International Journal of Plasticity最新文献

In this study, we identified a specific phenomenon of coordinated deformation of twins in near-α titanium alloys during dwell fatigue (DF). The main crack source regions and internal cracks in the micro-texture region (MTR) and no-MTR samples with inconsistent orientation characteristics were characterized. The results demonstrate that the main cracks in all specimens are aligned with the (0001) basal plane, which is associated with basal slip. Notably, twins are found and confirmed to be involved in the DF crack initiation process in high Al content near-α Ti60 alloys where deformation twins are rare, and tend to nucleate at the DF basal cracks. Further in-situ dwell investigation reveals and proposes that the dislocation pile-up and prismatic-basal (PB) interfacial features between soft/hard grains lead to deformation twin nucleation and growth from hard grain boundaries. Concurrently, the pyramidal 〈c+a〉 dislocation slip is observed to be in concurrent operation with the induced twins. These findings suggest that deformation twins not only coordinate basal grain deformation but also hinder the initiation and propagation of basal cracks caused by basal 〈a〉 slip. Moreover, a high density of pyramidal 〈c+a〉 dislocations within the twin and their dissociation to form basal stacking faults (SFTs) with a specific nanometric spacing make the twinning process accompanied by significant lattice distortions inside the twin. These newly formed nanotwin boundaries and SFTs act as barriers to dislocation motion, enhancing the strength and DF lifetime of near-α Ti60 alloys and effectively reducing the dwell sensitivity of no-MTR alloys. Our findings extend the understanding of the coordinated roles of dislocation slip, twin nucleation and formation of basal SFTs in near-α titanium alloys in dwell fatigue.

In-depth knowledge of the coupling between grain refinement and the transformation-induced plasticity (TRIP) effect in metastable alloys is a viable approach for the improvement of strength-ductility synergy, which needs systematic research with consideration of commercial austenitic stainless steels and novel high-entropy alloys (HEAs). Accordingly, in the present work, two Si-containing metastable HEAs in the Fe₄₇Co₃₀Cr₁₀Ni₅V_8-xSi_x system (x = 3 and 6 at.%) were designed, and the TRIP-assisted AISI 304L stainless steel was also considered for comparison. The alloys were processed by cold rolling and annealing to obtain different grain sizes. Reducing the stacking fault energy (SFE) through adjusting chemical composition contributes to minimizing the detrimental effect of grain refinement on the ductility of TRIP alloys, while extremely low SFE must be avoided owing to the fast kinetics of deformation-induced martensitic phase transformation, which leads to the deterioration of ductility. In contrast to AISI 304L stainless steel, a strong TRIP effect was maintained upon grain refinement in the Fe₄₇Co₃₀Cr₁₀Ni₅V₂Si₆ HEA due to the remaining apparent SFE in the appropriate TRIP range. The tuned kinetics of martensitic transformation was found to be responsible for the exceptional ductility (∼65 %) of Fe₄₇Co₃₀Cr₁₀Ni₅V₂Si₆ HEA at an ultrahigh tensile strength of ∼1230 MPa. Therefore, considering the identical trend of SFE with grain size, an appropriate initial SFE value is important for tuning the grain size dependency of the TRIP effect. Moreover, the ultrahigh strength was attributed to the high volume fraction of α΄-martensite as well as the high strength of the martensite phase due to the high Si content. Accordingly, for achieving strong-yet-ductile HEAs, a high Si content is recommended to benefit from solid solution strengthening in the martensite phase, a specially-designed chemical composition is needed for attaining a high volume fraction of α΄-martensite, and SFE should be in a desirable range to tune the kinetics of martensitic phase transformation.

Precipitation strengthening is one of the most effective approaches for developing advanced structural materials with outstanding strength-ductility combinations. However, most compositional designs of precipitate-strengthened HEAs/MEAs compromise the cost-property tradeoff owing to the addition of expensive Co element. In this study, a Co-free FeCrNi-based precipitate-strengthened medium entropy alloy (denoted as Al_0.2Cr_0.9FeNi_2.2Ti_0.2) with a near-equiatomic FeCrNi matrix and a high content (∼ 35 %) L1₂ nanoprecipitates was designed using a mixing strategy. The microstructural features, mechanical performance, deformation substructure evolution, and strengthening mechanisms were systematically investigated using EBSD, TEM, and APT. Tensile tests indicated that the current alloy aged within a moderate temperature range achieved an exceptional strength-ductility combination compared to existing Co-containing and Co-free HEAs/MEAs. Particularly, the alloy aged at 700 ℃ (denoted as 700A) demonstrated a high ultimate tensile strength of 1606 MPa and a large ductility of 25 %, benefiting from both precipitation hardening and an unusual strain-hardening sustainability. Such anomalous strain-hardening sustainability can be attributed to the dislocation dipole-induced plasticity. High-density dislocation dipoles can simultaneously provide additional strain hardening by reducing the dislocation mean free path and enhance plastic deformation compatibility by acting as stress delocalization origins, thereby contributing to excellent strength-ductility synergy. These findings will not only open a new door for the future development of high-performance Co-free precipitate-strengthened HEAs/MEAs, but also deepen the understanding of the work-hardening mechanisms in these alloys.

