快速筛析法误差分析及其改进

快速筛析法被广泛应用于选矿研究和生产实践中,但其包含的计算误差却一直为人们所忽视．在对传统快速筛析法进行详细误差分析的基础上,提出了一种切实可行的新快速筛析法,在保证同样“快速”的同时,完全消除了传统快速筛析法因近似计算所产生的误差．     

3-D Modeling and Simulation of Mold Filling and Solidification by Direct Finite Difference Method

0INTRODUCTIONAlthoughrecentl}tvarioussolidificationanalysissoftwareforcastinghavebeendeveloped,themeltflowandheattransferduringfillingmoldcavityarenotsufficientlyconsideredinmostsoftWare.SOmeapproachesforsimulationhavebeenrePOrted,includingMAC,SMAC,PatankcrandSOLAVOFtechnicces.However,allmodelsmentionedabovehavesomeproblems,suchasdivergenceofthepressureiterationwhencalculatingthevelocityfield.Fulther,sincenearlyallpapersemploytheconventionalfinitedifferencemethod,theyaredifficultto…     

Second phases of rapidly solidified AlFeCrZrVSi alloy and their thermal stabilities

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Columnar to equiaxed transition mechanism of pure copper induced by La

The solidification process of copper with and without La was observed by a high-temperature confocal laser scanning microscopy. The solidification microstructure was simulated by cellular-automaton and finite-element (CAFE) method and the source of equiaxed grains, the constitutional supercooling and nucleation rate were investigated. The results showed that some floats with regular shape appeared in copper melt with La addition, which is the source of equiaxed grains. The simulation results are in a good agreement with experimental results. The mechanism of columnar to equiaxed transition was that the spontaneous nucleation probability of copper melt was increased with La addition. The nucleation rate was increased due to the increase in critical nucleation temperature and constitutional supercooling, and the reduction of nucleation undercooling.     

Effects of ultrasonic treatment on microstructure and mechanical properties of 6016 aluminium alloy

Ultrasonic treatment was applied during solidification forming of 6016 aluminium alloys. The effects of ultrasonic vibration on the microstructure and mechanical properties of the 6016 aluminium alloy ingot were studied. Compared with conventional casting, the ingot prepared with ultrasound applied to the molten metal had a fully refined microstructure and greater material homogeneity. Ultrasonic treatment reduced the amount of porosity developed by embedded gas and also resulted in an obvious decrease in solidification defects, like shrinkage. In addition, component segregation was minimised and the mechanical properties were enhanced.     

一种亲水反应型聚氨酯在高寒草原生态修复中的应用研究

高寒草原退化以及沙化现象对当地的生态系统造成严重破坏。在多种生态修复措施中,以材料措施为技术核心的生态修复措施受到广泛关注。本工作选用一种亲水反应型聚氨酯(OH-1A)作为主要材料,对其进行相关性能研究。结果表明:在15 ℃条件下,OH-1A可分散于水中,发生固化反应形成弹性凝胶体,且固化速率与浓度成正比;当OH-1A浓度达到3%时,可在300 s内渗透50 mm,并发生固化反应,形成柔性固结层;固结层表面静态接触角可达143°,优异的表面疏水性能有助于减缓植物生长所需水分的蒸发。在沙化严重的高寒草原,以OH-1A为基础的材料措施,可为植物的生根发芽提供有利的保障环境,防止草种或幼苗受到恶劣环境的影响,即建设“植物栖息”环境。因此,本工作提出的材料措施生态修复技术在高寒草原的植被恢复研究和应用中具有较高的潜在价值。     

金属凝固过程枝晶生长相场法模拟研究进展

近年来,相场法发展迅速,在许多方面得到了应用。本文主要介绍了相场法的发展进程,并对比分析了凝固相场中三种典型的相场模型(WBM模型、Karma模型和KKS模型)。在此基础上,简要概括了凝固相场方法的国内外研究现状,并对相场法今后的发展趋势进行了展望。     

Melt-spinning and semi-solid processing of bainitic steel

A steel with a chemical composition meant to form nanostructured bainite following appropriate heat treatment, was, cooled rapidly from the liquid phase (1550°C) using melt spinning and modified injection-suction methods, as well as from a semi-solid temperature (1430°C) through thixoforming. The hardness of the as-cast melt spun ribbons was ～960?HV due to a fine martensite–austenite mixture surrounded by three-dimensional skeleton-like primary carbides of length scale 0.2–0.3?µm. The suction-injection cast method led to a similar structure but less hard (780?HV) due to a lower cooling rate. The thixoformed material showed unmelted globular, fine grains and a fine eutectic mixture formed directly from the liquid phase. The variety of processed steel samples were tempered and their microstructures, examined.     

Effects of TiC formation on the microstructure and hardness of wear-resistant steel

In this study, as-cast low alloy wear-resistant steels with Ti contents of 0.6 and 3.0?wt-% were prepared at different solidification cooling rates, and the effects of TiC formation on their microstructures, hardness values, and wear resistances were investigated. The obtained phase diagrams and experimental data revealed that the TiC phase was formed via a divorced eutectic reaction in a residual liquid phase during solidification. The larger Ti content promoted the formation of TiC particles, while the solidification cooling rate represented the main influencing factor. Moreover, the produced TiC phase increased the wear resistance of the studied steel and decreased the matrix hardness, suggesting a new method for enhancing its mechanical properties through the formation of a hard ceramic phase.