机械合金化粉末冶金制备块体非晶材料

从热力学和动力学角度比较了机械合金化和快速凝固制备非晶材料的成分差异,介绍了Desr6和Yavari等人提出的非晶形成的固态多层反应模型,评述了非晶粉末固结过程的影响因素,最后提出了在今后的研究及应用中需要重点解决的几个问题。     

基于渣-气耦合运动模型的铝合金铸件渣气孔形成研究

针对铝合金铸件中常见的渣气孔缺陷,综合考虑铸造过程中渣粒的聚合运动与氢气的析出吸附之间的动态耦合特征,构建了渣气耦合运动数学模型。研究了铝合金充型及凝固过程中氢气析出、吸附长大、碰撞聚合及随流运动过程,并对圆柱形试样中渣气孔的分布及形貌进行了试验与模拟研究。结果表明,渣气耦合现象促进了渣粒与氢气的上浮,降低了铸件内部渣、气缺陷出现几率。所建立的渣气耦合运动模型提升了对渣气孔缺陷预测的准确性。     

污水冷热源系统污垢类型及其增长特性

对污水换热器常用的多种换热管进行了实验测试.结果表明,管内污垢为典型的有机污垢,其中水和有机物的含量大于96％;污垢的增长函数为以时间为自变量的渐近型函数;管材与管内流速对污垢增长影响明显.     

基于两级Smith预估的黑液浓度模糊串级控制系统设计

针对黑液浓度具有大滞后、大时变、非线性以及精确模型难以建立等特性导致的工况复杂、控制难度大的问题,提出基于主副回路Smith预估补偿的模糊串级控制,在主副回路分别加入Smith预估器,对黑液浓度和蒸汽流量进行补偿,并利用模糊控制器为主调节器。仿真结果表明,该种控制方案相比传统的PID串级控制方案具有更有的动态特性和鲁棒性。实际生产中的应用同样验证了其可靠性。     

基于脉宽调制的反作用控制系统技术

反作用控制系统(RCS)技术是高超声速飞行器再入初期主要的姿态控制手段,与常规舵面操纵相比,RCS输出为一离散力矩,这给连续系统控制带来困难。基于RCS的离散工作特性,采用脉宽调制(PWM)技术设计控制器。首先把RCS当作连续力矩输出,在连续系统控制下进行姿态反馈律设计。然后再根据脉宽调制算法把连续的控制量调制成离散控制量,控制RCS开启状态和开启时间。并根据离散控制理论分析了PWM控制器的稳定性。仿真结果表明,PWM控制器能够保证控制的稳定性和±1°姿态控制精确度,并较好地实现RCS对飞行器姿态运动的控制。     

损伤力学理论在混凝土结构中的应用技术进展

总结了最近几年国内外基于损伤力学理论的混凝土结构性能研究。详细概述了静力损伤本构关系、动力损伤本构关系、弹塑性损伤本构关系、混凝土随机损伤本构关系、徐变损伤模型、冻融作用下的损伤模型和腐蚀-化学作用下的损伤模型。总结了该研究领域存在的一些问题,并对今后的研究方向提出了建议。     

Phase selection,microstructure and properties of laser rapidly solidified FeCoNiCrAl2Si coating

A high-entropy alloy (HEA) coating with the composition of FeCoNiCrAl₂Si was prepared under laser-induced rapid solidification condition. The difference of atomic radius between Si (1.11 Å) and Al (1.43 Å) elements increases the atomic packing density. The coating has high microhardness (900 HV_0.5) and electrical resisitivity (265 μΩ mm) with simple supersaturated ordered and disordered body-centered cubic (BCC) structure. Besides the thermodynamic reason of high-entropy effect on the phase selection in the coating, the calculated incubation times of the nucleation for various competing phases during solidification indicate that the high cooling rate also plays a key role on preventing precipitation of intermetallic compounds.     

Effects of Annealing on the Microstructure and Properties of 6FeNiCoCrAlTiSi High-Entropy Alloy Coating Prepared by Laser Cladding

The content of each constituent element in the newly developed high-entropy alloys is always restricted in equimolar or near-equimolar ratios to avoid the formation of complex brittle phases during the solidification process. In this article, a high-entropy alloy coating of 6FeNiCoCrAlTiSi has been prepared by laser cladding and subsequently annealed at 500, 750, 1000, and 1150 °C for 5 h. Surprisingly, the coating has a simple BCC solid solution phase with high microhardness, good resistance to softening, and high electrical resistivity properties. After annealing <750 °C, the coating shows high thermal stability, the electrical resistivity decreases slightly and the microhardness almost remains unchanged. After annealing above 750 °C, the microhardness of the coating slowly decreases with the decomposition of the supersaturated BCC solid solution.     

基于虚拟样机技术的变频空调配管系统动力学优化设计

基于有限元分析方法,建立了变频空调器压缩机一配管系统虚拟样机分析模型,结合变频空调器压缩机工况多变的特征,对变频空调器配管系统动力学分析及优化设计方法进行了探讨。以研发中的某型号变频空调器为例,对其配管系统进行了结构优化设计,实验结果表明上述优化设计方法取得了预期的效果。     

Synthesis and characterization of FeCoNiCrCu high-entropy alloy coating by laser cladding

The influences of Si (1.2 mol.%), Mn (1.2 mol.%) and Mo (2.8 mol.%) additions on the microstructure, properties and coating quality of laser cladded FeCoNiCrCu high-entropy alloy coating have been investigated. The multi-component alloy coating is found to be a simple face-centered cubic (FCC) solid solution with less component segregation and high corrosion resistance, microhardness and softening resistance properties. For the coating without Si, Mn and Mo additions, the microstructure is mainly composed of columnar and equiaxed grains with uniformly distributed alloying elements. The microhardness reaches 375 HV_0.5, which is about 50% higher than that of the same alloy prepared by arc melting technique. But the coating quality is very poor. While for the coating with Si, Mn and Mo additions, the coating quality is greatly improved, the microhardness increases to 450 HV_0.5, but the microstructure transforms to dendrite due to a slightly increase in component segregation.