Parallel Dislocations Research Articles

Mechanisms of laser non-uniform shock peening on the mechanical properties of SUS 304 stainless steel weld joints

The technique of Laser Non-Uniform Shock Peening (LNUSP) is proposed based on the residual stress distribution in welded joints and the shock wave peak pressure of SUS 304 stainless steel. The study investigated the effects of LNUSP on the mechanical properties of laser beam oscillation welded (LWW) joints of SUS 304 stainless steel. The results indicate that LNUSP induced residual compressive stress with an affected layer depth exceeding 0.9 mm, leading to a more uniform residual stress distribution. LNUSP also induced martensitic phase transformation, altered the grain structure orientation, formed parallel dislocation arrays that refined the grains, increased dislocation density leading to dislocation tangles, and induced mechanical twins of 20–70 nm. Furthermore, LNUSP significantly enhanced microhardness and promoted a more uniform hardness distribution, favoring a better balance between strength and ductility. LNUSP notably increased the yield strength (YS) and ultimate tensile strength (UTS) by 49.4% and 5.1%, respectively, compared to the original samples. The LNUSP-treated samples demonstrated superior strength and plasticity, attributed to the uniformity of internal plastic deformation.

Origins of functional fatigue and reversible transformation of precipitates in NiTi shape memory alloy

The work clarifies several key questions in shape memory research that have eluded previous studies. The findings show that dislocation slip emanates at austenite-martensite interfaces during unloading and aligns with the internal twin boundary interface of martensite. It was observed that the type II internal twins of the martensite become parallel dislocations in the austenite. During reloading, these dislocations act as nucleation sites for the martensitic twins, reducing the nucleation barrier and the transformation stress. The precipitates facilitate martensite nucleation but also act as an obstacle to martensite front motion, restrict detwinning, and pin the interfacial dislocations during unloading, thereby contributing to residual strains and martensite stabilization. Martensite nucleation is not suppressed by the size of the thin film, which is of the order of 85 to 105 nanometers thick, and repeated transformation occurred cycle after cycle. Single crystals deformed in the <101>LD exhibited the best recoverability of up to 5.5 % and tensile stresses of up to 1.4 GPa. It was demonstrated for the first time that, when favorably oriented, Ni4Ti3 precipitates undergo a reversible phase transformation to R-phase and can accommodate up to 4 % reversible strains.

Synergistic grain boundary engineering for achieving strength-ductility balance in ultrafine-grained high-Cr-bearing multicomponent alloys

Precipitation strengthening is a crucial strategy for ensuring the overall performance of conventional and multicomponent alloys to meet industrial demands. However, the mechanical properties of high-Cr-bearing alloys are often compromised by brittle Cr-rich precipitates at grain boundaries (GBs), leading to severe embrittlement. In this work, a multi-step thermomechanical process is employed to regulate discontinuous dynamic recrystallization (DDRX) and static recrystallization, achieving an ultrafine-grained microstructure. This optimized approach simultaneously impedes the continuous precipitation of the ordered L12 nanocrystals within the matrix and actively encourages the synergistic discontinuous precipitations of submicron L12 and Cr-rich σ particles at GBs, thereby enhancing (yield) strength and high-temperature thermal stability. The ultrafine grains facilitate uniform plastic deformation, characterized by pronounced parallel dislocation slip and stacking faults (SFs) within face-centered cubic (fcc) grains, while second-direction slips, SFs, and Lomer-Cottrell (L-C) lock networks near GB precipitates greatly alleviate stress concentration. Critically, the submicron L12 particles enveloping σ precipitates at GBs also display plastic deformation via mechanical twinning and dislocations, effectively impeding rapid crack propagation along GBs. This research not only provides new insights into the ductility-strength balance in advanced alloys but also proposes a compelling route for optimizing biphasic precipitation, expanding the applicability of high-Cr multicomponent alloys.

