Nb-Ti-Al合金及其硅化物涂层的高温氧化行为

采用电子束和真空自耗电弧熔炼法制备Nb-40Ti-7Al(质量分数,%)合金,利用料浆熔烧法在合金表面制备Si-Cr-Ti涂层,研究在1 400℃下合金与涂层的氧化行为。通过X射线衍射(XRD)、扫描电镜(SEM)、能谱分析(EDS)及电子探针微区分析(EPMA)研究基体与涂层氧化前后的组织形貌变化及成分分布。结果表明:Nb-40Ti-7Al合金在1 400℃氧化1～11 h后,氧化产物均主要为TiNb2O7、TiO2、Al2O3;氧化前,涂层主要由(Nb,Ti,Cr,Al)Si2主体层与(Ti,Nb,Al)5Si3过渡层组成,高温氧化后涂层表面形成含有Al2O3、TiO2的SiO2阻挡层;合金与涂层的氧化行为均遵循抛物线规律,合金在1 400℃氧化11 h的单位面积质量增量为161.98 mg/cm2,而涂覆涂层后单位面积质量增量降至9.56 mg/cm2,表明Si-Cr-Ti涂层具备良好的高温抗氧化性能。     

Elevated-temperature oxidation behavior of titanium silicide and titanium silicide-based alloy and composite

The oxidation behavior of Ti₅Si₃ has been studied in air in the temperature range of 1200 °C to 1400 °C. The oxidation kinetics is slower than that predicted by the parabolic-rate law equation at 1200 °C, but is sharply enhanced beyond a temperature of 1300 °C. The oxidation kinetics of a Ti₅Si₃-8 wt pct Al alloy and a Ti₅Si₃-20 vol pct TiC composite at 1200 °C has also been investigated and compared to that of Ti₅Si₃. Alloying with Al does not alter the oxidation resistance much, but the presence of TiC reinforcements enhances the rate of oxidation significantly. The oxidation products have been identified and the mechanism of oxidation has been analyzed using thermodynamic and kinetic considerations.     

Entrainment behavior of copper and copper matte in copper smelting operations

In copper smelting, the loss of copper to the slag due to entrainment is largely influenced by the flotation of copper metal and/or matte in the slag phase. To evaluate this behavior, the surface tension of copper as a function of temperature and oxygen pressure and the interfacial tension of the copper-iron matte-slag system as a function of matte grade were measured. From the surface and interfacial tension values, the spreading and flotation coefficients of the copper, matte, and slag system were calculated. Ternary interfacial energy diagrams were also con-structed using these data. It is shown that matte droplets containing higher than 32 mass pct Cu will not form a film on rising gas bubbles when they collide in the slag phase. However, matte droplets will attach to gas bubbles upon collision and thus can be floated over the entire range of matte composition. Spreading of copper on bubbles is not possible at oxygen pressures between 10⁻¹² and 10⁻⁸ atm. Flotation of copper by gas bubble in slag is possible at oxygen pressure higher than 10⁻⁹ atm. However, it is feasible for rising matte droplets (attached to rising bubble) to trap and float copper irrespective of the matte grade.     

Deformation behavior of silicon

Dynamic processes of individual dislocations in Si, such as generation, motion, and multiplication, are reviewed on the basis of direct observations by means of X-ray topography and transmission electron microscopy. The characteristics in the reaction of oxygen impurities with dislocations are clarified by real time observations with these techniques. Immobilization of dislocations due to the reaction is demonstrated. Stress-strain behavior of Si in the yield deformation is described in detail. It is sensitive to the deformation temperature, strain rate, and also to the density of dislocations initially contained in the crystal. Though the yield behavior of Si crystals free from dislocations is not influenced by oxygen impurities contained, that of dislocated crystals is affected significantly by these impurities. All of these characteristics in the yield deformation of Si are shown to be successfully described with a model that takes into account the dynamic processes of individual dislocations revealed by the direct observations.