Dislocation Energy Research Articles

Subsurface hardening of Al irradiated with ultrafast infrared laser

The effect of femtosecond laser shock peening on a model Al-0.3Mn alloy was investigated experimentally and numerically by molecular dynamics. Micro-diffraction experiments performed at synchrotron source revealed the depth profiles of the residual stress and the stored energy of dislocations, a measure of local plasticity. The depth of the maximum compressive stress did not coincide with that of the maximum dislocation energy, which was found at the surface. The interaction between the laser and the metal was simulated with LAMMPS using a two-temperature molecular dynamics package. The model accurately described the equation of state of aluminum and showed nearly equal resolved shear stresses on all slip systems at the wavefront. The dislocation density at a depth of 1 μm, predicted by the Meyers' model [1], was higher than the experimental data, suggesting possible recovery due to the increased temperature of the sample after repeated shock loading.

Fatigue reliability analysis methodology based on fatigue life and failure mechanism for carburized gear

Gears are one of the important components in mechanical products, and their fatigue reliability determines the safety performance of mechanical products. In this paper, the fatigue characteristics of carburized gears under different torque and constant rotational speed conditions are investigated by using a gear contact fatigue testing machine, and combined with the dynamic maximum contact stress distribution on the subsurface of the meshing gears, the very-high cycle fatigue P-S-N curves of carburized gears under a stress ratio of −1 is established. Local stress concentration in the surface or subsurface of carburized gears causes grain dislocation movement under the combined influence of maximum contact and residual stresses, and then causes dislocation pileup and transcrystalline rupture after being hindered by grain boundaries, ultimately leading to pitting and fatigue failure of gears. Based on the dislocation energy method and combined with the fatigue failure mechanism of gears, a life prediction model of gears with good prediction results is established by considering the interaction of factors such as dynamic load, grain size, initial crack length, residual stress, slip band length and width. A fatigue reliability analysis method of gears is established based on the life state equation of gears considering the life prediction model. Further analyses of the influence of rotational speed, grain size, residual stress, slip band width, slip band length and initial crack size on the fatigue life reliability index of the gears resulted in the conclusion that the fatigue reliability of the gears not only decreases with the increase of the above-mentioned parameters, but also shows decreasing trend with the increase of time. This is of significance for evaluating the fatigue reliability of gears under very-high cycle fatigue conditions.

Microstructure control and DRX characteristics of Ni–Co–W superalloys affected by changing deformation direction on [001] columnar grain

Controlling the evolution process of columnar grains is benefits to achieve microstructure regulation during subsequent hot processing in superalloys. In present research, it takes a Ni–Co–W superalloy as an example, aims to clarify the underlying connections between the compression direction and dynamic recrystallization (DRX) behaviors in microstructure evolution. The compression direction (CD) was parallel or perpendicular to [001] columnar has been defined as CD∥[001] and CD⊥[001], respectively. The columnar evolution and DRX characteristics under two sets of experimental during hot deformation were identified deeply. The results show that complete DRX is more easily to occur when CD⊥[001], but fine DRX grains are tendency to form when CD∥[001]. DRX nucleation within CD∥[001] and CD⊥[001] deformed microstructure under dislocation energy was discussed deeply. The critical size of nucleation is decreased while the nucleation density is increased in CD∥[001] with high dislocation density, which benefits to form numerous fine DRX grains along the original columnar boundaries. In addition, according to Taylor factors (TFs) criterion, TFs difference will always existed in CD∥[001], which promotes the necklace structure gradually replaced columnar structure and some of them developed into fine DRX bands. With increasing of trues strain, TFs difference gradually decreased in CD⊥[001], DRX nucleation was inhibited, thus the existed DRX grains further grow and finally coarse DRX grains were obtained. The findings clarified the flow behaviors and DRX characteristics of [001] columnar in two directions, and then proposed a microstructure control mechanism of superalloys with [001] columnar based on deformation vector and evolution decomposition.

