Microstructure and mechanical properties of Zr-Cu-Al bulk metallic glasses

Zr49Cu46Al5 and Zr48.5Cu46.5Al5 bulk metallic glasses（BMGs） with diameter of 5 mm were prepared through water-cooled copper mold casting. The phase structures of the two alloys were identified by X-ray diffractometry（XRD）. The thermal stability was examined by differential scanning calorimetry（DSC）. Zr49Cu46Al5 alloy shows a glass transition temperature, Tg, of about 689 K, an crystallization temperature, Tx, of about 736 K. The Zr48.5Cu46.5Al5 alloy shows no obvious exothermic peak. The microstructure of the as-cast alloys was analyzed by transmission electron microscopy（TEM）. The aggregations of CuZr and CuZr2 nanocrystals with grain size of about 20 nm are observed in Zr49Cu46Al5 nanocrystalline composite, while the Zr48.5Cu46,5Al5 alloy containing many CuZr martensite plates is crystallized seriously. Mechanical properties of bulk Zr49Cu46Al5 nanocrystalline composite and Zr48.5Cu46.5Al5 alloy measured by compression tests at room temperature show that the work hardening ability of Zr48.5Cu46.5A15 alloy is larger than that of Zr49Cu46Al5 alloy.     

可动凝胶体系渗流流变特性及其表征

通过室内流变实验和渗流流变特性实验,研究了可动凝胶体系的流变特征,分析了可动凝胶体系的损耗模量和储能模量的量值变化关系,阐明了可动凝胶体系的粘弹特性及触变性。根据实验和非牛顿流变学理论,建立了多参数粘弹-触变性本构关系,并在实验和应用中得到验证。模型计算结果与实验数据相吻合,本构方程的稳定性较好。     

Microstructure and wear resistance of laser-melted TiC reinforced nickel aluminide dual-phase matrix in situ composite

A laser-melted TiC-reinforced nickel aluminide matrix in situ composite was fabricated. The composite consisted of well-developed TiC dendrites and a (NiAl–Ni₃Al) dual-phase matrix. The microstructure of the laser-melted in situ composite was characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results show that the TiC/(NiAl–Ni₃Al) composite has excellent wear resistance for both room- and high-temperature sliding wear test conditions.     

Effects of La2O3 on microstructure and wear properties of laser clad γ/Cr7C3/TiC composite coatings on TiAl intermatallic alloy

The effects of La₂O₃ addition on the microstructure and wear properties of laser clad γ/Cr₇C₃/TiC composite coatings on γ-TiAl intermetallic alloy substrates with NiCr–Cr₃C₂ precursor mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS) and block-on-ring wear tests. The responding wear mechanisms are discussed in detail. The results are compared with that for composite coating without La₂O₃. The comparison indicates that no evident new crystallographic phases are formed except a rapidly solidified microstructure consisting of the primary hard Cr₇C₃ and TiC carbides and the γ/Cr₇C₃ eutectics distributed in the tough γ nickel solid solution matrix. Good finishing coatings can be achieved under a proper amount of La₂O₃-addition and a suitable laser processing parameters. The additions of rare-earth oxide La₂O₃ can refine and purify the microstructure of coatings, relatively decrease the volume fraction of primary blocky Cr₇C₃ to Cr₇C₃/γ eutectics, reduce the dilution of clad material from base alloy and increase the microhardness of the coatings. When the addition of La₂O₃ is approximately 4 wt.%, the laser clad composite coating possesses the highest hardness and toughness. The composite coating with 4 wt.%La₂O₃ addition can result the best enhancement of wear resistance of about 30%. However, too less or excessive addition amount of La₂O₃ have no better influence on wear resistance of the composite coating.     

由纳米棒和纳米叶组成的铁磁性的MnSb薄膜

提供了一种利用物理蒸发沉积技术在单晶硅上生长纳米尺度的MnSb薄膜的方法.X射线衍射分析表明薄膜的主要成分是MnSb合金.场发射扫描电镜观察到薄膜是由纳米尺寸的棒状物和叶状物组成.纳米棒的平均直径为20nm,长度在几百纳米范围内.纳米叶的厚度大约为20nm,宽度为100nm左右.用可变梯度磁力计测量了薄膜的磁滞回线,结果显示薄膜有很强的几何各向异性.     

FINITE ELEMENT ANALYSIS OF VISCOUS FLOW PAST A ROTATING SPHERE

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A simple a-posteriori error estimation for adaptive BEM in elasticity

In this paper, the properties of various boundary integral operators are investigated for error estimation in adaptive BEM. It is found that the residual of the hyper-singular boundary integral equation (BIE) can be used for a-posteriori error estimation for different kinds of problems. Based on this result, a new a-posteriori error indicator is proposed which is a measure of the difference of two solutions for boundary stresses in elastic BEM. The first solution is obtained by the conventional boundary stress calculation method, and the second one by use of the regularized hyper-singular BIE for displacement derivative. The latter solution has recently been found to be of high accuracy and can be easily obtained under the most commonly used C ⁰ continuous elements. This new error indicator is defined by a L ₁ norm of the difference between the two solutions under Mises stress sense. Two typical numerical examples have been performed for two-dimensional (2D) elasticity problems and the results show that the proposed error indicator successfully tracks the real numerical errors and effectively leads a h-type mesh refinement procedure.     

CMOS图像传感器中卷帘式快门特性及其应用

结合CMOS图像传感器研究了CMOS图像传感器卷帘式快门的具体应用.介绍了卷帘式快门的特点和工作原理,分析了具有卷帘式快门的CMOS图像传感器的成像特性,并对其进行了成像实验.探讨了一种利用卷帘式快门相机拍摄的单精度视图来计算高速物体在三维空间中的位姿和速度的新方法.最后,提出了一个运动目标的透视投影模型,讨论了估计目标位姿和速度的方法.实验结果表明:具有卷帘式快门的CMOS图像传感器对运动物体成像时会产生一定程度的畸变,畸变的程度与积分时间等传感器参数的设置有关.在误差最小化的情况下得到了运动物体的位姿和速度参数,计算误差在2.5%以内,测量精度为0.01 rad/s.对实验结果的分析证明了方法的可行性.这种计算方法能够使得低价格、低耗能的CMOS相机转化为一种新的速度传感器.