超塑性材料断裂的理论分析

本文评述了近年超塑性材料断裂研究理论进展。理论分析得出的一系列关系式可以反映这两个参数对塑性的贡献。其中 L-Z-B 关系式可以将经典理论和现代分析结合,描述了材料塑性和超塑性的基本规律。在众多限制超塑性变形能力的因素中,孔洞的影响可以通过综合了 m 值和孔洞长大速率两个参数(宏观参数和微观参数)的“超塑性断裂机构图”得以反映;当 m 值在变形中变化时,可以建立延伸率与最终 m 值之间的定量关系,这一关系又恰好与 G-A 的 m-ef 关系在形式上完全一致;各种缺陷(初始的或环境的)影响可以在理论分析中被反映,并且建立了它们之间的定量关系。     

LY12CZ 铝合金超塑性孔洞长大及其对断裂的影响~*

供应状态 LY12CZ 铝合金具有超塑性,平均晶粒尺寸为15.3μm,在490℃,(?)_0=1.67×10~(-4)s~(-1)时,延伸率为346%,m 值为0.52—0.6。该材料为孔洞敏感材料,孔洞长大规律可用本文提出的二阶段孔洞模型描述。同时考虑材料的应变速率敏感性(m)和孔洞长大效应,可从理论上预测该材料的延伸率。     

超塑性材料研究的新进展

介绍了超塑性的基本概念和超塑性材料的研究历史,叙述了金属、精细陶瓷的超塑性及其加工方法。     

材料参数及静水压力对超塑性胀形影响的数值模拟

本文将含有变形损伤的本构关系引入刚粘塑性有限元程序,用于超塑性胀形的数值分析,讨论了应变速率敏感性,孔洞长大及静水压对极限成形应变的影响,并与文献发表的实验结果进行了比较。     

表面涂层对等温锻造TiAl合金超塑性的影响

通过板状试同温拉伸试验，研究了表面涂层对等温锻造ＴｉＡｌ合金超塑性的影响。结果表明，试样涂以纯铝，可以提高ＴｉＡｌ使金的超塑性，其原因是涂层既避免了表面高温氧化。又优先形成孔洞。释施表面的局部应力推迟了表面孔洞的形成和长大。     

粉末冶金法生产SiCp／MR64复合材料及其超塑性的研究

本文用粉末冶金法生产SiCp/MR64复合材料,并对其超塑性进行了研究。在500℃～520℃、应变速率为8.33×10~(-3)s~(-1)获得最大延伸率为210％。SiCp数量和尺寸对超塑性有很大影响,复合材料超塑性低的原因在于变形过程中产生大量孔洞,孔洞是应变软化的主要原因。     

孔洞材料动态破碎的细观机理

采用Ｃ－Ｈ－Ｊ动态微孔长大细观模型研究孔洞材料中的动态破碎的细观机理，导出了微孔动态演化方程及动态破碎尺寸与材料孔隙度的关系，利用本文给出的动态破碎的细观机制可对破甲弹的破甲机理给出合理的解释。     

板材超塑性拉延过程的数值模拟

板料超塑性成形是一种全新的成形方法.用刚塑性有限元法对Zn-22Al合金U形拉延过程进行了数值模拟,分析了变形过程中工件的应力、应变、摩擦和厚度分布,揭示了成形过程中金属的塑性变形规律,为成形工艺设计提供了有效的分析工具.     

超塑焊接接头变形特点分析

本文以结构钢 (4 0Cr)与工具钢 (T1 0A)为研究对象 ,探讨了两种压前组织超细化预处理工艺 (整体循环淬火和高频淬火 )及压接工艺因素对恒温超塑焊接头变形的影响。试验结果表明 :恒温超塑焊接属小变形焊接 ,其接头变形主要表现为应变的时间积累。压前组织越细 ,其接头变形越大 ,与 4 0Cr侧相比 ,T1 0A侧接头变形均较大     

超塑性变形微观结构变化的研究

本文研究了A1-10Si-1Mg合金在超塑性拉伸过程中微观组织的变化。揭示出该合金在超塑性变形中随应变量增加,晶内位错密度增加,是由两方面原因造成的:一是晶粒长大和晶界上第二相粒子给晶界滑移造成困难,使晶内位错调节作用增强;二是晶粒内的第二相粒子阻碍了晶内位错运动使位错堆积在第二相粒子周围。     