The Application of an Electrocoagulation Process to the Sustainable Treatment of Initial Rainwater and the Simulation of a Flow Pattern in an Experimental Device

The pollutant content in initial rainwater is very high, so the treatment and research of initial rainwater has become an engagement issue in controlling non-point source pollution and realizing sustainable development in Chinese cities. This study explores the best flow pattern suitable for treating initial rainwater by electrocoagulation (EC), and a pilot-scale experiment is conducted to analyze the effect of the EC process on the treatment of initial rainwater. The findings indicate that the latter enhances the turbulent flow effect and the EC process treatment effect better under the two flow modes of parallel perforation flow and dislocation perforation flow. For the dislocation perforated flow pattern, the removal rates of suspended matter (SS), chemical oxygen demand (COD), and phosphorus (TP) are 94.00%, 81.95%, and 98.97%, respectively, which reach the expected treatment targets. Using the electrocoagulation–filtration (ECF) process to treat initial rainwater, the final effluent exhibits high quality and could be used as urban circulating cooling water. Specifically, SS, COD, and TP concentrations are 15.00 mg/L, 21.06 mg/L, and 0.11 mg/L, respectively. The hydraulic retention time of the process is short, only 30 min, and the energy consumption is low, 0.57 kWh. This study provides a reference for the sustainable treatment of early urban rainwater and the design of the flow pattern of the EC process.

Combined Screw and Wedge Dislocations

Elastic media with defects are considered manifold with nontrivial Riemann–Cartan geometry in the geometric theory of defects. We obtain the solution of three-dimensional Euclidean general relativity equations with an arbitrary number of linear parallel sources. It describes elastic media with parallel combined wedge and screw dislocations.

Alumina precipitate along dislocations in rutile single crystal of diffusion couple during cooling from 1200° to 1400°C

Diffusion couples of rutile and corundum single crystals were prepared and examined for the solid solution and precipitation of corundum in rutile during cooling. Alumina dissolves in rutile according to the following equation, Al2O3→2AlTi′+3OO+VO∙∙. In the sample air-quenched from 1200 °C, the supersaturated oxide ion vacancies, VO⋅⋅, reacted with the edge component of screw dislocation parallel to c axis to form helical dislocations, along which corundum was precipitated. When air-quenched from 1300 °C and 1400 °C, corundum was precipitated in the form of stacked rectangular loops. Corundum grains with eight lobes extending in the < 101 > directions were precipitated in the samples cooled at 10 °C/min from 1300 °C and 1400 °C. The solid solution reaction increased the volume of rutile single crystals and caused voids outside the reaction region at the interface. Both the corundum and rutile components of the voids also contributed to the solid solution reaction.

An ultrahigh strain-independent damping capacity in Mg–1Mn alloy by cold rolling process

An ultrahigh strain-independent damping in Mg–1Mn alloy was prepared by cold rolling process. Combined with microstructure characterization, the mechanical properties and damping capacities of Mg–1Mn alloy with different reduction were systematically investigated. By the appropriate cold rolling process, numerous parallel dislocations, stacking faults (SFs) and a few non-basal <c> dislocations are introduced into Mg matrix. Due to the non-basal <c> dislocations and stacking faults coexists with basal <a> dislocations, their reaction with each other leads to the activation of more non-basal slips and increase of strain hardening rate, which simultaneously improves the strength and plasticity of Mg–1Mn alloy. On the other hand, the increase of number of moveable dislocations and SFs, acting as dissipated source, effectively improves the damping capacity. Especially, the Mg–1Mn alloy shows an ultrahigh strain-independent damping capacity, which outperforms the high-damping Mg-0.6Zr alloy. When the reduction is 20%, the alloys show a good comprehensive mechanical properties: the ultimate tensile strength (UTS), the yield strength (YS) and plasticity is 206 MPa, 156 MPa and 49.8%. This work provides a new strategy for preparing high-strength, high-plasticity and high-damping magnesium alloy.

