Mechanical,electrical, and thermal properties of the directionally solidified Bi-Zn-AI ternary eutectic alloy

A Bi-2.0Zn-0.2A1 （wt%） ternary eutectic alloy was prepared using a vacuum melting furnace and a casting furnace. The samples were directionally solidified upwards at a constant growth rate （V= 18.4 μm/s） under different temperature gradients （G = 1.15-3.44 K/mm） and at a constant temperature gradient （G = 2.66 K/mm） under different growth rates （V= 8.3-500 μm/s） in a Bridgman-type directional so- lidification furnace. The dependence ofmicrostructure parameter （2） on the solidification parameters （G and V） and that of the microhardness （Hv） on the microstructure and solidification parameters were investigated. The resistivity （ρ） measurements of the studied alloy were per- formed using the standard four-point-probe method, and the temperature coefficient of resistivity （α） was calculated from the ρ-Tcurve. The enthalpy （AH） and the specific heat （Cp） values were determined by differential scanning calorimetry analysis. In addition, the thermal conductivities of samples, obtained using the Wiedemann-Franz and Smith-Palmer equations, were compared with the experimental results. The results revealed that, the thermal conductivity values obtained using the Wiedemarm-Franz and Smith-Palmer equations for the Bi-2.0Zn-0.2Al （wt%） alloy are in the range of 5.2-6.5 W/Km and 15.2-16.4 W/Km, respectively.     

Competitive growth of different phases in eutectic alloys under directional solidification

Directional solidification technique is widely applied not only to the research on the basic solidification theory, but also to manufacturing high-performance products, such as superalloy turbine blades with single crystal structure in aeronautical engines. In the field of eutectic solidification, eutectic structure can be designed more flexibly and serve at different properties compared to the single-phase structure. Furthermore, eutectic structure of in-situ composite produced by directional…     

共晶凝固理论的研究与发展状况

根据共晶凝固问题的复杂性,重点从共晶层片间距的选择机制和形态转变这一核心问题入手,分析了共晶凝固理论的建立和发展过程,较系统地总结了迄今为止关于共晶凝固理论的国内外研究动态和最新进展,并在此基础上,提出了今后的研究方向．     

自生复合Cu-Cr合金定向凝固新方法

简述了高强度高导电性铜合金的制备方法．指出,基于热型连铸工艺制备具有定向凝固组织的Cu-Cr合金自生复合材料由于充分利用铜基体的导电和第二相Cr纤维强化的作用,因而具有比较好的综合性能,具有广阔的应用前景．     

钛合金冷坩埚定向凝固过程温度场数值模拟

基于电磁场Maxwell方程组以及带有一定运动速度的连续介质凝固模型,建立了连续熔铸与定向凝固过程温度场数值计算模型,并对线圈匝数为4匝、输入电流密度为6.6×1010A/m2、电源频率为50 000 Hz时,扁形锭的电磁感应加热升温过程进行了模拟研究,得出了Ti-6Al-4V合金的温度场变化情况.结果显示,从开始加热的几十秒时间内,扁形铸锭温度上升很快;接近100 s时,铸锭温度分布趋于稳定;接近300 s时,铸锭自身基本达到热量平衡.     

Effect of interface kinetics on the eutectic growth

Eutectic alloy is widely used as structural and/or functional materials. The first mathematical model for the eutectic growth was established by Jackson and Hunt (JH)[1]. Assuming that crystals grow at low velocities, the lamellar spacing is much smaller than the solute diffusion distance, and the liquid composition at the solid-liquid interface is approximately the same as the equilibrium eutectic composition. They gave a relation- ship between the undercooling at the interface ?T and the e…     

等温方型通道方向辐射特性

为了比较辐射通道几何形状变化对通道出口逸出辐射能的方向分布特性的影响,本文采用蒙特卡罗法,研究了等温方管、等温方管空腔两种方形通道的方向辐射特性,计算并分析了相关参数如管内壁发射率、管长与当量直径比变化对通道出口表面方向辐射系数的影响.结果表明:经方管、方管空腔辐射通道出口处的辐射加热比经圆管、圆管空腔的定向集中辐射加热特性更好.该计算结果为定向辐射器辐射通道几何结构选取提供参考.     

