unclear. Therefore, the purpose of this investigation was to reveal the relationship between slip behavior and mechanical response at low temperatures. A quasi-in situ scanning electron microscope was used to observe the evolution of slip bands in the selected aluminum single crystals with two typical orientations at 25 °C, −100 °C, and −180 °C. The results showed that irrespective of orientation, the density of the slip plane was increased with the decline in temperature, which inhibited slip localization and significantly improved plasticity and work hardening. In detail, at RT, the slip bands were widening until the micro-cracks were generated, causing early failure during deformation. When the temperature was decreased to −180 °C, the slip plane density was increased, and the deformation was more homogenous. Moreover, the slip mode was influenced by orientation and temperature. In particular, a single slip system was activated in the sample with the [112] orientation at all the temperatures investigated. Multiple slip systems were found to activate at 25 °C and −100 °C, and only the primary slip system was activated in the sample with [114] orientation at −180 °C. These findings deepen the understanding of slip behavior at cryogenic temperatures, providing new insights into the deformation mechanism of aluminum and its alloys.

To investigate the effect of temperature on microcracking mechanisms of modified 9Cr‐1Mo steel, low cycle fatigue tests were performed at 350°C and room temperature (RT). At RT, the cyclic stress response at low strain amplitude (<0.5%) is controlled by friction stress while dominated by back stress at high strain amplitude. By comparison, the disappearance of sub‐grain boundaries induced by dislocation annihilation occurs at 350°C, which contributes to the decrease in back stress, resulting in more significant effects of back stress compared to RT. As a result of the accumulated fatigue damage, the distance between two parallel extrusions at 350°C is larger than that at RT, which is ascribed to the disappearance of low angle sub‐grain boundaries due to dislocation annihilation at 350°C. Due to the disappearance of small‐angle grain boundaries at 350°C, microcracks initiate along high‐angle grain boundaries at 350°C instead of along low‐angle grain boundaries at RT. Highlights: The temperature‐dependent fatigue microcrack initiation mechanisms are revealed.Cyclic stress response of modified 9Cr‐1Mo steel is controlled by back stress at 350°C.Increased width of slip bands at 350°C is induced by disappearance of lath boundaries.Microcracks initiate along HAGB at 350°C while along laths at RT. [ABSTRACT FROM AUTHOR]

In order to study the influence of hydrogen environment on the initiation and propagation of fatigue cracks in duplex stainless steel and establish the correlation mechanism between the fatigue strain microstructure evolution and hydrogen induced cracking in hydrogen environment，slow strain rate tensile and fatigue crack growth rate tests were carried out on 2205 duplex stainless steel specimens in 5 MPa hydrogen and 5 MPa nitrogen environments.Results showed that the hydrogen embrittlement sensitivity of 2205 duplex stainless steel was not high in the process of slow strain rate tensile in hydrogen environment，while it was significant during the fatigue process.The fatigue crack growth rate of 2205 duplex stainless steel in a hydrogen environment of 5 MPa was 18 times higher than that in a nitrogen environment.Hydrogen could promote local plastic deformation around the fatigue crack tip of 2205 duplex stainless steel and further led to hydrogen-induced cracking.In the process of fatigue deformation of 2205 duplex stainless steel in a hydrogen environment，different phase structures had different hydrogen-induced cracking mechanisms.The ferrite phase was easy to form a river-like pattern fracture morphology (cleavage fracture)，while the austenite phase fracture appearance mostly presented the characteristics of parallel slip bands.Austenite phase hindered cracks during the cleavage and cracking process of the ferrite phase.

This study used a digital imaging technique (DIC) to obtain the strain distribution at various locations in undermatching X80 pipe girth-weld joints under uniaxial tensile loading. In addition, the microstructure characteristics and deformation patterns in different regions were analyzed by scanning electron microscopy (SEM). The results showed that there was strain heterogeneity between the various regions of the welded joint. Strain concentration existed only in the 12.8 mm base metal heat-affected zone (HAZ) and only in the elastic deformation stage. There was strain concentration in the weld metal (WM) and both sides of the HAZ close to the near-fracture stage, and the maximum deformation was in the WM. When ε M = 12.2%, the K C was 6.27 and the K F was 1.73, and the K F was 113% and 152% of the K C and the K G , respectively. The large number of slip strips generated indicated serious damage in the WM near the fracture stage. In the elastic deformation stage, the strain concentration of the N1 HAZ was caused by the softened ferrite. The maximum deformation of the WM near the fracture stage was caused by the large grain size and the non-uniform martensite–austenite (M–A) islands, which may also lead to better local toughness of the cover weld and further affect the fracture mechanism of the welded joint. [ABSTRACT FROM AUTHOR]

