大变形异步叠轧技术制备高强高导超细晶铜材研究

采用大变形异步叠轧并结合退火处理制备出了超细晶铜材。讨论了大变形异步叠轧的搓轧区、界面以及变形量等技术特征,测试了超细晶铜材的组织及性能。结果表明,搓轧区的存在促进了界面的复合和晶粒的细化;纯铜经过室温六道次AARB变形(累积真应变4.01)后,包含有许多亚结构,之后再经过220℃/35min退火处理,亚结构消失,获得了平均晶粒大小为200nm、抗拉强度、屈服强度分别为424.5MPa,323.1MPa、电导率为76.3 MS.m-1的高强高导超细晶铜;晶界面积的增加提高了超细晶铜的显微硬度;超细晶粒的变形不均匀性小和应力集中小,使得超细晶铜的塑性好、强度高;超细晶铜材的塑性变形机制受晶界行为控制。     

TB-13钛合金动态再结晶行为研究

研究TB-13钛合金在β单相区热轧变形过程中不同变形量对组织演变规律的影响.进行了32％,50％,59％和75％变形量的热轧后,利用光学显微镜和透射电子显微镜观察了该合金热轧变形后的组织变化.结果表 明,TB-13钛合金在热轧变形过程中的动态再结晶发生机制是连续动态再结晶.当变形量为32％时,沿着轧制方向存在拉长的扁平状原始β晶粒,晶界平直,晶粒内部存在大量无规则位错和胞状结构位错.随着变形量的增加,晶界处形成亚晶,大量位错在亚晶界处聚集,使亚晶界角度不断增大,最终由小角度晶界转为大角度晶界,从而形成细小的动态再结晶晶粒.     

等径角挤扭变形过程中纯铝粉末材料的显微组织与力学性能

采用EBSD和TEM研究了200℃下,纯铝粉末材料经不同道次ECAPT变形后的微观组织,并进行了显微硬度和相对密度测试。结果表明,1道次ECAPT变形后,材料显著细化但变形不均匀,晶粒基本沿剪切方向呈条带状分布,平均晶粒尺寸约为5.20μm,但多为小角度晶界结构。随着变形道次的增加,亚晶在不断被细化的同时晶粒间的取向差不断增大,形状更加趋于等轴,该过程可认为发生了连续动态再结晶。4道次变形后,材料内部形成了均匀、细小且呈大角度晶界分布的等轴再结晶组织,最小晶粒尺寸可达0.5μm。ECAPT变形过程中,晶粒细化机制为机械剪切、应变累积和动态再结晶三者的综合作用,粉末材料力学性能的提高与组织致密、细晶强化和位错强化等因素有关。     

120°模具室温8道次ECAP变形纯钛的组织演化

在室温下以等径弯曲通道变形(ECAP)技术制备超细晶工业纯钛,利用光学显微镜(OM)和透射电子显微镜(TEM)研究室温ECAP变形纯钛微观组织演变过程,并讨论纯钛室温ECAP变形的显微组织演化机制。结果表明:显微组织演化分为3个不同阶段,分别对应3种不同机制:第一阶段在真应变ε≤1.27时,为位错滑移和孪生交互作用细化机制,形成含有高密度位错和孪晶的板条状组织;第二阶段在真应变量1.27<ε<2.54时,为动态回复细化机制,晶粒进一步细化至~0.25μm,形成典型的变形亚晶组织;第三阶段在真应变量ε≥2.54时,为不平衡晶界的转动细化机制,形成平均晶粒尺寸约为0.2μm的等轴状大角度晶界超细晶组织。     

等截面通道角形挤压对高纯铝微观组织及力学性能的影响

采用等截面通道角形挤压技术对高纯铝进行室温大塑性变形 ,通过不同角度模具沿路径 A组合挤压 ,实现了高纯铝的晶粒细化 ,晶粒尺寸可达 0 .6 μm以下 ,且硬度和屈服强度显著增加。微观组织分析表明 :不同角度模具组合挤压可以得到不同的剪切平面组合 ,使得相邻两次挤压剪切平面的夹角为 75°,从而使得高纯铝在相对较小的塑性变形情况下得到超细晶粒结构 ,证明等截面通道角形挤压方法中剪切平面对晶粒细化效果的影响是非常大的     

纯铝累积叠轧焊界面及其性能

通过室温下L2纯铝的累积叠轧焊试验,利用光学显微镜观察研究了叠轧道次对连接界面的影响;利用常温拉伸试验研究了叠轧道次和退火温度对其力学性能的影响.研究表明:随着叠轧道次的增加,试样的连接效果越来越好,材料的强度提高,但延伸率却急剧下降.此外,退火温度对叠轧材料的性能影响显著.     