高温合金定向凝固枝晶间距与冷却速率的关系

利用高梯度快速定向凝固设备,对ＤＺ２２高温合金定向凝固组织进行了研究．研究结果表明,一次和二次枝晶组织随冷却速率的增长,都有明显细化,横向分枝的生长受到抑制．一次和二次枝晶间距与冷却速率之间都符合指数关系．在冷却速率达到５４℃／ｓ时,一次枝晶间距为２８８μｍ,二次枝晶间距８４μｍ．     

Effects of the types of overlap on the mechanical properties of FSSW welded AZ series magnesium alloy joints

The effects of the types of overlap on the mechanical properties of the friction stir spot welding(FSSW) welded AZ series magnesium alloy joints were investigated by microstructural observations,microhardness tests,and tensile tests.The results show that the micro-structure of the stir zone adjacent to the periphery of the rotating pin is mainly composed of the upper sheet.The average distance D between the longitudinal segment of the curved interface and the keyhole periphery,the tensile shear force,and the microhardness of the stir zone of the FSSW welded AZ61 alloy joint are the highest in all samples.During FSSW of AZ31 and AZ61 dissimilar magnesium alloys,the ir-regular deformation of the longitudinal segment of the curved interface appears,while the microhardness of the stir zone is higher when AZ61 alloy is the upper sheet.Moreover,the microhardness of the stir zone increases initially and then decreases sharply in the longitudinal test position.     

定向凝固技术制作单晶铸件的实验研究

用定向凝固技术制作单晶铸件、摸索合理可行的工艺方法;分析晶粒生长淘汰过程。     

材料物理参数选取对钢结构焊接模拟的影响

基于有限元方法,对二维对接焊在选取不同热物理参数的情况下进行了数值分析。主要分析了比热容C、焓值H随温度的变化对二维对接焊X型坡口和V型坡口焊接残余应力的影响。结果表明比热容对模拟结果影响很大,而焓值的影响很小。因而,在模拟计算中可以不考虑焓值的变化,有利于提高计算效率。     

Phase field simulation of the interface morphology evolution and its stability during directional solidification of binary alloys

The influences of pulling speed V and temperature gradient G on morphology evolution, concentration distribution, solute trapping and interface stability during directional solidification of binary alloys have been studied with the B-S phase field model. Simulated results reproduced the morphology transitions of deep cell to shallow cell and shallow cell to plane front. The primary cellular spacing, depth of groove and effective solute redistribution coefficient for different V and G are compared. The absolute stability under high pulling speed and high temperature gradient has also been predicted, which is in agreement with the Mullins-Sekerka (M-S) stability theory. Supported by the National Natural Science Foundation of China (Grant No. 50401013)     

非晶合金凝固过程模拟与界面换热关系

为了准确模拟块体非晶合金凝固过程的温度场,对浇注温度为840℃的非晶合金凝固期间的温度场进行了数据采集.根据界面换热模型与热量守恒定律建立了液固相与铜模之间的界面换热关系式,从而实现了对非晶凝固温度场的模拟.结果表明,合金与铜模之间的界面换热系数随温度的增加而增大.合金在液态阶段降温曲线的模拟值与实测值基本吻合,且当凝固温度降至500℃后,二者偏差也较小.利用界面换热模型并结合实测温度场可以表征非晶合金凝固时的界面换热关系.     

激光熔凝处理对轧辊钢组织及性能的影响

应用3KW连续CO2激光器对轧辊钢进行激光熔凝处理,用金相用显微镜、、SEM及71型显微硬度计,进行湿微组织分析和显微微硬度测试。结果发现,其剖面组织区域分为熔化区（粗大的马氏体＋残余奥氏体→奥氏体)、相变区（马氏体＋残余奥氏体＋碳化物）、热影响区和基体4个部分,各区域的尺寸及显微硬度与功率、扫描速度等工艺参数有关,且激光处理后硬化效果明显。     