An iron-rich high entropy alloy Al0.65CoCrFe2Ni comprising of both FCC and BCC phases was designed and fabricated using induction melting at a large industrial scale and suction casting at a small lab scale. Spinodally decomposed interdendritic regions were uniformly distributed in the industrially melted alloy, and a finer dendritic structure with smaller sized spinodal structures was observed in the alloy suction cast at lab scale. The suction cast alloy fabricated at the lab scale exhibited significantly higher compressive yield strength compared to the industrially cast alloy. The relative strengthening contributions in the alloys due to solid solution, grain boundary, dislocation interactions and interphase boundary were analyzed. Dislocation hardening was the major contributor responsible for the higher strength of the SC alloy. The deformation behavior in the alloys was examined with the help of orientation image mapping. Intense slip band formation at large strains in the industrially melted alloy indicates that cold working can be an effective technique to enhance the strength of the dual-phase high entropy alloy processed at a large scale. [ABSTRACT FROM AUTHOR]

A model is proposed to describe the accommodative plastic deformation and the relaxation of the elastic energy of planar shear mesodefects, which appear at grain boundaries due to the inhomogeneous plastic deformation of polycrystals. The relaxation is shown to occur via sequential splitting off of dislocation walls from a mesodefect and their motion into the grain body. [ABSTRACT FROM AUTHOR]

This study used a digital imaging technique (DIC) to obtain the strain distribution at various locations in undermatching X80 pipe girth-weld joints under uniaxial tensile loading. In addition, the microstructure characteristics and deformation patterns in different regions were analyzed by scanning electron microscopy (SEM). The results showed that there was strain heterogeneity between the various regions of the welded joint. Strain concentration existed only in the 12.8 mm base metal heat-affected zone (HAZ) and only in the elastic deformation stage. There was strain concentration in the weld metal (WM) and both sides of the HAZ close to the near-fracture stage, and the maximum deformation was in the WM. When εM = 12.2%, the KC was 6.27 and the KF was 1.73, and the KF was 113% and 152% of the KC and the KG, respectively. The large number of slip strips generated indicated serious damage in the WM near the fracture stage. In the elastic deformation stage, the strain concentration of the N1 HAZ was caused by the softened ferrite. The maximum deformation of the WM near the fracture stage was caused by the large grain size and the non-uniform martensite–austenite (M–A) islands, which may also lead to better local toughness of the cover weld and further affect the fracture mechanism of the welded joint.

ω-embrittlement is ubiquitous in metastable β-titanium (Ti) alloys, while the fundamental understanding on the damage-fracture mechanism hitherto remains elusive. In this study, we systematically investigate ω-embrittlement of high misfit Ti-10Cr (wt.%) alloys by coupling experiments and first-principles calculation. It is found that brittle cleavage-like fracture prevails in tensile samples, irrespective of the quenching or subsequent aging states. Microscopically, cracks nucleation and propagation proceed along slip bands, inside which ω-lattices are first disordered and then the localized (β + ω)-amorphous-like structures are developed in the shape of white patches. The underlying mechanism of mechanically-driven localized amorphization is that due to the remarkable covalent character of atomic bonding of ω-precipitates caused by composition partitioning of the Cr element, ω-precipitates impart extremely high energy barrier opposed to dislocation gliding and render dislocations pile-up ahead of ω-precipitates, thus leading to their lattice disordering. It is unveiled that the hydrostatic pressure, serving as the driving force for dislocations pile-up, plays a critical role in this unusual cleavage-like fracture of Ti-10Cr alloys caused by mechanically-driven ω-mediated localized amorphization. Accompanied by the transition from the co-operation of deformation twining and ordinary dislocation slip in the quenched Ti-10Cr alloys to the exclusive ordinary dislocation slip in the long-time aged Ti-10Cr samples, it is unexpected that the resulting tensile fracture strength monotonically decreases to a stress level of ~ 100 MPa. These findings provide new insights into the damage and fracture behavior of high misfit β-titanium alloys, such as Ti-Cr alloys.

