Xiao Dong He

Oxidation and ablation of 3D carbon-carbon composite at up to 3000 °C

Abstract The reactivity of fine-weave pierced 3D carbon-carbon composites in air at temperatures up to 3000 °C was studied. The corrosion morphology and microstructure of oxidized samples were investigated by XPS, SEM, and XRD techniques, and the non-equilibrium nature of the oxidation process was pointed out. A thermochemical ablation model of CC composites controlled by gas phase diffusion and reaction kinetics was developed.

A simple engineering approach in the prediction of the effect of stress ratio on fatigue threshold

In situ SEM observations [1] have revealed that fatigue crack propagation is caused by the shear band decohesion around the crack tip and the formation and cracking of the shear band is mainly caused by the plasticity generated in the loading part of a load cycle. Based on the crack tip plasticity a theoretical analysis has been performed and a model has been set up to consider the effect of the applied stress ratio on fatigue threshold. The obtained results have been compared with a wide range of published test data and good agreement has been achieved. This method is very easy to use and no fatigue crack closure measurement is needed, therefore this model is significant in engineering application.

Self-propagating high temperature synthesis of intragranular TiC-Ti3AlC2 composites

Abstract Abstract TiC-Ti3AlC2 composites with a novel intragranular structure were fabricated by self-propagating high temperature synthesis technique using Ti, Al and C elemental powders. X-ray diffraction results indicated that the as synthesised composites were composed of TiC and Ti3AlC2, where the amounts of TiC were measured to be 5·4, 9·2 and 16·7 wt-%. Transmission electron microscopy observation showed that the globular TiC was located within the plate-like Ti3AlC2 grain, which confirms the ubiquitous existence of intragranular structure in the composites.

Preparation of Ternary Layered Ti3SiC2 Ceramic by SHS/PHIP

Ternary-layered Ti3SiC2 ceramic was prepared by self-propagation high temperature combustion synthesis with pseudo hot isostatic pressing (SHS/PHIP). The effect of Ti/C mol ratio, Si content and Al content on the phase composition of the products was investigated. Experimental results showed that the phase composition of SHS/PHIPed products was influenced greatly by Ti/C mol ratio and Si content in the raw material. When Ti/C mol ratio is 1.5, the main phase was TiC with only a little Ti3SiC2; the content of Ti3SiC2 increased greatly with increase of Si content. The main phase turned to Ti3SiC2 while TiC became the main impurity when the Ti/C mol ratio arrived at 2. With addition of aluminum, the content of Ti3SiC2 increased obviously and the distortion of lattice was caused in Ti3SiC2 crystals.

Optimum Design, Microstructure and Mechanical Properties of Ti/Ti3Al Multi-Layered Materials

This study concerned with the optimum design, microstructure and mechanical properties analysis of a multi-layered metal/intermetallic materials consisting of Ti and Ti3Al prepared by the electron beam physical vapor deposition (EB-PVD) technology. Based on fracture mechanics and numerical simulation method, the optimized microstructure of Ti-Ti3Al multi-layered materials has been obtained by analyzing the relation curve between structural parameters and work of fracture of materials, then dual-target evaporating method was used to evaporate Ti and Ti-47Al bar alternately to form Ti/Ti3Al thin sheet about 0.12mm thickness. Pattern and phase analysis by SEM and XRD showed that there was homogeneous and continuous interface between layers and the intermetallic layers were made up of α2 phase alloy. The tensile curve of Ti/Ti3Al microlaminates represented the characteristic of multi-layered materials and the maximal extensibility of sample as deposited reached 5.83% and the fracture appearance showed ductile rupture feature.

Numerical and Experimental Studies on Cured Shape of Thin Unsymmetric Carbon/Epoxy Laminates

An analytical model was established by means of Ritz method to calculate the cured shape of cross-ply unsymmetric composite laminates. A number of experiments of Carbon/Epoxy laminates were conducted. It was found in the experiment that the warped surface could be a multiple-value function, which should be studied further. The result of calculation correlates well with the experimental result except the regions very near the laminate edge. The conclusion is instructive to manufacture of composite laminates.

