板料超塑性拉伸失稳研究

基于板料超塑性变形的特点，本文将超塑性变形全过程分为稳定变形、准稳定变形、应变路径漂移和集中性失稳发展四个阶段，依据增量理论，用数值方法建立了一普遍适用的失稳模型。然后在此基础上，依板料发生集中性失稳（ｄε＿２＝０）为许用变形程度的极限，预测了板料超塑变形时的成形极限曲线。对铝合金ＬＹ１２ＣＺ和半硬态黄铜Ｈ６２的超塑性实验研究表明：用本文提出的失稳模型预测的超塑性板料的成形极限与实验结果具有较好的一致性。     

TC4钛合金在中低温下(超)塑性及微观组织研究

对TC4钛合金的塑性以及微观组织进行了分析,研究了宏观组织与微观组织的变化。对TC4钛合金板材在中低温区(550~700℃)、不同拉伸速度下进行了单向拉伸试验。通过对材料伸长率及真应力-真应变曲线的分析,探索了材料从普通塑性变形到超塑性变形的变形机理。结果表明,变形温度和拉伸速度对材料真应力影响明显,变形温度越高,拉伸速度越小,材料真应力越小,塑性越好,在该状态下有更好的塑性加工性能。     

超塑性拉伸断裂分析

材料的拉伸断裂问题同时也是断裂延伸率问题,而材料的超塑性以其大的断裂延伸率为主要特征.自超塑性现象发现以来,人们从来没有停止过对超塑性大延伸率变形本质的探索.这方面的文献特别多,但主要集中在超塑性微观机理和变形机制方面,而对于超塑性变形力学规律方面的研究则相对较少.实际上,超塑性大延伸率与其力学稳定性密切相关,并由其特殊的断裂机制所决定.因此,本文首先从超塑性的微观断裂机制出发,着重回顾超塑性孔洞的形核、生长和连接的微观物理机制的研究进展.然后,主要从宏观力学稳定变形出发,回顾国内外有关超塑性拉伸过程中颈缩的产生和发展导致的断裂延伸率或极限应变的力学分析的研究工作,并作了相应的归类和评述.结论指出:尽管超塑性断裂机制的研究很多,但是缺乏统一的认识,仍需要长期的基础性工作.目前的首要任务就是从超塑性拉伸宏观力学规律出发,依据现代数值分析技术深入研究其力学稳定变形机制,以便揭示超塑性大延伸率现象的力学本质.在分析过程中,应采用精确定量的本构方程,并考虑变形路径等外部条件的影响.     

低温环境下Ti6Al4V合金超塑性拉伸变形行为分析

通过在低温(700⁸50℃)环境下,对未经预处理的Ti6Al4V合金板材进行超塑性拉伸变形,分析其超塑性变形能力和力学行为,并对其低温超塑性变形机制进行了研究。结果表明:Ti6Al4V合金在常压空气中具有优异的的低温超塑性变形性能;在700850℃)环境下,对未经预处理的Ti6Al4V合金板材进行超塑性拉伸变形,分析其超塑性变形能力和力学行为,并对其低温超塑性变形机制进行了研究。结果表明:Ti6Al4V合金在常压空气中具有优异的的低温超塑性变形性能;在700⁸50℃温区内应变速率敏感性指数约为0.3;850℃条件下,Ti6Al4V合金的超塑性变形机制为晶界滑动;700850℃温区内应变速率敏感性指数约为0.3;850℃条件下,Ti6Al4V合金的超塑性变形机制为晶界滑动;700⁷50℃时合金发生非典型超塑性变形。     

磁脉冲成形板坯动态结构失稳力学分析

为揭示磁脉冲成形过程中板坯的塑性失稳机制,基于板坯磁脉冲拉伸成形工艺试验,结合板坯在脉冲电磁力作用下的变形特点,对板坯在动态加载条件下的结构失稳行为进行了力学解析。结果表明,脉冲电磁力作用的板坯动态变形过程中惯性力的影响显著。惯性力作用下,板坯变形依次经历脉冲力加载和惯性运动两个典型阶段,其动态塑性变形符合初期塑性变形伴随着动能的吸收、后期塑性变形产生于动能的耗散模式。惯性力的存在使得板坯对自身的结构失稳具有自我抑制作用,有助于分散变形,提高板坯的塑性。     

单晶体单滑移的变形和稳定性分析

从细观的晶体塑性力学出发,研究了在单向拉伸下的单晶体单滑移的变形和稳定性问题,定量给出了滑移面的方位和滑移方向随应变ε的变化规律.定义了失稳参数S,把用正应力和正应变表示的塑性变形稳定性条件,变换成适合于细观塑性力学应用的用切应力和切应变表示的稳定性条件.结果表明:材料滑移面向拉伸方向偏转并趋于一致,即应变ε增加时,滑...     