Fracture at interface causes plastic deformation in the vicinity region. Conventional plastic energy dissipation theory indicates that ductile vicinity toughens the interface by absorbing plastic deformation energy. However, the microstructure in the vicinity directly affects local plastic deformability and fracture behaviour, implying a more complicated toughening mechanism. In this study, the effect of microstructure and hardness on fracture behaviour of Fe/Ni interface was investigated. By experimental approach, interfaces with and without dynamic recrystallization (DRX) were fabricated by controlling the bonding conditions. It showed that compression-induced plastic deformation is the main source of the hardening behaviour in the vicinity. Moreover, the interfaces with hardened DRX vicinities exhibited improved fracture toughness, which is inconsistent with the plastic energy dissipation theory. To clarify this observation, the crystal plasticity finite element method (CPFEM) approach was employed to distinguish the effects of plastic deformation and interfacial microstructure. The result showed that although higher plastic deformability in the vicinity absorbs more dissipated plastic energy, severe stress concentration at the interface leads to early fracture and poor toughness. On the other hand, the interfacial hardened DRXed grains disperse interfacial stress distribution and provide potential sub-crack sites. A combined result of uniform plastic deformation and fracture energy dissipation is responsible for the improved toughness at interfaces with DRXed grains.

In this article, we introduce a novel physically-based anisotropic damage visco-hyperelastic model designed to predict the history-dependent inelastic behavior of multiaxially stretched filled rubber. The model integrates both the anisotropic Mullins effect and intrinsic viscosity through the consideration of internal physics, represented by two distinct networks: an elastic ground network and a superimposed viscous network. The rupture of molecular bonds within the elastic network chain backbone is modeled using statistical mechanics, while the effects of anisotropy-induced chain orientation at the upper scale are addressed through a microsphere-based scale transition method. The intrinsic viscosity is represented by the viscous network, which is governed by time-dependent equations to account for the viscous overstress. The influence of fillers is captured through the concept of strain amplification, applied to the two networks within the rubber matrix. The effectiveness of the model in capturing the biaxial behavior of filled rubber is evaluated by comparing its outputs with experimental data from a filled rubber system. This assessment specifically considers the impact of pre-stretching under various loading conditions and across a wide range of filler concentrations. Notably, it successfully predicts anisotropic stress-strain response and energy dissipation, and the coupled effects of damage and viscosity.

{10$\overline{1}$3}$〈30\bar{3}\bar{2}〉$ twinning is usually activated at the later stage of plastic deformation of Mg alloys, which is closely relevant to their fracture behavior. Reactions between slip dislocations and twin boundaries (TBs) are suggested to facilitate TB migration, retarding the premature TB cracking. Here, dislocation-assisted evolution of {10$\overline{1}$3} TBs in a Mg alloy subjected to cyclic deformation were studied and modeled, according to transmission electron microscopy observations, theoretical analyses of interfacial defects, and molecular dynamics simulations. Atomic-resolution experimental observations showed that symmetric tilt grain boundaries (STGBs) near the {10$\overline{1}$3} twin orientation with steps were generated in the deformed Mg alloy. Theoretical analyses and atomistic simulations indicated that transformation of {10$\overline{1}$3} TBs into the STGBs could occur by reactions with incident basal $〈a_{60}〉$ dislocations in pairs from the twin and matrix respectively under the normal stress. STGB steps would be produced by reactions of individual basal $〈a_{60}〉$ dislocations with GB dislocations at the STGB. Importantly, resultant steps could further emit {10$\overline{1}$3} twinning dislocations to facilitate the STGB migration. Moreover, STGBs near the {10$\overline{1}$3} twin orientation could evolve back into {10$\overline{1}$3} TBs either by reactions with an array of basal $〈a_{60}〉$ dislocations, or by a GB sliding of b = $〈30\bar{3}\bar{2}〉$ theoretically. Our results may provide insights into the mechanisms of {10$\overline{1}$3} TB evolution in Mg alloys, which plays important roles in their plastic deformation and plasticity.

