A three‐dimensional model describing stress‐temperature induced solid phase transformations: solution algorithm and boundary value problems

An always increasing knowledge on material properties as well as a progressively more sophisticated production technology make shape memory alloys (SMA) extremely interesting for the industrial world. At the same time, SMA devices are typically characterized by complex multi‐axial stress states as well as non‐homogeneous and non‐isothermal conditions both in space and time. This aspect suggests the finite element method as a useful tool to help and improve application design and realization. With this aim, we focus on a three‐dimensional macroscopic thermo‐mechanical model able to reproduce the most significant SMA features (Int. J. Numer. Methods Eng. 2002; 55 : 1255–1264), proposing a simple modification of such a model. However, the suggested modification allows the development of a time‐discrete solution algorithm, which is more effective and robust than the one previously discussed in the literature. We verify the computational tool ability to simulate realistic mechanical boundary value problems with prescribed temperature dependence, studying three SMA applications: a spring actuator, a self‐expanding stent, a coupling device for vacuum tightness. The effectiveness of the model to solve thermo‐mechanical coupled problems will be discussed in a forthcoming work. Copyright © 2004 John Wiley & Sons, Ltd.     

S-N-P curves in 7075 T7351 and 2024 T3 aluminium alloys subjected to surface treatments

The S-N-P (stress, number of cycles, failure probability) curves for 2024 T3 and 7075 T7351 aluminium alloys were obtained. Previously, surface treatments of degreasing and different types of anodizing were applied to samples, evaluating the influence of these treatments on the fatigue life of the alloys. The determination of the S-N-P curves was done using Maennig's method. Rotary fatigue was used because this technique produces greater stress on the sample surfaces, the zone in which it is important to evaluate fatigue resistance. Both the transition range and the finite life range were evaluated, calculating the 1, 50 and 99% fracture probability. SEM was performed in order to characterize the fracture micromechanism. The conclusions were that Maennig's method is useful to evaluate fatigue life of these materials in a fast and efficient manner. Moreover, surface treatments produce a decrease in the fatigue life of both alloys, associating this effect with the surface damage produced on each sample during the treatment.     

高镁瓷工艺特性研究和应用

本文总结了ＭｇＯ－ＳｉＯ２－Ａｌ２Ｏ３系的高镁瓷配方、增塑及烧成工艺特性的研究过程与应用结果；介绍了适应大生产的高镁瓷制作工艺。     

灰色关联分析在腐蚀非晶态镍基合金中的应用

用灰色关联分析方法取代传统的数理统计方法,对非晶态镍基合金在FeCl_3溶液中的腐蚀速率与影响因素之间的相互关系进行处理,确定各影响因子之间的主次关系。结果表明溶液流速是最关键因子,次关键因子为溶液pH值,其次为溶液温度和溶液浓度,并根据分析结果提出实际应用时的相应对策。     

海水介质中高活性镁合金负极的电化学性能

研制了一种新型镁合金负极材料；用电化学方法测定了镁合金负极在人造海水介质中的电化学性能，用浸泡法测定了材料在人造海水介质中的自腐蚀速度，用扫描电子显微镜观察了镁合金腐蚀后的表面形貌，并与AP65合金和纯镁进行了比较。结果表明，新研制的镁合金在人造海水介质中的开路电位增加，自腐蚀速度降低，稳定工作电位提高，电极表面腐蚀均匀，可开发用于高电性能电池的负极材料。     

Failure analysis of a hot extrusion die used for Al-Li alloy processing

Al-Li alloys being developed as lighter, substitutes for conventional high strength Al alloys are to be processed by routine methods. During extrusion of a 8090 Al-Li alloy, the extrusion die container failed causing some alarm. This failed die container was analysed to examine if the failure was caused by interaction of Li diffusing out of Al-Li alloy with the carbides of die steel. The evidence, although not conclusive, is sufficient to exercise caution during such processing.     

A numerical model for the dissolution of spherical particles in binary alloys under mixed mode control

A general numerical model is described for the dissolution kinetics of spherical particles in binary systems for any combination of first order reactions at the particle-matrix interface and long distance diffusion within the matrix. The model is applicable to both finite and infinite media and handles both complete and partial particle dissolution. It is shown that interfacial reactions can have a strong effect on the dissolution kinetics, the solute concentration at the particle-matrix interface and the solute concentration profile in the matrix.     

Peculiarities of erosion-corrosion processes

Investigations have been carried out on an erosion-corrosion apparatus to investigate the behaviour of corrosion-resistant highalloy iron-base materials containing hard phases. These materials had been optimized for increased wear resistance under complex stress conditions. As expected, in dry erosion tests, very low mass losses were established; there was little difference between the materials. Also, in corrosive environments (NaCl, H₂SO₄), the materials showed good stability; however, the duplex structures were superior to the martensitic ones. The combination of erosion and corrosion produced large differences and, in some cases, markedly reduced resistance to damage. These results confirmed observations that it is impossible to deduce the environmentally influenced mechanical behaviour of an alloy from its behaviour in separate corrosion and erosion experiments. The basic mechanisms underlying these processes have been investigated only tentatively.     

Ti,N,Mg对M2高速钢凝固组织和硬度的影响

为了改善Ｍ２高速钢共晶碳化物的分布，本文利用小凝固试样变质的方法研究了Ｔｉ，Ｎ和Ｍｇ对Ｍ２高速钢凝固组织和硬度的影响。试验结果表明，加入Ｔｉ或Ｔｉ－Ｎ后，共晶碳化物形态和分布有很大改善，而加入Ｔｉ－Ｎ后对凝固组织有轻微的细化作用，但只添加Ｔｉ不补碳时，钢的淬火硬度和回火硬度均下降；加入适量的Ｍｇ可以使片状的Ｍ２Ｃ型共晶碳化物转为鱼骨状的Ｍ６Ｃ型共晶碳化物，使其分布有所改善，Ｔｉ和Ｍｇ复合加入可以明     

镁法海绵钛生产工艺中大型无隔板镁电解槽的节能实践

以镁法海绵钛生产工艺中大型无隔板镁电解槽的实际节能情况为例，探讨了在镁电解生产中的非生产耗电、生产耗电、漏电等因素造成的能量浪费，阐述了生产中粗镁直流电耗、电流效率、工作电压3者之间的关系，指出了影响电解槽工作电压的有关因素及降低电解槽工作电压的途径。