Zhang Xinghong

Self-propagating high temperature combustion synthesis of TiC/TiB2 ceramic-matrix composites

TiC/TiB2 ceramic–matrix composites were produced by self-propagating high temperature combustion syntheses combined with pseudo hot isostatic pressing using Ti, B4C and carbon powder. The results of XRD and SEM analysis showed that the final product was pure and no unreacted B4C, Ti or carbon appeared. The microstructure of synthesized products consisted of the clubbed TiB2 grains and equiaxed or irregular TiC grains. The optimal ratio with Ti:B4C=3:1 of the reactant powder was determined by experiments. The maximum relative density, hardness value, compression strength and bending strength was attained for TiC–2TiB2 ceramic when the delay time is 5 s, keeping pressure time is 5 s and the pressure is 160 MPa, which is higher than TiC–TiB2 and 2TiC–TiB2 ceramics. The introduction of more clubbed TiB2 grains into TiC/TiB2 ceramics resulted in a drastic increase in the fracture toughness for TiC–2TiB2 synthesized compacts.

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.

Theoretical studies on the structural, electronic, and optical properties of Ag2HgSnSe4

We investigate the electronic structure of Ag 2 HgSnSe 4 in a wurtzite-stannite structure with the first principles method.This crystal is a direct band-gap compound.In addition the dielectric function,absorption coefficient,reflectiv-ity,and energy-loss function are studied using the density functional theory in the generalized gradient approximation.We discuss the optical transitions between the valence bands and the conduction bands in the spectrum of the imaginary part of the dielectric function at length.We also find a very high absorption coefficient and a wide absorption band for this material.The prominent structures in the spectra of reflectivity and the energy-loss function are discussed in detail.We investigate the electronic structure of Ag2HgSnSe4 in a wurtzite—stannite structure with the first principles method. This crystal is a direct band-gap compound. In addition the dielectric function, absorption coefficient, reflectivity, and energy-loss function are studied using the density functional theory in the generalized gradient approximation. We discuss the optical transitions between the valence bands and the conduction bands in the spectrum of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and a wide absorption band for this material. The prominent structures in the spectra of reflectivity and the energy-loss function are discussed in detail.

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.