Yongqiang Tan

Enhancement of sinterability and mechanical properties of B4C ceramics using Ti3AlC2 as a sintering aid

Boron carbide (B4C) ceramics are currently the leading control rod materials in fast nuclear reactors and promising high temperature structural materials. However, several drawbacks such as poor sinterability and low toughness seriously limit their wide applications. In order to enhance the sinterability and mechanical properties of B4C ceramics, titanium aluminum carbide (Ti3AlC2) was chosen as a new efficient sintering aid to densify B4C ceramics using spark plasma sintering. Fully dense B4C ceramics were obtained at a lower sintering temperature of 1500 °C by adding a small amount of Ti3AlC2. Meanwhile, the mechanical properties were enhanced remarkably. For B4C ceramics sintered with 15 vol% Ti3AlC2, optimized mechanical properties were obtained with Vickers hardness of 40.2 GPa and indentation fracture toughness of 4.7 MPa m1/2. These results indicate that Ti3AlC2 can be used as a novel sintering aid for the densification of B4C ceramics.

Lightweight graphene nanoplatelet/boron carbide composite with high EMI shielding effectiveness

Lightweight graphene nanoplatelet (GNP)/boron carbide (B4C) composites were prepared and the effect of GNPs loading on the electromagnetic interference (EMI) shielding effectiveness (SE) has been evaluated in the X-band frequency range. Results have shown that the EMI SE of GNP/B4C composite increases with increasing the GNPs loading. An EMI SE as high as 37 ∼ 39 dB has been achieved in composite with 5 vol% GNPs. The high EMI SE is mainly attributed to the high electrical conductivity, high dielectric loss as well as multiple reflections by aligned GNPs inside the composite. The GNP/B4C composite is demonstrated to be promising candidate of high-temperature microwave EMI shielding material.

Electromagnetic interference shielding performance of nano-layered Ti3SiC2 ceramics at high-temperatures

The X-band electromagnetic interference (EMI) shielding properties of nano-layered Ti3SiC2 ceramics were evaluated from room temperature up to 800°C in order to explore the feasibility of Ti3SiC2 as efficient high temperature EMI shielding material. It was found that Ti3SiC2 exhibits satisfactory EMI shielding effectiveness (SE) close to 30 dB at room temperature and the EMI SE shows good temperature stability. The remarkable EMI shielding properties of Ti3SiC2 can be mainly attributed to high electrical conductivity, high dielectric loss and more importantly the multiple reflections due to the layered structure.

Cathodic voltage-dependent composition, microstructure and corrosion resistance of plasma electrolytic oxidation coatings formed on Zr-4 alloy

Plasma electrolytic oxidation (PEO) coatings are fabricated on Zr-4 alloy by a pulsed bipolar power supply. When the anodic voltage remains constant, the variation of cathodic voltage exhibits a significant impact on the microstructure and corrosion resistance of the oxide coatings. Here we systematically investigate the influence of cathodic voltage on the phase composition, morphology, thickness, and elemental composition of the PEO coatings. Corrosion behaviors are evaluated by electrochemical impedance spectroscopy (EIS). The coating thickness and the electrolyte borne elements incorporated in the coatings both increase with the increase of cathodic voltage. It is interesting to note that the relative content of tetragonal ZrO2 and monoclinic ZrO2 also shows a strong cathodic voltage dependence. The coating formed at 50 V cathodic voltage shows the most compact microstructure with the largest amount of tetragonal ZrO2 and correspondingly exhibits the optimized corrosion resistance. The presence of t-ZrO2 is found to be beneficial for dense oxide coatings and better corrosion resistance. Therefore, cathodic voltage is an important parameter during PEO process to adjust the microstructure and the corrosion resistance performance of PEO coatings.

Dependences of microstructure on electromagnetic interference shielding properties of nano-layered Ti 3 AlC 2 ceramics

The microstructure dependent electromagnetic interference (EMI) shielding properties of nano-layered Ti3AlC2 ceramics were presented in this study by comparing the shielding properties of various Ti3AlC2 ceramics with distinct microstructures. Results indicate that Ti3AlC2 ceramics with dense microstructure and coarse grains are more favourable for superior EMI shielding efficiency. High EMI shielding effectiveness over 40 dB at the whole Ku-band frequency range was achieved in Ti3AlC2 ceramics by microstructure optimization, and the high shielding effectiveness were well maintained up to 600 °C. A further investigation reveals that only the absorption loss displays variations upon modifying microstructure by allowing more extensive multiple reflections in coarse layered grains. Moreover, the absorption loss of Ti3AlC2 was found to be much higher than those of highly conductive TiC ceramics without layered structure. These results demonstrate that nano-layered MAX phase ceramics are promising candidates of high-temperature structural EMI shielding materials and provide insightful suggestions for achieving high EMI shielding efficiency in other ceramic-based shielding materials.