Simulation on Grain Boundary Sliding during Superplastic Deformation Using Molecular Dynamics Method

Grain growth and grain boundary sliding are the two main superplastic deformation mechanisms. In the paper, simulation work is focused on the sliding of a∑3 (111) symmetric twist coincidence grain boundary, a ∑13 (110) asymmetric tilt coincidence grain boundary, and a ∑3 (110) symmetric tilt coincidence grain boundary in AI, and the energies of grain boundary for each of equilibrium configurations are computed. An embedded atom method (EAM) potential was used to simulate the atomic interactions in a bicrystal containing more than 2000 atoms. At 0 K, the relationships between total potential energy and time steps for ∑3 (111) symmetric twist coincidence grain boundary and ∑3 (110) symmetric tilt coincidence grain boundary during sliding at 2 m/s represent the periodic characteristic. However, the relationship between total potential energy and time steps for ∑13 (110) asymmetric tilt coincidence grain boundary represents the damp surge characteristic. It is found that grain boundary sliding for ∑3 (110) symmetric tilt coincidence grain boundary is coupled with apparent grain boundary migration.     

超塑性变形的应力应变速率关系

文章详细分析了方程σ=kε~m的优缺点及适用范围,提出了超塑性的定义并引入了极限超塑性和有效应变速率敏感性指数的概念。在此基础上,讨论了流动应力不同部分—内应力及有效应力对超塑性变形的作用,据此导出一个超塑性流动应力与应变速率之间的关系式。该关系式能深入地说明有关的超塑性行为,理论结果与实验数据一致。     

铝锌镁锆合金超塑变形后位错结构与空洞长大的研究

本文对铝锌镁锆合金超塑变形后位错结构及空洞长大规律进行了研究。实验证明该合金在晶界滑移中存在位错蠕变的协调机制。在超塑变形中出现了品界位错并参与了品界滑移,它们是由晶界吸附晶格位错而形成的,或由晶界结构本身在品界滑移中形成的。各种应变速率下测定了空洞长大速率的参数η,探讨了η与 m 值的关系。     

Superplastic Microforming of Zn-A122 Alloy Ribs

Research on microforming of fine-grained superplastic Zn-AI22 alloy was carried out in this paper by means of superplastic forming. With the selected material, microformability tests have been carried out with the specially developed evaluation method by using two kinds of stainless steel dies. With these dies, micro-extrusion tests have been carried out and the characteristics of microformability of the material have been clarified. Effects of processing parameters and die structure on forming have been analyzed. SEM and metallographic microscope have been used to analyze the formed specimens. Through analysis of flow lines of the formed specimen, behavior of material could be understood well.     

一个新的超塑变形内部损伤预测模型

超塑变形往往具有空洞敏感性，对空洞的研究引起国内外学者的重视并取得较大进展，但现有描述超塑变形时空洞损伤行为的力学模型普遍存在精度问题，利用神经网络对超塑变形时的空洞损伤程度进行预测，不仅可提高精度，同时亦能充分反映超塑变形工艺参数对损伤的影响规律。因此，这就为研究超塑变形时的空洞损伤提供了一种新方法，同时也为神经网络的应用开辟了一个新领域。     

Cavitation Behavior during Superplastic Deformation of AZ31 Magnesium Alloy

Superplasticity of AZ31 Mg alloy at the temperature range of 250～450℃ and stain rate range of 0.7x10-3～ 1.4x 10-1 s-1 was examined through uniaxial tensile test. Optical microscopy (OM) and scanning electron microscopy (SEM) were employed to investigate the morphology of cavities and surface relief near fracture surface, respectively.It is shown that AZ31 Mg alloy starts to exhibit superplasticity from 300℃. The maximum elongation of 362.5%was obtained at 400℃ and strain rate of 0.7×10-3 s-1. There exist many O-shaped cavities and filaments at the boundaries near fracture surface. The fracture of filaments results in intergranular cavity and the model for the formation of intergranular cavities is proposed. The growth of cavities is plasticity-controlled and the serrated boundaries of intergranular cavities agree with the results of surface relieves.     

Modeling of Material Deformation Kinetics in the Prefracture Zone

Based on the concept of complete stress–strain diagrams, we propose a new model describing the law of stress distribution in the prefracture zone in plastic materials in view of the type of the stressed state.