Papers by Author: Wei Gang Zhang

Abstract: Ni/BN and NiCrAl/BN abradable sealing coatings used in turbo engines were prepared by plasma spray technology. The phases and the microstructures of the coatings were characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Corrosion behaviors of these coatings were investigated with open-circuit potential (OCP) and salt spray corrosion test. The results showed that the NiCrAl/BN possess better corrosion resistance as compared with Ni/BN.

Abstract: In this study, two kinds of NiCr/Cr3C2-BN composite powders were prepared with individual cladding (FKBN) and low pressure spray granulation (YLBN) methods, and the derived NiCr/Cr3C2-BN coatings were fabricated by plasma spraying technology. The microstructure, mechanical and tribological properties of the two coatings were systematically investigated. Both NiCr/Cr3C2-BN coatings have relatively high adhesive strength and microhardness, but the porosity of YLBN coating is much lower than that of FKBN coating. With comparison to FKBN coating, YLBN coating showed lower friction coefficient and better wear resistance, which was attributed to the more compact microstructure and uniform distribution of BN in the coating.

Abstract: CaB2O4 was added into hexagonal boron nitride (hBN) to improve the sintering behaviors of hBN. CaB2O4 and hBN were mixed and then pressed into plates. The plates were sintered at 2000°C for 5h under a N2 ambience. The phase compositions with different CaB2O4 contents were examined with X-ray diffraction analysis. The fracture cross-sections of the hBN plates were investigated by SEM. The apparent density and Rockwell hardness were also measured. The results show that the hBN particles had a plate-like shape and the grain sizes of hBN increased with increasing CaB2O4 contents. The apparent density and Rockwell hardness decreased with increasing CaB2O4 contents. When the CaB2O4 content was 15(wt) %, the hBN has the average grain sizes of 3μm in diameter and 200nm in thickness, the apparent density of 1.06 g/cm3 and the Rockwell hardness of 3, respectively.

Abstract: ZrB2-SiC-BN ultrahigh-temperature ceramic (UHTC) was fabricated by hot-pressing at 1800°C under 23MPa pressure of argon. Compared to ZrB2-SiC, the flexural strength of ZrB2-SiC-BN composite material was enhanced by adding 30% BN, and the fracture toughness showed a slight decrease, while the hardness decreased sharply. The addition of 30% BN also noticeably improved the machinability of the composites. Furthermore, ablation resistance tests were carried out using an oxyacetylene torch under subsonic conditions. Results indicated that a coherent compact scale of zirconium silicate was formed, which acted as an effective barrier against the inward diffusion of oxygen.

Abstract: La2Ce2O7 nano-powders with cubic fluorite structure have been firstly prepared by Molten Salts method. These nano-powders were prepared at relatively low temperatures(800°C and 900 °C) at different time, using La(NO3)3•6H2O and La(NO3)3•6H2O as raw materials, as well as K2SO4 (anhydrous) and Na2SO4 (anhydrous) as molten salts and dispersant. XRD, SEM were used to characterize the composition, morphology and size of prepared products. The procedure is facile and suitable for the synthesis of the La2Ce2O7 nano-particles and it will be an excellent method for preparation of other pyrochlore type of rare earth zirconate (Re2Zr2O7, Re=rare earth).

Abstract: In order to improve the surface properties of the machine parts, the NiAl cladding Cr3C2 powder were flame and plasma sprayed. The morphology, microstructure, composition and wear properties of the coatings were examined. The results show that due to the exothermal reaction of the Ni and Al elements, the bonding strength of the coatings are improved, and the main compositions of the coatings are Ni3Al inter-metallic compound and Cr3C2. The flame sprayed and plasma sprayed coatings show almost the same micro-hardness and friction coefficient. But the microstructure of the plasma sprayed coating is more compact than that of the frame sprayed one and the wear resistance of the flame and sprayed coatings is 30% and 120% higher than that of the 1045 steel, respectively. The main wear mechanisms of the coatings are plastic deformation and spallation, and the high bonding strength and the uniformly distributed Cr3C2 particles play important anti-wear roles.