镁系准晶与高性能镁合金

综述了Mg-Al-X(X=Cu,Zn,Pd,Ag,Pt)、Mg-Zn-(Ga,Al)、Mg-Zn-RE(RE=Y,以及Gd到Er的稀土元素)等系列的镁系准晶的结构、形成机理、准晶形成的成分范围,以及准晶的力学性能.介绍了近年来利用镁系准晶的优异性能,采用各种制备工艺,开发含准晶的高性能镁基材料的研究进展.     

NiCr合金在KCl-ZnCl2盐膜下含氯氧化性气氛中的腐蚀

研究了纯Ni、纯Cr以及3种不同Cr含量的NiCr合金在600℃KCl-ZnCl2盐膜下含氯氧化性气氛中的腐蚀行为.结果表明,5种材料均发生了严重的加速腐蚀.在材料表面形成了多孔的氧化膜,并发生了开裂,在氧化膜与基体金属的界面处有金属氯化物生成.NiCr合金的腐蚀增质比纯Ni和纯Cr的小.Ni50Cr和纯Cr有较高的腐蚀速度,前者与其具有的双相组织有关,后者是其氧化膜易脱落所致.材料的加速腐蚀机制是氯化物蒸汽的气相输运加速了金属离子向外扩散速度的‘活化氧化'.     

纳米TiO2和紫外线吸收剂对丙烯酸酯涂层抗光氧化性能的影响

讨论了锐钛矿型和金红石型纳米TiO2以及2．4-二羟基二苯甲酮和2-(2-二羟基-5-苯甲基)苯并三唑等有机紫外线吸收剂的光活性．并借助失重分析和SEM分析探讨它们对丙烯酸复合涂层抗光氧化性能的影响。UV分析表明：2，4-二羟基二苯甲酮、2-(2-二羟基-5-苯甲基)苯并三唑等有机紫外线吸收剂对400nm以下的紫外线有强烈的吸收作用；金红石和锐钛矿型纳米TiO2对紫外线也有较强烈的吸收和散射作用，紫外光透过率低。且有机紫外线吸收剂随着辐射时间的延长会分解失效，而纳米TiO2较稳定。失重分析和SEM分析结果显示：锐钛矿型纳米TiO2具有光催化性，加速丙烯酸酯聚合物的光降解，而金红石型纳米TiO2则是一种有效的遮光剂。同时添加金红石型纳米TiO2和有机紫外线吸收剂能更有效提高丙烯酸酯复合涂层的抗光氧化性能。     

A three-dimensional model describing stress-temperature induced solid phase transformations: thermomechanical coupling and hybrid composite applications

Between composite materials, shape memory alloy (SMA) composites are having a more and more relevant role. Typically, SMA wires are embedded in a metallic or a polymeric matrix to obtain materials with native multi-functionality and adaptive properties. This work approaches the computational study of the mechanical response of a composite in which SMA wires, previously deformed, are activated by electrical current heating, and accordingly try to recover the original shape inducing a shape change or a prestress in the structure. In particular, since the SMA behaviour is strongly affected by the thermo-mechanical coupling, in the first part of this work we present a 3D phenomenological model able to take into account this aspect. The model time-discrete counterpart is used to develop a 3D solid finite element able to describe the thermo-electro-mechanical coupled problem due to shape memory alloy response and to Joule effect. Finally, in the second part of the paper, we employ the developed computational tool to simulate different feasible SMA composite applications. Copyright © 2004 John Wiley & Sons, Ltd.     

Ni-Cr-Al合金在1000℃空气中的氧化

研究了两种不同Cr含量的常规熔炼Ni-Cr-Al合金在1000℃空气中的氧化行为.合金氧化动力学遵循抛物线规律,Ni-20Cr-2.5Al合金在1000℃的氧化增重略小于Ni-15Cr-2.5Al合金,二者的氧化增重都明显小于Ni-20Cr合金.Ni-20Cr-2.5Al合金1000℃氧化后形成了外层的Cr2O3及内层极薄的Al2O3型氧化膜,在Ni-Cr合金中加入Al,由于Cr、Al的相互作用,降低了形成Cr2O3和Al2O3外氧化膜所需的Cr或Al的临界含量,促进了保护性Al2O3或Cr2O3膜的生成.     