定向凝固纯铜组织性能研究

采用高真空多功能定向凝固及悬浮熔炼设备,以不同凝固速度制备纯铜试样,并对定向凝固纯铜试样的显微组织和机械性能进行了分析研究.通过实验获得了定向凝固纯铜的组织性能.当凝固速度小于500μm/min时,定向凝固的纯铜试样横、纵截面的晶粒形貌都是等轴晶,晶粒内存在孪晶,凝固速度较小时,其孪晶组织数量较多.当凝固速度大于500μm/min时,定向凝固的纯铜试样横截面的晶粒形貌是等轴晶,而纵截面的晶粒形貌是柱状晶,晶粒内基本不存在孪晶组织.定向凝固纯铜的室温机械性能是:当凝固速度在50μm/min的条件下,试样的抗拉强度约153 MPa,较普通铸造纯铜试样的低,而屈服强度约91.8 MPa,延伸率约80.12%,都优于普通铸造纯铜试样.透射电镜分析表明,纯铜定向凝固过程中形成的孪晶B=[110].     

合金元素对Cu-Te-Cr合金时效组织与性能的影响

采用扫描电镜(SEM)、X射线衍射仪(XRD)、电子能谱(EDS)分析Cu-Te-Cr合金时效析出相的形貌与组成,研究合金元素对Cu-Te-Cr合金时效组织与性能的影响。结果表明,时效过程中Te、Cr以多元化合物或细小的单质Cr析出,合金的硬度明显升高,随时效温度的升高,Cr粒子长大,共格度降低;同时基体晶粒内,部分析出相重溶,使合金硬度下降;由于Cr和Te两种元素互不相溶,其交互作用生成CrxTey化合物,随着Te含量的增加,铸造过程中生成这种化合物越多,减少Cr元素在铜基体的固溶度,从而合金硬度下降,而导电率有所提高。     

从处所宾语看趋向动词与趋向结构

传统语法对趋向动词的界定存在对内不一致、对外不排他的缺陷,趋向动词和趋向结构与处所宾语密切相关,以此为角度,重新界定趋向动词和趋向结构的外延和内涵。认为传统的趋向动词外延过窄,而趋向补语也存在着两类不同的结构。最后,根据处所宾语的语义性质对趋向动词和趋向结构进行了分类,发现了处所宾语的语义类别和处所性存在联系。     

Si对K40S合金凝固过程及显微组织的影响

研究了Si对K40S合金凝固过程及显微组织的影响。结果表明,随着Si含量的升高,K40S合金凝固时界面生长由枝晶生长转向明显的内生生长;Si元素主要在枝晶间或晶界偏析,但当Si含量升高到一定程度后,枝晶内的浓度逐步升高而达到显著水平;Si元素对合金中Cr、Ni、W等元素的分布有影响,进而影响碳化物的形成。     

脉冲电流对纯Si凝固组织及性能的影响

用频率为3Hz、6Hz、10Hz脉冲电流处理了纯Si熔体试样。用金相显微镜、原子力显微镜对试样进行观察,可以看出经过脉冲电流处理后的纯Si,组织及晶粒粗大化,晶界也变的越来越不明显;利用扫描电子显微镜观察试样断口形貌,经脉冲电流处理后使纯Si的脆性增强;由测得的试样的电阻率,表明经脉冲电流处理试样的电阻率比未经脉冲电流处理的试样电阻率显著降低,并且随着脉冲电流频率的增大,电阻率不断减小。     

Cu对热挤压Al-Mg-Si合金力学性能及导电率的影响

为了满足铝合金架空输电导线的使用需求,以热挤压法制备的Al-Mg-Si合金电工铝杆为研究对象,通过调节Cu元素的添加量,研究了Cu对Al-Mg-Si合金的力学性能及导电率的影响.结果表明,向Al-0.35Si-0.45Mg-0.13Fe合金中添入微量Cu元素后,Mg2Si析出相得到细化且时效强度提高.随着Cu元素含量的增加,峰时效时间缩短,合金抗拉强度不断提高,但伸长率逐渐降低.当Cu含量为0.06%时,合金抗拉强度达到最大值145.7 MPa.合金导电率随着Cu元素含量的增加先升后降,当Cu含量为0.03%时达到最大值60.18%IACS.