Electron Concept of Hydrogen Embrittlement and Hydrogen-Increased Plasticity of Metals

Based on theoretical and experimental studies of hydrogen effect on the electron structure of iron, nickel and titanium, an electron concept is proposed for hydrogen embrittlement as well as for hydrogen-improved plasticity of engineering metallic materials. This concept implies a hydrogen-caused redistribution of valence electrons across their energy levels and an increase in the density of electron states at the Fermi level, causing a softening of the crystal lattice and, thereby, leading to a decrease in the specific energy of dislocations with consequent increase in their mobility. Innate phenomena in metallic solid solutions, namely, short-range atomic order in its two versions, short-range ordering and decomposition, are shown to be a precondition for the localization of plastic deformation. Hydrogen enhances merely this effect resulting in pseudo-brittle fracture. The role of hydrogen-induced superabundant vacancies in hydrogen-caused localization of plastic deformation and grain-boundary fracture in pure metals is discussed. Using the temperature- and strain-dependent internal friction, the enthalpies of hydrogen diffusion and hydrogen–dislocation binding are studied, and their controlling effect on the temperature- and strain-rate-dependent hydrogen embrittlement is demonstrated. Finally, a physical rationale is proposed for using hydrogen as a temporary alloying element in the technological processing of titanium alloys, and for a positive hydrogen effect on the fatigue life and plasticity of austenitic steels.

Ultrafast fabrication of porous NF/Ni for water splitting in alkaline media

In this study, a rapid hydrogen-bubble template electrodeposition method was employed to synthesize a dual-functional catalyst (NF/Ni) for alkaline water splitting. Physical characterization revealed that a coarsened NF/Ni with a porous structure was obtained, providing an enlarged surface area. In addition, it revealed that the CV activation is beneficial to the formation of Ni-Ni(OH)2 coupling interface, which is responsible for reducing of water dislocation energy barrier and providing a balanced H adsorption energy on the Ni site. Consequently, the overpotential of oxygen/hydrogen evolution reaction at 10 mA cm−2 is 290 and 71 mV. In-situ Raman spectroscopies confirm that the generated NiOOH serves as the active center for OER process. When assembled to a two-electrode cell, it showed a cell voltage of 1.62 V@10 mA cm−2, which was 160 mV lower than that of NF‖NF. Furthermore, the university study confirms the formation of hydroxide on the surface of the metal is beneficial to boosting the hydrogen evolution activity.

Influence of magnetic field on the mechanical behavior of friction stir processed paramagnetic alloy

The study investigated the influence of an externally applied static magnetic field (MF) on the mechanical behavior of a friction stir processed paramagnetic 1100 aluminum (Al 1100) alloy. The aim was to take advantage of the solid-state friction stir processing (FSP) technique to modify the microstructure and further improve the properties by testing in the presence of MF. Al 1100 was tested in tension under different static MFs (B = 0, 150, 1000, 1400, 1800, and 2200 Gauss) perpendicular to the stress axis. The strong effect of a comparatively weak static MF was observed on the elongation of both base and processed Al 1100 alloy, in both rolling and transverse directions, attributed to the magneto-plasticity effect (MPE) where the motion of dislocations in crystals is influenced in the presence of magnetic fields. Amongst the different mechanisms associated with MPE, the major effect in the current study was observed from the magnetization force, spin transition, and increase in strain energy of dislocations. This knowledge will open new lanes to improve the properties of a processed sample by exposing it to an MF which is a non-contact, pollution-free route; saving time and cost by avoiding in-between thermo-mechanical steps to break the cast microstructure.

Propagation behaviour of threading screw dislocations during 4H-SiC crystal growth using a hybrid method combined with solution growth and physical vapour transport growth on high-off-angle seeds

The propagation behaviour of threading screw dislocations (TSDs) during 4H-SiC crystal growth using high-off-angle seeds was investigated. By studying the conversion ratio of TSD to basal plane defects during physical vapour transport (PVT) growth and hybrid growth (combination of solution growth and PVT growth) on various off-angle seeds, we suggest an energy diagram showing the off-angle dependence of the dislocation energy which explains the activation barrier of dislocation conversion.

