SUPERPLASTIC BEHAVIOUR OF A FINE GRAINED TiAl BASED ALLOY TREATED BY MULTI-STEP THERMO-MECHANICAL TREATMENT

ＳＵＰＥＲＰＬＡＳＴＩＣＢＥＨＡＶＩＯＵＲＯＦＡＦＩＮＥＧＲＡＩＮＥＤＴｉＡｌＢＡＳＥＤＡＬＬＯＹＴＲＥＡＴＥＤＢＹＭＵＬＴＩＳＴＥＰＴＨＥＲＭＯＭＥＣＨＡＮＩＣＡＬＴＲＥＡＴＭＥＮＴ①ＨｕａｎｇＢａｉｙｕｎ,ＤｅｎｇＺｈｏｎｇｙｏｎｇａｎｄＨｅ...     

电沉积纳米镍薄板的超塑微拉深性能

采用脉冲电沉积工艺制备了厚度为0．1mm的纳米镍薄板，在不同的温度和应变速率下对该薄板进行单向拉伸试验，确定了其超塑性变形的最佳工艺条件，在此基础上进行了纳米镍薄板的微拉深性能实验。实验结果表明：纳米镍薄板的微拉深性能随成形温度的升高而提高；在温度为723K、半球形拉深凸模直径为1mm、拉深速度为1～5mm／min的条件下，均可成功拉深出半球件。采用透射电镜和扫描电镜对拉深变形前的沉积态组织和拉深变形后的微观组织进行了观察比较，结果表明，微拉深后大部分镍晶粒长大到微米量级。根据实验结果，初步探讨了超塑微拉深的主要变形机制。     

金属间化合物大晶粒超塑性行为

在所研究的Fe3Al、Fe3Si、FeAl、Ni3Al、NiAl和TiAl等金属间化合物中均发现大晶粒超塑性。研究发现，超塑性变形过程中最大流变应力随温度升高而减小，随初始应变速率增大而增大；超塑性变形过程中的应变速率敏感因子不是一项重要指标。激活能的分析表明，不同种类金属间化合物大晶粒超塑性变形的控制速率可能不同。金相分析表明，超塑性变形过程中原始大晶粒逐步细化，最终获得明显细化的显微组织。     

Zn-5Al共晶合金的表面效应对超塑变形的影响

用光学显微镜，扫描电镜研究了Zn-5Al共晶合金超塑变形的表面效应及其影响因素。结果表明：超塑变形中的晶界滑移机制导致某些晶界由材料内部滑移至表面，从而使外表面增加；Zn-5Al合金的超塑性表面流动具有长程性，而且表面流动对超塑变形具有协调作用，表面镀层由于破坏了表面流动的协调性，对合金的超塑变形产生阻碍作用。空洞是材料的内自由表面，其形核长大与（2γs-γgb）有关，提高表面能，降低晶界能可增强材料的超塑性。     

热变形态TiAl基合金超塑性拉伸过程中应变速率敏感系数的分析

研究了具有热变形组织的TiAl基合金在1 000℃1 075℃温度区间内以不同应变速率拉伸时的应变速率敏感系数(m)值。实验结果表明,m值随超塑性拉伸变形温度及应变速率的变化而变化;在较大温度范围及较宽的应变速率区间内这种材料都有大于0.3的m值;并且,ε     

Manufacturing advantages of superplastically formed fine-grain Ti-6Al-4V alloy

Superplastic forming (SPF) of Ti-6Al-4V has traditionally been performed at 900 °C. Although SPF equipment and dies have been developed to withstand this high temperature, their life is limited and maintenance is high. In addition, the formed sheets need chemical milling after processing to remove a significant layer of alpha case, and parts require hand polishing due to a rough die surface caused by high temperature oxidation. The recent development of a Ti-6Al-4V alloy with a grain size of around 1 μm has led to the possibility of superplastic forming at a much lower temperature than regular Ti-6Al-4V. In addition, the forming speed can be increased. This work looks at some of the SPF attributes of fine-grain titanium, in particular, the optimum forming temperature, the thinning characteristics, alpha case formation, and forming speeds. The authors also address manufacturing advantages, such as die life, equipment needs, and operator comfort. Some prototype and preproduction aircraft components on Boeing airplanes are presented. The results show that the new fine-grain material could significantly lower the cost of SPF Ti-6Al-4V part production for the aerospace industry. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Microstructure evolution and low temperature superplasticity of ZK40 magnesium alloy subjected to ECAP

