Search

The rafting of the microstructure of Ni-based superalloys significantly deteriorates the mechanical properties. According to the plastic rafting model based on the dislocation mechanism, the directional atomic diffusion induced by the interaction between the alloying atom and the interfacial dislocation is critical to the evolution of the rafting microstructure. In the present work, the interactions between the alloying atom and dislocation core in both matrix γ phase and the precipitate γ′ phase are investigated by using a first principles method in combination with the semi-discrete variational Peierls-Nabarro dislocation model. We show that the alloying atoms Al, Cr, Co, Mo, Ru, Ta, W, Re lower the (edge for Cr and Co) dislocation core energy in the γ phase, indicating that the alloying atoms are attractive to the dislocation core. For the γ′ phase, Cr, Mo, Ta, W, Re raise whereas Co and Ru lower the dislocation core energy, i.e., Cr, Mo, Ta, W, Re are repulsive but Co and Ru are attractive to the dislocation core. With the calculated interaction between the alloying atoms and the dislocation core, the influence of these alloying elements on the rafting of the superalloy is discussed.

The phase transition of titanium alloys is sensitive to the heat-treatment procedure, accompanied with the latent heat induced by phase transition. However, the latent heat during phase transition of titanium alloy has not been systematically studied, which may result in the gap between designed and actual temperature of the sample and affect the final mechanical properties. In this work, DSC (differential scanning calorimetry) and first-principles simulate methods were used to study the β → α phase transition process of TB18 (Ti–Al-Mo-V-Cr-Nb-Fe system) metastable β titanium alloy, especially to reveal the influence of the heating rate on latent heat. The ratio of latent heat to endothermic heat of the sample during temperature rising was introduced to interpret the effect of latent heat to actual temperature. The ratio of latent heat to endothermic heat at 1 ℃/min is about 15 to 20 times higher than that at 10 ℃/min. The higher ratio indicates that the latent heat of phase transition has a more significant effect on the temperature, which is related to the temperature range of phase transition and the α volume fraction. Compared with the heating rate of 1 ℃/min, the β → α phase transition takes place at higher temperature and the volume fraction of α is smaller at 10 ℃/min. Meanwhile, there is a precipitation free zone between grain boundary α and intragranular α and the distribution of α lamellae is heterogeneous when the heating rate is 10 ℃/min. Both of the experimental and theoretical results suggest that the latent heat of phase transition is the main cause of the temperature fluctuation during heat-treatment process. This work has guiding significance for microstructure optimization affected by temperature, to achieve the desired mechanical properties.

Determining how to stimulate public employees’ voice behaviors has become a critical issue in both theory and practice. This article draws on the theories of participative management, leadership, role theory, and social identity theory and proposes a moderated mediation model to explore the mechanism by which participative leadership shapes public employees’ voice behaviors. To test this study’s hypotheses, we conduct a three-wave investigation of 739 public tax agency employees in the Yangtze River Delta area of China. The results show that participative leadership significantly predicts employees’ voice behaviors by enhancing their organizational identification. Furthermore, power distance moderates the relationship between participative leadership and organizational identification. These findings advance our understanding of how to motivate employees’ voice behaviors from the perspective of participative leadership in public organizations.

By employing high-throughput first-principles calculations, the segregation capacity of fifteen widely used metallic alloying elements (viz., Be, Mn, Co, Cr, Ni, Al, Mo, W, Mg, Ta, Nb, Sb, Sn, Zr, and Bi) at ∑3 grain boundary in low alloy ferritic steel, as well as their impact on grain boundary stability, interfacial separation work, and other properties, were systematically investigated. The findings reveal that, for alloying atoms Sb, Sn, Bi, Nb, and Zr, whose size is notably larger than that of the matrix Fe atoms, the effect of strain energy minimization in segregation is comparable to that of chemical energy minimization. Furthermore, the impact of strain energy minimization is closely related to the volume of the alloying atoms both at the solid solution sites in the crystal and at the segregation sites at the grain boundary. Thus, the segregation of large alloy atoms on the grain boundaries can be predicted by atomic volume of each segregation site, which can provide valuable insights for the development of new alloys and for grain boundary engineering.