Strengthening Mechanism and Damping Properties of SiCf/Al-Mg Composites Prepared by Combining Colloidal Dispersion with a Squeeze Melt Infiltration Process.

SiC-fiber-reinforced Al-Mg matrix composites with different mass fractions of Mg were fabricated by combining colloidal dispersion with a squeeze melt infiltration process. The microstructure, mechanical and damping properties, and the corresponding mechanisms were investigated. Microstructure analyses found that SiCf/Al-Mg composites presented a homogeneous distribution of SiC fibers, and the relative density was higher than 97% when the mass fraction of Mg was less than 20%; the fiber-matrix interface bonded well, and no obvious reaction occurred at the interface. The SiCf/Al-10Mg composite exhibited the best flexural strength (372 MPa) and elastic modulus (161.7 GPa). The fracture strain of the composites decreased with an increase in the mass fraction of Mg. This could be attributed to the strengthened interfacial bonding due to the introduction of Mg. The damping capacity at RT increased dramatically with an increase in the strain when the strain amplitude was higher than 0.001%, which was better than the alloys with similar composition, demonstrating a positive effect of the SiC fiber on improving the damping capacity of composite; the damping capacity at a temperature beyond 200 °C indicated a monotonic increase tendency with the testing temperature. This could be attributed to the second phase, which formed more strong pinning points and increased the dislocation energy needed to break away from the strong pinning points.

Korn–Maxwell–Sobolev inequalities for general incompatibilities

We establish a family of coercive Korn-type inequalities for generalized incompatible fields in the superlinear growth regime under sharp criteria. This extends and unifies several previously known inequalities that are pivotal to the existence theory for a multitude of models in continuum mechanics in an optimal way. Different from our preceding work [F. Gmeineder, P. Lewintan and P. Neff, Optimal incompatible Korn–Maxwell–Sobolev inequalities in all dimensions, Calc. Var. PDE 62 (2023) 182], where we focused on the case [Formula: see text] and incompatibilities governed by the matrix curl, the case [Formula: see text] considered in this paper gives us access to substantially stronger results from harmonic analysis but conversely deals with more general incompatibilities. Especially, we obtain sharp generalizations of recently proved inequalities by P. Lewintan, S. Müller and P. Neff [Korn inequalities for incompatible tensor fields in three space dimensions with conformally invariant dislocation energy, Calc. Var. PDE 60 (2021) 150] in the realm of incompatible Korn-type inequalities with conformally invariant dislocation energy. However, being applicable to higher-order scenarios as well, our approach equally gives the first and sharp inequalities involving Kröner’s incompability tensor inc.

The mechanism of ferroelectric phase transformation in Gd2O3 modified BCZT ceramics: Experimental studies and first-principles calculations

Lead-free (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 (BCZT)-based piezoelectric ceramics have attracted considerable interest due to their excellent piezoelectric properties and abundant phase structures. However, there is a serious lack in the theoretical calculations for the ferroelectric phase transition behavior. Here, the experimental and first-principles calculations were utilized to analyze the ferroelectric phase transition process of (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3-xGd2O3(BCZT-xGd, x = 0, 0.02, 0.04, and 0.05) ceramics. The incorporation of Gd2O3 has induced a transformation from tetragonal to rhombohedral phase due to the decrease in the dislocation energy with A-site cations and the attenuation of the bonding energy between B-site cations and the planar O atoms. Moreover, the hybridization between the d orbitals of B-site atoms and the O 2p orbitals, coupled with the reduction of the polarization vector along the [001] axis, leads to enhanced weak coupling relaxation. This work provides a theoretical basis for the ferroelectric phase transition behavior of other piezoelectric systems.

