Search

AbstractA silicide coating was prepared on Ti3SiC2- based ceramic by pack cementation to improve the oxidation resistance of Ti3SiC2, which is a technologically important material for high temperature applications. The microstructure, phase composition and oxidation resistance of the coated sample were investigated. The results demonstrated that the silicide coating was mainly composed of TiSi2and SiC. A single layer of a mixture of SiO2and TiO2was formed on the surface of the coated sample during isothermal oxidation at 1100 °C and 1200 °C for 20h. Compared to Ti3SiC2, the parabolic rate constant of silicide coated Ti3SiC2decreased by 2~3 orders of magnitude. Furthermore, the coated sample showed much better cyclic oxidation resistance than Ti3SiC2during the cyclic oxidation at 1100 °C for 400 times. However, during the preparation of the coating, a number of fine cracks formed in the outer layer of the coating. When these cracks penetrated the whole coating during the cyclic oxidation, the oxidation rate was accelerated, which degraded the oxidation resistance.

Abstract: Deformation of polycrystalline Ti2AlC under room and high temperature compression was investigated. The results demonstrated that Ti2AlC was damage tolerant at room temperature and the samples were shear fractured upon failure. At high temperatures Ti2AlC deform plastically. The brittle-to-ductile-transition temperature (BDTT) of Ti2AlC was between 1000 °C and 1050 °C. The microstructure and fracture surfaces were examined using scanning electron microscopy. Due to insufficient number of dislocation systems, the room-temperature deformation was constitute of kinking and delaminating of laminated Ti2AlC grains, basal plane dislocation slip, formation of voids and cavities in the vicinity of main crack. At high temperatures below BDTT, the deformation was a combination of cavities formation and intergranular sliding. At temperatures above BDTT, the deformation was mainly plastic flow.

Abstract: Titanium tin carbide (Ti2SnC) is a novel layered ternary compound. The ab initio calculations on the electronic structure and bonding properties indicated that Ti2SnC exhibit anisotropy of chemical bonding and properties. The electrical conductivity parallel to the basal plane is metallic and is much higher than that in c-axis. Thus Ti2SnC material in two-dimensional quasi-infinite form with the sheet surface parallel to the basal plane will show superior properties and have diverse device applications. Based on the theoretical predicted anisotropic electronic structure and properties, two-dimensional Ti2SnC plates were synthesized through a solid–liquid reaction process utilizing elemental Ti, Sn and C as starting materials. X-ray diffraction and scanning electron microscopy demonstrated that the morphology of the as-prepared plates were two-dimensional sheets. And the sheet surface was parallel to the (001) plane of Ti2SnC.

Abstract:  Polycrystalline copper (I) oxide films were deposited on stainless steel substrate by galvanostatic electrodeposition method and were characterized by X-ray diffraction and scanning electron microscopy. The effect of bath temperature, bath pH and current density on the compositon, grain size, surface texture and surface morphology of the electrodeposited films were investigated. The films deposited at low bath pH (≤7) consisted of copper (I) oxide and metallic copper; while the films deposited at bath pH between 8 and 12 and bath temperature of 60°C were pure copper (I) oxide. The preferred orientation of the copper (I) oxide films depended on the relative growth rate of {111} and {200} faces and could be controlled by adjusting the bath pH and/or the cathodic current density. (100)-oriented copper (I) oxide films could be deposited at pH=9 and current densities in the range of 0.25–1 mA/cm2, while (111)-oriented films could be prepared at pH=12 or at pH=9 using the current densities between 1.5–2.5 mA/cm2. Computer simulated crystallite shapes showed that the crystal shape changed from octahedral for (100)-oriented film to trucated pyramids and cubs for (111)-oriented film. And they were approved by scanning electron microscopy.