Mechanoluminescence (ML) phosphors have made significant progress in various fields, such as artificial intelligence, the Internet of Things, and biotechnology. However, enhancing their weak ML intensity still remains a challenge. Here, we report a new series of Na1–xMgxNbO3:Pr3+(x= 0.00, 0.10, 0.20, 0.40, 0.60, 0.80, and 1.00 mol %) heterojunction systems, which exhibit significant ML enhancement as compared with either the Pr3+-doped NaNbO3or MgNbO3, and the physical mechanisms behind the ML enhancement have been explored comprehensively from both the experiment and theory points of view. Experimental tests, including thermoluminescence and positron annihilation lifetime measurements, combined with first-principles calculations, consistently indicate that the ML enhancement observed in these newly reported systems is due to the formation of heterojunctions, which plays a crucial role in modulating the defect configuration of the phosphors and facilitating efficient charge transfer. By controlling the Na/Mg ratio in conjunction with Pr3+doping, continuous changes in the band offset and the concentrations of certain types of traps in the forbidden gap are achieved, leading to the optimum conditions in the 8/2 ratio samples. These findings demonstrate a novel type of ML phosphor and provide a theoretical basis for the design of high-performance ML phosphor.

Peierls stress (τp) of face-centered-cubic (FCC) structures from the Peierls-Nabarro (PN) model calculation is extremely sensitive to the input parameters including the shear modulus (μ), Poisson's ratio (ν) and generalized stacking fault energy (GSFE), which makes the model not a very reliable tool for the prediction of τpbecause uncertainties occur inevitably in the theoretical calculation or experimental measurements of these input parameters. In the present work, we scrutinized systematically the sensitivity of τps of the FCC metals to the input parameters within the framework of semi-discrete variational PN (SVPN) model. We showed that τposcillates drastically with varying input parameters. The period of the oscillation is associated with the dependence of the distance between the two partials of the extended dislocation (D) on μ, νand GSFE while the amplitude of the oscillation is modulated by the dependence of the half-width of the partial dislocation (ζ) on these input parameters. Based on the explored origin of the oscillation, a modified SVPN model is proposed to relieve the sensitivity of τpon the input parameters. The Peierls stresses evaluated with the modified SVPN model are in general agreement with the available experimental values for all the FCC metals.

Determining the competition between the {110}⟨111⟩, {112}⟨111⟩ and {123}⟨111⟩ slip systems in body-centered cubic (BCC) metals is important to understand their mechanical properties. In this paper, the unstable stacking fault energy (γus) and Peierls stress (σp) of the three slip systems of a series of BCC metals are calculated in order to evaluate the competition among them. We find that γusof BCC metals is proportional to (B+G)/a2/3, where B, Gand aare the bulk modulus, shear modulus and lattice constant, respectively. The calculations of γuss predict that the {110}⟨111⟩ dislocation slip is prior to the {112}⟨111⟩ and {123}⟨111⟩ slips, however, γusmay not be used to identify the priorities of the latter two slips because γuss of these two slip systems are too close to each other. According to σps, the mobility of dislocations decreases in the sequence of {110}⟨111⟩, {112}⟨111⟩, {123}⟨111⟩ for all the metals considered except for K. Noticeably, it is shown that γusand σpare not monotonically related to each other.

Myosin VI dimer walks toward the minus end of the actin filament with a large and variable step size of 25–36 nm. Two competing models have been put forward to explain this large step size. The Spudich model assumes that the myosin VI dimer associates at a distal tail near the cargo-binding domain, which makes two full-length single α-helix (SAH) domains serve as long legs. In contrast, the Houdusse–Sweeney model assumes that the association occurs in the middle (between residues 913 and 940) of the SAH domain and that the three-helix bundles unfold to ensure the large step size. Their consistency with the observation of stepping motion with a large and variable step size has not been examined in detail. To compare the two proposed models of myosin VI, we computationally characterized the free energy landscape experienced by the leading head during the stepping movement along the actin filament using the elastic network model of two heads and an implicit model of the SAH domains. Our results showed that the Spudich model is more consistent with the 25–36 nm step size than the Houdusse–Sweeney model. The unfolding of the three-helix bundles gives rise to the free energy bias toward a shorter distance between two heads. Besides, the stiffness of the SAH domain is a key factor for giving strong energetic bias toward the longer distance of stepping. Free energy analysis of the stepping motion complements the visual inspection of static structures and enables a deeper understanding of underlying mechanisms of molecular motors.

