Mei Bingchu

Fabrication of Ti2AlC by spark plasma sintering from elemental powders and thermodynamics analysis of Ti-Al-C system

A ternary-layered carbide Ti2AlC material could be synthesized by spark plasma sintering(SPS) technology using elemental powder mixture of Ti, Al and active carbon. By means of XRD and SEM, phases were identified and microscopically evaluated. The experimental results show that the main phase in the product was fully crystallized Ti2AlC with small particle size when sintered at 1200 °C. The synthesis temperature of SPS was 200–400 °C lower than that of hot pressing (HP) or hot isostatic pressing (HIP). Through thermodynamics calculations, the mechanism of Ti2AlC was studied by calculating changes of Gibbs free energy of reactions.

Effect of Aluminum on Synthesis of Ti3SiC2 by Spark Plasma Sintering (SPS) from Elemental Powders

The effect of aluminum on synthesis of Ti3SiC2 by spark plasma sintering (SPS) from elemental powders was investigated in this paper. X-ray diffraction patterns and scanning electron microscopy photographs of samples with different content of aluminum indicated that proper addition of aluminum both favored the formation and accelerated the crystal growth of Ti3SiC2. The process parameters in the sintering course revealed that addition of aluminum decreased the temperature for the synthesis reaction of Ti3SiC2. Polycrystalline bulk Ti3SiC2 material with high purity and density could be fabricated by spark plasma sintering from the elemental powder mixture with starting composition of Ti3Si1−xAlxC2, where x = 0.05–0.2. SEM photographs showed Ti3SiC2 synthesized from elemental powders was in plane-shape with a size of about 10–20 µm in the elongated dimension. Solid solution of aluminum decreased the thermal stability of Ti3SiC2 and made the temperature at which Ti3SiC2 decomposed be as low as 1300°C.

Preparation of TiAl/Ti2AlC composites with Ti/Al/C powders by in-situ hot pressing

TiAl/Ti2 AlC composites were prepared by in-situ hot pressing of Ti/Al/C powders mixtures and sintered at different temperatures were investigated by X-ray diffraction (XRD) of samples. The reaction procedure of Ti-Al-C system could be divided into three stages. Below 900°C, Ti reacts with Al to form TiAl intermetallics; above 900°C, C reacts with remain Ti to form TiC triggered by the exothermal reaction of Ti and Al; TiAl reacts with TiC to produce dense TiAl/Ti2 AlC composites. In the holding stage, ternary Ti2AlC develops to layered polycrystal and composites pyknosis in the meanwhile. The mechanism of synthesis and microstructure was especially discussed.

Preparation of Ti3SiC2 with aluminum by means of spark plasma sintering

Polycrystalline bulk Ti3SiC2 material with a high purity and density was fabricated by spark plasma sintering from the elemental powder mixture with starting composition of Ti3Si1−xAlxC2, where x=0.05–0.2. X-ray diffraction patterns and scanning electron microscopy photographs of the fully dense samples show that a proper addition of aluminum promotes the formation, and accelerates the crystal growth rate of Ti3SiC2, conse-quently results in a high purity of the prepared samples. The synthesized Ti3SiC2 is in plane-shape with a size of about 10–25μm in the elongated dimension. Solid solution of aluminum decreases the thermal stability of Ti3SiC2, and lowers the temperature of Ti3SiC2 decomposeing to be 1300°C.

Gradient Structure of Ti-Al-C Ternary Carbide Prepared by Hot-pressing Sintering

X-ray diffraction (XRD) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC, Ti3AlC2+TiC, pure Ti3AlC2 and Ti2AlC+Ti3AlC2, no matter elemental powder or TiC is used as raw materials. It is found that ternary-layered carbide Ti2AlC samples synthesized at 1500°C by hot-pressing sintering are inhomogeneous and have a gradient structure. Electron probe X-ray micro-analysis (EPMA) indicates that the Al content along the hot pressing axis is parabolic, it is the highest in the center and the lowest at the both ends, while the Ti content is constant along the axis. The experimental result reveals that the evaporation of Al in samples in an open system during hot pressing sintering results in a gradient structure.

Electronic Structure and Chemical Bond of Ti3SiC2 and Adding Al Element

The relation among electronic structure, chemical bond and property of Ti3SiC2 and Al-doped was studied by density function and discrete variation (DFT-DVM) method. When Al element is added into Ti3SiC2, there is a less difference of ionic bond, which does not play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti becomes somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before adding. Therefore, in preparation of Ti3SiC2, adding a proper quantity of Al can promote the formation of Ti3SiC2. The density of state shows that there is a mixed conductor character in both of Ti3SiC2 and adding Al element. Ti3SiC2 is with more tendencies to form a semiconductor. The total density of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al.