TA15合金超塑性变形空洞演化及断裂行为

对TA15合金在SANS CMT4104型高温电子拉伸实验机上进行恒应变速率超塑性拉伸试验,研究了合金超塑性变形过程中空洞演化及断裂行为。结果表明:超塑性变形过程中,TA15合金空洞含量和大小受变形量、应变速率和应变速率敏感性指数m值的影响较大。随变形量增大,空洞分别沿拉伸轴方向和垂直于拉伸轴方向发生了聚合和连接,空洞长大由形核时的一般扩散机制向塑性变形机制转变。TA15合金超塑性拉伸试样断口呈针点状,断口上含有大量的韧窝状空洞,空位聚集-空洞连接是TA15合金超塑性断裂的主要机制。     

陶瓷超塑性变形机理研究进展

由于微纳米陶瓷材料在超塑性成形方面的潜在应用,近年来,关于陶瓷材料超塑性的研究已成为陶瓷领域研究的热点之一。关于陶瓷超塑性变形机理,目前普遍认为微观结构对陶瓷超塑性变形产生重要影响,细小晶粒之间晶界相互滑移在陶瓷超塑性变形过程中发挥重要作用,并且在改善和发展纳米陶瓷的超塑性方面已经取得了明显的进步。大多数学者对于陶瓷超塑性的变形机理的研究,目前还主要集中于晶粒局部变形的一些基本原则。文章在总结陶瓷超塑性影响因素和晶界滑移模型的基础上,以研究的氮化物陶瓷为例,对陶瓷超塑性变形机理进行了分析与探讨。     

Fe_3Al－Ti超塑性变形过程中晶粒形态演化规律

对Ｆｅ_３Ａｌ－Ｔｉ合金超塑性变形中不同应变量下的晶粒形态进行了研究。发现Ｆｅ_３Ａｌ－Ｔｉ超塑性行为与连续再结晶有关，随变形量增大，晶粒逐渐细化，但晶粒形状变化不大，并沿拉伸方向有所伸长。ＴＥＭ分析表明，晶粒细化过程与超塑性过程中亚晶界向大角晶界的演化有关。本文对Ｆｅ３Ａｌ－Ｔｉ合会超塑性变形机理进行了初步的探讨。     

Ti-6Al-4V合金超塑性变形及微观组织演变

通过高温拉伸试验研究了Ti-6Al-4V合金的高温变形力学行为和超塑性,并对试样断口附近的组织进行了观察。结果表明,随着变形温度的升高或初始应变速率的降低,Ti-6Al-4V合金的流动应力明显减小;Ti-6Al-4V合金的最佳超塑性变形工艺参数为880℃/0.001s-1,最大延伸率为689%,峰值应力仅为30.03MPa;在超塑性拉伸过程中,试样变形区发生明显的动态再结晶,使片层状的α相晶粒破碎、细化和等轴化,促进超塑性的增加;随着变形温度的提高、变形量增大和变形时间的加长,再结晶α相发生了聚集长大,从而使显微组织明显粗化。对于双态组织的两相钛合金,最佳超塑性变形温度应低于或等于片层状α→β转变的终了温度。     

Superplastic deformation behavior and hot-processing map of the TiNp/2014 Al composite

The superplastic deformation behavior and hot-processing map of the TiN_p/2014 Al composite were investigated based on tensile tests conducted at various temperatures (773 K, 798 K, and 818 K) with various strain rates (0.033, 0.167, 0.33, and 0.67 s^-1). The results revealed that the influence of strain on the energy dissipation map is negligible. The optimal superplastic deformation parameters corresponding to the peak power dissipation efficiency of 0.65 differ from those corresponding to the maximum elongation of 351%. For the superplastic deformation of TiN_p/2014 composite, the deformation activation energy is much higher than that for the lattice self-diffusion in pure aluminum, which can be explained by the combination of mechanisms including grain (subgrain) boundary sliding accommodation, interface sliding accommodation, liquid-phase helper accommodation and load transfer. To avoid voids and wedge cracks, two obvious instability domains in the hot-processing maps should be avoided. The hot-processing maps obtained can approximately, but not accurately enough, optimize superplastic deformation parameters of the TiN_p/2014 Al composite.     

材料超塑变形后室温机械性能的变化和预测

超塑性材料在变形过程中往往空洞化。空洞的存在严重降低超塑成形零件的室温使用性能，因此必须建立超塑变形后材料室温机械性能变化的理论预测模型。本文以铝合金LY12CZ为例，以实验数据为基础，利用人工神经网络首次建立了预测经超塑变形后的材料室温机械性能变化的理论模型。所建模型不但可以预测铝合金LY12CZ超塑变形后的刚度．强度以及韧性等室温性能指标，而且亦能充分反映超塑变形工艺参数对其室温机械性能变化的影响规律。同时，由于本文建模方法具有通用性，因此，该模型的建立为超塑成形零件的使用性能提供了理论依据和一般方法。     

Constitutive Equation with Varying Parameters for Superplastic Flow Behavior

In this study, constitutive equations for superplastic materials with an extra large elongation were investigated through mechanical analysis. From the view of phenomenology, firstly, some traditional empirical constitutive relations were standardized by restricting some strain paths and parameter conditions, and the coefficients in these relations were strictly given new mechanical definitions. Subsequently, a new, general constitutive equation with varying parameters was theoretically deduced based on the general mechanical equation of state. The superplastic tension test data of Zn-5%Al alloy at 340 °C under strain rates, velocities, and loads were employed for building a new constitutive equation and examining its validity. Analysis results indicated that the constitutive equation with varying parameters could characterize superplastic flow behavior in practical superplastic forming with high prediction accuracy and without any restriction of strain path or deformation condition, showing good industrial or scientific interest. On the contrary, those empirical equations have low prediction capabilities due to constant parameters and poor applicability because of the limit of special strain path or parameter conditions based on strict phenomenology.     