High-entropy alloy nanocrystals with low-angle grain boundary for superb plastic deformability and recoverability

High entropy alloys (HEAs) have received widespread attention as structural and functional materials owing to their large atomic lattice distortion and vast compositional space. Recently, nanoscale HEAs have been proven to exhibit exceptional combinations of mechanical properties, thermal stability, and oxidation resistance. The structural and functional stabilities of nanoscale HEAs under practical loading conditions are vital to their applications. Here, based on a grain boundary (GB) design strategy, we introduced custom-designed low-angle GBs (LAGBs) into quinary face-centered cubic HEA nanocrystals, intending to improve the mechanical stability of nanoscale HEAs under external loading through molecular dynamics simulations. Using CuCoNiPdFe and FeNiCrCoCu HEAs as examples, we reveal two distinct LAGB-mediated deformation behaviors of nanoscale HEAs, which stem from the differences in lattice distortion and shear modulus of the materials. In the case of CuCoNiPdFe, the LAGB is composed of separate Shockley dislocations, endowing the material with extraordinary plastic deformability and structural stability. In the case of FeNiCrCoCu, the LAGB contains a series of parallel stacking faults cross-linked immobile dislocation segments, which severely damages the plastic deformability of the material. Based on the atomistic understanding of LAGB structure and migration behavior, we have screened out a range of material systems with small lattice distortion and shear modulus, realizing superb plastic deformability and structural recoverability in HEAs designed with LAGBs. These findings promote the understanding of GB-mediated deformation mechanisms in HEAs and provide insights into the structural and composition design of HEA nanomaterials.

Simultaneous improvement of strength and damping capacity of Mg-Mn alloy by tailoring bimodal grain structure

A high damping capacity and a high strength is paradox in magnesium alloys needed to be addressed immediately. In this work, adding Mn into Mg matrix, and combined with low extruded temperature, alloys with bimodal grain structure that is made up of fine recrystallized grains and coarse unrecrystallized grains were obtained. The fine recrystallized grains are conducive to the activation of grain boundary slip, leading to alloy exhibits good plasticity. A large number of parallel dislocations exist in unrecrystallized grains, due to the dislocation recovery and dynamic recrystallization rate are evidently suppressed at low extruded temperature and the Mn precipitates impede the movement of dislocations, which cause a high work hardening rate in bimodal grain structure. This phenomenon not only brings about a high yield strength, but also improves damping capacity of Mg-Mn alloys at room temperature. Because the unrecrystallized grains initial to recrystallize at high temperature, the P2 internal friction peak rises and moves toward the low temperature. When the extruded temperature is 220 °C, the comprehensive properties of the Mg-1Mn alloy outperform the high-damping Mg-0.6Zr alloy, and the yield strength, plasticity and damping capacity at ε = 1 × 10−3 are 169 MPa, 32.5% and 0.042, respectively. Tailoring bimodal grain structure is an effective strategy to ensure strength, plasticity and damping capacity of the Mg alloy at the same time.

Director anchoring on a simple edge dislocation at the surface of induced smectic-C_{A} films.