深冷异步轧制技术,提升金属材料性能新方法——访青年千人、中南大学喻海良教授

正您从事深冷异步轧制技术研究,这是比较新的领域,请简单为我们介绍一下这项技术。喻海良:传统轧制技术,主要包括热轧、温轧和冷轧。这些工艺均是在室温及其以上温度情况下进行的轧制。深冷异步轧制,采用液氮或者超低温氮气对轧件进行冷却,实现材料超低温,同时利用剪切应变实现晶粒细化,利用超低温情况下轧件的材     

摩擦导致的纯铜表面纳米化研究

提出了一种全新的利用摩擦实现表面纳米化的方法,并在纯铜上得到验证.纯铜经过摩擦处理后,在亚表层形成了200-500μm的变形层.结果表明,变形层深度随载倚升高而增加,但在400 N时接近饱和,这可能与涡流层的产生有关系.显微硬度结果表明,硬度随距表层距离递减,表层晶粒尺寸细化到纳米最级.     

Al-0.27Zr-0.064B实验合金的设计、熔炼及其变形特征

为研究等截面通道角形挤压过程中超细晶粒结构形成的机理及晶界变化过程 ,专门设计并熔铸了含微量Zr和B元素的Al 0 .2 7wt %Zr 0 .0 6 4wt%B合金 ,合金晶界上分布有大量的B2 Zr细小化合物颗粒 ,晶内几乎没有B2 Zr粒子。通过室温轧制、热锻以及随后的退火实验表明 ,B2 Zr具有很高稳定性 ,且再结晶后B2 Zr仍位于原变形后的位置 ,不随退火再结晶时新形成晶界的迁移而迁移 ,证明该合金可用于塑性变形时晶粒变形细化及晶界变化过程的研究     

纯铝累积叠轧焊连接机理及力学性能

对退火态L2纯铝在室温条件下进行了10道次的累积叠轧焊试验,利用光学显微镜观察叠轧道次对连接界面的影响,并利用室温拉伸试验与显微硬度试验研究叠轧道次对其力学性能的影响.研究表明:随着叠轧道次的增加,试样的连接效果越好,其连接机理为N.Bay机理:材料的强度与显微硬度随道次的增加显著提高.但延伸率却急剧降低.第10道次材料的抗拉强度、屈服强度和延伸率分别为190.44MPa、152.27MPa和4.73%.     

The effect of inlet conditions on the flow and heat transfer in multiple rotating cavity with axial throughflow

This paper discusses experimental results from two different build configurations of a heated multiple rotating cavity test rig.Measurements of heat transfer from the discs and tangential velocities are presented.The test rig is a 70% full scale version of a high pressure compressor stack of an axial gas turbine engine.Of particular interest are the internal cylindrical cavities formed by adjacent discs and the interaction of these with a central axial throughflow of cooling air.Tests were carried out for a range of non-dimensional parameters representative of high pressure compressor internal air system flows(Re up to 5×106 and Rez up to 2×105).Two different builds have been tested.The most significant difference between these two build configurations is the size of the annular gap between the(non-rotating) drive shaft and the bores of the discs.The heat transfer data were obtained from thermocouple measurements of surface temperature and a conduction solution method.The velocity measurements were made using a two component,LDA system.The heat transfer results from the discs show differences between the two builds.This is attributed to the wider annular gap allowing more of the throughflow to penetrate into the cavity.There are also significant differences between the radial distributions of tangential velocity in the two builds of the test rig.For the narrow annular gap,there is an increase of non-dimensional tangential velocity V/Ωr with radial location to solid body rotation V/Ωr=1.For the wider annular gap,the non-dimensional velocities show a decrease with radial location to solid body rotation.      

Research on Auto-detection for Remainder Particles of Aerospace Relay Based on Wavelet Analysis

Aerospace relay is one kind of electronic components which is used widely in national defense system and aerospace system. The existence of remainder particles induces the reliability declining, which has become a severe problem in the development of aerospace relay. Traditional particle impact noise detection (PIND) method for remainder detection is ineffective for small particles, due to its low precision and involvement of subjective factors. An auto-detection method for PIND output signals is proposed in this paper, which is based on direct wavelet de-noising (DWD), cross-correlation analysis (CCA) and homo-filtering (HF), the method enhances the affectiv-ity of PIND test about the small particles. In the end, some practical PIND output signals are analysed, and the validity of this new method is proved.     

Preparation of Highly Dispersed Antimony-doped Tin Oxide Nano-powder via Ion-exchange Hydrolysis of SnCl4 and SbCl3 and Azeotropic Drying

Antimony-doped tin hydroxide colloid precipitates have been synthesized by hydrolysis of SnCl4 and SbCl3 using: (1) an ion-exchange hydrolysis to remove chlorine ions, and (2) isoamyl acetate as an azeotropic solvent to obviate water. The obtained dried powder is of high dispersivity without any need for further grinding. The size and dispersivity of the final particles are investigated with the aid of TG-DTA, BET, XRD and TEM. After having calcined, the antimony-doped tin oxide nanopowder possesses a tetragonal rutile structure with high dispersivity, uniform particles and low hard agglomeration.     

