Papers by Keyword: Hot-Press Sintering

Abstract: TiCN-based cermets were prepared by hot-press sintering through adding various amounts of AlN nanopowder (0-20 wt.%) into a 64 wt.% TiC_0.5N_0.5-10 wt.% WC-8.5 wt.% Mo-12.5 wt.% Ni-5 wt.% Co system. The microstructure and mechanical properties of the prepared cermets were investigated. For the prepared cermets, samples with 5 wt.% AlN nanopowder exhibited optimum mechanical properties of Vickers hardness 2191 HV₁₀, bending strength 601 MPa, and fracture toughness 6.03 MPa.m^1/2, respectively.

Abstract: In order to enhance the hydrogen permeation, Silicon carbide (SiC) was prepared with CeO₂-NiO mixed oxides via sol-gel process and the SiC membranes with various contents of χ wt% mixed oxides (χ = 20, 40, 60 and 80) were fabricated by hot-press sintering (HPS) at 1173 K under vacuum condition. The effect of the CeO₂-NiO mixed oxides was studied in terms of properties on hydrogen permeation. All the membranes were characterized by XRD, FE-SEM and BET instrument. The hydrogen permeation test was carried out at various temperatures under 0.1 MPa. Hydrogen permeation flux of the 80 wt% CeO₂-NiO/SiC membrane, which has the highest value, was obtained at 2.92×10^-6 mol/m²sPa, 323 K. The reaction enthalpy (ΔH°) was calculated as - 4.95 J/mol by Arrhenius’s plot.

Abstract: In this paper, full-density Al-Zn-Mg-Cu-Zr powder metallurgy (P/M) alloy is prepared by hot-press sintering in vacuum at 600°C. Experiments are conducted to evaluate the effects of Zn additive in the range of 7.2-8.4 wt.% on the microstructure and mechanical properties of Al-Zn-Mg-Cu-Zr alloys. X-ray diffraction (XRD), scanning electron microstructure (SEM) and electron probe micro-analyzer (EPMA), and mechanical properties such as tensile strength are measured. The porosity decreases gradually with increasing of Zn and it achieves 0.01% with a density of 2.95 g/cm³ at 8.4% Zn. The tensile strength reaches the maximal value of 436 MPa at 8.4% Zn.

Abstract: Mo-9Si-8B-3Hf alloy consisting of a Mo solid solution and intermetallic phases Mo₃Si and Mo₅SiB₂ was fabricated by hot pressing sintering to yield a fine microstructure with all three phases being in the size range of micrometer. The tensile properties of this alloy at elevated temperature were evaluated in vacuum at elevated temperatures. This alloy displayed extensive plasticity or superplasticity at temperatures ranging from 1400 °C to 1560 °C with strain rate of 3×10^-4 s^-1. The tensile elongation of 410% is measured at 1560 °C. Grain boundary sliding is the main mechanism of plastic deformation for this alloy.

Abstract: The nano Al₂O₃ -Cu/Cr composite was prepared by a simplified internal oxidation technique of the vacuum hot-press sintering-internal oxidizing method. The tensile strength and microhardness were determined respectively. The microstructures were analyzed by means of a scanning electron microscope (SEM). On the basis of above results, the main strengthening mechanisms were investigated by quantitative calculation of several strengthening effects. The experimental results show that the microhardness and tensile strength obviously increase with increased cold deformation. The main strengthening mechanisms of the nano Al₂O₃ -Cu/Cr composites are mainly attributed to the dispersion of the nano-scale of alumina particles and the aggregate of the Cr particle phase, of which the former can restrict the mobility of the dislocations and increase the density of dislocations. Meanwhile, the cold deformation strengthening has some important effect to a certain extent.

