Advanced Materials Research Vol. 709

Abstract: Residual stress produced on the surface of nanostructured ceramic coatings when they were grinded by diamond superhard abrasive wheel, these residual stresses affected directly the fracture strength, fatigue strength and corrosion resistance of the ceramic parts, they affected the surface quality of machined ceramic parts, and thus they affected the working reliability and the service life of ceramic parts. The tests show that the distribution of residual stress is directional, the residual compressive stress can make the hardness of the material increase, they can reduce the wear rate of the material, for the tested specimen, grinding surface whole residual stress σ is the sum up original residual stress σ₀ (existed in the part’s surface ) and grinding residual stress Δσ (formed by grinding process.), σ=σ₀ + Δσ.

Abstract: A series of semi-interpenetrating polymer materials of poly (vinyl alcohol)/poly (N, N-diethylacrylamide-co-methacrylic acid)(PVA/PDM) were synthesized by free radical copolymerization techniques and semi-interpenetrating polymer network techniques at room temperature with ammonium persulfate and N,N,N',N'-tetramethylethylene diamide as initiators and N,N'-methylenebisacrylamide as a crosslinker. The interior morphology by scanning electron microscopy (SEM) revealed that PVA introduced PDM materials have interconnected porous network structures. The release behaviors of the model drug, aminophylline, are found dependent on material composition and environmental temperature, which suggests that these materials have potential application as intelligent release carriers.

Abstract: Reported here is a new method of fabricating the graphene/silicon schottky junction. Using a femtosecond laser, graphene oxides are reduced to graphene and behave a metal. The junction of reduced GO and Si shows rectifying behavior indicating that the junction is schottky junction. Take advantage of the laser fabricating method, one can get reduced GO at any position on the substrate. Xps spectra shows that the reduced GO has only 12% oxygen content, and it is truly have a good conductivity similar to metal. This method opens a new effective way to graphene-based micro nano electronics.

Abstract: The hot deformation behavior of U720Li was investigated by isothermal compression tests at temperature ranging from 1060-1180°C and strain rate from 0.001s^-1 to 20s^-1. The flow stress-strain curves and microstructures were investigated and a constitutive equation was established. It is found that flow stress is sensitive to stain rate and deformation temperature greatly. The higher stain rate resultes in a larger fluctuation in flow stress. The hot deformation activation energy is determined to be 552.8kJ/mol. Grain size increases with increasing temperature and decreases firstly and then increases with increasing strain rate. U720Li alloy should be deformed below the solve temperature of γ primary phase with lower strain rate in order to obtain the even and fine grain size.

Abstract: Germanium nanocrystals (Ge-nc) were produced by the implantation of Ge+ into a SiO₂ film deposited on (100) Si, followed by a high-temperature annealing. High-resolution transmission electron microscopy (HRTEM) has been used to investigate the defect structures inside the Ge-nc produced by different implantation doses (1×10¹⁶, 2×10¹⁶, 4×10¹⁶ and 8×10¹⁶ cm^-2). It has been found that the planar defects such as nanotwins and stacking faults (SFs) are dominant in Ge-nc (60%) for the samples with implantation doses higher than 2×10¹⁶ cm^-2, while for the sample with an implantation dose lower than 1×10¹⁶ cm^-2, fewer planar defects are observed in the Ge-nc (20%). The percentages of nanotwins in the planar defects are 87%, 77%, 67% and 60% in four samples, respectively. The twinning structures include single twins, double twins and multiple twins. We also found that there are only SFs in some nanocrystals, and in others the SFs coexist with twins. These microstructural defects are expected to play an important role in the light emission from the Ge-nc.

Abstract: In this work, characteristic temperatures of thermal analysis cooling curves of ductile iron melt during fading process were compared, and the graphite morphology of the corresponding samples were studied. Results show that the cooling curves response degradated nodularization promptly, and there are correspondences between the characteristic temperatures of cooling curve and graphite morphology. It indicates that it is feasible to estimate the fading situation of the melt rapidly by identifying the characteristic temperatures of the thermal analysis cooling curves.

Abstract: A facile hydrothermal route has been developed to prepare MnO2/graphene nanocomposites and MnO2 nanoparticles are uniformly anchored on graphene nanosheets. The composite were studied as the anode material for lithium-ion batteries. The surface of graphene is modified by MnO2 nanoparticles which are 10-30 nm in size and homogeneously anchor on graphene sheets. The composite exhibits superior lithium battery performance with higher reversible capacity and better cycling performance. The reversible capacity is up to 781.5 mAh g-1 at a current of 100 mA g-1 and maintains 96% after 50 cycles. The enhanced lithium storage performance is due to the synergetic effect of graphene and MnO2.

Abstract: In the present work, experimental research on grain growth kinetic at different temperatures and times of heat treatment for superalloy U720Li has been carried out. The average grain sizes have been obtained under different heat treatment temperatures and times. The aim of the present study was to quantify the progress of grain growth and the corresponding activation energy and growth exponent. It has been found that both the activation energies for grain growth and growth exponent differ a lot between before and after the solution of the primary γ phase. The activation energies increase with the increase in holding time. Those trends might be due to the different solute drag effect and the variational lattice constant of γ phase.

Abstract: The three kinds of WC-12Co coatings were sprayed by High Velocity Oxygen/Air Fuel Spray (HVO/AF) in three different spray conditions, HVOF、HVO-AF and HVAF. The high velocity flame flow was produced by HVO/AF with the burning of kerosene and propellant which was mixed by oxygen and air at different ratio, it can be controlled from 1400°C to 2800°C.The microstructure was investigated by SEM, the phase composition was tested by XRD, and the microhardness and elastic modulus of coatings were investigated. The results indicate that the coatings with better adhesive strength and little porosity than conventional ones are dense and have a large value of elasticity and a high microhardness which is 0.4 times harder than the conventional coatings. The coatings are mainly composed of WC and Co, and there are also traces of W2C and Co6W6C. As temperature decreased, the decomposition of WC is being reduced.

Abstract: Single crystals of Bi₂Se₃ topological insulators have been prepared though melt-grown reaction. The sintering parameters of holding time and cooling rate obviously affect the phase structure and electrical properties. The samples with layered structure can be perpendicular cleaved with (0 0 L) axis. All the samples show n-type conductivity caused by the existence of Se vacancies. For low cooling rate, more Se atoms anti-occupy Bi lattice sites, which decreases c-axis lattice parameter and increases carrier concentration n; high cooling rate increases c and decreases n because of less Se atoms occupying Bi lattice sites. Increasing holding time firstly decreases the ratio of Se atoms occupying Bi lattice sites and then increases it, which gives rise to c firstly increase then decrease and n firstly decrease then increase.