固溶温度对2205双相不锈钢超塑性的影响

观察2205双相不锈钢固溶处理后的组织,并对组织中铁素体与奥氏体的两相比例进行统计分析;对2205双相不锈钢经过不同温度的固溶处理、冷轧变形后,在一定条件下进行恒温拉伸试验,观察研究材料的超塑性延伸率随着固溶温度和两相比例的变化规律。试验结果表明,当固溶温度从1050℃升高到1100℃时,奥氏体相所占比例变化不大,材料的延伸率变化也不明显;当固溶温度从1150℃增加到1350℃时,奥氏体相比例从42.76%降低到26.07%,铁素体与奥氏体的两相比变大,其延伸率也逐渐增大。冷轧变形量为80%的材料,其延伸率从560%增大到1690%;冷轧变形量为85%的材料,其延伸率从810%增大到1500%。     

High strain rate superplasticity of TiNP/2014Al composite

Superplasticity of the TiN_p/2014AI composite prepared by powder metallurgy method was investigated by tensile tests conducted at different temperatures (773, 798, 818 and 838 K) with different strain rates range from 1·7×10° to 1·7×10^?3s^?1. Results show that a maximum elongation of 351% is achieved at 818 K and 3·3·10^?1s^?1. At different deformation temperatures, the curves of m value can be divided into two stages with the variation of strain rate and the critical strain rate is 10^?1 s^?1. Superplastic deformation activation energy in the TiN_p/2014AI composite is 417 kJ mol^?1, which is related to liquid phase formation at triple points of grain boundaries and interfaces between the matrix and the reinforcement. Superplastic deformation mechanism of the TiN_p/2014AI composite is grain boundary sliding accommodate mechanism when the strain rate is lower than 10^?1 s^?1, and transfers to grain boundary sliding accommodation mechanism plus liquid phase helper accommodation mechanism when the strain rate is higher than 10^?1 s^?1     

EBSD Study on the Superplastic Deformation of Mg-7.0Al-0.4Zn Magnesium Alloy

采用EBSD分析技术研究了Mg-7.0Al-0.4Zn镁合金超塑性变形机制。结果表明,超塑拉伸变形主要是通过晶界滑动和晶内塑性滑移协调完成的。变形初期,随着变形量的增大,{0002}//ED的织构明显增强,晶内滑移起主要协调变形作用。变形中后期孪生开动,接近断裂时,晶内滑移基本消失,孪生成为主要的协调变形机制,但孪生的贡献较小。     

TA32钛合金超塑性变形行为及本构模型研究

通过单向拉伸实验研究了TA32钛合金在温度880~940 ℃、初始应变速率5×10-4~1×10-2 s-1条件下的超塑性变形行为和微观组织演变,构建了修正Johnson-Cook本构模型和BP神经网络本构模型。结果表明,TA32钛合金的流动应力与断后伸长率对温度和应变速率敏感,应变速率敏感性指数随应变量增加而减小,随温度升高而增大。温度升高和变形程度增大促进了α→β相转变和两相晶粒长大,应变速率降低使得两相晶粒有所长大。β相晶粒形貌随变形条件改变有显著变化,α相晶粒则保持等轴状。TA32钛合金的超塑性断裂模式为孔洞生长扩展导致的微孔聚集性断裂。相较于修正Johnson-Cook本构模型,BP神经网络本构模型在大范围变形条件下的预测精度更高。     

超塑性固态焊接研究进展

主要介绍了超塑性固态焊接原理和应用研究现状,概述了国内外超塑性焊接研究的最新进展,并对热点问题的研究进行了评述,重点介绍了常见的超塑性固态焊接方法,展望了超塑性固态焊接的发展趋势,进一步指出应深入研究超塑性变形规律,扩大超塑性焊接材料的应用范围。     

