Papers by Author: Zheng Yi Fu

Abstract: In this text, 5083 aluminum alloy was prepared with the method of the liquid nitrogen cryogenic milling (cryomilling). The microstructure,microstructural evolution and thermal stability of sample powder was investigated by XRD,SEM and DSC. The experimental results show that the particles size of 5083 aluminum alloy power during cryomilling was gradually reduced; milling time and milling speed are the main factors of affected alloy structure and performance, and high speed cryomilling could result in more uniform nanometer grains. The microstructure of the cryomilling 5083 aluminum alloy for 5 hours is micron-sized agglomerates with an average grain size of 45 nm.

Abstract: SnO2 nanocrystals with various morphologies were synthesized via a hydrothermal method assisting by the surfactant CTAB. The morphologies of the products were significantly dependent on the synthesis conditions. The products were characterized by X-ray diffraction (XRD) and field scanning electron microscopy (FESEM).The results showed products SnO2 nanoparticles and spheres like structure assembled with nanocones were obtained by varying the dosage of CTAB and the concentration of NaOH. The forming process of SnO2 sphere like structure was discussed and the proposed mechanism was put forward in this work.

Abstract: Within a very short heating period, fine mullite powder with practicle size below 1µm was obtained in a novel synthesis system, a self-propagating high-temperature synthesis (SHS) chemical furnace, from which the tremendous heating derived. The combustion reactants consisting of Ni, Al and TiC were chosen as a chemical furnace in this system to supply the heat, calcining temperature was increased at a heating rate of 1350K/min in the heating process, till the maximum temperature (1350°C). The rapid mullitization process was performed within 1 min, microstructure analysis indicated that small mullite grains (<50nm) were crystallized, fine mullite particles (<1µm) with narrow particle size distribution, favorable activity for sintering were derived. And significant grain growth was observed in mullite powder, when the combustion reactants consisting of Ni, Al and <30 mol.% TiC.

Abstract: Dense nanocrystalline Y2O3 ceramics without grain growth have been successfully obtained by a new method, which is based on the self-propagating high temperature synthesis and quick pressing. A suitable self-propagating system with a maximum combustion temperature of 1350 °C and a heating rate of 1300 °C/min was chosen as a chemical furnace to supply the heat to densify nanocrystalline Y2O3. Dense samples without grain growth were obtained when the applied pressure was 120 MPa.

Abstract: The Indium Tin Oxide(ITO) is known as a poorly sinterable material. The Spark Plasma Sintering(SPS) and the hot-pressing sintering(HP) were used to fabricate Indium Tin Oxide Ceramics from ITO nanoparticles. The maximum bulk density of 7.02 g/cm2(relative density; 98.2% TD)was obtained when sintered in Ar at 1000oC for 1min by SPS sintering. While the bulk density of 7.08 g/cm2(relative density; 99% TD) was obtained when sintered in Ar at 1050 oC for 4h by HP sintering.

Abstract: Mullite-based FeCr multifunctional composites were prepared by reducing (Fe, Cr)-doped mullite solid solution powders with different Cr/Fe ratio and successively hot pressing. Structural characterization revealed that the dispersion of intragranular FeCr alloy nanoparticles and intergranular iron grains in mullite matrix was obtained in nanocomposite powders. Dense mullite-FeCr composites were fabricated from nanocomposite powders by sintering at 1650 °C. The microstructures, mechanical and ferromagnetic properties of composites were strongly affected by the Cr/Fe ratio in initial solid solutions.

Abstract: Ultra-fine zirconium diboride (ZrB2) powders have been synthesized by borothermal reduction reaction, using zirconium oxychloride (ZrOCl2•8H2O) as the precursors of zirconia. The thermodynamic variation in the amorphous ZrO2-B system was studied by thermogravimetric and differential thermal analysis (TG-DTA). The precursors containing amorphous ZrO2 and B were heat-treated under a high heating rate. It is shown that the borothermal reaction can be completed at a relatively low temperature (~950 °C) and short duration (~5 min) under a heating rate of 200 °C/min. The synthesized powders have an average crystalline size of 300 nm with oxygen content less than 2.62 wt%.

Abstract: In this paper, a carbothermal reduction and nitridation (CRN) synthesis for cubic aluminum oxynitride (γ-AlON) powders is reported. The CRN reaction was conducted via a two-step synthesis procedure at a heating rate of 100 °C/min. In the first step, the mixture of fine γ-Al2O3 and soluble starch was annealed at 1550~1580 °C for different duration. It is found that the mixture of α-Al2O3 and AlN with an appropriate ratio can be obtained by CRN reaction. The content of AlN in mixture is closely related with the reaction condition. In the second step, the as-received mixture of α-Al2O3 and AlN was heat-treated at 1700 °C for 10 min. The single phase γ-AlON powders with particle size less than 3 µm were obtained.

Abstract: Here we have prepared B4C/CNTs composites using the spark-plasma sintering (SPS) method. Mechanical property measurements reveal obvious enhancement confirming the fabrication of true B4C/CNTs composite materials with improved toughness properties.The addition of 1wt% CNTs in the B4C increased the fracture toughness by about 1.6 times from 2.5 to 4 MPa.m1/2 because the CNTs presented at the B4C grain boundaries, made the length of cracks shorten.

Abstract: Pulse current heating technology is used to join TiB2-Ni cermets with Ti6Al4V at different temperatures (1023K, 1073K and 1123K) with 7MPa pressure and Cu foil and Ni foil are used as joining interlayer. Joint points increase with welding temperature. The microstructure of joints is observed through SEM images and micrographs. The diffusion coefficient (D0) of Cu at the Cu/TiB2 interface is calculated by the EPMA patterns. The diffusion principle of pulse current heating and influences of electric field and current on atom diffusion are studied.