Zhou Xingtai

Coalescence of Multi-Walled Carbon Nanotubes and their Electronic Conduction Nano-Networks

A random two-dimension electronic conduction nano-network of MWCNTs is fabricated by N ion beam irradiation. The CNTs networks were fabricated by the coalescence of MWCNTs at the crossing and the parallel positions. An increase in electrical conductivity of CNT network was observed by a factor of 1.44 after it was subjected to ion beam irradiation. The increased electrical conductivity resulted from increased inter-CNT transport of charge carriers, with the cross-links acting as bridges between successive CNTs. This phenomenon of increased electronic conduction resulting from coalescence through N ion beam irradiation is discussed.

EFFECT OF LONG-TERM AGING ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALLOY C276

Nickel-based superalloy C276 had become one of the alternative materials in simulation loop of thorium molten salt reactor (TMSR) nuclear power system. The strength and plasticity decay of C276 alloy under high temperature environment for long time will directly threatened the security of simulation loop of TMSR. The microstructure of C276 alloy after long-term aging at 700 degrees C was studied by TEM and SEM with EDS, and the high temperature mechanical performance of C276 alloy after aging was researched at 700 degrees C with an universal high-temperature materials testing machine. At the same time, the morphology of tensile fracture was analyzed by SEM. The results show that massive block mu phase and M6C carbides are precipitated after long-term aging with 700 degrees C at the grain boundaries and within grains of C276 alloy, and the block precipitated phase grains grow up with aging time, some precipitated grains at boundaries extend forward the interior of based crystal. The alloy is strengthened by the effect of precipitation phase, so the strength is not reduced after long-term aging at 700 degrees C high temperature. As aging time increases, the plasticity of C276 alloy reduces firstly and then increases to the peak after aging 720 h, and decreases again. However, the plasticity of C276 alloy still maintain well after longer aging time. The high temperature tensile fracture mode of C276 alloy is ductile fracture after long-term aging.

Strain Induced Metastable Phase and Phase Revolution in PbTiO3-CoFe2O4 Nanocomposite Film

An inter-component epitaxial strain-induced PbTiO3 metastable phase is observed in a PbTiO3-CoFe2O4 epitaxial composite film, corresponding to the dielectric anomaly reported previously. High-resolution synchrotron radiation X-ray diffraction and first principles calculation demonstrate the coexistence of different PbTiO3 phases, even a possible morphotropic phase boundary in the film, elucidating the underlying microscopic mechanism of the formation of PbTiO3 metastable phase. This sheds light on the design and manipulation of electromechanical properties of epitaxial films, through the strain engineering.

Effect of Long Time Thermal Exposure on Microstructure and Mechanical Properties of C276 Superalloy

Due to the perfect mechanical properties and acceptable corrosion resistance, nickel-based superalloy C276 has been selected as the primary structure material of the experimental loop in thorium molten salt reactor (TMSR) program. In this work, microstructures and mechanical properties of C276 after long time exposure at700 °C have been investigated. SEM and TEM results indicate that the major precipitations of the alloy are μ phase and M6C carbides, which dispersing at grain boundary are transformed gradually to continuous-chain distribution with aging time. The shapes of μ phase are massive, layered and needle-like. The increase of tensile strength and decrease of elongation have been observed with aging time, which relate to μ phase at both grain boundary and grain interior of the aged alloy. The optimum of ductility is obtained at 700°C for 720h and the high temperature tensile fracture presents ductility feature.