Abstract: Si3N4 ceramics have been fabricated through pressureless sintering and hot-pressing sintering with MgSiN2-Y2O3 or only MgSiN2 as sintering additive, respectively. The effects of MgSiN2 and Y2O3 and sintering methods on sintering properties of Si3N4 ceramics were studied. The results indicate that the bend strength of Si3N4 ceramic with 5.6wt.%MgSiN2-15.8wt.%Y2O3 sintered at 1820°C for 4h could achieve 839MPa. The bend strength of Si3N4 ceramic with 4.76wt.%MgSiN2 produced by hot-pressing sintering at 1750°C for 1h under uniaxial pressure of 20MPa is 1149MPa. The thermal conductivity of the Si3N4 ceramic was 92Wm-1K-1 and could remarkably increase to 129Wm-1K-1 by prolonging the sintering time from 1 h to 12 h. The present work demonstrated that MgSiN2 additives and hot-pressing sintering were effective to improve the thermal conductivity of Si3N4 ceramic.

Abstract: Si3N4-based composite ceramic tool materials reinforced with TiC0.5N0.5 particles were fabricated by using hot-press-sintering technique with Al2O3 and Y2O3 as sintering aids. The effects of the content of TiC0.5N0.5 on the microstructure and properties of composite ceramic were investigated. The experimental results show that optimal mechanical properties were achieved for the composite with the addition of 20 vol.% TiC0.5N0.5 microparticles, with the flexural strength, fracture toughness and Vicker's hardness being 838 MPa, 8.5 MPa•m1/2 and 15.6 GPa. The fracture surface microstructure of the composites is characterized by scanning electron microscopy (SEM). Phase identification was carried out by X-ray diffraction (XRD). It was found that the microstructure of the material was homogenous and the elongated grain of β-Si3N4 was interlaced. And the fracture surfaces were observed to exhibit a mix of intergranular and transgranular fracture.

Abstract: Aluminum nitride (AlN) is a stoichiometric compound with the hexagonal wurtzite structure. AlN has excellent thermal conductivity and good properties as electronic insulator. It displays good mechanical resistance up to elevated temperatures and is resistant against corrosion by molten metals. Bulk AlN may therefore be used as a refractory structural material as well as a substrate for high power microelectronic devices. However, it is very difficult for sintering high-density AlN at lower temperature than 1800°C. Nano-sized AlN powders were sintered by hot press sintering at low temperature of 1500~1700°C and mechanical properties were investigated. β-AlN and β-Al2O3 were detected when the sintering temperature is 1600°C. The phase transition β-AlN to α-AlN was discovered at a 1700°C sintering temperature. Relative density and average grain size were increasing with the increasing of sintering temperature, and fracture form is intercrystalline crack in 1500°C and transcrystalline crack in 1700°C. 97.3% relative density and 850nm average grain size were deserved at 1700°C.

Abstract: Nowadays, the most promising methods for high purity hydrogen production are membranes separation such as polymer, metal, ceramic and composites. It is well known that Pd and Pd-alloys membranes have excellent properties for hydrogen separation. However, it has hydrogen embrittlement and high cost for practical applications. Therefore, most scientists have studied new materials instead of Pd and Pd-alloys. On the other hand, TiN powders are great in resistance to acids and chemically stable under high operating temperature. In order to get specimens for hydrogen permeation, the TiN powders synthesized were consolidated together with pure Co powders by hot press sintering. During the consolidation of powders at HPS, heating rate was 10K/min and the pressure was 10MPa. It was characterized by XRD, SEM, and BET. Also, we estimated the hydrogen permeability by Sievert's type hydrogen permeation membrane equipment.

Abstract: Hydrogen has attracted clean energy media as a high-quality and renewable energy source in recent years. On the one hand, a ceramic catalyst and/or catalyst support such as Al2O3 has often been a preferred choice due to their specific properties such as thermal stability and high surface area. Al2O3-CuO-ZnO was synthesized by using the sol-gel process with aluminum isopropoxide and primary distilled water as the precursor and solvent. In this synthesized process, metal oxides caused to precursors such as copper and zinc nitrate were added. To prepare membranes, cobalt metal powder was used to increase the strength and durability. The Al2O3-CuO-ZnO/Co composite membranes were produced using hot press sintering for consolidation of powders following reactively mechanical alloying process. The characterizations of membrane were measured XRD, FE-SEM and EDS. Hydrogen permeation evaluations were examined at a room temperature to 773 K under increasing pressure. Hydrogen permeation rate was obtained with 0.18 mol m-2 s-1 at 773 K result from complex diffusion mechanism such as Sievert’s type, Knudsen diffusion and/or molecular sieving.