We present a detailed analysis of c-director anchoring measurements on simple edge dislocations at the surface of smectic-C_{A} films (steps). Indications show that the c-director anchoring on the dislocations originates from a local and partial melting of the dislocation core that depends on the anchoring angle. The SmC_{A} films are induced on isotropic puddles of 1-(methyl)-heptyl-terephthalylidene-bis-amino cinnamate molecules by the surface field, while the dislocations are located at the isotropic-smectic interface. The experimental setup is based on the connection of a three-dimensional smectic film sandwiched between a one-dimensional edge dislocation on its lower surface, and a two-dimensional surface polarization spread over the upper surface. Applying an electric field produces a torque that balances the anchoring torque of the dislocation. The film distortion that results is measured under a polarizing microscope. Exact calculations on these data, anchoring torque versus director angle, yield the anchoring properties of the dislocation. A specificity of our sandwich configuration is to improve the measurement quality by a factor of N^{3/2}∼600, where N=72 is the number of smectic layers in the film. We fit a second-order Fourier series on the torque-anchoring angle data, which has the advantage of converging uniformly over the entire anchoring angle range, i.e., over more than 70^{∘}. The two corresponding Fourier coefficients, k_{a1}^{F2} and k_{a2}^{F2}, are anchoring parameters that generalize the usual anchoring coefficient. When changing the electric field E, the anchoring state evolves along paths in a torque-anchoring angle diagram. Two cases occur depending on the angle α_{∞} of E relative to the unit vector S, perpendicular to the dislocation and parallel to the film. When α_{∞}<130^{∘}, the operating point Q that represents the anchoring state in the diagram follows reversible and "at-equilibrium" paths. Its free displacement velocity is infinitely slow, so that we have to push it with electric torque steps smaller than the experimental error bar δΓ∼10^{-14}N. On the other hand, for α_{∞}>130^{∘}, Q describes a hysteresis loop similar to the usually encountered ones in solids. This loop connects two states that exhibit broken and nonbroken anchorings, respectively. The paths that join them in an out-of-equilibrium process are irreversible and dissipative. When coming back to a nonbroken anchoring state, both the dislocation and smectic film spontaneously heal back in the very same state they were before the anchoring broke. The process does not produce any erosion thanks to their liquid nature, including at the microscopic scale. The energy that is dissipated on these paths is roughly estimated in terms of the c-director rotational viscosity. Similarly, we can evaluate the maximum time of flight along the dissipative paths to be of the order of a few seconds, which is consistent with qualitative observations. In contrast, the paths located inside each domain of these anchoring states are reversible and can be followed in an "at equilibrium" manner all along. This analysis should provide a basis for understanding the structure of multiple edge dislocations in terms of parallel simple edge dislocations interacting with each other through pseudo-Casimir forces arising from c-director thermodynamic fluctuations between them.

Statistical properties of fractal type dislocation cell structures

The dislocation microstructure developing during plastic deformation strongly influences the stress-strain properties of crystalline materials. Resent theoretical investigations based on the 2D continuum theory of straight parallel edge dislocations were able to predict a periodic dislocation microstructure. The results obtained, however, can only be considered as a very first step toward the understanding of the origin of dislocation patterning. One of the most challenging problems is the modeling of the formation of the fractal like dislocation microstructure. So, it is crucial to determine the statistical properties of such a structure developing at ideal multiple slip orientation. In the paper, by x-ray line profile analysis and the method of high resolution electron backscatter diffraction (HR-EBSD) a complex experimental characterization of dislocation microstructure developing in uniaxially compressed Cu single crystals is presented. With these methods, the maps of the internal stress, the Nye tensor, and the geometrically necessary dislocation (GND) density were determined at different load levels. It is found from the fractal analysis of the GND maps that the fractal dimension of the cell structure is decreasing with increasing average spatial dislocation density fluctuation. Moreover, it is shown that the evolution of different types of dislocations can be successfully monitored with the HR-EBSD-based technique.

Influence of dislocations on ionic conductivity and dendrite formation in solid electrolytes

In order to study the recently proposed strategy to tailor the electrical property of ceramics by the introduction of dislocations, numerical calculations are performed on the influence of parallel straight dislocations on ionic conductivity and dendrite formation in single-crystal solid electrolytes. If the diameter of a dislocation pipe is more than √2 times larger than the distance between neighboring dislocations, the ionic current density is nearly uniform on the electrode and the dendrite formation would be avoided. Furthermore, under the condition, the mean ionic conductivity is higher than that without dislocations by several orders of magnitude. It may be practically possible to increase the ionic conductivity by several orders of magnitude without dendrite formation by introducing appropriate dislocations because the required dislocation density in the order of 1017 m−2 has already been reported experimentally although the reports were not for metal oxides.

