Wang Fuchi

Research on the deformation strengthening mechanism of a tungsten heavy alloy by hydrostatic extrusion

The microstructure mechanical properties of the 93 tungsten alloy and the deformation strengthening mechanism of the tungsten alloy by hydrostatic extrusion are studied by static and dynamic tensile experiments, quantitative metallography experiments and the transmission electron microscopy (TEM) analysis in this paper. Varied laws on tungsten grains effective contiguity on different deformation directions and dislocation densities in tungsten grain and matrix along with the increase of the extrusion ratio are obtained. Through the research we can conclude that a decrease of the axial effective contiguity, a increase of the dislocation density and aspects of the sub-grain in a tungsten grain with large deformation are the main factors to strengthen the tungsten alloy by hydrostatic extrusion.

Enhanced mechanical behaviour of lead zirconate titanate piezoelectric composites incorporating zinc oxide nanowhiskers

This paper reports that the lead zirconate titanate (PZT) piezoelectric composites incorporating zinc oxide nanowhiskers (ZnOw) were prepared by the conventional solid state processing. The whisker-dispersed PZT composites (PZT/ZnOw) presented a significant enhancement in the mechanical properties such as Youngs modulus, tensile strength and compressive strength. Especially, the compressive strength increased from 153 MPa for the PZT to 228 MPa for the PZT/ZnOw composites. The reinforcement mechanism in strength of the composites was discussed. The mechanical quality factors of the PZT/ZnOw composites increased considerably, while the piezoelectric constants and electromechanical coupling coefficient decreased slightly. The composites with good electrical and excellent mechanical properties are promising for further applications.

Study of ZrO2 phase structure and electronic properties

The phase structure and electronic properties of c-ZrO2, t-ZrO2 and m-ZrO2 are calculated and compared using density functional theory. By calculating the energies for different lattice constants, the crystal structures of the three zirconia polymorphs are optimised. The calculation results are in good agreement with related experimental data and the cohesive energies do reflect the relative phase stability of the three zirconia polymorphs. The valence electronic density of states and the charge distributions on some typical planes are presented and discussed to investigate the valence electronic structure, the special electronic properties, and the Zr–O bond strength. The calculation results in this paper would be helpful to further predict the zirconia phase transition and some basic physical properties.

Synthesis and photoluminescence study on ZnO nano-particles

A new technique, namely low pressure sputtering, has been developed to fabricate Zn nanoparticles, with a subsequent oxidation to synthesize ZnO nanoparticles in the ambient atmosphere at 500°C. The synthesized ZnO nanoparticle has a size of 6–8 nm with a preferred orientation of c-axis. The produced ZnO nanoparticles have a good UV photoluminescence (PL) emission energy of 3.349 eV with a significant enhancement of donor–acceptor pair emission located at 3.305 eV which implies a number of donor and acceptor bounded excitons existing in the synthesized ZnO nano particles. The near band edge PL emission of the fabricated ZnO is dominated by the bounded excitons at 10 K.

Prediction of the intrinsic thermal conductivity of phonons in dielectric and semiconductor materials based on the density of the lattice vibration energy

A novel method is proposed to simulate the intrinsic thermal conductivity of the phonons in dielectric and semiconductor materials by introducing the concept of the density of the lattice vibration energy, which is a function of frequency and temperature. A quantitative relationship between the density of the lattice vibration energy and the mean free path of the phonons is established. The heat capacity and sound velocity can also be calculated by using the phonon density of states, the theoretical densities, and the elastic modulus. The thermal conductivities of some typical dielectric and semiconductor materials are then calculated, and it is found that the agreement with experimental data is good for some materials. In contrast to traditional semi-empirical methods, there is no need to input any experimental data.

Study of Flying Particles in Plasma Spraying

In this article, the trajectories of ceramic and metal particles in plasma spray are calculated by solving related momentum and energy equations. Meanwhile, the spatial distributions, temperatures, velocities, as well as diameters of the particles are measured by employing an online, in-flight particle sensor (DPV2000). The experimental and computational results are in good agreement. It has been found that the particle flying trajectories are dependent on material types and particle diameters, and in a plane vertical to the spraying axis, there is a certain corresponding relationship between the particle diameter and the particle velocity, as well as particle temperature.

Numerical simulation of temperature and velocity fields in plasma spray

Based on the turbulence jet model, with respect to Ar-He mixture plasma gas injecting to ambient atmosphere, the temperature filed and velocity field under typical working conditions were investigated. Given the conditions of I=900 A, FAr = 1.98 m3/h, FHe = 0.85 m3/h, it is found that both the temperature and the velocity undergo a plateau region near the nozzle exit (0–10 mm) at the very first stage, then decrease abruptly from initial 13 543 K and 778.2 m/s to 4 000 K and 260.0 m/s, and finally decrease slowly again. Meanwhile, the radial temperature and radial velocity change relatively slow. The inner mechanism for such phenomena is due to the complex violent interaction between the high-temperature and high-velocity turbulent plasma jet and the ambient atmosphere. Compared with traditional methods, the initial working conditions can be directly related to the temperature and velocity fields of the plasma jet by deriving basic boundary conditions.

Modeling the Dynamic Damage Process of the SiC3d/Al Interpenetrating Phase Composites

In the current study, a 3D mesoscopic structure FE-Model of interpenetrating SiC3d/Al composite is built based on the digital image-based modeling technique together with optimized methods of three-dimensional mesh generation. Subsequently, the finite element method is proposed to simulate the dynamic damage process of the interpenetrating phase composites SiC3d/Al under dynamic axial crushing. The cracking process in micro 3D space is clearly presented in the current study. It is shown that the cracks initialization and propagation mainly appear in the region of interface between ceramic and metallic phase. Moreover, the ceramic phase attributes to the models damage predominantly. The method proposed in this paper would be of help in the microstructure design of Interpenetrating Phase Composites.

Numerical Simulation in relation to Adiabatic Shearing Behaviors in Titanium Alloy

The adiabatic shearing phenomena are commonly found in titanium alloys, but they are rarely simulated in the microstructure scale. In the current study, the macro-dynamic compression is implemented and the microstructures are successfully embedded into the macro model by introducing a multiscale simulation technique, thus help to reveal the adiabatic shearing deformation mechanism of titanium alloy. The simulation results show that for the equiaxed titanium alloy, the adiabatic shearing process is determined by the phase proportion outside the shear band instead of the phase proportion inside; the study further shows that within a certain proportion of α phase, with the increase of α phase proportion, the adiabatic shear sensitivity decreases.

The influencing mechanism of modification layer on the performance of SiC3D/Al multi-function gradient composite

SiC skeleton surface was oxidized in this paper. Vacuum-pressure infiltration method is used to prepare SiC3D/Al composite. The effects of the thickness of the interface modification layer were investigated. The results showed that the thickness of SiO2 layer increases with the prolonged time of the skeleton oxidation. The brittle phase basically disappeared at the interface of the composite with 9 hours pre-oxidized, which lead to the high interface bonding strength. As a result, fracture morphology of the oxidized composite is mainly composed with plastic toughening of pure aluminum. Therefore, the static compressive strength of the composite raises up to 1165.2Mpa.