Acute massive abdominal hemorrhage after radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC) is an infrequent and severe complication. Delayed diagnosis and treatment may be life-threatening. We herein describe a 60-year-old man with a history of postoperative HCC. A new nidus of HCC was found in his right liver lobe after abdominal magnetic resonance imaging and intraoperative angiography. The patient then underwent computed tomography-guided RFA. However, 7 hours after RFA, he suddenly developed dizziness, nausea, abdominal distension, hematuria, a decreased blood pressure, and an increased heart rate. Diagnostic abdominal puncture produced bloody liquid, and angiography demonstrated hemorrhage in the right hepatic artery. Transarterial embolization was performed following the administration of an appropriate amount of tissue emulsion to embolize the source of hemorrhage. Following this treatment, the patient had no further bleeding. Neither the hemorrhage nor the HCC lesions had recurred after 3 months of follow-up.

Microalloying is an effective approach to improve the mechanical properties of γ-TiAl intermetallic compound. Knowledge about the site occupancy of the ternary alloying element in the crystal lattice of γ-TiAl is highly demanded in order to understand the physics underlying the alloying effect. Previous first-principle methods-based thermodynamic models for the determination of the site occupancy were based on the point defect gas approximation with the interaction between the point defects neglected. In the present work, we include the point defect interaction energy in the thermodynamic model, which allows us to predict the site occupancy of the ternary alloying element in γ-TiAl beyond the point defect gas approximation. The model is applied to the γ-TiAl–Nb alloy. We show that, at low temperature, the site occupancy of Nb atoms depends on the composition of the alloy: Nb atoms occupy the Al sublattice for the Ti-rich alloy but occupy Ti sublattice for the Al-rich alloy. The fraction of Nb atoms occupying Al sublattice in the Ti-rich alloy decreases drastically, whereas the fraction of Nb atoms on the Ti sublattice in the Al-rich alloy decreases slightly with increasing temperature. At high temperature, Nb atoms occupy dominantly the Ti sublattice for both the Ti-rich and Al-rich alloys. The interaction between the point defects makes the Ti sublattice more favorable for the Nb atoms to occupy.

Abstract

To determine the effect of an esculetin formulation (at 97.4% purity) on osteoporosis, and to investigate the potential underlying molecular mechanism(s).

This study investigated the expression of lung surfactant proteins (SP-B and SP-C), and regulatory factors [forkhead box A2 (FOXA2) and nitrolyogenic FOXA2 (N-FOXA2)] in the fetal lung of rats with gestational diabetes mellitus (GDM) in order to study the mechanism of pulmonary dysplasia. The rat GDM model was established by using streptozotocin intraperitoneally in the first stage of pregnancy. There were 10 rats in the GDM group, and 10 healthy rats in normal control group without any treatment. Fetal lungs of two groups were taken at day 21 of pregnancy. Blood glucose levels of maternal rats and fetal rats were measured by Roche blood glucose meter. The histological changes in the fetal lung were observed under the light microscope in both groups. The SP-B, SP-C and FOXA2 were determined in the fetal lung of two groups immunohistochemically. The expression levels of SP-B, SP-C, total FOXA2, FOXA2 in nucleus (n-FOXA2), N-FOXA2 proteins were detected by Western blotting, and the relative expression levels of SP-B, SP-C, FOXA2 mRNA in the fetal lung of two groups were detected by RTPCR. The results showed that blood glucose levels of maternal rats and fetal rats in GDM group were higher than those in control group. The light microscope revealed fetal lung development retardation in GDM group. The expression of SP-B and SP-C in GDM group was significantly reduced as compared with control group (P<0.05). As compared with control group, the n-FOXA2 expression was significantly decreased in the fetal lung tissue, and N-FOXA2 was significantly increased in control group (P<0.05), but there was no significant changes in the total FOXA2 (P>0.05). It was concluded that GDM can cause fetal lung development and maturation disorders, and FOXA2 in fetal lung tissue decreases while nitrocellulose FOXA2 increases.

The properties of the ground and the lowest excited state of methyl bromide (CH3Br) have been studied with and without inclusion of the solvent effects in this work. The geometric parameters, energies, and frequencies of the ground state and the triplet state are calculated by using the MP2(full)/6-311++G** level of theory. The vertical excitation for the singlet state is also investigated. It is found that the theoretical results performed by the TDDFT/B3P86/6-311++G** method are in the best agreement with the experimental results. In addition, the dissociation energy of CH3Br molecule is computed at MP2(full)/6-311++G** level of theory for the gas phase and in water. The ionisation potential (IP), electron affinity (EA), electronegativity (χ), electrophilicity index (ω), hardness (η), softness (S), and chemical potential (μ) values are calculated from HOMO-LUMO energies both in the gas phase and in solvent (water). These theoretical results could serve as a guide for future experimental investigations.