Fatigue of Magnesium Alloys

Magnesium alloys show a high specific strength and are therefore increasingly used for light‐weight constructions in transportation industry.^[1,2] To predict the behaviour of the material under the influence of cyclic loading it is vital to understand the fatigue behaviour of magnesium alloys. Only when understood properly, it is possible to fully apply the potential weight reduction by using magnesium alloys. A very important aspect in fatigue of magnesium alloys is the influence of a corrosive media and elevated temperatures, of which both are relevant in automotive applications. These two factors tend to have deleterious effects on magnesium alloys and therefore also have to be considered in investigations on the fatigue behaviour of magnesium alloys.     

The influence of manganese addition on mechanical properties of commercial Al‐4Mg casting alloys

The aim of this study was to investigate the mechanical properties of Al‐Mg‐Si alloys aged to peak hardness with different dispersoid volume fraction. It was found that the tensile strength increases with dispersoid content, for alloys having similar ductility. The effect of an increasingly triaxial stress state on a fracture strain above mentioned alloys were measured using a series of notched tensile specimens whose notch root radius of curvature was changed. The alloy ductility was found to increase with dispersoid content and root radius and to decrease with increased stress triaxiality. The fracture toughness of these alloys was determined as a function of dispersoid content and notch root radius of curvature. It was observed that the fracture toughness increased as the dispersoid content and the notch root radius increased. scanning electron microscope analysis of the fracture surfaces revealed that fracture mechanism was transgranular fracture with dimples formation. It is argued that optimum mechanical properties in these alloys can be achieved at about 0.5 % Mn content.     

Micromechanics of Tension‐Compression Asymmetry of Polycrystalline Shape‐Memory‐Alloys

The asymmetry associated with martensitic transformations observed in tension/compression experiments of shape‐memory‐alloys (SMAs) is investigated on the basis of a recently suggested micromechanical model. The approach is based on crystallographic theory and utilizes a framework of energy minimization in a finite deformation context. Polycrystalline NiTi under tension demonstrates smaller phase‐transformation start‐strain, differe phase‐transformation stress‐levels and flatter phase‐transformation stress‐strain slopes than that under compression in our numerical simulation. The phase‐transformation start‐stress is followed to have a linear relationship with respect to the temperature within a certain range. These results agree well with experimental results reported in the literature.     

二氧化钛直接制取金属钛工艺简介

阐述了各种二氧化钛直接电解制取金属钛的工艺及其原理，指出了熔盐电解TiO2法在工业应用上存在的问题。     

V,Mn和Co对AB2型贮氢电极合金Zr-Cr-Ni相结构和电化学性质的影响

研究了元素Mn ,V和Co部分替代ZrCr0 .7Ni1 .3合金中的Cr和Ni后对其相组成、晶格常数和电化学性质等方面的影响。结果表明 :母体合金由主相立方C15型Laves相和少量六方C14型Laves相和第二相Zr7Ni1 0 组成。在ZrCr0 .7-xVxNi1 .3(x =0 .1～ 0 .6)合金中 ,随着V含量的增加 ,合金主相中C15型Laves相含量逐渐减少 ,而C14型Laves相含量逐渐增多 ,而第二相Zr7Ni1 0 逐渐向Zr9Ni1 1 相转化 ,同时合金的电化学容量也迅速降低 ;当元素Mn和V同时进行替代时 ,合金ZrCr0 .7-x -yMnxVyNi1 .3(x y =0 .2～ 0 .4)的相组成不大 ,其中合金ZrCr0 .4 Mn0 .1 V0 .2 Ni1 .3放电容量最高 ( 3 11mAh·g- 1 )。元素Co对合金ZrCr0 .4 Mn0 .1 V0 .2 Ni1 .3中的Ni进行替代时 ,合金的主相中C14型Laves相显著增多 ,其中合金Zr Cr0 .4 Mn0 .1 V0 .2 Co0 .1 Ni1 .2 的电化学容量最高为 3 3 6mAh·g- 1 ,具有良好的循环稳定性和自放电率