The formation of void damage and spalling failure in ductile metallic materials under strong impact is a well-established phenomenon. In aerospace and defense technology engineering design, understanding the spalling failure process and related mechanisms is of utmost importance. This paper develops an explicit Gurson-type phase-field model that can simulate the void evolution and spalling damage of three-dimensional ductile metallic materials under high-velocity impacts based on the study of Aldakheel et al.. The model incorporates the Gurson-type void evolution equation and the phase-field approach while taking into account the pressure-dependent bulk modulus and inertia effects. This model is used to study the main processes and mechanisms of impacted layer cracking of metals in different dimensions. Meanwhile based on the study of complex spallation cracking processes in metals in two and three dimensions, observing and proposing the formation mechanism of complex spallation cracking modes in materials due to lateral and edge (base angle) rarefied effects.

Ionic-bonded ceramics are featured by their thermal stability, corrosion resistance, hardness and strength, but their applications are limited by the inherent brittleness. Ceramics are composed of strong chemical bonding and intricate crystal structures, making plastic deformation by dislocation slip highly challenging. A nanostructured amorphous Al₂O₃-ZrO₂ ceramic comprising nanoscale amorphous particles and amorphous interfaces between particles was achieved in practice, where the amorphous interface is in scale of approximately 2.34 nm and amorphous particles is in width of approximately 6.75 nm. Based on nano-indentation tests, the shear transformation zone (STZ) volumes of nanostructured amorphous ceramics hot-pressed under various conditions are calculated, suggesting attenuation of free volume with the increase in pressure and temperature. The medium-temperature compression test of the samples exhibits a permanent plastic deformation of 14.6 %, with the presence of hierarchical shear bands in the deformed samples. The main shear bands (MSBs) in width of 0.84–9.15 μm are generated by the stress concentration in crystal-amorphous interface, and the small shear bands (SSBs) of 31–428 nm are related to abundant free volumes in the interface between amorphous particles.

Backstresses, associated with certain dislocation arrangements and their inter-dislocation long-range stresses, are known to contribute significantly to deformation response of metals, including kinematic hardening, the Bauschinger effect (BE) and the Hall-Petch effect. Various methods have been employed to quantify these backstresses at the macro-scale. One of these approaches, which has received relatively little attention, is the stress dip test. The strain rate observed during a load dip and hold, after previous plastic deformation, can be positive or negative, depending upon the level at which the load is held, and the relative magnitudes of competing friction and backstresses. The most direct interpretation of previously reported tests indicates a surprisingly high level of backstress in common materials, and which is generally also higher than the value extracted from an unload-reload test. In this paper, stress dip tests are performed on pure polycrystalline tantalum, along with unload-reload tests. A plateau is seen in the strain rate observed during the stress dip test, which has not been previously reported. If the backstress is interpreted to correspond with the stress level associated with the middle point of the plateau, in line with the friction/backstress model of the unload-reload test, the resulting backstress obtained from both tests are very similar. A novel crystal plasticity model, incorporating backstress, reversible dislocations and non-Schmid effects, is used to help justify this new approach. The model predicts the observed plateau in strain rate, and provides a slip-level interpretation of the macroscopically observed backstress. The slip-level backstress (when considered as a fraction of the stress prior to the dip) is reasonably similar to the values interpreted from the dip test experiment. The ∼23% lower value in the simulation may be due to the lack of certain aspects of the actual physics in the model.

In-situ synchrotron X-ray diffraction experiments were conducted on the pearlitic steel sample with a carbon content of 0.74% by weight. Specimens were subjected to uniaxial loading that induced shear deformation and two-dimensional diffraction patterns were acquired. The evolution of the lattice microstrain and the strain-resolved crystallographic texture development of both ferrite (α-BCC) and cementite (θ-orthorhombic) phases were followed. The analysis revealed that the texture changed from {110}<113>_α to {113}<121>_α component and then, stabilized at {013}<uvw>_α orientations. The θ phase exhibited a weak texture in the {100, 010, and 001}_θ family planes. Additionally, it was revealed that the nucleation of interfacial defects at the α/θ interface promotes the amorphization of cementite and the activation of slip systems in less densely packed {310}_α planes. The influence of microstructural changes on mechanical properties is discussed.