Two methods for the determination of geometrically necessary dislocation (GND) densities are implemented in a lower-order strain-gradient crystal plasticity finite element model. The equations are implemented in user material (UMAT) subroutines. Method I has a direct and unique solution for the density of GNDs, while Method II has unlimited solutions, where an optimization technique is used to determine GND densities. The performance of each method for capturing the formation of slip bands based on the calculated GND maps is critically analyzed. First, the model parameters are identified using single crystal simulations. This is followed by importing the as-measured microstructure for a deformed α-zirconium specimen into the finite element solver to compare the numerical results obtained from the models to those measured experimentally using the high angular resolution electron backscatter diffraction technique. It is shown that both methods are capable of modeling the formation of slip bands that are parallel to those observed experimentally. Formation of such bands is observed in both GND maps and plastic shear strain maps without pre-determining the slip band domain. Further, there is a negligible difference between the calculated grain-scale stresses and elastic lattice rotations from the two methods, where the modeling results are close to the measured ones. However, the magnitudes and distributions of calculated GND densities from the two methods are very different.

The plastic deformation processes and fracture behavior of a Ti–5Al–5Mo–5V–1Cr–1Fe alloy with bimodal and lamellar microstructures were studied by room-temperature tensile tests with in situ scanning electron microscopy (SEM) observations. The results indicate that a bimodal microstructure has a lower strength but higher ductility than a lamellar microstructure. For the bimodal microstructure, parallel, deep slip bands (SBs) are first noticed in the primary α (αp) phase lying at an angle of about 45° to the direction of the applied tension, while they are first observed in the coarse lath α (αL) phase or its interface at grain boundaries (GBs) for the lamellar microstructure. The β matrix undergoes larger plastic deformation than the αL phase in the bimodal microstructure before fracture. Microcracks are prone to nucleate at the αp/β interface and interconnect, finally causing the fracture of the bimodal microstructure. The plastic deformation is mainly restricted to within the coarse αL phase at GBs, which promotes the formation of microcracks and the intergranular fracture of the lamellar microstructure.

We investigated the flow behavior of γ/γʹ-strengthened Co-12Ti and Co-12Ti-4Mo (at.%) alloys at room and elevated temperatures (up to 900°C) by electron microscopy and density functional theory. The Mo-added alloy exhibited an enhanced compressive yield strength and strain hardening behavior as compared to the reference binary alloy. This behavior could be attributed to a ~25% larger γʹ volume fraction and ~7% higher planar fault energies in Co-12Ti-4Mo. Using electron channeling contrast imaging, we observed interrupted slip bands in the Co-12Ti-4Mo alloy deformed to a strain of 6%, which led to enhanced strain hardening, in contrast to extended slip bands along {111} planes in the Co-12Ti alloy. Interrupted slip band formation in Co-12Ti-4Mo could be explained by rapid exhaustion of dislocation sources and a higher energy barrier required to cut the γʹ precipitates. These effects are due to a reduced γ channel width and substantial hardening effect of γʹ-Co 3 (Ti,Mo) in the ternary alloy as well as due to the large shear modulus difference between γʹ and γ. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Shear strain profiles along slip bands in a modified Rolls-Royce nickel superalloy (RR1000) were analyzed for a tensile sample deformed by 2%. The strain increased with distance away from a grain boundary (GB), with maximum shear strain towards the center of the grain, indicating that dislocation nucleation generally occurred in the grain interior. The strain gradients in the neighborhood of the GBs were quantified and generally correlated with rotation about the active slip system line direction. This leads to an ability to determine the active slip system in these regions. The dislocation spacing and pileup stresses were inferred. The dislocation spacing closely follows an Eshelby analytical solution for a single ended pileup of dislocations under an applied stress. The distribution of pileup stress values for GBs of a given misorientation angle follows a log-normal distribution, with no correlation between the pileup stress and the GB misorientation angle. Furthermore, there is no observed correlation between various transmissivity factors and slip band pileup stress. Hence it appears that the obstacle strength of any of the observed GBs is adequate to facilitate the dislocation pileups present in the slip bands. However, slip band transmission does correlate with transmissivity factors, with the current study focusing on the Luster and Morris m'-factor. Observation of strain profiles of transmitted bands indicate dislocation nucleation locations. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Systematic study was conducted on the microstructures and mechanical properties of nickel samples with two distinct types of heterostructures. The first is featured with coarse-grained lamellae embedded in a matrix consisting of a very high density of dislocation structures. The second is featured with coarse-grained zones embedded in the ultrafine-grained matrix. The second type of heterostructures exhibits better strength and ductility, although it has a smaller average grain size than the first type. The zone boundaries in the second type of heterostructures are less prone to cracking than those in the first type. Intersecting micro-shear-bands formed net-like patterns in the second type of heterostructures during tensile deformation. This is the first ever observation of structural micro-shear-bands in a heterostructured material. It supports the claim that heterostructure promotes the formation of dispersive shear bands. In contrast, a macroscopic shear band formed and caused early failure of the sample with the first type of heterostructures. Our results indicate that well-developed ultrafine/nano grained matrix in heterostructured materials are necessary for preventing crack formation and shear band localization. This should be considered as a key factor for optimizing the mechanical properties of heterostructured materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