Effects of Mo on the Microstructure and Hydrogen Sorption Properties of Ti-Mo Getters

The effects of Mo on the microstructure evolution, porosity and hydrogen sorption properties of Ti-Mo getters are investigated in this work. The results show that the addition of Mo prolongs the densification process of Ti-Mo getters and results in a significant amount of sintered pores. With the Mo content increasing, the porosity of getters firstly increases reaching the maximum value as it at- tains about 7.5wt.%, and then drops. At the room temperature, the hydrogen sorption property of getters increases progressively with the Mo content increasing, but the tendency is not very clear before its content lies below 2.5wt.%. When the Mo content achieves about 7.5wt.%, the hydrogen sorption property proves to be the best. The discussion is made about the above mentioned phenomena inclusive of hydrogen sorption properties of getters under different activation conditions (from 500-750 ℃).     

超声速燃烧数值模拟中的湍流与化学反应相互作用模型

高精度数值模拟有助于理解超声速湍流燃烧中湍流与化学反应的相互作用,可为发动机燃烧室等工程应用设计提供可靠的预测模型。除直接数值模拟外,目前在湍流燃烧应用中使用的大涡模拟和雷诺平均Navier-Stokes模拟均需要借助模型模化发生在湍流小尺度上的流动与化学反应过程对湍流大尺度运动的影响。现有的湍流与化学反应相互作用模型大致可分为:火焰面类模型和概率密度函数类模型,2类模型在不同的应用中各自具有优势和局限性。此外,现有模型大都基于低马赫数燃烧,而超声速燃烧中通常会伴随快速混合、局部熄火和再着火以及激波等复杂过程,这为发展其中的湍流与化学反应相互作用模型提出了更多的挑战。     

适于低轨卫星IP网络的单核共享树组播算法(英文)

为了解决低轨卫星IP网络中现有典型源组播算法的信道资源浪费问题,本文提出了一套单核共享树组播算法,即核心群合并共享树(CCST)和加权核心群合并共享树(w-CCST)算法。CCST 算法包括动态近似中心(DAC)选核方法和核心群合并组播路径构建方法。DAC方法专为周期、规律运动的低轨卫星网络提出,不需要复杂的星上计算。在核心群合并方法中,以核节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,从而使得组播树的树代价最小,大大提高了网络的带宽利用率和组播传输效率。w-CCST 算法中所提出的加权因子可以调整树代价和端到端传播时延之间的折衷程度,因此,可以通过调整加权因子来适度增大树代价、降低端到端传播时延以支持某些端到端时延要求苛刻的实时组播业务。最后,与低轨卫星 IP 网络中典型算法进行了性能比较,仿真结果说明,CCST 算法的平均树代价比其它算法显著降低,w-CCST 算法的平均端到端传播时延小于 CCST 算法。     

Jet Vectoring Control Using a Novel Synthetic Jet Actuator

A primary air jet vectoring control system with a novel synthetic jet actuator (SJA) is presented and simulated numerically. The results show that, in comparison with an existing traditional synthetic jet actuator, which is able to perform the duty of either “push” or “pull”, one novel synthetic jet actuator can fulfill both “push” and “pull” functions to vector the primary jet by shifting a slide block inside it. Therefore, because the new actuator possesses greater efficiency, it has potentiality to replace the existing one in various appli- cations, such as thrust vectoring and the reduction of thermal signature. Moreover, as the novel actuator can fulfill those functions that the existing one can not, it may well be expected to popularize it into more flow control systems.     

Nonlinear Adaptive Slewing Motion Control of Spacecraft Truss Driven by Synchronous V-gimbaled CMG Precession

The slewing motion control of a truss arm driven by a V-gimbaled control-moment-gyro (CMG) is a nonlinear control problem. The V-gimbaled CMG consists of a pair of gyros that must precess synchronously. The moment of inertia of the system, the angular momentum of the gyros and the external disturbances are not exactly known. With the help of feedback linearization and recursive Lyapunov design method, an adaptive nonlinear controller is designed to deal with the unknown items. Performance of the proposed controller is verified by simulation.     

An SOR Implicit Time-accurate Scheme in Calculating Unsteady Flows

A new time-accurate marching scheme for unsteady flow calculations is proposed in the present work. This method is the combination of classical Successive Over-Relaxation (SOR) iteration method and Jacobian matrix diagonally dominant splitting method of LUSGS. One advantage of this algorithm is the second-order accuracy because of no factorization error. Another advantage is the low computational cost because the Jacobian matrices and fluxes are only calculated once in each physical time step. And, the SOR algorithm has better convergence property than Gauss-Seidel. To investigate its accuracy and convergency, several unsteady flow computa- tional tests are carried out by using the proposed SOR algorithm. Roe’s FDS scheme is used to discritize the inviscid flux terms. Un- steady computational results of SOR are compared with the experiment results and those of Gauss-Seidel. Results reveal that the numerical results agree well with the experimental data and the second-order accuracy can be obtained as the Gauss-Seidel for unsteady flow computations. The impact of SOR factor is investigated for unsteady computations by using different SOR factors in this algorithm to simulate each computational test. Different numbers of inner iterations are needed to converge to the same criterion for different SOR factors and optimal choice of SOR factor can improve the computational efficiency greatly.