Papers by Author: Yue Zhang

Abstract: In this paper, the effect of heat treatment on the microstructure and mechanical properties of a deformed Co-Cr-Ni-W superalloy strip was investigated. The cold-rolled superalloy was annealed at different temperatures 500°C~1240°C for 10min. It was found that hardness increased in the range temperature 500°C~800°C, the annealing had aging strengthening effect, this was due to the fcc~hcp transformation. As the annealing temperature is higher than 800°C, the hardness decreased with the increase of the annealing temperature. There were four inflection points in the influence of annealing temperature on the hardness of the alloy, which were about 800°C,900°C,1050°Cand 1150°C. From 800°C to 900°C, the hardness of the alloy decreased rapidly, recovery and recrystallization was initial. From 900°C to 1050°C, the hardness of the alloy decreased slower, recrystallization was finished and grain growth slowly. The temperature reaches 1050°C to 1150°C, the hardness curve decreased rapidly, carbides dissolution and grain growth was considerable. Above 1150°C, the hardness tended to be stable, the grain growth of the alloy was obvious, and more annealing twins were also formed. As the annealing temperature increased, the tensile strength decreased and the elongation increased. Keywords Cobalt-base superalloy; Heat treatment; Microstructure; Mechanical Properties Yong-Ji Niu,Yue Zhang University of Science and Technology Beijing,Beijing 100083,china; e-mail: niuyongji@163.com Yong-Ji Niu, Zhi-Wei Zhang, Ning An, Yang Gao Beijing Beiye Functional Materials Corproration, Beijing 100192, China

Abstract: Piezoelectric properties of ZnO nanowires orientated along [0001] are investigated via density functional theory (DFT). A new method to calculate the volume of nanowires was proposed, which is crucial to the value of piezoelectric coefficients. Results show that the axial effective piezoelectric coefficients are 29.99 Cm^-2, 25.93 Cm^-2, 22.82 Cm^-2 for ZnO nanowires with diameters of about 0.6 nm, 1.2 nm, 1.8 nm, which are considerably larger than that of the bulk (20.19Cm^-2). It is found that the change in volume during the strain played a dominated role in size effects. This work helps to gain a deeper understanding of the piezoelectric size effects in ZnO nanowires.

Abstract: Large quantities of ZnS dentalation nanostructures were synthesized successfully at low temperature using a simple chemical vapor deposition method, and the microstructures and field emission properties of the dentalation structures were investigated. The results indicated that the stem of the dentalation structures is single-crystalline but the surfaces of the teeth are amorphous. The photoluminescence properties show a strong green emission at 520.89 nm due to S vacancy. Investigations on the field emission properties of the ZnS dentalation nanostructures imply that the turn-on field is about 5.56V/μm at an anode-cathode distance of 150μm, which should be attributed to the specific sharp tips and high aspect ratios of the present needle-shaped structure. The field emission behavior of the ZnS obeys Fowler-Nordheim relationship. The results could be valuable for using the ZnS nanostructure as cold-cathode field-emission materials.

Abstract: At present, it is scarcely possible to represent results in deterministic calculation in the definite finite element analysis. Stochastic finite element method is on the basis of the combination of mathematical statistics and the finite element method. Then we can use mathematical statistics to analyze the randomness of the parameters, get the data of dependent displacement and stress, and finally calculate all kinds of features. In this paper, modeling and calculation function and unique PDS module offered by ANSYS are applied to analyze the reliability of lateral load bearing single-piles.

Abstract: Combined SHS with casting, in-situ Al₂O₃ particle-reinforced copper matrix composite was fabricated. The effects of the load and Al₂O₃ particle on the friction coefficient and wear volume were investigated. And the wear resistance of composite was compared with that of pure copper. The results show that with the increase of load, the coefficient of the copper increases, while it decreases slightly as to composite. The wear volume of the composite is always lower than that of copper. The highest relative wear ability is 4.5, which indicates a better wear resistance..

Abstract: Mn doped ZnS nanowires with typical wurtzite single-crystalline structure were successfully synthesized via H₂ assistant chemical evaporation deposition method. The investigations indicated that the diameter of Mn/ZnS Nanowire with high aspect ratio is 25~40nm, EDS results show that the content of Mn element is about 4.45at%. HRTEM and SAED results demonstrated that the Mn/ZnS nanowires grow along [101] direction, which was different from the common direction reported in literatures. Room temperature photoluminescence properties were also examined, showing a strong green emission centered at 523.04 nm, and a weak emission at 382.53 nm was also observed, showing a red shift of 45.53 nm comparing to the intrinsic luminescence.

Abstract: First-principles density functional calculations were performed to investigate mechanical properties of ZnO nanowires and the size effects. Structural optimizations were performed first, and a series of strains were applied to the nanowires in the axial direction. The ground state energies were calculated and the elastic moduli of ZnO nanowires were obtained from the energy versus strain curves. It is found that the elastic moduli of the ZnO nanowires with three different diameters (1.2, 1.5 and 1.8nm) are 136.3, 138.7 and 138.0 GPa, respectively, and that of bulk ZnO along [0001] direction is 140.1 GPa. The elastic modulus of ZnO nanowire is slightly lower than that of the bulk and it decreases as the diameter decreases. Comparisons to experimental results and theoretical predications are made.

Abstract: The electrical properties of single ZnO nanowire were researched in the chamber of a scanning electron microscope under high-vacuum conditions using nanomanipulator and measurement system. The result shows that ZnO nanowire resistivity was about 1.4 Ω•cm with Ohmic contact. The local change of electron density induced by Shottky contacts or Ohmic contact with tip and semiconductor/metal materials significantly affects the current transport through the nanowire. Single ZnO nanowire was configured as field effect transistors (FET) and based on metal tantalum (Ta) as electrodes show a pronounced n-type gate modulation with an electron concentration of ~1.0×1019 cm−3 and an electron mobility of ~52 cm2 /V s at a bias voltage of 1 V.

Abstract: We report the poly(3iophene) (P3HT)/ZnO nanobelt hybrid p-n junction diodes characterized by using a conductive atomic force microscope (C-AFM). The diodes exhibited a turn-on voltage of about 2.5 V and ideality factor of about 11.6. The obvious current steps in the I-V characteristics under the reverse bias were clearly observed at room temperature. The origin of these steps is suggested to be attributed to the charge injection-trapping induced by nanoparticles on the surface of the ZnO nanobelt.

Abstract: The plasma-induced emission properties of ZnO nanorod and carbon nanotube (CNT) arrays were investigated under the pulse electric field. The formation of plasma on the array surface was found and high intensity electron beams were obtained from the two kinds of arrays. The plasma-induced emission properties of the ZnO nanorod and CNT arrays have big differences. Under the same electric field, the CNT arrays have higher emission current than the ZnO nanorod arrays. With the emission currents changing, the electron emissions of the ZnO nanorod arrays always are very uniform; but that of the CNT arrays are non-uniform. The plasma expansion velocity of the ZnO nanorod arrays is lower than that of the CNT arrays. Accordingly, the emission stability of the ZnO nanorod arrays is better than that of the CNT arrays.