For a new type of thermomechanical controlled process steel, when stress intensity factor was about 32 MPa m1/2, several slip bands with different orientations occurred in cyclic plastic zone. Some slip bands had strong interaction with dominant crack, which led to crack bifurcation and aggregation. After that, electron back-scattered diffraction technique was employed to evaluate the cyclic plasticity effect on crystallographic features of kernel average misorientation (KAM), strain distribution and fraction of different categories of grains for fatigue loading sample in crack tip zone. Before fatigue loading, KAM distribution map revealed relatively homogeneous plastic deformation and few grains displayed distortion based on strain distribution map. After fatigue loading, KAM showed higher cyclic plasticity in the middle, and lower value on both sides. Strain network structure formed. Meanwhile, when fatigue loading was executed, proportion of recrystallized grains had a little variation from 3.15 to 5.58%. Ratio of substructured grains increased to 19.63%, and deformed grains reduced to 74.79%. [ABSTRACT FROM AUTHOR]

A surface slip band due to contact by a rectangular rigid flat-ended indenter is investigated. An inclined Zener–Stroh crack model is proposed to simulate the slip band. By using the fundamental solution of a single dislocation in a half plane as Green's function, the Zener–Stroh crack is modeled with continuously distributed dislocations. It leads to a singular integral equation of the first kind, which is solved with the Gauss–Chebyshev numerical quadrature, and then stress intensity factors (SIFs) at the crack tips are evaluated. It is demonstrated that the Zener–Stroh crack model can efficiently capture micro deformation behavior of the surface slip band due to contact. With this model, the corresponding relations of the applied load, the slip band length, the relative sliding displacement of slip band and SIFs are obtained. Compared with the experimental results, it is shown that the surface Zener–Stroh crack model to contact slip band can well address such kind of contact damage problems. [ABSTRACT FROM AUTHOR]

Recently, a technique for rapidly determining a material's fatigue limit by measuring energy dissipation using infrared thermography has received increasing interest. Measuring the energy dissipation of a material under fatigue loading allows the rapid determination of a stress level that empirically coincides with its fatigue limit. To clarify the physical implications of the rapid fatigue limit determination, the relationship between energy dissipation and fatigue damage initiation process was investigated. To discuss the fatigue damage initiation process at grain size scale, we performed high-spatial-resolution dissipated energy measurements on type 316L austenitic stainless steel, and observed the slip bands on the same side of the specimen. The preprocessing of dissipated energy measurement such as motion compensation and a smoothing filter was applied. It was found that the distribution of dissipated energy obtained by improved spatial resolution measurement pinpointed the location of fatigue crack initiation. Owing to the positive correlation between the magnitude of dissipated energy and number of slip bands, it was suggested that the dissipated energy was associated with the behavior of slip bands, with regions of high dissipated energy predicting the location of fatigue crack initiation. [ABSTRACT FROM AUTHOR]