Fracture mechanism of Zr2Si precipitate equilibrated in a solution-treated Si-modified Zircaloy-4

Secondary phase precipitates are vital to control corrosion, mechanical and irradiation response of multi-phase metallic alloys. As a model system, this work analysed hcp-Zr to fcc-Zr transformation-induced failure in a C16 type body-centred tetragonal Zr2Si binary precipitate using transmission electron microscopy and related techniques. The configurations of two types of dislocations, 〈001〉 {110} and 〈110〉 {001}, were approximated which interlocked along the major axis of Zr2Si precipitate constituting the sessile junctions. Threading dislocations resisted further glide, and failure occurred along the minor axis. Peierls stress and dislocation energy were estimated for the most favourable <001> {110} slip system and, in turn, probability of dislocation climb in Zr2Si precipitate was evaluated as a high temperature phenomenon, also evidenced by a prismatic dislocation loop along (11¯0) plane.

Quantitative analysis of microstructure evolution, stress partitioning and thermodynamics in the dynamic transformation of Fe-14Ni alloy

Dynamic transformation (DT) of austenite (γ) to ferrite (α) in the hot deformation of various carbon steels was widely investigated. However, the nature of DT remains unclear due to the lack of quantitative analysis of stress partitioning between two phases and the uncertainty of local distribution of substitutional elements at the interface in multi-component carbon steels used in the previous studies. Therefore, in the present study, a binary Fe-Ni alloy with α + γ duplex microstructure in equilibrium was prepared and isothermally compressed in α + γ two-phase region to achieve a quantitative analysis of microstructure evolution, stress partitioning, and thermodynamics during DT. γ to α DT during isothermal compression and α to γ reverse transformation on isothermal annealing under unloaded condition after deformation were accompanied by Ni partitioning. The lattice strains during thermomechanical processing were obtained via in-situ neutron diffraction measurement, based on which the stress partitioning behavior between γ and α was discussed by using the generalized Hooke's law. A thermodynamic framework for the isothermal deformation in solids was established based on the basic laws of thermodynamics, and it was shown that the total Helmholtz free energy change in the deformable material during the isothermal process should be smaller than the work done to the deformable material. Under the present thermodynamic framework, the microstructure evolution in the isothermal compression of Fe-14Ni alloy was well explained by considering the changes in chemical free energy, plastic and elastic energies, and the work done to the material. In addition, the stabilization of the soft α phase in Fe-14Ni alloy by deformation was rationalized since the γ to α transformation decreased the total Helmholtz free energy by decreasing the elastic and dislocation energies.

An electroplastic constitutive model of fcc metals and their alloys under high current density

The mechanical behavior of fcc (face center cubic) metals and their alloys such as copper-based and aluminum-based materials changes obviously under high current density, but there is a lack of suitable constitutive model to describe the electroplastic behavior of these materials, which limits the accuracy of the mechanical response prediction in applications, such as electromagnetic launch. In this paper, a novel nonlinear constitutive model for electroplastic behavior under the high current density of fcc metals and their alloys is proposed. The model proposed is based on the theory of dislocation evolution, energy transfer theory and electron transport theory and takes into account the effects of high current density on dislocation density, strain rate and resistivity. Considering the evolution of forward and reverse dislocations caused by pulsed current, the relationship between the evolution rate of reverse dislocation and strain is established. Due to the sensitivity of the electroplastic effect to strain rate, the strain rate under electric current is obtained by combining the theory of dislocation thermal activation and energy transfer. According to the concept of thermal resistance and dislocation resistance, the relationship between resistance and current density is derived. The quantitative results demonstrate that this model can well capture the flow stress softening under high current density (>3000 A/mm2) and the transient hardening after current removal because of the consideration of a more suitable strain rate and dislocation evolution. The critical current density that has a significant effect on the strain rate and the current density corresponding to the subsection point of the resistivity are quantitatively obtained. Especially, it is shown that the evolution rate of the reverse dislocation decreases nonlinearly with the increase of strain after the current is removed. These results will be helpful to study the mechanical behavior of the rail during electromagnetic launch and further optimize the design of electromagnetic launch device.

