Structure studies of ball-milled ZrCuAl, NiTiZrCu and melt-spun ZrNiTiCuAl alloys

ZrNiTiCu and ZrNiTiCuAl alloys were amorphized using either a melt‐spinning or ball‐milling process in a high‐energy planetary mill. The elemental powders were initially blended to the desired composition (in at.%) of Zr, 65; Cu, 27.5; Al, 7.5 and of Ti, 25; Zr, 17; Cu, 29; Ni, 29, respectively. The composition of alloys was chosen to be the same as for the bulk amorphous ZrCuAl and easy glass‐forming ZrNiTiCu alloys. An almost fully amorphous structure was obtained after 80 h of milling in the case of both compositions. Transmission electron microscopy studies of ball‐milled powders revealed the presence of nano‐crystallites [2–5 nm for ZrCuAl and smaller (1–3 nm) for the ZrTiNiCu alloy]. High‐resolution transmission electron microscopy of melt‐spun ZrNiTiCuAl ribbons provided evidence of the amorphous structure.     

异构网络中多模终端业务流分发技术研究

伴随着异构网络的迅猛发展,多模终端日益普及.当终端上有多种不同类型的会话业务流需要传输时,如何根据不同类型业务流的特点、不同网络的当前链路状况、通信费用、传输功耗等因素,在终端所接入的多个网络之间自动地、合理地分发业务流就成为一个非常重要的问题.文中提出了一套针对多模终端业务流分发问题的解决方案,包括支持业务流自动分发的多模终端框架结构及其包含的业务流分发算法.方案引入优先级的概念使得高等级的业务流在网络负载较重时具有使用网络的优先权,同时方案包含了一种权重自生成方法,为影响业务流分发决策的多个属性自动生成权重,减轻了用户负担,避免了由用户直接指定权重的困难.仿真实验的结果表明,文中方案能够根据当前各接入网络的链路状况、不同类型业务流的服务质量需求、传输功耗、通信成本等多个属性,自动为多模终端上运行的各条业务流选择合理的接入网络,同时方案在吞吐量、会话完成率等性能指标上也拥有显著改进.     

Transmission electron microscopy studies of microstructure of Ti–Nb and Ti–Ta alloys after ball milling and hot consolidation

Two Ti alloys with compositions Ti?10Ta and Ti?10Nb (at.%) were milled in a high‐energy mill for a maximum of 80 h in an argon atmosphere. A nanocrystalline structure of α‐Ti(X) (X = Ta or Nb) solid solution was formed in both investigated alloys after milling, as shown by X‐ray diffraction. Transmission electron microscopy observations of powders milled for 80 h revealed chemical inhomogeneity of particles in nanometre‐scale regions and an average crystallite size of about 10 nm. The pulse plasma sintering method was applied for hot consolidation of milled powders. The mean density of pulse plasma sintering compacts of Ti–Nb alloy was about 99.5% of the theoretical value, whereas the density of the Ti?10Ta sample was lower, close to 92% of the theoretical value. Transmission electron microscopy observation of compacted samples showed that the sintering process caused the formation of a two‐phase α + β structure in both investigated alloys, with a mean grain size of 220 nm. The chemical inhomogeneity and high degree of deformation in nanometre‐scale regions of milled powders led to a martensitic transformation, resulting in formation of a 9R martensite structure.     

基于调度集合的多播单播数据联合调度算法

首先定义和分析了IEEE802.16e无线城域网中的一个新问题,即如何在保证移动终端服务质量的前提下,通过合理地调度终端的单播业务和多播业务来降低终端能耗.针对该问题,提出一种基于调度集合的联合调度算法(scheduling set based integrated scheduling,简称SSBIS).SSBIS算法将所有移动终端划分到多播调度集合或单播调度集合中,并利用多播数据的传输特点,在多播数据传输的相邻时隙内发送多播调度集合中所有终端的单播数据,而对于单播调度集合中的终端,则通过凸优化方法求得使终端休眠时间最长的单播业务调度方案,以达到降低终端能耗的目的.仿真实验显示,SSBIS算法在满足移动终端的最小数据速率要求的同时,可以明显地降低终端能耗.     

Microstructure and properties of hot compacted powders of aluminium alloys

Atomized 6061 aluminium alloy powders with and without the addition of 2 wt% Zr were milled for 80 h in a planetary ball mill and hot pressed in vacuum. The milled powders showed microhardness of about 170 HV, which increased after hot pressing up to 260 HV and up to 280 HV for powders without and with the Zr additions, respectively. Compression tests showed the high yield stress of 300 MPa obtained for the hot-pressed sample produced from the initial powders compared with ultimate compression strength of above 800 MPa for that of the milled sample and slightly higher for that with Zr additions. The effect of hot pressing on the structure of powders was investigated using a conventional analytical and high-resolution electron microscopy and high angle annular dark-field scanning transmission electron microscopy combined with energy dispersive X-ray microanalysis. The samples of initial powders hot pressed in vacuum showed a cell structure with particles of the Mg₂Si and AlFeSi phases in intercell areas. In the milled and hot-pressed sample, the homogeneous structure of small grains of size below 200 nm was observed. The AlFeSi and Mg₂Si particles with size 20–100 nm were uniformly distributed as well as the Zr rich particles in the Zr containing alloy. The Zr-rich particles containing up to 80 at% Zr were identified as a metastable fcc cubic phase with lattice parameter a = 0.48 nm.