Structural Evolution and Property Changes in Nd_{60}Al_{10}Fe_{20}Co_{10} Bulk Metallic Glass During Crystallization

The structural evolution and property changes in Nd60Al10Fe20Co10 bulk metallic glass (BMG) upon crystallization are investigated by the ultrasonic method, x-ray diffraction, density measurement, and differential scanning calorimetry. The elastic constants and Debye temperature of the BMG are obtained as a function of annealing temperature. Anomalous changes in ultrasonic velocities, elastic constants, and density are observed between 600–750 K, corresponding to the formation of metastable phases as an intermediate product in the crystallization process. The changes in acoustic velocities, elastic constants, density, and Debye temperature of the BMG relative to its fully crystallized state are much smaller, compared with those of other known BMGs, the differences being attributed to the microstructural feature of the BMG.

Nd_(60)Al_(10)Fe_(20)Co_(10)金属玻璃的变形行为

利用材料测试系统(MTS)、X-Ray 衍射(XRD)和扫描电镜(SEM)等手段研究了Nd 基大块金属玻璃的变形行为和断裂特征。Nd 基大块金属玻璃样品在室温下是脆性断裂,大约在500 K 时变形模式从非均匀变形转变为均匀变形,在523 K 以上表现出显著的塑性变形。在5×10-4 m/s 的应变速率下,这种Nd 基大块金属玻璃材料在523 K~600 K 之间出现明显的屈服应力下降现象,随后进入1 种稳定的粘性流动状态,而且这种屈服下降现象与温度和应变速率有关。这种在过冷液相区的变形行为与其他大块金属玻璃变形特征相似。合金的这种塑性变形行为表明了其存在稳定的过冷液相区,同时对其变形行为的研究有助于进一步了解Nd 基大块金属玻璃的反常热稳定性。

20���21世纪的力学

<正> 一、力学发展的趋势 1.20���纪力学的巨大成就 本世纪初边界层理论的提出,对力学的发展起了划时代的作用。从此,流体力学能够成功地解释流动对物体的阻力与升力,为航空、航天的发展奠定了科学基础。这个典型也影响与推动了其他力学分支的发展,使力学研究的内涵有了空前的充实、扩大与深化。早在20���代初便形成了活跃于整个20���纪内容广泛的应用力学,成为工程与应用科学的支柱。人们把空气动力学的研究看作是本世纪以科学为基础将航

加卸载响应比20���及其展望

地震孕育过程是一个非线性、不可逆的过程,震源区介质的加载响应不同于卸载响应,这种加载响应与卸载响应的差别可以定量地刻画地震的孕育过程。基于这个物理概念,提出了一个新的参数加卸载响应比,作为一类地震前兆,用来定量预测强震的发生。在本文中,首先简单回顾了加卸载响应比的发展历史,然后详细介绍了地震震例检验、数值计算、实验研究、地震预测精度、可信度等方面的内容,最后对加卸载响应比的前景进行了展望。

当代的力学热点——由介绍第20���国际理论和应用力学大会引起的思考

本文通过介绍第２０ 届国际理论和应用力学大会的概况，分析了当代力学发展的现状和热点，并由此提出了对我国力学发展的思考和构想。

微重力落管法制备Nd_(60)Al_(10)Fe_(20)Co_(10)非晶薄片的磁性能研究

采用微重力落管法制得了Nd6 0 Al1 0 Fe2 0 Co1 0 非晶薄片 .利用X衍射 (XRD)分析了Nd6 0 Al1 0 Fe2 0 Co1 0 非晶薄片的结构特征 .用振动样品磁强计 (VSM)研究了其磁性能 .结果表明微重力落管法制得的非晶薄片具有硬磁性 ,与快速非平衡凝固(如甩带法 )试样的XRD相比 ,尽管其曲线还是较为典型的非晶相漫散衍射峰 ,但已有少量的不规则的类似晶化的突起小峰 ,表明该非晶片中已经有微量晶态合金或者细小晶粒析出 ,初步分析可能是生成了类似于亚稳A1 相的短程有序原子团簇或者是较大尺寸的纳米晶 ,这种短程有序原子团簇或纳米晶是Nd6 0 Al1 0 Fe2 0 Co1 0 非晶薄片显示硬磁性的主要原因