A Cu-20Ni-20Mn alloy was prepared and the aging characteristic of this alloy was investigated in this paper. The experimental results showed that the strength of solution treated Cu-Ni-Mn alloy was enhanced by more than 500MPa when aged for more than 20h. Much more rapid increase of tensile strength was found in the cold rolling samples during the aging process, and the strength was much higher in the range from 1200-1600MPa. The side peaks found beside (200) X-ray diffraction peaks are believed to be corresponding to the Cu-rich and Mn/Ni-rich phase regions formed by up-hill diffusion. It is also known that this fluctuation of composition is usually described by sinusoidal wave, the wave length of which is estimated to be 10-15nm.

Inconel 625 superalloy tubes were hot extruded using a horizontal extruder. Optical microscope, scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) technique were employed to investigate the extrusion defects mainly caused by the primary MC carbides. The results showed that a lot of surface cracks, internal cracks, grooves and shrinkage cavity defects existed in the outer surface and internal of the Inconel 625 superalloy tube after hot extrusion. However, the inner surface of the tube was smooth and no cracks were observed. In addition to the external factors during hot extrusion, the cracks are mainly caused by the primary MC carbides or large dimension of C particles formed due to a relatively short smelting time and large dimension of C particles during smelting with the decreasing plasticity of the grain boundary. This kind of cracks can be avoided through improving the uniformity of the chemical composition by reducing the size of C particles and extending the diffusion time during the smelting of Inconel 625 superalloy.

To improve the using efficiency of clean energy, in this investigation, three wind-heating devices, nonlayered-stirring heating device, layered-stirring heating device and layered extruded stirring heating device, were designed, fabricated and tested. The performance of these three devices was investigated experimentally. Results show that, under the experimental conditions, the layered extruded stirring heating device is the most efficient, and its heating efficiency reaches 46.4%. Then, the computational fluid dynamics (CFD) models were established base on these three devices. The comparative analysis of the simulation and experimental results, both obtained consistent heating law. This suggests that the use of the software CFD simulating the stirring heating device is feasible.

A Cu-24 wt % Ag composite alloy is prepared to reveal the evolutions of microstructures, mechanical properties and textures formed by cold rolling. A typical alternating distribution of Cu and Ag phase layers is observed, which becomes much finer with increasing cold rolling reduction. Copper texture ((112)&lt;11-1> texture) and Goss texture ((110)&lt;001> texture) with high intensities are found in the Cu phase of cold rolled samples. Ag phase containing strong Goss texture and weak Brass texture are observed, quite different from the case in cold rolled pure Ag. Significant change of textures, from the Goss texture to (111) textures with increasing rolling reduction, has been found of Ag phase. The strengthening mechanism of this Cu-Ag composite is described by a equation similar to the HallPetch relationship, the fitted results based on which shows good agreement with the experimental data when the layer thickness is lower than 100-200 nm.

The pure copper tube with strong axial orientation columnar grain and equiaxed grain respectively were rolled using a three-roller precision tube mill. Optical microscope, hardness testing machine and universal testing machine were used to investigate the microstructure and mechanical properties of the pure copper tube rolled with different deformation degrees. The results show that the pure copper tube with two kinds of microstructure can be directly rolled from the dimension of Φ68.5mm×57.9mm to Φ34.7×30.4mm by 8 passes with accumulated deformation degree nearly 80% and without intermediate annealing. With the increasing deformation degree, the primary columnar grain boundaries of the pure copper tube with columnar grain blurred gradually until completely disappeared. However, the microstructures of pure copper tube with equiaxed grain completely transformed into fibrous microstructures when the deformation degree reaches to 79.11%. The columnar grain is without transverse grain boundaries but with small-angle boundary, which is conducive to axial deformation. It is also found that with the increasing deformation degree, the tensile strength of pure copper tube increased steadily, while the elongation decreased gradually. The elongation of pure copper tube with columnar grains is higher and the microhardness is lower than that of equiaxed grains, indicating that the cold deformation properties of pure copper tube with columnar grain was more excellent.

