Bi2O3-ZnO-Nb2O5(BZN)系陶瓷的熔融物性研究

在ＢＺＮ系陶瓷中,立方焦绿石结构的α相与低对称结构的β相是２个重要的基本物相,以差热分析（ＤＴＡ）与Ｘ射线衍射（ＸＲＤ）分析为研究手段,明确了α相与β相的熔融物相,结果表明：α相是同成分熔融化合物,熔占１１９０℃;β相是异成分熔融化合物,在１１００℃吸热分解为α相与液相。在自然冷却时,发生转熔过程,α相转入熔融液相中,析出β相,转熔温度１１００℃;在淬火冷却时,液相中析出的ＢＺＮ系立方萤石相。     

定向凝固包晶相变微观组织演化的相场方法研究Ⅰ.三相交节点的延伸

通过对当前包晶相变相场模型特征参数的优化,建立了适合对具体合金包晶相变微观组织演化进行模拟的相场模型．利用该模型对高Olvp定向凝固Ti—Al合金的单个包晶相核心依附初生相表面的生长行为进行了模拟．结果表明,三相交节点延伸特性的差异将导致形成离散带状和岛屿带状两种典型组织．并且,计算域宽度,包晶相形核过冷度和初始成分直接影响到定向凝固包晶合金三相交节点的延伸,也就影响到其最终的微观组织．     

定向凝固包晶相变微观组织演化的相场方法研究Ⅱ.形核控制的微观组织模拟

采用包晶相变相场模型分别模拟了高G／vp定向凝固Ti—Al合金在小直径试样的连续形核和大直径试样的多重形核情况下,包晶两相微观组织演化．模拟结果表明,对于小直径试样,减小试样尺寸或减小包晶相形核过冷度倾向于形成岛屿带状组织;而对于大直径试样,包晶相所占体积分数以及形核率的不同将导致形成离散带状、岛屿带状和耦合生长组织．     

拉速对包晶钢镀锡板连铸坯中夹杂物的影响

为了研究提高拉速对包晶类镀锡板连铸坯中夹杂物的影响,采用自动扫描电镜研究了不同拉速下包晶类镀锡板连铸坯中夹杂物的分布规律。结果表明,将包晶类镀锡板连铸拉速从1.3 m/min依次提高到1.4和1.5 m/min时,结晶器液面波动大于3 mm的比例都小于0.40%。拉速为1.4和1.5 m/min下连铸坯厚度四分之一处大于3μm的夹杂物数密度平均值分别为1.15和1.36个/mm²,面积百分数平均值分别为0.001 9%和0.002 4%,均低于拉速为1.3 m/min时的测量值。将拉速从1.3 m/min提高到1.5 m/min过程中,结晶器液面控制平稳,连铸坯表层大于10μm夹杂物数密度和面积百分数均呈减小趋势,最终实现了包晶类镀锡板高拉速稳定的工业化生产。     

包晶凝固研究进展

综合评述了近十几年来包晶凝固领域有关理论和实验研究的进展情况 ,指出了目前所存在的不足之处以及今后的研究方向     

Preparation of YBCO Superconducting Thick Films on MgO Substrates by Modified Melt Growth Process

Superconducting thick films (200–300 m) of YBCO have been fabricated successfully on MgO substrates by a new approach. The precursor powders (YBa₂Cu₃O_7– (Y123) + 0.1 mol Y₂BaCuO₅(Y211)) are placed between two MgO (10 mm×10 mm) slices to form sandwich structure. The YBCO thick films have been obtained from the precursors by modified melt growth process. Resistance measurements of YBCO thick films show T _con of 87.3 K and T of 4.5 K. Estimates using hysteresis loops and the Bean model give a value of 2.78×10³ A/cm² (77 K, 0T) for the critical current density. The observations of scanning electron microscopy (SEM) and X-ray diffraction (XRD) patterns show the supercoducting Y123 phase matrix containing discrete Y211 inclusions.     

The B-rich side of the B–C phase diagram

The melting behavior of ß-boron at the boron-rich side of the B–C binary phase diagram is a long standing question whether eutectic or peritectic. Floating zone experiments have been employed to determine the melting type on a series of C-containing feed-rods prepared by powder metallurgy and sinter techniques. Melting point data as a function of carbon-content clearly yielded a peritectic reaction isotherm: L+B_4+δC=(ßB). The partition coefficient of carbon is ~2.6. The experimental melting point data were used to improve the existing thermodynamic modeling of the system B–C. Relative to the thermodynamically accepted melting point of pure ßB (T_M=2075 °C), the calculated reaction isotherm is determined at 2100.6 °C, a peritectic point at 0.75 at% C and a maximum solid solubility of 1.43 at% C in (ßB) at reaction temperature. With the new melting data the refractory system Hf–B–C has been recalculated and the liquidus surface is presented. The influence of the melting behavior of (ßB) on the phase reactions in the B-rich corner of M–B–C diagrams will be discussed and demonstrated in case of the Ti–B–C system.     

Microstructure evolution of Ti-47Al-2Cr-2Nb alloy in the liquid-metal-cooling (LMC) directional-solidification process

The microstructure evolution of Ti-47Al-2Cr-2Nb alloy was investigated on liquid metal cooling type directional solidified apparatus at high temperature gradient.The analysis shows that it is solidified with primary β cells/dendrites,and then α phase is formed through peritectic reaction.Once the columnar grains grow into the steady state,the lamellar orientation inclined with the angle of 45° to the withdrawal direction is more favored than that with parallel to the withdrawal direction.In addition,α phase...     

大方坯低碳包晶钢连铸坯表面凹陷成因及对策

浅析南钢大方坯钢低碳包晶钢连铸坯表面凹陷的成因及所采取的对策。     

Analysis on Surface Longitudinal Cracking of Q345D Slab

The surface longitudinal cracking of peritectic steel Q345D slab was studied by means of metallographic microscopy and scanning electron microscopy. The results show that the surface longitudinal cracking is caused by the shell repeatedly tearing and healing under the action of stress, which is due to disruption of the steel matrix continuity with inclusion aggregation on the shell surface. The relative precautions of reducing the cracking are raised according to the practical situation.