Deformation Mechanisms of Ti-6Al-4V During Tensile Behavior at Low Strain Rate

A superplastic Ti-6Al-4V grade has been deformed at a strain rate of 5 × 10⁻⁴ s⁻¹ and at temperatures up to 1050 °C. Structural mechanisms like grain boundary sliding, dynamic recrystallization, and dynamic grain growth, occurring during deformation, have been investigated and mechanical properties such as flow stress, strain hardening, and strain at rupture have been determined. Dynamic recrystallization (DRX) brings on a decrease in the grain size. This could be of great interest because a smaller grain size allows a decrease in temperature for superplastic forming. For DRX, the driving force present in the deformed microstructure must be high enough. This means the temperature must be sufficiently low to ensure storing of enough dislocation energy but must also be high enough to provide the activation energy needed for DRX and to allow superplastic deformation. The best compromise for the temperature was found to be situated at about 800 °C; this is quite a bit lower than the 925 °C referenced in the literature as the optimum for the superplastic deformation. At this medium temperature the engineering strain that could be reached exceeds 400%, a value high enough to ensure the industrial production of complex parts by the way of the superplastic forming. Microstructural, EBSD, and mechanical investigations were used to describe the observed mechanisms, some of which are concurrent. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6-9, 2005.     

陶瓷材料的超塑性研究

介绍了陶瓷材料超塑性研究的现状，陶瓷材料超塑性的主要工艺特点及参数，重点讨论了陶瓷材料超塑性的机理，并指出了其应用前景。     

铍青铜(QBe2)超塑性预处理工艺的研究

通过工艺试验发现,供应态的铍青铜(QBe2)经一定的预处理,可获得良好的超塑性。在550℃和ε=1.67×10~(-3)s~(-1)的应变速率拉伸,合金能呈现大于1000％的高延伸率。文中提出的淬火+时效;淬火+冷轧,淬火+时效+冷轧的三种预处理工艺都能使合金获得超塑性的组织状态。分析和讨论了预处理工艺参数和所需的最佳组织条件。     

陶瓷材料的超塑性

虽然陶瓷材料在本质上是一种脆性材料；然而研究已表明细晶陶瓷材料具有超塑性，在高温下能产生很大的拉伸形变．本文综述了超塑性的特征和Y2O3稳定四方ZrO2多晶体这种典型的超塑性陶瓷材料的形变机理，形变特征以及动态晶粒生长、玻璃相和产生孔穴对其超塑性形变的影响，此外，还总结了其他陶瓷材料，包括Al2O3、Al2O3－Y2O3稳定四方ZrO2、纳米陶瓷和玻璃陶瓷的超塑性行为和特征．     

Effects of cooling rate on mechanical properties of near-eutectic tin-lead solder joints

This paper reports the results of a study on the effect of the cooling rate during solidification on the shear creep and low cycle shear fatigue behavior of 60 Sn/40 Pb solder joints, and on bulk solder tensile properties. Solder joints were made with three different initial microstructures by quenching, air-cooling and furnace-cooling. They have similar steady-state strain rates under creep at relatively high shear stresses (i.e. in the matrix creep region) but creep at quite different strain rates at lower shear stresses (i.e. in the grain boundary creep region). These results are ascribed to the refined grain size and less lamellar phase morphology that results on increasing the cooling rate. Tensile tests on bulk solders that were cold-worked, quenched and furnace-cooled show that a faster cooling rate decreases the ultimate strength and increases the ductility at low strain rates. The fatigue life of quenched solder joints is shown to be longer than that of the furnace-cooled joints.     

Superplasticity and Diffusion Bonding of Ti_3AI Intermetallic Compounds

The superplasticity of Ti_3Al intermetallic compounds has been investigated in this paper.TheTi-14Al-21Nb ternary alloy showed 477% elongation at the strain rate of 1.49×10~(-5) s~(-1) and950℃.The elongation of Ti-14Al-21 Nb-3Mo-1V quinary alloy approached to 573% at the strainrate of 4.52×10~(-5) s~(-1) and the same temperature,and it was found that the elongation value in-creased to 1096.4%as temperature was raised up to 980℃ at the same strain rate.Ti_3Al base al-loys were bonded by diffusion bonding technology and good joints were created,the simulatedspecimens were performed by SPF/DB process.     

温轧态2618A铝合金高应变速率超塑性的研究

对温轧态２６１８Ａ铝合金在不同温度（４７０～５５０℃）和应变速率为１０￣（－３）～１０￣（０）ｓ￣（－１）范围内的超塑性进行了研究，确定了最佳超塑性变形规范：在５００～５３０℃温度范围内，应变速率为２．８×１０￣（－１）ｓ￣（－１）的条件下，可获得大于２３０％的延伸率，表明该合金具有高应变速率超塑性的特性。     

热轧镁合金AZ31B板材的超塑性变形行为与机制

研究工业态热轧 AZ31B镁合金板材的超塑性及变形机制,在应变温度为 723K,应变速率为 1× 10-3s-1的实验条件下,其最大断裂延伸率达到 216%,应变速率敏感指数达 0.36;研究结果表明:晶界滑动( GBS)是工业态热轧 AZ31B镁合金超塑性的主要变形机制,变形初期有动态再结晶发生,断裂是由晶界处形成的空洞不断长大、连接而引起的.     

Grain refinement and superplasticity of pipes processed by high-pressure sliding

ABSTRACT

The high-pressure sliding (HPS) process was applied for grain refinement of a pipe form of an Al-3wt%Mg-0.2wt%Sc alloy by developing two types of straining techniques (called in this study anvil sliding and mandrel sliding). To achieve a homogeneous microstructure throughout the cross-section of the pipe, the sample is rotated around the longitudinal axis every after sliding operation by introducing multi-pass technique, named multi-pass HPS (MP-HPS) as developed earlier for rods. The MP-HPS-processed sample shows ultrafine-grained structures with an average grain size of ～260 and ～300?nm after the HPS processing using anvil sliding and mandrel sliding. The samples also exhibit superplasticity with total elongations well more than 400%, respectively. A finite-element method is used to simulate the evolution of strain in the HPS processing and demonstrates that the simulation well represents the experimental results.     

SUPERPLASTICITY OF A WATER-QUENCHED AND TEMPERED 40Cr STEEL

1.IntroductionSuperplasticity possesses many good characteristics such as high elongation, low flow stress and high atom diffusion ability, which make it show good application in metal forming and diffusion bonding of complex shape structure. Up to now, the superplasticity of steel has been more investigated, however the pretreatment in order to obtain fine grain and then superplasticity was often carried out by circular quenchingof typically 3 times and subsequent high-temperature tempering, …