Plastic deformation during low cycle fatigue in fcc materials with low stacking fault energy is accumulated in slip bands, which become preferential sites for crack initiation. Whilst these dislocation structures have been studied before, little has been done to assess the effect and evolution of the individual slip lines within them. In this study, samples of a γ ′ precipitate strengthened nickel-based superalloy are fatigued at room temperature and 700 ∘C for 1, 40 and 500 cycles. The resulting dislocation structures are characterised via Electron Channeling Contrast Imaging and Transmission Electron Microscopy. We introduce a new methodology to measure slip band parameters such as the slip line spacing and shear step length by analysing the holes left by sheared precipitates in γ ′-etched secondary electron micrographs. Statistics of these parameters are obtained and compared for different conditions. Advantages of this technique include resolution at the scale of individual planes, acquisition of true three-dimensional data and applicability in the bulk of the material. The combination of these techniques provides a unique mechanistic and quantitative insight into the slip band and precipitate morphology evolution. [ABSTRACT FROM AUTHOR]

The LCF behaviors of two Ni-based single-crystal superalloys at room temperature and 600 °C have been studied. Superalloy with 3 wt% Ru-containing (3Ru alloy) had more excellent fatigue performances than that of non-Ru superalloy (0Ru alloy). Microstructures observed by transmission electron microscope showed that 0Ru alloy exhibited slip bands with orthogonal slip directions after the test. (1ī1) [011] and (1ī1) [0ī1] slip systems were activated in plastic deformation process. While (111) [0ī1] and (1ī1) [0ī1] slip systems of 3Ru alloy were along the single slip direction. Therefore, adding alloying element Ru to the superalloy promoted uniform deformation and prolonged fatigue life. Unlabelled Image [ABSTRACT FROM AUTHOR]

• We perform atomistic simulations of deformation in Ni with He bubbles and SIA clusters. • Nanotwins form in a model with free surfaces, slip bands form in a model without free surfaces. • He bubbles deform severely within slip bands and nanotwins, but do not coalesce or form incipient cracks. This paper presents molecular dynamics (MD) simulations of plastic deformation in single-crystal Ni models containing internal distributions of helium (He) bubbles and self-interstitial atom (SIA) clusters corresponding to experimental characterization of ex-service Inconel X-750 components. We simulate single crystals with and without free surfaces at room temperature and 588K, the latter temperature corresponding to the Inconel X-750 service conditions. Both models are deformed under multiple slip to a maximum deviatoric strain of ∼10 %. A dislocation slip band forms in the model without free surfaces, but not in the model with free surfaces. However, the latter exhibits nano-twin nucleation from surfaces. Helium (He) bubbles that overlap with a slip band or a nano-twinned region deform more severely than other bubbles in the model. Nevertheless, the bubbles do not link up and do not form configurations that resemble incipient cracks. [ABSTRACT FROM AUTHOR]

• Novel technique for visualizing laser-induced strain/slip generation. • Effects of crystallographic orientation with respect to laser trajectory. • Effects of process parameters and extent of melting on resulting slip characteristics. • Establishes basis for validation of crystal plasticity modelling of full thermo-elastoplastic process. The capability to characterize the inelastic response of a material induced by laser processing is particularly relevant within the context of laser-based additive manufacturing. While many efforts have been directed toward elastic residual field measurements, determining the extent of plastic deformation significant experimental challenges. The present effort seeks to offer direct insight into the nature of plastic strain generation in nickel single crystals subjected to melt-mediated laser processing. Ultra-high purity nickel single crystals were chosen for their FCC crystal structure and their lack of potential for dislocation interactions with either grain boundaries or solutes, thus significantly simplifying their analysis. [ABSTRACT FROM AUTHOR]

