Papers by Author: Ping Feng

Abstract: Effect of pH value and dispersant of polyethylene imine (PEI) on dispersion of nano TiN in ethanol liquid was investigated by sedimentation volume and viscosity, surface electric characteristic of particles was measured by Zeta potential. Results showed that pH value and PEI concentration had an important effect on dispersion of nano TiN. Excellent dispersibility was obtained through adjusting PEI amount and pH value. It was found that PEI was an efficient dispersant for nano TiN to disperse in ethanol liquid. The dispersibility follows by electrostatic and space steric stability mechanism.

Abstract: Element Mo plays a significant role in Ti(C,N)-based cermets. In this work, mixing was carried out in water and cermets with high mechanical properties were fabricated. The effect of Mo₂C content on microstructure and composition was investigated by field emission scanning electron microscope (FSEM) and energy dispersive spectrometer (EDS). Results showed that microstructure becomes uniformly distributed, binder distribution becomes symmetrical and the particle size becomes small with increase of Mo₂C content. The volume fraction of (outer + inner) rim structure increases, the volume fractions of core structure and binder phase decrease instead. It was found that Mo₂C content in raw material affects compositions in phases. With the level of Mo₂C content rising, the concentration of element Mo in rim structure increases, the concentration of element Ti in binder decreases.

Abstract: The invention of functionally graded structure cemented carbide is a significant revolution. In this paper, graded structure cemented carbide with cubic carbide free layer (CCFL) was prepared. Using scanning electron microscope (SEM), metallographical microscope, electroprobe microanalyzer and microindentation, the gradient characteristics were investigated. The variation in elemental compositions from surface to inner is gradient, the concentrations of nitrogen and titanium are very low in surface layer, only element of tungsten, cobalt and carbon exist. A cobalt concentration peak occurs, which is higher than the average composition in bulk. Wherein binder phase piles up, its volume fraction is much higher than nominal value, resulting in a decrease in hardness and forming a tough layer.

Abstract: Ti(C, N)-based cermet and functionally gradient Ti(C, N)-based cermet were prepared by vacuum sintering and post surface heat-treatment in nitrogen, respectively. Tribological behaviors of obtained cermets were comparatively studied. Dry sliding wear and cutting test were conducted against quenched medium carbon steel. It was found that a graded structure formed and the surface hardness of functionally gradient Ti(C, N)-based cermet was improved. Friction coefficients of both cermets decreased with the increase of the sliding speed. The friction coefficient of Ti(C, N)-based cermet was lower than that of functionally gradient Ti(C, N)-based cermet at the conditions of higher sliding speed and higher load. The cutting test demonstrated that Ti(C, N)-based cermet exhibited better cutting performance and higher wear resistance than the cemented carbide YT15, cermet TN20 and functionally gradient Ti(C, N)-based cermet, while the functionally gradient Ti(C, N)-based cermet exhibited a similar performance as YT15 and TN20.

Abstract: Barium strontium titanate Ba0.6Sr0.4TiO3 (BST) thin films were fabricated by pulsed laser deposition (PLD) technique on Pt/TiO2/SiO2/Si substrate with and without high (100) oriented LSCO buffer layer. Crystal structure and surface morphology of BST thin films with and without LSCO buffer layer were characterized by X-ray diffraction (XRD) and atom force microscope (AFM). The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 100 Hz to 1M Hz and at room temperature. It was found that the LSCO buffer layer was beneficial for BST films to decrease surface roughness, dielectric loss and to increase grain size, dielectric constant, tunability and figure of merit (FOM). The influence of LSCO buffer layer on the microstructure, dielectric and tunable properties of BST thin films were analyzed. At 1M Hz, the dielectric constants of BST films with and without LSCO buffer layer are 684 and 592, respectively. The tunability of BST thin film with LSCO buffer layer was about 65.48%, which was higher than that (about 41.84%) of BST thin film without LSCO buffer layer.