Nd_(60)Al_(10)Fe_(20)Co_(10)大块金属玻璃的玻璃转变和晶化过程

本文利用DSC、X射线衍射和动态力学分析以及扫描电子显微镜研究了Nd_(60)Al_(10)Fe_(20)Co_(10)大块金属玻璃(BMG)的玻璃转变和晶化过程。结果表明,合金的动态力学分析结果清楚地反映出材料的玻璃转变和晶化过程。由此确定材料的玻璃转变温度为493K,初始晶化温度为590K。X射线衍射和组织分析表明合金的晶化过程为:非晶α→非晶α’+未知亚稳NdFeAl相→非晶α’+初晶δ相→初晶δ相+共晶δ相+Nd_3Co+Nd_3Al。

High-energy ion emission from cooled deuterium clusters in 20 TW laser fields

High-energy ion emission from intense-ultrashort (30fs) laser-pulse- cooled deuterium-cluster (80K) interaction is measured. The deuterium ions have an average energy 20keV, which greatly exceeds Zweiback's expectation [Phys. Rev. Lett. 84 (2000) 2634]. These fast deuterium ions can be used to drive fusion and have a broad prospect.

Femtosecond optical Kerr effect study of Ge(10)AS(40)S(30)Se(20) film

The results of the femtosecond optical heterodyne detection of optical Kerr effect at 805 nm with the 80 fs ultrafast pulses in amorphous Ge10As40S30Se20 film is reported in this paper. The film shows an optical non-linear response of: 200 fs under ultrafast 80 fs-pulse excitation and the values of real and imaginary parts of non-linear susceptibility chi((3)) were 9.0 X 10(-12) and -4.0 X 10(-12) esu, respectively. The large third-order non-linearity and ultrafast response are attributed to the ultrafast distortion of the electron orbits surrounding the average positions of the nucleus of Ge, As, S and Se atoms. This Ge10As40S30Se20 chalcogenide glass would be expected as a promising material for optical switching technique. (c) 2005 Elsevier Ltd. All rights reserved.

Preparation, characterization and gas sensing properties of lead tetra-(tert-butyl)-5,10,1 5,20-tetraazaporphyrin spin-coating films

A spin-coated film of lead tetra-(tert-butyl)-5,10,15,20-tetraazaporphyrin complex (PbTAP(t-Bu)(4)) was obtained and characterized by IR spectra, absorption spectra and atomic force microscopy. The response and recovery characteristics of the film to NH3, NO2 and C2H5OH vapor were investigated at room temperature. In addition, the reversibility and stability of the film to NH3 were also studied. The results indicate that the PbTAP(t-Bu)(4) derivative can be exploited as an NH3 sensor at room temperature. (c) 2007 Elsevier B.V. All rights reserved.

20-W average power, high repetition rate, nanosecond pulse with diffraction limit from an all-fiber MOPA system

In this article, we report an all-fiber master oscillator power amplifier (MOPA) system, which can provide high repetition rate and nanosecond pulse with diffraction-limit. The system was constructed using a (2 + 1) X 1 multimode combiner. The Q-Switched, LD pumped Nd:YVO4 solid-state laser wets used (is master oscillator. The 976-nm fiber-coupled module is used as pump source. A 10-m long China-made Yb3+-doped D-shape double-clad large-mode-area fiber was used as amplifier fiber. The MOPA produced as much as 20-W average power with nanosecond pulse and near diffraction limited. The pulse duration is maintained at about 15 its during 50-175 kHz. The system employs a simple and compact architecture and is therefore suitable for the use in practical applications such as scientific and military airborne LIDAR and imaging. Based oil this system. the amplification performances of. the all fiber amplifier is investigated. (C) 2008 Wiley Periodicals, Inc.

气相传输平衡法在（11-20���面蓝宝石上制备γ铝酸锂膜

为了寻找可能替代蓝宝石作为氮化镓外延的新型衬底，通过48h的气相传输平衡，分别在1000℃、1030℃、1050℃、1070℃和1100℃制备了一层单相多晶的γ铝酸锂膜。X射线衍射和扫描电镜分别用于表征膜的物相、取向和表面形貌。结果显示，γ铝酸锂择优取向的好坏取决于气相平衡传输温度，在1050℃制备的γ铝酸锂具有高度的[100]择优取向；在γ铝酸锂（001）面上的双轴拉应力可能有助于[100]择优取向的形成；γ铝酸锂晶粒表面裂纹的方向一致性与其择优取向紧密相关。上述结果表明在合适的工艺条件下，气相传输平衡