Grain refinement, strain hardening and fracture in thermomechanically processed ultra-strong microalloyed steel

The current research in microalloyed steel has witnessed a continuous improvement in strength-ductility combination. The intention is to reduce the gauge thickness of automotive body sheets without compromising formability, thereby enhancing fuel efficiency. In this light, the present work has devised a novel thermomechanical controlled processing (TMCP) for a low-carbon automotive-grade (Nb+V)-stabilized microalloyed steel. The microstructural modification by TMCP has resulted in an excellent combination of yield strength (782 MPa), ultimate tensile strength (1059 MPa) and ductility (21%). The critical factor translating the investigated alloy towards advanced high strength steel is the ferrite grain refinement by dynamic recrystallization (DRX) and deformation-induced ferrite transformation (DIFT). The DRX predominated during TMCP at the intercritical temperature domain of 800–700 °C, imparting the average recrystallized grain size of 2 ± 0.8 µm. In contrast, the DIFT starts well above the upper intercritical temperature regime (i.e., around 810 °C), but it contributes less to the ferrite grain refinement. The thermodynamic reason has been analyzed keeping in view the changes in grain boundary energy and dislocation energy. The plastic deformation additionally leads to precipitation of cubic (Nb, V)-rich carbides in ferrite. The incoherency, coarse precipitate size (70–80 nm), and a poor phase fraction (⁓0.5%) are the key factors that the strengthening mechanism is governed by ferrite grain refinement majorly, followed by dislocation and solid solution strengthening. The segregation of Mn, Nb and S leads to MnS-type inclusion formation, which acts as potential sites for crack initiation due to plasticity mismatch with ferrite matrix during the tensile deformation.

Comparing interatomic potentials in calculating basic structural parameters and Peierls stress in tungsten-based random binary alloys

The field of machine learning-based interatomic potentials (ML-IAPs) has seen increasing development in recent years. In this work, we compare three widely used ML-IAPs–the moment tensor potential (MTP), the spectral neighbor analysis potential (SNAP), and the tabulated Gaussian approximation potential (tabGAP)with a conventional non-ML-IAP, the embedded atom method (EAM) potential. We evaluated these potentials on the basis of their accuracy and efficiency in determining basic structural parameters and Peierls stress under equivalent conditions. Three tungsten (W)-based alloys (Mo-W, Nb-W, and Ta-W) are considered, and their lattice parameter, formation energy, elastic tensor, and Peierls stress of edge dislocation are calculated. Compared with DFT results, MTP demonstrates the highest accuracy in predicting the lattice parameter and the best computational efficiency among the three ML-IAPs, while tabGAP accurately predicts two independent elastic constants, C 11 and C 12. Despite being the slowest, SNAP shows the highest accuracy in predicting the third independent elastic constant C 44 and its Peierls stress value is comparable to that based on MTP.

Effect of machining processes on the quenching and tempering surface layer of ultra-high strength steel

The initial characteristics of the surface layer following the quenching and tempering treatment of ultra-high-strength steel play a significant role in determining the subsequent precision machining. This study focus on investigating the influence of machining processes on the quenching and tempering surface layer. The machining processes affect both the oxidation of the quenching and tempering treatment and the development of a distinct preferred grain orientation. Gradual diminishment of surface abrasions leads to the transformation of the needle-like oxidation pattern into a layered oxidation structure. The preferred orientation of the grains prevents the grains from shear sliding, thereby enhancing the Taylor effect. Formation mechanisms of the microhardness and residual stress of the quenching and tempering surface layer induced by machining processes were also discussed and completely revealed. The microhardness is mainly attributed to the dynamic Hall-Petch effect, while plastic strain, dislocation energy storage, and phase transformation contribute to the residual stress changes.

The Effect of Defect Characteristics on Prediction of Fatigue Life of TC4 Titanium Alloy Welded Joints

The size and depth of defects significantly affect fatigue performance; the main purpose of this article is to clarify the effect of stress correction factors caused by defects on the fatigue life of α + β Type titanium alloy welded joints. In order to investigate the fatigue characteristics of α + β Type titanium alloy welded joints, axial constant amplitude loading fatigue tests were performed with a stress ratio of −1. The test results show that the fatigue life continues to increase as the stress amplitude decreases, and the failure modes can be classified into two types: interior failure and surface failure. A fatigue parameter (λ) determined by both defect depth and size was proposed which allowed for a good generalization of the data point distribution in short and long-life regions. The stress correction factor (W) related to the S–N characteristics was constructed by combining the λ and average defect size, and it effectively improved the dispersion of the test data. Continuing, the fatigue life prediction model was established under the condition that the defect type and size can be estimated or detected on the basis of the dislocation energy method. The results indicated that the evaluated values of the new life model associated with W are in good agreement with the test results.

