Studies on nucleation kinetics of InxGa1−xN/GaN heterostructures

Nucleation kinetics during the growth of In_xGa_1−xN on a GaN substrate have been studied. The behavior of nonequilibrium between the In_xGa_1−xN and the GaN substrate has been analyzed, and hence, the expression derived for the stress-induced supercooling/superheating has been numerically evaluated. The maximum amount of stress-induced supercooling is found to be 1.017 K at x=0.12. These values are incorporated in the classical heterogeneous nucleation theory. Using the regular solution model, the interfacial tension between the nucleus and substrate and, hence, the interfacial tension between nucleus and mother phase and thermodynamical potential of the compounds have been calculated. The amount of driving force available for the nucleation has been determined for different compositions and degrees of supercooling. It has been shown that the value of the interaction parameter of InN-GaN plays a dominant role in nucleation and growth kinetics of In_xGa_1−xN on a GaN substrate. These values have been used to evaluate the nucleation parameters. It is shown that the nucleation barrier for the formation of a In_xGa_1−xN nucleus on a GaN substrate is minimum in the range of x=0.12 to x=0.17, and it has been qualitatively proved that good quality In_xGa_1−xN on GaN can be grown only in the range 0<x≤0.2.     

高温精炼处理对铸造镍基高温合金组织与性能的影响

研究了高温精炼处理对铸造镍基高温合金组织与性能的影响.普通铸造镍基合金枝晶组织粗大,晶界碳化物呈链状分布,晶内碳化物呈草体汉字状密集分布于枝晶间,是合金塑性低的主要原因.经高温精炼处理后,合金的枝晶组织细化,晶界及枝晶间的碳化物数量减少,γ γ共晶相数量增加,晶界碳化物呈不连续质点状分布,晶内碳化物的密集程度下降,拉伸塑性和蠕变(持久)寿命得以明显提高.经1 650℃,5 min高温熔体处理后,合金室温延伸率由3.5%提高到9.2%,700℃高温塑性由2.0%提高到8.0%,900℃高温塑性由2.8%提高到9.6%,蠕变寿命由34 h提高到52 h,蠕变塑性由4.3%提高到6.11%.推荐的最佳高温精炼处理制度为1 650℃保温4 h.分析了高温精炼处理对合金液态结构、凝固组织与性能的影响机理.     

升温速率对金属熔化和过热的影响

采用分子动力学方法和QSC(Quantum Sutton-Chen)力场研究了升温速率对金属银和金属铅的熔化和过热行为的影响。研究结果表明，升温速率对金属银和铅的熔化和过热行为有很大影响，随着升温速率的升高，金属的熔点有所升高。高的升温速率会导致金属体系内部无序化程度增加，降低了熔化相变的能垒。升温速率导致的银和铅完美晶体的过热极限分别为1450K和800K。     

影响双螺杆冰机稳定运行的原因分析及解决办法

阐述了双螺杆式制冷机的工作原理,对其主要工作部件进行了研究,分析了影响冰机稳定运行的原因.结果表明：检查清理热力膨胀阀,防止膨胀阀堵塞;定期清理换热器（冷凝器、油冷却器）,优化换热效果;更换干燥器,清除系统内进入空气和少量的水.通过以上措施可有效地降低双螺杆式制冷机的故障.     

Relaxation Process of Thermal Non-Equilibrium in Boiling Two-Phase Flow, (I)

The thermo-hydraulics in a thermal non-equilibrium state, which may appear during a postulated loss-of-coolant accident, is one of phenomena which have never been understood enough. In this paper, accelerating boiling two-phase flow is dealt with which realizes thermal non- equilibrium conditions in a steady state in order to clarify the relaxation process of superheated liquid. The following insight is clarified from the results; Jones' model cannot explain the underpressure and relaxation time unless an empirical constant is changed. Therefore, the effect of interfacial area density on the macroscopic relaxation inception is experimentally investigated by adding artificially bubbles in accelerating boiling two-phase flow in order to offer a fundamental data base for modeling the relaxation process of superheated liquid. It is made clear that the macroscopic relaxation inception can be evaluated by a relationship between the integration of liquid superheating by the travelling time and the initial interfacial area density.     

绕线式电机集电环过热原因及解决措施

通过对冶金企业中常用绕线式交流电动机集电环发热原因的分析，提出了相应的处理方法及预防措施，对电动机的维护、修理具有指导意义。     

高压下晶体过热熔化的分析及模拟

针对冲击波加载实验中晶体的过热熔化现象,分析了静高压和冲击压缩后的样品的实验数据,给出了晶体发生过热熔化的充分条件.并采用分子动力学模拟的方法,验证了所得结论的正确性.     

上汽670MW超临界汽轮机闷缸经验

对华电潍坊发电有限公司670MW超临界汽轮机闷缸经验进行介绍,对闷缸过程中的有关注意事项进行总结,为同类型机组抢修时快速停盘车提供实践依据.     

低压脉冲磁场对铸态IN718高温合金凝固组织细化的影响

研究低压脉冲磁场对IN718高温合金凝固组织细化的影响。结果表明：在低压脉冲磁场作用下可以获得完全细小的等轴晶组织。熔体冷却速度和过热度显著影响低压脉冲磁场的细化效果,降低冷却速度和过热度有利于提高脉冲磁场的细化效果。利用商业有限元软件模拟计算高温合金凝固过程中熔体中的电磁力和流场分布情况以揭示脉冲磁场的细化机制。认为脉冲磁场引起的熔体对流,以及同熔体冷却速度和过热度的合理配合是合金凝固组织细化的主要原因。