Xinyun Wang

Facile modification of nanoscale zero-valent iron with high stability for Cr(VI) remediation

In this study, a highly stable nanoscale zero-valent iron composite (HS-NZVI) was obtained via modifying nanoscale zero-valent iron (NZVI) with tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMOS), and used for Cr(VI) remediation in aqueous solution. The obtained HS-NZVI remained stable in water without being oxidized for over 12h. After four consecutive runs, the Cr(VI) removal efficiency of HS-NZVI maintained a value of more than 82%. Moreover, the Cr(VI) removal capacity per unit weight of NZVI in HS-NZVI reached 292.8mg/g within 60min at the initial Cr(VI) concentration of 120mg/L at pH5. The Cr(VI) removal efficiency of HS-NZVI increased with decreasing solution pH, and the experimental data for Cr(VI) removal by HS-NZVI were well-described by the pseudo-first-order reaction model. Additionally, scanning electron microscope (SEM) images, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) measurements of the product after reaction revealed that the mechanism of Cr(VI) remediation by HS-NZVI mainly involved adsorption, reduction and co-precipitation. Considering the advantages of easy preparation, excellent stability and reusability, and high Cr(VI) removal capacity as well as the magnetic recovery property, HS-NZVI is expected to have notably promising applications for the remediation of Cr(VI) contaminated sites.

High-temperature deformation behavior and processing map of 7050 aluminum alloy re]20101008

The high-temperature deformation behavior and processing map of 7050 aluminum alloy were investigated by tensile tests conducted at various temperatures (340, 380, 420, and 460 °C) with various strain rates of 10−4, 10−3, 10−2, and 0.1 s−1. The results show that the instability region with a peak power dissipation efficiency of 100 % occurs at the low deformation temperature region of 340 °C to 380 °C and high strain rates (>10−3 s−1). The 7050 aluminum alloy exhibited a continuous dynamic recrystallization domain with power dissipation efficiency of 35% to 60 % in the deformation temperature range of 410 °C to 460 °C and the strain rate range of 10−4–10−3 s−1. The domain with a power dissipation efficiency of 35 % to 50 % occurring at high deformation temperatures and strain rates was interpreted to represent dynamic recovery. Dynamic recovery and continuous dynamic recrystallization provide chosen domains for excellent hot workability.

Tuning apparent friction coefficient by controlled patterning bulk metallic glasses surfaces.

Micro-honeycomb structures with various pitches between adjacent cells were hot-embossed on Zr35Ti30Cu8.25Be26.75 bulk metallic glass surface. The effect of pitch geometry on the frictional behavior of metallic glass surface was systematically investigated. The results revealed that all textured metallic glass surfaces show a reduction in friction coefficient compared to smooth surface. More intriguingly, the friction coefficient first decreased and then increased gradually with increasing pitches. Such unique behavior can be understood fundamentally from the perspective of competing effects between contact area and local stress level with increasing pitches. This finding not only enhance the in-depth understanding of the mechanism of the significant role of surface topography on the frictional behavior of metallic glass surface, but also opens a new route towards other functional applications for bulk metallic glasses.

Optimization of gear blank preforms based on a new R-GPLVM model utilizing GA-ELM

A novel R-GPLVM is proposed to screen out critical dimensions of the preform.A newly GA-ELM framework seamlessly integrated with R-GPLVM is proposed.Discussions demonstrate that Gaussian kernel function has the higher accuracy.The relevant parameters of ELM are optimized with the improved performance.Engineering applications and FEM validate the feasibility of the proposed method. The determination of the key dimensions of gear blank preforms with complicated geometries is a highly nonlinear optimization task. To determine critical design dimensions, we propose a novel and efficient dimensionality reduction (DR) model that adapts Gaussian process regression (GPR) to construct a topological constraint between the design latent variables (LVs) and the regression space. This procedure is termed the regression-constrained Gaussian process latent variables model (R-GPLVM), which overcomes GPLVMs drawback of ignoring the regression constrains. To determine the appropriate sub-manifolds of the high-dimensional sample space, we combine the maximum a posteriori method with the scaled conjugate gradient (SCG) algorithm. This procedure can estimate the coordinates of preform samples in the space of LVs. Numerical experiments reveal that the R-GPLVM outperforms the pure GPR in various dimensional spaces, when the proper hyper-parameters and kernel functions are solved for. Results using an extreme learning model (ELM) obtain a better prediction precision than the back propagation method (BP), when the dimensions are reduced to seven and a Gaussian kernel function is adopted. After the seven key variables are screened out, the ELM model will be constructed with realistic inputs and obtains improved prediction accuracy. However, since the ELM has a problem with validity of the prediction, a genetic algorithm (GA) is exploited to optimize the connection parameters between each network layer to improve the reliability and generalization. In terms of prediction accuracy for testing datasets, GA has a better performance compared to the differential evolution (DE) approach, which motivates the choice to use the genetic algorithm-extreme learning model (GA-ELM). Moreover, GA-ELM is employed to measure the aforementioned DR using engineering criteria. In the end, to obtain the optimal geometry, a parallel selection method of multi-objective optimization is proposed to obtain the Pareto-optimal solution, while the maximum finisher forming force (MFFF) and the maximum finisher die stress (MFDS) are both minimized. Comparative analysis with other numerical models including finite element model (FEM) simulation is conducted using the GA optimized preform. Results show that the values of MFFF and MFDS predicted by GA-ELM and R-GPLVM agree well with the experimental results, which validates the feasibility of our proposed methods.