Growth of CdZnTe (2 1 1) epilayers on GaAs by close spaced sublimation as an alternative substrate for HgCdTe growth

Cd0.96Zn0.04Te crystals are perfect substrates for epitaxial growth of HgCdTe films due to good lattice matching, but they are limited by cost factors. To grow a replacement substrate for the subsequent growth of low-cost, high-yield HgCdTe IR materials, CdZnTe epitaxial films have been fabricated by close-spaced sublimation on GaAs substrates, and the effect of substrate temperature on the crystalline quality of CdZnTe films has been investigated. The results of EBSD and TEM indicate that the surface is oriented in (211) and the low temperatures enhance the crystalline quality of the film. The results of dislocation density (average etch pit density ∼3.6 × 105 cm−2) and energy dispersive spectrometer (Zn content ∼5 %) indicate that CdZnTe films with appropriate Zn content and excellent crystal quality can be obtained by the close spaced sublimation method, which is expected to be applied for molecular beam epitaxy growth of HgCdTe films.

Epidemiology and risk factors for premature physeal closure in distal femur fractures.

Premature physeal closure (PPC) is a common and concerning complication to distal femoral fractures as the distal growth plate accounts for 70% of the growth of the femur. The literature is not unanimous in determining the risk factors of PPC, and the epidemiological characterization of these fractures is limited. Our aim was to calculate the population-based incidence and investigate risk factors for PPC in these fractures. In this register-based study, between 2014 and 2021, 70 children with distal femoral physeal fractures presented to our hospital. Demographic data, and fracture- and treatment-related details were collected using the Kids' Fracture Tool. A directed acyclic graph (DAG) was constructed to determine confounding factors used in the risk analysis. Physeal fractures of the distal femur occurred with an annual incidence of 6/105children, and a resulting PPC occurred in 16/70 (23%) with an annual incidence of 1.3/105children. In multivariable analysis, dislocation exceeding 10 mm was a risk factor for PPC (OR 6.3, CI 1.4-22). One-fourth of distal femoral physeal fractures developed PPC. Greater dislocation and higher injury energy were significant risk factors, whereas choice of fracture treatment was not an independent risk factor. All patients with PPC belonged in the age group 11-16 years.

Solute drag-controlled grain growth in magnesium investigated by quasi in-situ orientation mapping and level-set simulations

Critical properties of metallic materials, such as the yield stress, corrosion resistance and ductility depend on the microstructure and its grain size and size distribution. Solute atoms that favorably segregate to grain boundaries produce a pinning atmosphere that exerts a drag pressure on the boundary motion, which strongly affects the grain growth behavior during annealing. In the current work, the characteristics of grain growth in an annealed Mg-1 wt.%Mn-1 wt.%Nd magnesium alloy were investigated by advanced experimental and modeling techniques. Systematic quasi in-situ orientation mappings with a scanning electron microscope were performed to track the evolution of local and global microstructural characteristics as a function of annealing time. Solute segregation at targeted grain boundaries was measured using three-dimensional atom probe tomography. Level-set computer simulations were carried with different setups of driving forces to explore their contribution to the microstructure development with and without solute drag. The results showed that the favorable growth advantage for some grains leading to a transient stage of abnormal grain growth is controlled by several drivers with varying importance at different stages of annealing. For longer annealing times, residual dislocation density gradients between large and smaller grains are no longer important, which leads to microstructure stability due to predominant solute drag. Local fluctuations in residual dislocation energy and solute concentration near grain boundaries cause different boundary segments to migrate at different rates, which affects the average growth rate of large grains and their evolved shape.