Papers by Author: Xing Long Duan

Abstract: The transition-metal carbide cemented by metal has excellent combined properties. In this study, cermets were prepared by vacuum sintering from carbide-metal composite powders. The transition- metal oxides (Cr2O3, MoO3, V2O5, Nb2O5 and TiO2), cementing-metal oxides (Co3O4 and NiO), and carbon black were used as raw materials to pre-synthesize composite powders such as Cr3C2-Co, Mo2C-Co, VC-Co, NbC-Co and TiC-Ni, by a direct reduction and carburization process in vacuum. Results show that the participation of Co3O4 and NiO as well as the vacuum circumstance were greatly propitious to the carburization of transition-metal oxides into carbides. The carbothermal condition was greatly improved by the direct reduction and carburization process.

Abstract: Tungsten carbide (WC) targets with low cobalt (Co) content (0.1 - 0.2 wt.%) were prepared by hot-press sintering at 1700°C for 60 minutes in argon, from element starting powders of tungsten, cobalt and carbon. Results show that the as-fabricated targets yield relatively high relative density above 99% and high HRA above 92. WC with low Co content is formed easily than pure WC. The hot-press sintering process, while element starting powders are used, is an in-situ reaction technique for accelerating the WC’s diffusion rate to obtain a dense sintered body.

Abstract: YSZ-NiCr powder was synthesized by gel-reduction process at 850°C for 2 h. YSZ-NiCr cermet was fabricated by hot-press sintering at 1350°C for 1 h. The powder has a mean particle size of 42 nm and the sintered specimen has a fine and homogeneous microstructure with a mean crystalline size of 0.2 &m. The conductivity has a tendency to decrease with increasing temperature. This behavior can be accounted for that there are two conduction paths through the cermet, an electronic path through the Ni/Cr metal phase and an ionic path through the ZrO2-Y2O3 phase. The objective of this work is to give a possible improvement in the cermet anode of SOFC.

Abstract: Nanocomposite WC-10Co powder produced by spray pyrolysis-continuous reduction & carbonization technology and cubic boron nitride (CBN) plated with titanium by vacuum vapor deposit were used, and this paper adopted spark plasma sintering (SPS) process to prepare CBN enhanced ultrafine WC-10Co cemented carbide cermets composite material. The microstructure and mechanical properties of CBN-WC-10Co composites were investigated. The results show that CBN-WC-10Co composites consolidated by spark plasma sintering can reach 95.0 % relative density, and transverse rupture strength (TRS) is 1050 MPa, the average grain size of cermets matrix is less than 420 nm, and CBN-WC-10Co composites with excellent properties are achieved. The CBN still remains very good crystal shape after 1240°C spark plasma sintering, and there is not obvious clearance between CBN plated with titanium and the cermets matrix, the coated titanium layer can not only improve the thermal stability of CBN, but also increase the properties of CBN-WC-10Co composites.

Abstract: WC-10Co nanocomposite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing (HIP). Influences of ball-milled time on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that ultrafine WC-10Co cemented carbides can reach 99.79% relative density, and transverse rupture strength is more than 3750MPa, Rockwell A hardness is more than 92.6, the average grain size is less than 440 nm, when ball-milled time is 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and fine microstructure is obtained. The optimum ball-milling time is 48 hours.

Abstract: WC-10Co nanocomposite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing (HIP). Influences of ball-milled time on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that ultrafine WC-10Co cemented carbides can reach 99.79% relative density, and transverse rupture strength is more than 3750MPa, Rockwell A hardness is more than 92.6, the average grain size is less than 440 nm, when ball-milled time is 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and fine microstructure is obtained. The optimum ball-milling time is 48 hours.