The microstructure evolution and mechanical properties of a Fe-Mn-Al-C austenitic low-density steel at different hot-rolling reductions have been investigated. It was found that with the increase in hot-rolling reduction from 45% to 82%, the grain size was uniformly refined and the dislocation density was continuously increased. As a result, both yield strength and ultimate tensile strength were effectively enhanced while the ductility and toughness only slightly decreased. An excellent combination of yield strength, ultimate tensile strength, total elongation, and toughness of 648 MPa, 976 MPa, 50%, and 105 J/m2, respectively, was obtained. The yield strength increment was interpreted by the stronger grain boundary strengthening and dislocation strengthening, and the minor loss of ductility and toughness was arising from the faster saturation of the slip band refinement (slip band spacing reached ∼50 nm) and an earlier occurrence of microbands due to the finer grain size. Based on this research, it is proposed that increasing the hot-rolling reduction was an effective approach to enhance the overall mechanical properties of the low-density steel with a fully austenitic microstructure. • Excellent ductility was kept while strength was enhanced by increasing hot-rolling reduction. • The increase in hot-rolling reduction effectively refined the mean grain size. • Stronger grain-boundary and dislocation strengthening led to improved yield strength. • The slip band spacing was reduced with finer grain size at the same strain level • Ductility decreased due to earlier saturation of slip band refinement and formation of microbands. [ABSTRACT FROM AUTHOR]

The Wujiang landslide is located on the right bank of Centianhe reservoir near the entrance of the Wujiang gorge, approximately 300 m upstream of the original dam. As a typical ancient landslide, this landslide's total volume is approximately 1.327 × 10 7 m 3 . The stability of the landslide affects the operation and safety of the dam and flood-release structures after the reservoir of the Expansion Project impounding. First, the observed internal landslide displacement is analyzed and shows that the Wujiang landslide is a long-term creep slope along the control shear plane, and the shear strength of the slip band has either approached or reached its long-term strength. Then, a typical cross section parallel to the sliding direction is selected for the calculation, and the strength parameters are back-analyzed based on the limit analysis method. Next, a finite element model of a typical cross section for the landslide is constructed, and the viscoplastic strain rate is calculated based on Mohr–Coulomb yield criterion and Perzyna's assumption; therefore, the annual displacement creep rate calculated by the elasto-viscoplastic finite element program is obtained. Finally, the annual creep rate of the observed displacement and that of the calculated displacement are combined, and the elastic modulus and viscosity coefficient of the landslide are back-analyzed based on the orthogonal design method and simplex optimization algorithm. These parameters provide a basis for the analysis and control of the landslide and serve as a reference for similar projects. [ABSTRACT FROM AUTHOR]

Abstract The characteristics of slip band and its interplay with dynamic precipitation of α phase during the thermo–mechanical coupling process in titanium alloy is really interesting but is not sufficiently ascertain. In the present work, the formation of slip bands, dynamic microstructure evolution and crystallographic orientation relationship during warm deformation of Ti-5553 alloy were investigated using Scanning Electron Microscopy/Transmission Electron Microscopy/crystallographic calculations. Results reveal that multiple-slip bands with two or three different propagating directions would form during the warm compression. These three distinctly oriented bands could be estimated as slip bands of (112) [ 11 1 ¯ ] , (1 2 ¯ 3 ¯ ) [ 1 1 ¯ 1 ] and ( 2 ¯ 13) [ 1 1 ¯ 1 ] types. Nano/ultrafine-trimorphic structure (lamellar α, equiaxed α and irregular α) formed dynamically during the warm deformation process due to the dynamic interplay between the initiation of the slip bands and the nucleation of α phase. There is an obvious competitive mechanism between dynamic recovery/dynamic recrystallization and α phase nucleation, which depended on the deformation parameters and modes. These results could provide valuable reference for process optimization and the microstructural evolution controlling. Graphical abstract Image 1 Highlights • The multiple-slip bands were formed in Ti-5553 alloy during the warm deformation. • Slip systems were identified accurately via crystallographic and matrix calculations. • The hot deformation mechanisms of titanium alloys were systematically considered. • Nano/ultrafine-trimorphic structure can be successfully produced in Ti-5553. [ABSTRACT FROM AUTHOR]

