Papers by Author: Jian Feng Yang

Abstract: The electroplating behavior of nanocrystalline CoNiFe soft magnetic thin film with high saturation magnetic flux density and low coercivity was investigated using cyclic voltammetry and chronoamperometry methods in conjunction with the scanning electron microscopy (SEM/EDX) and X-ray diffraction (XRD) techniques. The results show that, the co-deposition of CoNiFe alloy behaves anomalously. And the nucleation/growth process of CoNiFe ternary alloy followed 3D instantaneous mechanism at higher potentials, while in the case of lower potentials it followed 3D progressive mechanism.

Abstract: The Ni-TiN nanocomposite films have been successfully fabricated onto commercial brass copper substrates using dc electroplating technique, and the microstructure and anti-corrosion properties of the optimized Ni-TiN nanocomposite have been respectively characterized using scanning electron microscopy (SEM). The results show that the morphology of Ni-TiN composite film is sensitively dependent on the electroplating current density, the concentration of TiN nanoparticles, the solution stirring speed, the bath temperature and the solution pH value.

Abstract: Dense multiwall carbon nanotubes (MWNTs) reinforced barium aluminosilicate (BAS)–silicon nitride (Si3N4) composites were fabricated by hot-pressing sintering. The effect of MWNTs on the microstructure, compositional investigations, as well as mechanical characterization of the composites was investigated. The results show that MWNTs were preserved in the composites after sintering and present good adherence to matrix grains. The incorporation of 3% 1-2μm MWNTs effectively improved the fracture toughness of the BAS/Si3N4 composites from 8.02 to 8.6 MPa•m1/2.

Abstract: C/C-SiC brake materials were prepared by improved chemical liquid vaporized infiltration (CLVI) combined with liquid silicon infiltration (LSI) process, which needed less than thirty hours. The microstructure and frictional properties of the material were investigated. The density and porosity of the C/C-SiC brake material were 2.05 g/cm3 and 4.8%, respectively. The average dynamic friction coefficient of the materials was about 0.36, and the friction coefficient was stable. The average linear wear rate was less than 4.7 µm cycle-1 for rotating and stationary disk. The matrix composition and microstructure resulted in the high frictional performances.

Abstract: The self-propagating combustion reaction 0.741Mg + 0.247Fe2O3 + 0.188Ni + 0.318Cr → 0.741MgO + Fe0.494Ni0.188Cr0.318 was applied to prepare a nano-MgO reinforced Fe-Cr-Ni composite, by reactive hot pressing (RHP) under a condition of 700°C/30MPa/2h. The densification was enabled by the low temperatures produced by the exothermic reaction. According to TG-DTA and X-ray diffractometry (XRD), the highly-exothermic thermite reaction began at about 600°C and the in-situ formation of composites comprised predominantly of (FCC) Cr0.19Fe0.7Ni0.11, (FCC) Fe-Cr, (BCC) MgO and a small quantity of (BCC) MgFe2O4. The Vickers hardness was 3.67GPa, the three-point bending strength was 112.5±10MPa, and the fracture toughness was 3.28 MPa•m1/2. The microstructure of the composite was observed via scanning electron microscopy. This indicated that the distributions of in-situ-formed (BCC) MgO phases (~800 nanometers) were homogeneous into in a matrix of a fine-grained metallic alloy phases that gather together to form agglomerates in the composite.

Abstract: In this article, the microstructure, mechanical properties and machinability of the B4C/BN microcomposites and the B4C/BN nanocomposites were investigated. Homogenous distribution of the h-BN particles in the B4C ceramics appeared. The mechanical properties decreased gradually with the increasing content of h-BN for the both composites, while the nanocomposites demonstrated high performance. Machinability increased gradually with the increasing content of h-BN, and excellent machinability exhibited for both composites with more than 20wt% h-BN. The weak interface between the B4C matrix grains and the h-BN particles as well as the cleavage behavior of the laminate structured h-BN particles significantly attributed to the machinability of the B4C/BN composites.

Abstract: Effect of the warm processing parameters (the strain rate, forming temperature and deformation degree ) on the γ' metastable phase transformation in 2205 duplex stainless steel has been studied. The γ' metastable phase was located within the ferrite phase. Dynamic recovery took place only within the γ phase, and dynamic recrystallization underwent for the ferrite phase. The γ' metastable phase transformation was affected by the deformation degree and about 15% deformation led to appearance of the γ' metastable phase. γ' metastable phase formation by the precipitation of intragranular γ' was favored by increasing ageing time, and the size and content of γ' metastable phase were related to deformation temperature and strain rates.

Abstract: Effects of nitrogen content on hot ductility of duplex stainless steels have been investigated. With the increase of nitrogen content in the duplex stainless steels, mechanical strength increased, while hot ductility and elongation decreased. With the same strain rates and deformation degree, the high nitrogen content led to the high optimum hot ductility temperature for the high nitrogen DSS alloy. These results indicated the importance of control over the shape and volume fraction of phases in duplex stainless steels to achieve the optimum hot ductility.

Abstract: The barium aluminum silicate-silicon nitride (BAS-Si3N4) matrix-ceramic composite was fabricated using pressureless sintering, at temperatures ranging from 1720°C, which is below the melting point of BAS, to 1850°C. The effect of processing conditions on sinterability, crystalline structure, microstructure and mechanical properties was evaluated. It was demonstrated the BAS glass-ceramic served as an effective liquid-phase-sintering aid, to attain high densities and completed the α-Si3N4–β-Si3N4 phase transformation, and remained as a structural matrix that was reinforced by the rod-like β-Si3N4 grains. Si3N4 grains nucleated and grow in random directions in an almost completely crystallized matrix of hexacelsian BAS. High flexural strength (665±40 MPa) and fracture toughness (7.74 MPa•m1/2) could be obtained from 30wt%BAS-70wt%Si3N4 samples that have been sintered at 1800°C for 120 min with a fine-grained microstructure.

Abstract: Ti foil and Ni foil interlayers were selected for the bonding of tungsten to CuCrZr alloy. The effects of bonding temperature on the microstructures and shear strength of the joints were performed. The interfacial bonding mechanism was studied through microanalysis. The results show that Ti foil was transformed into liquid solution and extruded mostly out of the bonding zone at 980°C, the strength of the joints can reach 136MPa due to the chemical and mechanical interfacial bonding. Ni foil was used for bonding of tungsten to copper alloy, the EDS analyses shows that the solid solution Ni(W) and the intermetallic compound NiW2 form in the diffusion layer at 920°C.