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.     

APPLICATION OF GLEEBLE 1500 ON SUPERPLASTICITY

1.~nonSuperylasticityisakindofphenomenonthatdefonnationresistanceisreducedrelnalkablyandplasticity----especiallyelongation----isremarkablyincreased.Therehasbeenoaly30years'historyforsuperplasticityresearchintheworld.Anewsubjectandanewtechnologyofsuperplasticityincludingbranchesofmaterials,mechanism,mechhocs,forminghavebeenfoundedyet.Superplasticityisbasicallyanexperimentalsubject.Itstheoryandresultsareestablishedonthebaseofexperiments.Superplasticexperimentsmainlyincludetwokinds----mechwhcala…     

大晶粒FeAl合金超塑性变形的显微组织演变和变形激活能

本文对大晶粒ＦｅＡｌ金属间化合物塑性变形的微观组织演变进行了研究，并测定了其超塑性变形激活能，显微组织分析表明，合金的超塑性变形是一个晶粒变形，内部形成亚晶界，进而亚晶界向晶界转换，从而使晶粒得以细化的过程，Ｆｅ－３６．５Ａｌ，Ｆｅ－３６．５Ａｌ－１Ｔｉ和Ｆｅ－３６．５Ａｌ－２Ｔｉ合金变形激活能的测定值分别为３７０，２９０和２６０ｋＪ．ｍｏｌ＾－１大大低于其他的ＦｅＡｌ基合金蠕变激活能，表明超塑性     

A mesoscale model to predict the effect of microstructural heterogeneities on superplastic deformation

A two-dimensional approach is proposed to describe superplastic deformation at a mesoscopic scale in order to predict the effect on the mechanical behaviour of microstructural heterogeneities, like grain size distribution or spatial distribution of grains. The grains in the microstructure may slide and plastically deform, the extent of each mechanism depending on the applied conditions. The degree of homogeneity of deformation through the material is estimated by the predictions of differences in shear rates along bands specifically oriented in reference to the stress axis. It is shown that the superplastic behaviour not only depends on the grain size distribution but also on the degree of dispersion of the large grains through the microstructure, despite a same mean grain size. This dependence may concern the macroscopic behaviour as well as the extent of localisation of deformation through the sample.     

The Effects of Stress State and Cavitation on Deformation Stability During Superplastic Forming

The current available models describing superplastic deformation do not account for a number of important characteristics, leading to the current limited predictive capabilities of deformation and failure. In this work, the effects of cavitation and stress state on deformation stability during superplastic forming are investigated using Finite Element simulations. The simulations are performed using constant strain rate forming and using a proposed optimization approach based on a multiscale failure criterion that accounts for stress state, geometrical necking, and microstructural evolution including grain growth and cavitation. The simulations are conducted for the superplastic copper-based alloy Coronze-638 and the superplastic aluminum alloy Al-5083 which are known to develop significant cavitation during deformation. The results clearly show the importance of accounting for microstructural evolution during superplastic forming, especially when the state of stress is biaxial. Furthermore, the results highlight the effectiveness of the proposed optimization technique in reducing the forming time and maintaining the integrity of the formed parts. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6-9, 2005.     

Er、Zr微合金化5083铝合金的超塑性

针对5E83合金(Er、Zr微合金化5083合金),采用超塑性拉伸试验、扫描电镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM),探究了Er、Zr微合金元素、晶粒尺寸、变形温度、应变速率对合金超塑性的影响。通过再结晶退火、空冷和水冷的搅拌摩擦加工(FSP),分别获得了晶粒尺寸为7.4、5.2、3.4μm的完全再结晶组织,作为初始状态进行超塑性拉伸。结果表明,初始晶粒尺寸越细小,超塑性伸长率越高。当晶粒尺寸>5μm时,超塑性变形过程晶粒粗化缓慢,细化初始晶粒可显著提高超塑性;而当晶粒尺寸<5μm时,超塑性变形过程晶粒粗化严重,进一步细化初始晶粒对超塑性的提高有限。不同变形温度、应变速率的超塑性拉伸结果显示在变形温度为450～540℃、应变速率为1.67×10^-4～1.67×10^-1 s^-1,超塑性伸长率随变形温度和应变速率的提高呈现先上升后下降再上升的趋势;变形温度为520℃、应变速率为1.67×10^-3 s^-1条件下,水冷FSP态合金获得最大伸长率330%...