Sun Xu-dong

Al2O3/TiCN-0.2% Y2O3 Composite Prepared by HP and Its Cutting Performance

Abstract Al2O3/TiCN-0.2% Y2O3 composites were fabricated by hot pressing sintering. The effect on mechanical property and microstructure of the sample composition and HP temperate was investigated. The results of Al2O3/TiCN-0.2% Y2O3 were satisfied. The bending strength, fracture toughness, Vickers hardness was respectively 1015 MPa, 6.89 MPa·m1/2 20.82 MPa at 1650 °C for 20 min. Good wear resistance was found for the kind of ceramic material when used as cutting tools in the machining of the hardened carbon steel. By the compared experiment for the cutting performances, it could be seen that the performance of this composite material was better than that of the ceramic tool material YT15 for continuously cutting quenched steel. This kind of composite tool material is suitable for continuously cutting quenched steel No.45, especially intermittently cutting quenched steel.

Synthesis of Al2O3/TiCN-0.2%Y2O3 Composite by Hot Pressing

Abstract Al2O3/TiCN composites were synthesized by hot pressing. The influences of components and HP temperature on mechanical properties, such as bending strength, breaking tenacity and Vickers hardness were investigated. The results showed that the mechanical properties of Al2O3/TiCN composite increased with temperature when hot pressing temperature is below 1650 °C. The mechanical properties reached their maximums when the composites were sintered at 1650 °C for 30 min under hot pressing pressure of 35 MPa, the value of bending strength, breaking tenacity and Vickers hardness was 1015 MPa, 6.89 MPa · m1/2, and 20.82 MPa, respectively. When hot pressing temperature was above 1650 °C, density decreased because of decomposition with increased temperature, and mechanical properties dropped because of rapid growth of grains in size at high temperature. Microstructure analysis showed that the addition of Y2O3 led to the formation of YAG phase so as to inhibit the growth of crystals. This helped to improve breaking tenacity of the composites. TiCN particles with diameters of 1 μm dispersed at Al2O3 grain boundaries, inhibited grain growth and enhanced mechanical properties of the composites. SEM study of the propagation of indentation cracks showed that the bridge linking behavior between matrix and strengthening phase might lead to the formation of the coexisted field of crack deflection, branching and bridge linking. The mechanism of this phenomenon was that the addition of Y2O3 improved the dispersion of TiCN particles so as to enhance the tenacity of the composites. The breaking tenacity was changed from 5.94 to 6.89 MPa · m1/2.

Synthesis of Scandium Oxide Nano Power and Fabrication of Transparent Scandium Oxide Ceramics

Abstract Synthesis of Sc 2 O 3 nanopowder from scandium sulfate and hexamethylenetetramine [(CH 2 ) 6 N 4 ] using a precipitation method was investigated. Fourier transform infrared spectroscopy combined with differential thermal analysis/thermo-gravimetry analysis showed that chemical composition of the precursor precipitates was (Sc(OH) 2.2 (SO 4 ) 0.04 )·0.4H 2 O. Phase transformation of the precursor precipitated during calcinations was investigated by X-ray diffractometry. A Sc 2 O 3 nanopowder with good dispersion and a mean particle size of 80 nm was obtained by calcining the sulfate precursor at 1100 °C for 4 h. The Sc 2 O 3 nanopowder was sintered into transparent Sc 2 O 3 ceramic by vacuum sintering at 1700 °C for 5 h without any additives.

Effect of Zn on Microstructures and Properties of Mg-Zn Alloys Prepared by Powder Metallurgy Method

Abstract Mg-Zn alloys were prepared by a powder metallurgy method using Mg powder and Zn powder as starting materials. The effects of the Zn content on sintering density, microstructure, phase composition, bending properties and micro-hardness of the Mg-Zn alloys were studied. The corrosion resistance of the Mg-Zn alloys was also measured. The function mechanism of Zn element during the powder metallurgy process was analyzed. Results show that the sintered compacts have finer grain size and higher sintered density upon Zn addition. The density of the sintered products increases with the increasing of Zn content. XRD analysis shows that the Mg-3 wt% Zn alloy is mainly composed of α -Mg phase. When the content of Zn is 4 wt%, the Mg-Zn alloys is composed of α -Mg and MgZn 2 phases. With the increase of the Zn content, the bending strength of the Mg-Zn alloys first increases and then decreases, but the micro-hardness HV of Mg-Zn alloys always increases. The bending strength and micro-hardness of Mg-3 wt% Zn alloys are 123.6 MPa and 1017 MPa, respectively, which are 58% and 45% higher than those of pure Mg samples. Corrosion resistance measurements show that the corrosion rate of the Mg-Zn alloys decreases with the addition of Zn element, and the Mg-3wt% Zn alloy shows the lowest corrosion rate and the best corrosion resistance.