Microstructure evolution and superplastic behaviors of ZK40 magnesium alloy were investigated in the temperature range of 473–623 K. Transmission electron microscopy (TEM) was used to study the microstructure changes. After the alloy had been processed by equal channel angular pressing (ECAP) for one pass through the die, significant twinning was found to have occurred, and the mean grain size was 5.6 μm. Finer grains were obtained after multi-pass ECAP, and the average grain size of the alloy ECAPed for three passes was as low as 0.8 μm; this alloy exhibited low temperature superplasticity at 473–523 K, and the elongations obtained at the initial strain rate of 1×10⁻³ s⁻¹ were 260% at 473 K and 612% at 523 K. Corresponding values for the ZK40 alloy processed by ECAP for only one pass were 124% at 473 K and 212% at 523 K. Poor superplastic behavior of the ZK40 alloy processed by ECAP for only one pass was related to the longrange stresses associated with the non-equilibrium grain boundaries within the coarse grains. The incompatibility between the fine grains and the coarse grains was thought to be unfavorable to the improvement of superplascity. This article is based on a presentation in “The 7th Korea-China Workshop on Advanced Materials” organized by the Korea-China Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju Hotel, Jeju Island, Korea on August 24–27, 2003.     

Superplasticity of a SiC particulate-reinforced 6A02AI matrix composite

The superplastic characteristics of a 15% (volume fraction) SiCp (14 μm)/6A02A1 composite, fabricated by stirring casting and cold-rolling after extrusion with a low extrusion ratio of 10:1 and hot-rolling, were investigated. The composite exhibits a tensile elongation of 250% at an initial strain rate of 8.9 x 10-4 s-l and at 833 K where an appropriate amount of liquid phase is presented in the composite. The superplastic deformation is uniform and the strain hardening exponent 2is as high as 1.6. The fracture surface is intergranual and the superplastic deformation mechanism of the composite is considered to be grain boundary (interface) sliding accommodated by an appropriate amount of liquid phase.     

供应态LY12CZ铝合金在超塑性形变中晶界形态的研究

采用光学显微镜、扫描电镜和透射电镜对未经任何预处理、晶粒尺寸为19μm～21μm之间的供应态LYl2CZ铝合金超塑性形变中晶界形态进行了观察、分析。结果表明，此状态下的铝合金在超塑性变形过程中晶界宽度和形态会发生改变。在较大伸长率的条件下，晶界出现宽边化和圆弧化。在超塑性变形过程中形成的宽边晶界属于介稳状态的界面，在高温下短时间保温，宽边晶界会发生晶化，变成细小的普通晶界。试样在超塑性变形时产生的伸长率与晶界宽度有密切联系。在此次试验中超塑性伸长率大的试样其晶界宽度在2．1μm～2．7μm之间。     

工业铝合金5182和6016的超塑性研究

研究了普通冷冲压成形的工业铝合金 5 182和 6 0 16的超塑性能。经超塑单向拉伸试验和自由胀形试验表明 ,铝合金 5 182在温度为 5 0 0℃ ,应变速率为 8 33× 10 - 3 s时 ,材料的伸长率达到 2 0 0 % ,应变速率敏感性指数m值达到0 2 4 ,具有一定的超塑性 ;而 6 0 16合金在 5 0 0℃时的伸长率为 89% ,应变速率敏感性指数m值为 0 13,超塑性较差