A size-dependent constitutive model of bulk metallic glasses in the supercooled liquid region

Size effect is of great importance in micro forming processes. In this paper, micro cylinder compression was conducted to investigate the deformation behavior of bulk metallic glasses (BMGs) in supercooled liquid region with different deformation variables including sample size, temperature and strain rate. It was found that the elastic and plastic behaviors of BMGs have a strong dependence on the sample size. The free volume and defect concentration were introduced to explain the size effect. In order to demonstrate the influence of deformation variables on steady stress, elastic modulus and overshoot phenomenon, four size-dependent factors were proposed to construct a size-dependent constitutive model based on the Maxwell-pulse type model previously presented by the authors according to viscosity theory and free volume model. The proposed constitutive model was then adopted in finite element method simulations, and validated by comparing the micro cylinder compression and micro double cup extrusion experimental data with the numerical results. Furthermore, the model provides a new approach to understanding the size-dependent plastic deformation behavior of BMGs.

Superplastic deformation behavior and hot-processing map of the TiNp/2014 Al composite

The superplastic deformation behavior and hot-processing map of the TiNp/2014 Al composite were investigated based on tensile tests conducted at various temperatures (773 K, 798 K, and 818 K) with various strain rates (0.033, 0.167, 0.33, and 0.67 s-1). The results revealed that the influence of strain on the energy dissipation map is negligible. The optimal superplastic deformation parameters corresponding to the peak power dissipation efficiency of 0.65 differ from those corresponding to the maximum elongation of 351%. For the superplastic deformation of TiNp/2014 composite, the deformation activation energy is much higher than that for the lattice self-diffusion in pure aluminum, which can be explained by the combination of mechanisms including grain (subgrain) boundary sliding accommodation, interface sliding accommodation, liquid-phase helper accommodation and load transfer. To avoid voids and wedge cracks, two obvious instability domains in the hot-processing maps should be avoided. The hot-processing maps obtained can approximately, but not accurately enough, optimize superplastic deformation parameters of the TiNp/2014 Al composite.

Microstructure evolution and modeling of 2024 aluminum alloy sheets during hot deformation under different stress states

In this work, specimens of the 2024 aluminum alloy sheet were compressed and stretched along the original rolling direction at elevated temperatures. The microstructure evolution was investigated by characterizing the metallographic structures via electron backscattered diffraction technology before and after deformation. It was found that while recrystallization occurred in the compressed specimens, it was not observed to the same extent in the stretched specimens. This difference in the grain morphology has been attributed to the different movement behaviors of the grain boundaries, i.e., their significant migration in the compression deformation and the transformation from low-angle to high-angle boundaries observed mainly during tension deformation. The empirical model, which can describe the grain size evolution during compression, is not suitable in the case of tension, and therefore, a new model which ignores the detailed recrystallization process has been proposed. This model provides a description of the grain size change during hot deformation and can be used to predict the grain size in the plastic deformation process.

g-C3N4/MgO nanosheets: light-independent, metal-poisoning-free catalysts for the activation of hydrogen peroxide to degrade organics

The huge amount of organic wastewater produced by dye manufacturing/consuming industries causes serious environmental pollution, which urges researchers to explore highly efficient and cost-effective Fenton-like catalysts. Herein, we report the synthesis of g-C3N4/MgO nanosheets through a simple two-step calcination method, exhibiting the excellent catalytic ability of activating hydrogen peroxide to degrade organic dyes in the dark. The results of this study indicate that the g-C3N4/MgO nanosheets are light-independent and metal-poisoning-free Fenton-like catalysts for enhanced degradation of organics. The efficient degradation performance is attributed to hydroxyl radical generation in the g-C3N4/MgO–H2O2 catalytic system. The bonding between the MgO and g-C3N4 parts of the g-C3N4/MgO nanosheets is considered to be a key role in activating H2O2 to produce a hydroxyl radical. This catalytic degradation process can be conducted in a wide pH range and at room temperature without external energy input. Additionally, the g-C3N4/MgO nanosheets are non-toxic, low-cost and easy to prepare. Therefore, it is reasonable to believe that g-C3N4/MgO nanosheets have a great potential in the catalytic degradation of organic contaminants and could be used in a wide range of environmental cleanup applications. Furthermore, this work provides an insight into exploiting novel Fenton-like catalysts without transition metal components or external energy excitation.

Stamping-Forging Processing of Sheet Metal Parts

SFP is a combined metal forming technology of stamping and forging for sheet metal parts. In an SFP, generally, stamping or drawing is used to form the spatial shape of the part first, and followed by a bulk forming employed to form the local thickened feature. It is suitable for making sheet metal parts which have local thickened feature, such as single or double layers cup parts with thickened inner or outer wall, disc-like parts with thickened rim, etc.

RESEARCHES ON FLOW BEHAVIOR AND CONSTITUTIVE EQUATION OF A390 ALUMINUM ALLOY

Flow behavior of an A390 Aluminum alloy was investigated at temperatures of 290-490 °C and at strain rates of 0.001-1 s. The true stress-strain curves were obtained from the hot compression tests. The results indicate that the flow stress of A390 aluminum alloy decreases with the increase of temperature and the decrease of strain rate. It is also proved that work hardening and dynamic softening phenomena occur during hot compression. By applying the hyperbolic sine constitutive model, the constitution equation of A390 aluminum alloy was obtained.