Highlights • Analysis of circa 12,000 micrographs of Antarctic ice from 8 depths and covering the range 94–853 m revealed two contrasting evolution regimes for the orientation of slip bands. • Unexpected behavior of slip bands in shallow bubbly ice reveals the inheritance of certain mechanical and microstructural features from ancient firn, probably related to former force chains within the firn skeleton. • Such inherited features gradually fade away in shallow bubbly ice, through the action of dynamic recovery and recrystallization, and the redistribution of internal stresses. This evanescence is explained through the postulation of a new hypothesis of microstructural fading memory. • The hypothesis of microstructural fading memory is compatible with a number of observations of microstructure evolution in firn and ice, and it lays the foundations for a new experimental and theoretical framework to study the elusive process of dynamic recovery in polar ice. Abstract The Antarctic Ice Sheet is a continental ice mass with circa 23 million gigatons of ice, which represent roughly 67 % of world's freshwater supply. This colossal mass of ice is by no means static, as the old ice slowly creeps under its own weight towards the ocean, while new ice is continually formed through the sintering of snow deposited on the ice sheet surface. A crucial role in this metamorphism is played by firn, which is the porous material in an intermediate state between the granular snow and the solid polycrystalline ice. Understanding the snow–firn–ice metamorphism is essential not only for a precise determination of the mechanical (creep) properties of polar ice, but also for comprehending the formation and decay of climate proxies widely used in ice-core studies. This work investigates the transition from firn to ice through the spatial and directional distributions of slip bands in bubbly ice. The analysis of high-resolution micrographs of ice sections extracted from the EPICA-DML Deep Ice Core allows us to identify a clear influence of strain-induced anisotropy (viz. c -axis preferred orientations) on the evolution of slip-band inclinations in deep bubbly ice. In contrast, we discover an unanticipated behaviour of slip bands in shallow bubbly ice, which prompts the introduction of the hypothesis of microstructural fading memory and the definition of a stabilization zone that may penetrate hundreds of metres into the bubbly ice. Within this stabilization zone, highly localized concentrations of strain energy and internal stresses once generated by force chains in the ancient firn are gradually redistributed by the newly formed bubbly-ice microstructure. We show that this hypothesis is compatible with the localized dynamic recrystallization episodes observed in polar firn (even at temperatures close to − 45 ∘ C), and it may also explain the sluggish rotation of c -axes observed in the upper hundreds of metres of polar ice sheets. [ABSTRACT FROM AUTHOR]

Abstract Microstructures and dislocations associated with the slip band (SB) fatigue cracks were investigated in Cu single crystal and bicrystal. It is found that there are high strain localizations with abundant dislocation cells around the cracked SBs. Due to the high local strain and slip irreversibility, the lattice rotates severely leading to large misorientation and hence low- or high- angle grain boundaries could form between the neighboring cells. Moreover, the dislocation walls can serve as preferential sites for nucleation and propagation of fatigue cracks with high density of dislocations, vacancies and high strain incompatibility. Graphical Abstract Unlabelled Image Highlights • Dislocation cells form near early slip bands fatigue cracks in wavy-slip materials. • Lattice rotates severely and grain boundaries form between neighboring cells. • The walls of dislocation cells are preferential sites for fatigue cracking. [ABSTRACT FROM AUTHOR]

• The local slip band in the grain orientation provided the preferred path for fatigue crack growth. • The fracture energy of 12 slip systems in the optimal {111}<110>slip system family was calculated through molecular dynamics. • A micro damage evolution model based on fracture energy was established to predict the fatigue life of IN 750H. • The proposed model can better realize the dynamic process of fatigue crack initiation and growth stage. The cyclic stress responses and microstructure analyses were carried out of short-term aged Inconel 750H under high temperature low cycle fatigue tests, the influence of strain amplitude on fatigue fracture mechanism of aged IN 750H was systematically analyzed. According to the slip traces, Schmid factor, and geometrically necessary dislocation density distribution on the fracture frontier, the paper revealed that the local slip band provided a preferred path for the fatigue crack growth of Inconel 750H. Due to the limitation of the inability to measure energy of slip system through experiments, a probability based statistical method on average fracture energy of the slip system was constructed. Coupling with the macro-scale constitutive models, a microstructural-sensitive strategy based on fracture energy exhaustion theory was established. Based on the proposed model, the dynamic process of fatigue crack initiation and growth stage were simulated. The predictive fatigue lives showed a good consistence with the experimental results of both as-received state and short-term aged Inconel 750H under various amplitudes. In addition, the validity of the proposed model was further confirmed by fatigue crack length under the initiation and propagation stages, accompanying by the 3D X-ray computed tomography. [ABSTRACT FROM AUTHOR]