Microstructure and Mechanical Properties of Biomedical Ti-Zr-Nb-Ta-Sn High-Entropy Alloys

Ti(50-x)Zr38NbxTa8Sn4 high-entropy alloys with x = 0, 10, and 20 at.% were produced by vacuum arc melting in a high-purity argon atmosphere. The initial microstructures consisted of equiaxial bcc grains with sizes of 115 ± 30 µm, 250 ± 60 µm, and 280 ± 70 µm for the Ti30Nb20, Ti40Nb10, and Ti50Nb0 alloys, respectively. The Ti30Nb20 and Ti40Nb10 alloys showed untypical mechanical behavior with a short strain-hardening stage followed by a gradual decrease in flow stress after reaching the yield point. Although these two alloys had some inclination toward macroscopic strain localization, their tensile elongation was similar to that obtained in the Ti50Nb0 alloy, which had a more extended stage of uniform deformation. The differences were associated with distinct microstructures observed after deformation to fracture. The formation of dislocation bands and the activation of cross-slip at the microscale, as well as the appearance of kink bands at the mesoscale, can result in plastic instability. In contrast, a lamellar-like microstructure with parallel dislocation bands, such as the one observed in the Ti50Nb0 alloy, can ensure a more stable mechanical behavior. The developed alloys (Ti30Nb20 and Ti40Nb10) have properties that make them highly attractive for biomedical application due to a combination of very high yield strengths (1090 and 930 MPa, respectively), low Young’s moduli (~78 and ~69 GPa, respectively), reasonable ductility, and excellent biocompatibility.

Ultrasonic constitutive model and its application in ultrasonic vibration-assisted milling Ti3Al intermetallics

Ultrasonic vibration-assisted technology is widely utilized in the performance research and manufacturing process of metallic materials owing to its advantages of introducing high-frequency acoustic systems. However, the acoustic plasticity constitutive model and potential mechanism, involving Ti3Al intermetallic compounds, have not yet been clarified. Therefore, the Ultrasonic-K-M hybrid acoustic constitutive model of Ti3Al was established by considering the stress superposition, acoustic thermal softening, acoustic softening and acoustic residual hardening effects according to the dislocation density evolution theory and crystal plasticity theory. Meanwhile, the mechanical behavior of ultrasonic vibration-assisted tension (UVAT) and microstructure of ultrasonic vibration-assisted milling (UVAM) for Ti3Al was investigated. Dislocation density to be overcome from initial deformation to failure of Ti3Al was calculated in UVAT and was verified in UVAM. The results indicated that the Ultrasonic-K-M model showed a good agreement with the experimental data. There was an obviously softening phenomenon after introducing the ultrasonic energy field in the Ti3Al whole deformation region, and the degree of softening was positively correlated with amplitude. Furthermore, the maximum reduction ratio in yield strength of Ti3Al was 16 % and the maximum reduction value in ultimate tensile strength was 206.91 MPa. The elongation rose first and then fell as amplitude enlarged, but only as the vibration was applied in the whole deformation region, the elongation was always greater than 14.58 %. In addition, The UVAM process significantly reduced the dislocation density increment to be overcome for Ti3Al material removal by 1.37 times, and promoted dislocation motion and cancellation to make twisted dislocations evolve into parallel dislocations. As the amplitude increased to 4 μm, the depth of the disturbed area of the plastic deformation layer increased by a maximum of 2.5 times.

Exploring low cycle fatigue anisotropy and the failure mechanism of the DD412 single crystal alloy for aeroengines

In this paper, the low cycle fatigue properties of the DD412 single crystal alloy with [001], [011] and [111] orientation at 760℃ were studied. A correlation between low cycle fatigue properties and orientation was found, and the microstructure evolution and fatigue failure mechanism were studied, which lays a solid theoretical foundation for the engineering application of the DD412 single crystal alloy. The fatigue testing was uniaxial. The experimental results show that the low cycle fatigue properties of the DD412 alloy with different orientations have significant anisotropy at 760℃. The single crystal alloy with a [001] orientation parallel to the loading axis exhibited the longest fatigue life at high strains, and the alloy with [111] orientation exhibited the shortest fatigue life at high strains, while the alloy with [011] orientation was located between these two durations, which is mainly related to the difference of elastic modulus. For the alloy with [001] orientation, elastic deformation is the main fatigue damage mechanism, and cleavage-like fracture occurs along a specific crystallographic plane. For the alloy with [011] orientation, under high strain amplitude, the fatigue fracture is caused by the joint action of plastic deformation and elastic deformation, and cleavage tear mixed fracture occurs. For the alloy with [111] orientation, under high strain amplitude, plastic deformation is the main fatigue damage mechanism. The dislocation configurations of the DD412 alloy with different orientations after low cycle fatigue at 760℃ are different. The main observation in the alloy with [001] orientation is the dislocations cross-slip in the γ channel to form serrated dislocations; while in the alloy with [011] orientation, there are a large number of dislocations entangled in the γ channel; and in the alloy with [111] orientation, there are two high density parallel dislocation bands in the γ channel.