To explore the screw centrifugal pump performance change, and the impact of solid-liquid two-phase flow on the screw centrifugal pump, the internal flow of type 150×100LN-32 centrifugal pump is used as the research object. Mixture multiphase flow model, standard k-ε turbulence model and the sliding mesh technique are used to carry out the unsteady numerical simulation to describe internal flow field in screw centrifugal pump. By Setting the monitoring point to get the pressure pulsation characteristics and predict the changes in the energy performance. Open laboratory bench tests are carried out to verify the reliability of the numerical methods. Based on this, the impact of the two-phase flow on the screw centrifugal pump is analyzed. The results indicate that the head-flow curve presents a hump-shaped with the increasing of the flow. The maximum of efficiency appears. At the same time, the change of the volume concentration of the solid phase has little effect on the energy performance of screw centrifugal pump. But at different times, the head decreases and the power increases with the increasing of the concentration.

We present a model for the oxidation of titanium combining nonequilibrium statistical mechanics and density functional theory (DFT). Using this model, we found that oxygen is more strongly bound as an interstitial in Ti metal than in the oxide TiO2, the energy difference being ∼1.6 eV. Therefore, a binary phase structure TiO2/Ti, such as the commonly observed oxide scale that protects titanium alloy against corrosion, is thermodynamically unstable. Likewise, various DFT functionals all showed that several TiO2–xcompounds have lower energies than the weighted average energy of Ti and TiO2. Thus, the scale is a nonequilibrium structure for which diffusion is the controlling process. We found that the barrier for O-vacancy migration in TiO2is Erutile= 0.9 eV, much lower than the interface migration barriers (1.0–1.9 eV). We introduce a particle-based diffusion model that captures this feature and explains the long-lived nature of the observed thin oxide layer.

We study the chemical nature of the bonding of an oxide layer to the parent metal. In order to disentangle chemical effects from strain/misfit, the Ti(101̅0)/TiO2(100) interface has been chosen. We use the density functional pseudopotential method which gives good agreement with experiment for known properties of bulk and surface Ti and TiO2. Two geometries, a film-like model (with free surface in the structure) and a bulk-like model (with no free surface in the structure), are used to simulate the interface, in each case with different terminations of Ti and TiO2. For the single-oxygen interfaces, the interface energies obtained using these two models agree with each other; however, for the double-oxygen ones, the relative stability is quite different. The disturbance to the electronic structure is confined within a few atomic layers of the interface. The interfacial bonding is mainly ionic, and surprisingly, there is more charge transfer from Ti to O in the interface than in the bulk. In consequence, the Ti/TiO2interface has stronger binding than the bulk of either material. This helps to explain why the oxide forms a stable, protective layer on Ti and Ti alloys.

Flow behavior and microstructures of GH625 superalloy were investigated by hot compression tests. Then the GH625 superalloy tube was hot extruded according to the hot deformation behavior, and the microstructures of different position of extruded tube was also analyzed. The results show that the actual deformation temperature of the specimen deformed at a strain rate of 10.0s-1 is higher than the preset temperature, resulting in a deformation thermal effect. Thus, the microstructure evolution of GH625 superalloy is controlled both by the strain rate and deformation temperature. It is also found that the GH625 superalloy tube can be successfully fabricated with a stable extrusion speed of 40 mm·s-1, extrusion ratio of 4.1 and preheating temperature of 1200°C. The microstructure of extruded tube was obviously fined due to the occurrence of dynamic recrystallization(DRX). Different degrees of DRX were observed in outer wall, center and inner wall of the tube, which is similar to that in the head, middle and tail of the tube. An extruded tube containing fully DRX grains can be obtained by cutting the head and tail of the tube, and machining a small amount of the inner wall.

Microstructure evolution during dynamic recrystallization (DRX) of hot deformed GH625 superalloy was investigated by optical microscope (OP) and transmission electron microscope (TEM). Hot compression tests were conducted using Gleeble-1500 simulator. It was found that the nucleation mechanism of DRX for the alloy deformed at 1150°C is composed of discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) in the vicinity of the serrated grain boundaries. With the increasing strain, the fraction of the DRX grains increases, while the size of the DRX grains almost remains in the same range. As the deformation temperature increasing, the size and fraction of the DRX grains increase, and no precipitation of intergranular carbides are found when the deformation temperature increases to 1150°C. At lower strain rate, the size and volume fraction of DRX grains decrease with the increasing strain rates. However, the size and volume fraction of DRX grains increase at higher strain rates due to the deformation thermal effect.