时效制度对2A97铝锂合金晶粒细化和超塑性的影响

采用金相、SEM和高温拉伸等手段,研究了不同时效制度对2A97铝锂合金晶粒细化和超塑性的影响。结果表明：合金在300～400 ℃时效可获得尺寸大于0.8 μm的第二相粒子,其中400 ℃×48 h过时效处理获得的第二相分布更均匀、体积分数更大,经过相同工艺轧制和再结晶退火后,获得的晶粒最为细小。在温度范围460~490 ℃,应变速率为1×10^-3~2.5×10^-3 s^-1的条件下进行高温超塑性拉伸,在490 ℃、2×10^-3 s^-1变形条件下获得伸长率最大,达到850%。     

纳米Ni和Ni/SiCp纳米复合材料的超塑性

研究了用电沉积方法制备的纳米Ni和Ni/SiCp纳米复合材料的超塑特性,在试验温度410℃和450℃,应变速率为8.3×10-4s-1～5×10-2s-1的条件下,纳米Ni和Ni/SiCp纳米复合材料均表现出超塑性.当温度为450℃、应变速率为1.67×10-2s-1时,在Ni/SiCp中获得最大延伸率为836%;在同样的温度下应变速率为1.67×10-3s-1时纳米Ni获得最大延伸率为550%.对超塑性变形后组织的分析表明,晶界滑移是主要变形机制,晶粒长大至亚微米/微米量级后,变形机制是位错协调晶界滑移和位错滑移塑性.     

诱发钛合金塑性增强的分步超塑性成形法

介绍了分步超塑成形法,从成形方式上探索一种增强材料塑性的途径。分步超塑成形过程中,分别以恒速度与最大m值法,分两步先后作用于拉伸试样,通过控制初始变形方式的变形量以及各步间隙时间等,来促使材料内部产生晶粒细化、组织结构改善等,从而增强材料塑性。实验比较了单步拉伸成形与分步拉伸成形,以及分步成形中恒速法的预应变量对金属延伸率与组织的影响。结果表明:未经特殊细化处理的TC6钛合金分步拉伸,其恒速变形的工程应变为2.0时,可获得延伸率为2053%,而同温度下单步恒速与最大m值法拉伸的延伸率为753.9%与1347%;TC4钛合金在分步拉伸中恒速应变量为1.5时,可获得2147%的大延伸率。可见分步成形显著诱发了塑性增强。此外,预应变量决定着拉伸试样的晶粒组织大小。     

Mesoscopic grain boundary sliding as the rate controlling process for high strain rate superplastic deformation

Important features observed during high strain rate superplastic deformation are enumerated. Starting from the premise that the phenomenon of structural superplasticity in different classes of materials results when grain boundary sliding that develops to a mesoscopic scale (defined to be of the order of a grain diameter or more) controls the rate of flow, the particular case of high strain rate superplasticity is explained. The rate equation developed is validated using experimental results concerning 5 alloy systems in which an ultra-fine grain size is developed by thermomechanical processing and retained in a similar condition during superplastic deformation by fine, grain boundary pinning particles and 3 alloy composites in which the volume fraction of the reinforcing constituent is significant (15–25%). It is demonstrated that the analysis results in estimates for the externally measured strain rates that are within a factor of two, in addition to providing a physically meaningful free energy of activation for the rate controlling process. This approach explains superplastic flow in different classes of materials in terms of a single rate controlling mechanism of deformation, viz., mesoscopic grain boundary sliding, with the help of a few constants that have the same values for all systems. The system-dependent variables of threshold stress needed for the onset of mesoscopic boundary sliding and free energy of activation are obtained directly from superplasticity stress–strain rate data, without external inputs.     

5083铝合金在400℃的超塑性变形行为和硬化特征

为研究5083铝合金在500℃以下的超塑性,在400℃进行了恒应变速率拉伸试验,获得了应变硬化指数n及应变速率敏感性指数m,分析了应变速率.ε对伸长率δ,n和m值的影响。结果表明:在400℃时5083铝合金可获得的最大伸长率为278%,对应的.ε=0.000 26 s-1,n=0.122,m=0.274;n随应变速率增大而减小,δ和m随应变速率增大先增大后减小,其中δ受应变速率影响显著。