Gradient microstructure response in different phases of Ti2AlNb alloy with laser shock peening

Ti2AlNb alloy is a new type of lightweight and heat-resistant structural material that has been an active research topic with multi-phases due to its improved mechanical properties. However, the phase response under severe plastic deformation (SPD) at high strain rates is unclear, which limits the understanding of its strengthening mechanism. Here, laser shock peening (LSP) was employed to investigate the microstructure response of α2, O, and B2/β phases in Ti2AlNb alloy. After LSP, the highest density dislocations were generated in the B2/β phases, followed by the O phases, and the least dislocations were observed in the α2 phases. In the B2/β phases, only dislocation tangles (DTs) were observed. Dislocation lines (DLs) and DTs were mainly distributed in the O phases. As for the α2 phases, DLs were generated while a small number of DTs were piled up at the grain boundaries. In addition, parallel dislocations (PDs) with a spacing of about 135 nm can be observed on the surface of the α2 phases, and the dislocations interspersed between PDs were composed of screw dislocations with long segments. In addition to dislocation structures, stacking faults (SFs) were observed in both α2 phases and O phases, and mechanical twins were formed in the O phases, which were generated to coordinate the SPD induced on the surface. These dislocation structures formed dislocation cells (DCs) and sub-grain boundaries which further developed into high-angle grain boundaries (HAGBs) together with mechanical twins, dividing the coarse grains and refining the microstructure. As the depth increased, the responses of the three kinds of phases decreased. The PDs in the α2 phases have widened spacing and could not penetrate the grains. The mechanical twins were gradually reduced until no obvious twin structure could be observed. Finally, dislocations, grain size, microhardness, and residual stress presented a gradient distribution. The improved microhardness (maximum 470 HV) and compressive residual stress (maximum −600 MPa) which were consistent with the refined grains and high-density dislocations gradually decreased to that of the base metal (BM).

Effect and Mechanism of Solidified Microstructure on Deformation Behavior, Mechanical Properties, and Residual Stress of Cu-Ni-Si Alloy.

Cu-Ni-Si alloy is the key raw material for the lead frame of large integrated circuits. The disordered grain orientation of alloy billet, high hardening rate, residual stress, and poor surface quality of cold working strips seriously affect its processability. In order to improve the cold-working properties of Cu-Ni-Si alloy, two kinds of C70250 copper alloy strips were produced through hot mold continuous casting (HMCC) and cold mold continuous casting (CMCC) technology. The effects of solidified microstructure on the cold-working deformation behavior, mechanical properties, and residual stress of the alloy were studied. The results show that C70250 copper alloys with columnar grain and equiaxed grain were prepared through HMCC and CMCC. After a 98% reduction in cold rolling, columnar grain strip surface quality was very good, and the elongation was still as high as 3.2%, which is 2.9 times that of equiaxed grain alloy. The residual stress of equiaxed grain strips reached 363 MPa, which is 2.7 times that of columnar grain strips. During the cold rolling process, equiaxed grain strips are prone to cause intersecting plane dislocations, stacking faults, shear bands, and grain breakage during large deformation cold rolling. The columnar grain strip causes parallel plane dislocations, stacking faults, and shearbands. Furthermore, the deformation structure was found to be uniform, and, ultimately, the alloy formed a fibrous structure. Therefore, the elongation and latter distortion of columnar grain strips improved after being put through large deformation cold rolling, which greatly reduced residual stress.

