High Temperature Flow Stress Prediction of Nano-Al_2O_3/Cu Composite Using an Artificial Neural Network

Alumina dispersion strengthened copper composite (nano-Al2O3/Cu composite) was recently emerged as a kind of potentially vi-able and attractive engineering material for applications requiring high strength, high thermal and electrical conductivities and resistance to softening at elevated temperatures. The nano-Al2O3/Cu composite was produced by internal oxidation. The microstructures of the composite were analyzed by the TEM and its hot deformation behavior was investigated by means of continuous compression tests per-formed on a Gleeble 1500 thermo-simulator. Making use of the modified algorithm–Levenberg-Marquardt (L-M) algorithm BP neural network, a model for predicting the flow stresses during hot deformation was set up on the base of the experimental data. Results show that the microstructures of the composite are characterized by uniform distribution of nano-Al2O3 particles in Cu-matrix. The sliding of dislocations is the main deformation mechanism. The dynamic recovery is the main softening mode with the flow stress decreasing gen-tly from 500 ℃ to 850 ℃. The recrystallization of Cu-matrix can be retarded late into as high as 850 ℃, when it happens only partially. The well-trained BP neural network model can accurately describe the influence of the temperature, strain rate, and true strain on the flow stresses, therefore, it can precisely predict the flow stresses of the composite under given deforming conditions and provide a new way to optimize hot deforming process parameters.     

硅的分布对铝—硅涂层抗热腐蚀性能的影响

利用ＲＦＬ热腐蚀试验装置，在温度为９００℃，盐浓度２０～１００ｐｐｍ，试验时间２００小时的条件下，研究了三种具有不同硅分布形式的Ａｌ－Ｓｉ涂层的抗热腐蚀性能。试验结果表明：涂层的抗热腐蚀性能与涂层中硅的分布形式密切相关。在涂层硅含量相当的情况下，硅呈内高外低的形式分布，可使涂层获得更佳的抗热腐蚀性能。     

热斑在1-1/2级涡轮内的非定常迁移数值模拟

对典型的1-1/2级高压涡轮叶栅,通过求解二维非定常N-S方程研究了燃烧室出口热斑对涡轮一级动叶和二级导叶流场和温度场的非定常影响。计算表明热斑的存在对涡轮级型面时均压力的影响微小,但是会显著地增大一级动叶和二级导叶型面压力随时间波动的幅度。计算印证了热斑会导致涡轮一级动叶压力面严重过热的结论,并显示在二级导叶上会出现与一级动叶类似的压力面过热现象。      

7A60超高强度铝合金流动应力的研究

采用等温恒应变速率压缩试验对 7A60超高强度铝合金的流动应力进行了研究。试验结果表明,该合金流动应力随着变形温度的升高而下降,随着应变速率的增加而增加。通过对试验数据的数理统计分析,确定了该合金流动应力对应变速率和变形温度敏感,对应变的变化不敏感。应变速率和变形温度是影响该合金流动应力的关键因素,从而也是变形工艺控制的主要因素。     

颗粒含量及粒度对SiCP/Al复合材料高温变形行为及组织的影响

采用无压浸渗法制备出不同体份的SiCp/Al复合材料.对该复合材料进行了高温(高于基体熔点)压缩实验.研究了不同颗粒含量及粒度规格的复合材料高温压缩流变规律,利用SEM观察分析了颗粒含量及粒度对复合材料组织的影响.研究结果表明:颗粒含量较高的SiCp/Al复合材料,在高温压缩过程中呈现为塑性流变规律;颗粒粒度规格对复合...     

Hot Corrosion Behavior of Double-ceramic-layer LaTi2 Al9O19/YSZ Thermal Barrier Coatings

LaTi 2 Al 9 O 19 (LTA) exhibits promising potential as a new kind of thermal barrier coating (TBC) material, due to its excellent high-temperature capability and low thermal conductivity. In this paper, LTA/yttria stabilized zirconia (YSZ) TBCs are produced by atmospheric plasma spraying. Hot corrosion behavior and the related failure mechanism of the coating are investigated. Decomposition of LTA does not occur even after 1 458 hot corrosion cycles at 1 373 K, revealing good chemical stability in molten salt of Na 2 SO 4 and NaCl. However, the molten salt infiltrates to the bond coat, causing dissolving of the thermally grown oxide (TGO) in the molten salt and hot corrosion of the bond coat. As a result, cracking of the TBC occurs within the oxide layer. In conclusion, the ceramic materials LTA and YSZ reveal good chemical stability in molten salts of Na 2 SO 4 and NaCl, and the bond coat plays a significant role in providing protection for the component against hot corrosion in the LTA/YSZ TBCs. LTA exhibits very promising potential as a novel TBC material.     

同轴剪切喷嘴出口壁厚对气-气燃烧性能的影响

以富氢/富氧燃气为推进剂,在单喷嘴燃烧室中开展同轴剪切喷嘴出口壁厚对燃烧性能影响的研究。通过求解N-S方程获得燃烧流场,分析氧喷嘴出口壁厚变化对燃烧产物、温度分布的影响,进行了壁厚变化对特征速度效率和热载影响的试验研究。结果表明,较厚的氧喷嘴出口壁厚有利于稳定火焰,氧喷嘴出口壁厚较薄时特征速度效率较低,并伴随有燃烧室压力不稳定现象。     

真空热试验中的温度控制算法

文章对真空热试验中温度控制算法进行了初步研究,主要论述了模糊控制算法、神经网络控 制算法。     

SiCf+p/LY12复合材料口盖板的制备与结构刚度

介绍了利用净成型液相压渗工艺的制备的ＳｉＣ纤维与ＳｉＣ颗粒混杂增强铝合金复合材料仪器舱口盖板。利用自行设计的热外压装置，考察了口盖板在室温和４００℃一外压时的刚度变化情况。结果表明ＳｉＣｆ＋ｐ／ＬＹ１２复合材料口盖板的室温结构刚度比ＬＹ１２铝合金口板提高约５０％，４００℃下复合材料口盖板的结构刚度比ＬＹ１２铝合金口盖板提高约８０％。     

表面凸起对机翼热气防冰腔内换热强化的影响

采用数值模拟对比研究了光滑表面和具有表面凸起结构热气防冰腔内湍流流动的换热特性。机翼防冰腔内笛形管具有三排射流孔,射流孔角度有0°±45°组合以及0°±30°组合。为了强化射流冲击光滑表面的流动换热,在防冰腔内表面正对射流孔的射流冲击区,设计了表面凸起结构,用来强化射流对壁面的冲击换热效果并起到引流作用。通过改变射流孔射流角度研究了射流角度对传热特性的影响。计算结果表明:与光滑防冰腔内表面射流冲击换热相比,表面凸起结构可以将均匀发散的壁面射流集中为高速壁面射流,提高壁面射流区的对流换热系数,从而增强射流冲击换热效果,机翼前缘的强化换热效果尤为明显。