Isothermal oxidation property of the Al2TiO5/Tio2/Zro2 composite coating on TC4 alloy prepared by micro-arc oxidation

Abstract The isothermal oxidation behaviours of Al2TiO5/TiO2/ZrO2 composite coating on titanium alloy (TC4) deposited by micro-arc oxidation technique were studied at different temperature points of 1073, 1173 and 1273 K in dry air. The surface morphology and phase composition of all coated samples were investigated before and after oxidation by SEM and XRD, respectively. The weight gaining curves of the coated samples were plotted and the high temperature oxidation rates were evaluated, showing that the oxidation kinetics followed the parabolic rate law. And with increasing oxidation temperature, their oxidation rates also increased. The original phases of Al2TiO5/TiO2/ZrO2 coating on TC4 alloy consisted mostly of Al2TiO5 and R-TiO2 intermixed with small amounts of ZrO2 and the phased changed into mainly of R-TiO2, Al2O3 and little Al2TiO5 when after 1273 K oxidation for 1 h, whose average parabolic rate constant was 6.43 × 10−13 g2 cm−4 s−1, greatly lower than that of blank samples, 6.01 × 10−12 g2 cm−4 s−1, indicative of a good oxidation resistance for the Al2TiO5/TiO2/ZrO2 composite coating on TC4 surface.

Characteristic of Microarc Oxidized Coatings on Titanium Alloy Formed in Electrolytes Containing Aluminate and ZrO2 Particles

Microarc oxidation (MAO) is a relatively convenient and effective technique to deposit ceramic coatings on the surfaces of Al, Ti, Mg and their alloys. This technique can introduce various desired elements into titania-based coatings and produce various functional coatings with a porous structure. Microarc oxidized (MAO) TiO2-based coatings on titanium alloy were formed in electrolytes containing aluminate and ZrO2 particles. The phase composition of the samples was analyzed by glance-angle X-ray diffraction and the surface morphologies of the samples were observed by a scanning electron microscopy (SEM). In addition, the element concentrations on the surfaces of the samples were measured by an energy dispersive X-ray spectrometer. The experiment results indicated that: MAO coatings, which are porous structures and exhibit good interfacial bonding to the substrate, may possess specific surface structures such as crystal phase, non-equilibrium solid and complex mixed-compounds since complex plasma physical and chemical reactions.

Investigation on Large-Sized Sapphire Crystalline Perfection by X-Ray Double-Crystal Diffraction Method

The large-sized sapphire (Ø225×205 mm, 27.5 kg) was grown successfully by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at cooled center). The surface quality of the specimens was characterized by micro-Raman spectroscopy, and double crystal X-ray diffractometry (DCD) was utilized to investigate its crystalline perfection. The measurement of rocking curves was performed on various specimens from different region of large sapphire boule. The experimental results showed that CMP (chemo-mechanical polishing) with subsequent suitable chemically etching can develop the best-quality sapphire crystal surface and the values of FWHM obtained by conventional DCD were in the range from 27” to 58”. The infrared spectral transmission (2.0-4.5 5m) of sapphire crystal exceeded 82%. It is confirmed of SAPMAC growth method characteristics with in-situ annealing, small temperature gradient and low residual stress level by numerical simulation analysis.

Preparation and Characterization of Properties of Microcapsules for Polymeric Composites Self-Repairing

Microcapsules self-repairing polymeric composites belong to a new kind of smart materials. In this work, microcapsules used for polymeric composites self-repairing were prepared by in-situ polymerization. Optical microscopy, scanning electronic microscopy (SEM), fourier transfer infrared spectroscopy (FT-IR), and thermal gravity analysis (TGA) were used to determine the properties of prepared microcapsules such as grain size and their distribution, wall thickness, content of core materials and thermal performances of microcapsules. Results showed that the average grain size was 210 μm and the wall thickness was in the range of 1.8-5 μm depending on agitation rate. Thermal analysis indicated that the repairing agent’s core materials were encapsulated in microcapsules.