Large-Scale Defect Clusters with Hexagonal Honeycomb-like Arrangement in Ammonothermal GaN Crystals

In this paper, we investigate, using X-ray Bragg diffraction imaging and defect selective etching, a new type of extended defect that occurs in ammonothermally grown gallium nitride (GaN) single crystals. This hexagonal “honeycomb” shaped defect is composed of bundles of parallel threading edge dislocations located in the corners of the hexagon. The observed size of the honeycomb ranges from 0.05 mm to 2 mm and is clearly correlated with the number of dislocations located in each of the hexagon’s corners: typically ~5 to 200, respectively. These dislocations are either grouped in areas that exhibit “diameters” of 100–250 µm, or they show up as straight long chain alignments of the same size that behave like limited subgrain boundaries. The lattice distortions associated with these hexagonally arranged dislocation bundles are extensively measured on one of these honeycombs using rocking curve imaging, and the ensemble of the results is discussed with the aim of providing clues about the origin of these “honeycombs”.

Dislocation singularities in layered magneto-electro-elastic plates

A general and unified theory is formulated to investigate static and time-harmonic field solutions induced by dislocation loops and dislocation arrays in three-dimensional multilayered structures. Each homogeneous plate consists of an orthotropic magneto-electro-elastic material including nonlocal effects. While the nonlocal constitutive relations with multi-phase coupling are treated by means of the original Eringen model using a Helmholtz-type operator, the field expressions are based on the mathematically elegant and computationally powerful Stroh formalism in matrix form, consistently combined with double Fourier series expansions and the dual variable and position technique to propagate the extended solutions among the different layers of the multilayered systems. The time-harmonic dislocation loops are represented by a discontinuity in the prescribed elastic displacement, electric potential, and magnetic potential on arbitrarily-located rectangular and elliptical surfaces in the multilayered structures, while the dislocation arrays are composed of infinitely long, straight and uniformly spaced parallel dislocations with the same local Burgers vectors. The new field solutions are first validated against existing frameworks limited to static and local elasticity theory of these two types of extrinsic and intrinsic dislocations, and subsequently applied to analyze several unexplored effects on the dislocation-induced magneto-electro-elastic fields, namely the material anisotropy, interaction with internal heterophase interfaces, multi-phase coupling, nonlocal core-spreading parameter, finite-valued driving forces, vibration frequency, and stacking sequences. The numerical outcomes indicate that each effect is significant and neglecting any one of them leads to an erroneous prediction on the extrinsic and intrinsic dislocation-induced response, thus providing a suitable route for the design of advanced magneto-electro-elastic fabrication devices for energy harvesting applications.

Microstructure evolution and mechanical properties of wrought/wire arc additive manufactured Ti-6Al-4V joints by electron beam welding

Wrought-additive hybrid manufacturing technology effectively combines the advantages of high efficiency of traditional manufacturing and high flexibility of additive manufacturing technology. Mechanical Properties of welded joints is the key to evaluate the performance of parts. In this study, the wire and arc additive manufacturing (WAAM) Ti-6Al-4V alloy was successfully connected with the wrought Ti-6Al-4V plate by electron beam welding (EBW). The effect of welding direction on microstructure and tensile properties of welded joints was studied. The results show that a large amount of needle martensite α’ phases exists in the joint due to the rapid cooling rate. The mechanical properties tests show that compared with the Wrought + SD (Scanning direction) sample, the Wrought + BD (Building direction) sample has higher tensile strength, but lower elongation. All samples fractured at the WAAMed Ti-6Al-4V side, which was related to the initial state of the WAAMed Ti-6Al-4V sample. The experiment also explored the fracture mechanism by TEM, which involved the nucleation, growth of cracks caused by vertical dislocation accumulation at the α/α’ phase interface, and occurrence of the displacement of the α (or α’)/β phase interface caused by the parallel dislocations.