Han Jiecai

In-situ combustion synthesis and densification of TiC-xNi cermets

The combustion synthesis reaction was combined with quasi-isostatic pressing (QIP) technique to fabricate full density TiC–xNi composites in a single processing operation. Combustion wave velocity and temperature of Ti–C–Ni were measured and the microstructure of the product was characterized by X-ray diffraction and scanning electron microscopy. With increasing Ni content in TiC–xNi, both the combustion wave velocity and temperature decrease. The Ni additive, mainly as a diluent and the binder of TiC grains in a matrix, formed a quasi-continuous phase enveloping spheroidal TiC particles and brought about a grain size decrease from 9 to 1 μm. TiC-20 wt% Ni cermet produced by the combustion synthesis/quasi-isostatic pressing process under 160 MPa for 20 s show near full density, high hardness and transverse rupture strength (1024.2 MPa).

Self-propagating high temperature combustion synthesis of TiB/Ti composites

Abstract Dense TiB/Ti composites were fabricated by Self-propagating High Temperature Synthesis connected with Pseudo Hot Isostatic Pressing (SHS/PHIP). T ad s, T c and combustion velocities of the TiB– x Ti system decrease with increasing the amount of Ti. The synthesized TiB–Ti cermets mainly consisted of TiB and Ti phases, but TiB 2 phase existed in some products with lower content of metal. Needle-like, rod-like or plate-like TiB grains formed in the microstructure of synthesized TiB– x Ti composites. The size of the TiB grains decreased with an increasing amount of metal addition. The hardness and relative density of the synthesized materials are all beyond HRA82 and 94%, respectively. The introduction of Ti into TiB– x Ti cermets resulted in a drastic increase in the bending strength, tensile strength, compression strength, fracture toughness and the maximum values were obtained with the addition of 40 wt.%Ti.

Manufacturing and Characteristics of Glass Reinforced PTFE

A study on reinforced Polytetrafluoroethylene (PTFE) with chopped glass fiber or glass cloth was described. This study included manufacturing process of fibrous PTFE, the effects of the content of chopped glass fiber or glass cloth on the tensile strength and dielectric properties of the reinforced PTFE and the effect of filling particles on tensile strength and morphology of PTFE composites, etc. Our results showed that about 11% chopped fiber or 37% glass cloth reinforcing PTFE had the highest tensile strength and acceptable dielectric properties. Crystallizing phenomenon of PTFE was readily observed with the adding of particles. Finally, predicting of dielectric properties was discussed.

A MOVING CRACK IN A NONHOMOGENEOUS MATERIAL STRIP

This paper considers an anti-plane moving crack in a nonhomogeneous material strip of finite thickness. The shear modulus and the mass density of the strip are considered for a class of functional forms for which the equilibrium equation has analytical solutions. The problem is solved by means of the singular integral equation technique. The stress field near the crack tip is obtained. The results are plotted to show the effect of the material non-homogeneity and crack moving velocity on the crack tip field. Crack bifurcation behaviour is also discussed. The paper points out that use of an appropriate fracture criterion is essential for studying the stability of a moving crack in nonhomogeneous materials. The prediction whether the unstable crack growth will be enhanced or retarded is strongly dependent on the type of the fracture criterion used. Based on the analysis, it seems that the maximum ‘anti-plane shear’ stress around the crack tip is a suitable failure criterion for moving cracks in nonhomogeneous materials.

General coupled solution of anisotropic piezoelectric materials with an elliptic inclusion

In this investigation, the Stroh formalism is used to develop a general solution for an infinite, anisotropic piezoelectric medium with an elliptic inclusion. The coupled elastic and electric fields both inside the inclusion and on the interface of the inclusion and matrix are given.

Field emission from amorphous carbon nitride films deposited on silicon tip arrays

Amorphous carbon nitride films (a-CNx) were deposited on silicon tip arrays by rf magnetron sputtering in pure nitrogen atmosphere. The field emission property of carbon nitride films on Si tips was compared with that of carbon nitride on silicon wafer. The results show that field emission property of carbon nitride films deposited on silicon tips can be improved significantly in contrast with that on wafer. It can be explained that field emission is sensitive to the local curvature and geometry, thus silicon tips can effectively promote field emission property of a-CNx films. In addition, the films deposited on silicon tips have a smaller effective work function (F = 0.024 eV) of electron field emission than that on silicon wafer (F = 0.060 eV), which indicates a significant enhancement of the ability of electron field emission from a-CNx films.

The research progress about the effect of carrier concentration and mobility on the infrared transparent properties and conductive properties of oxide thin films

Due to the high visible transmittance and conductivity, transparent conductive films caused more and more attention. However, according to the Drude’s theory, there still exist some doubts about the possibility of infrared transparent conductive film. It is the fact that, due to the electrical and optical properties determined by carrier concentration, the contradiction between the wide-range infrared transmission and high conductivity is difficult to coordinate. In this paper, firstly, according to interaction between electrons and photons, we explored the key of confliction between electrical and optical properties, and also discovered the feasibility of infrared transparent conductive films. Through theoretical analysis, we found the reasons of contradiction of electrical and optical properties. Secondly, by summarizing and analyzing the photoelectrical properties of the conventional transparent conductive oxide films, we put forward the relationship among free-electrical, mobility, plasma wavelength and conductivity properties. Lastly, as the result of our research, if the film has the wide-range infrared transmission and high conductivity properties at same time, the effect of carrier concentration and mobility on plasma wavelength is not overlooked.

The process of TiB2−Cu composite phase and structure formation during combustion synthesis

The reaction process of combustion synthesis for TiB2−Cu was investigated in detail using combustion-wave arresting experiment, X-ray diffraction (XRD) analysis, SEM analysis and differential thermal analysis (DTA). The XRD analysis results for the different parts of the quenched specimen show that TiCux intermetallic phase firstly forms with the propagation of combustion wave, and then Ti1.87B50 and Ti3B4 metastable phases come forth due to the diffusion of B atoms and finally the stable TiB2 phase forms because of the continuous diffusion of B atoms. The formation of TiB2 phase is not completed by one step, but undergoes several transient processes. The process of reaction synthesis for Ti−B−Cu ternary system can be divided into three main stages: melting of Cu and Ti, and the formation of Cu−Ti melt and few TiCux, TiBx intermetallic phases; large numbers of TiCux intermetallic phases formation and some fine TiB2 particles precipitation; and the TiB2 particles coarsening and the stable TiB2 and Cu two phases formation in the final product.