Al2O3陶瓷及其复合材料的超塑性研究

陶瓷材料的超塑性是细晶多晶陶瓷在高温下的固有属性.本文提出了陶瓷材料超塑性产生的条件、特征和变形机制.综述了国内外Al2O3陶瓷及其复合材料超塑性研究的最新进展,最后指出了今后Al2O3陶瓷材料超塑性研究发展方向.     

Superplastic deformation behavior and mechanism of 1420 Al-Li alloy sheets with elongated grains

True stress-true strain curve, microstructure and texture information were obtained to investigate the superplastic deformation behavior of 1420 Al-Li alloy sheets with initial elongated grains. From the true stress-true curve, the stress increases with the increase of strain to 0.15, then dramatically decreases with the increase of strain to 0.80, and finally keeps almost a horizontal line. Meanwhile, initial elongated grains are gradually changed into equiaxed grains and the initial strong Brass {0 1 1} 〈2 1 1〉 and S {1 2 3} 〈6 3 4〉 orientations are turned into nearly random orientation with increasing strain. All these results suggest that dislocation activity is the dominant mechanism during the first stage, then dynamic recrystallization occurs, and grain rotation is expected as an accommodation for grain boundary sliding (GBS). At larger strains, grain boundary migration (GBM) becomes necessary to accommodate GBS.     

拉伸条件对Al—Li—Cu—Mg—Zr合金超塑变形行为的影响

研究了拉伸条件对温轧态Al-Li-Cu-Mg-Zr合金超塑变形行为的影响.结果表明:该合金在变形初期发生了界面取向差逐渐增大,从亚晶组织向再结晶组织变化的形变促使连续再结晶过程;应变速率越高,再结晶速度越快,再结晶晶粒越细;经高应变速率的第一阶段拉伸变形后,形成的细晶组织具有高的应变速率敏感性,同时在低应变速率的第二阶段拉伸变形中发生晶粒长大而具有高的应变硬化效果,两者的综合作用是两段速率拉伸获得高延伸率的根本原因。     

EFFECT OF TENSION CONDITIONS ON SUPERPLASTIC BEHAVIOUR OF AN Al-Li-Cu-Mg-Zr ALLOY

A much higher elongation of a warm rolled superplastic Al-Li-Cu-Mg-Zr alloy was madeunder two-stage strain rate tests comparing with the single ones.During initial stage ofdeformation a deformation-induced continuous recrystallization which converted a subgrainstructure into a recrystallized grain structure by a continuous increase in boundarymisorientations had occurred.The higher the strain rate,the faster the continuousrecrystallization and the finer the recrystallized grains.The fine recrystallized grain structureformed during the first stage deformation is the essential condition for the material to havehigh strain rate hardening and strain hardening during the low second stage superplasticdeformation.The combination of strain rate hardening and strain hardening is the reason whythe higher elongation may be obtained during two-stage superplastic deformation of the alloy.     

挤压态AZ81镁合金的超塑性及变形机制

研究了挤压态AZ81镁合金的超塑变形行为及其变形机制.首先将AZ81镁合金进行热挤压处理,然后在不同的温度和初始应变速率下进行了超塑性拉伸试验,计算了应变速率敏感性指数.通过观察和比较不同温度下材料的稳态流变现象,分析了超塑变形机制随着温度的上升而发生变化的原因.挤压态AZ81的超塑性变形机制是晶界滑移,而孔洞的形核与断裂是变形的协调机制.     

基于BP神经网络的铝青铜超塑性流变应力预测模型

运用BP神经网络方法建立了铝青铜超塑性状态下流变应力与变形参数之间关系的预测模型。并利用该模型预测在不同拉伸条件下材料的流变应力。结果发现预测数据与试验数据吻合良好，误差小于8．5％。     

大晶粒单相Ni-48Al金属间化合物超塑性变形过程中的组织演化

原始平均晶粒尺寸约为200μm的单相Ni-48Al金属间化合物在温度为1025—1100℃、应变速率为1.25×10~(-4)—2.00~10~(-3)s~(-1)范围内呈现超塑性。在1100℃、应变速率为1.125×10~(-3)s~(-1)时,最大延伸率可达188.2％。金相分析表明,超塑性变形过程中晶粒明显细化;电子背散射衍射分析(EBSD)和透射电子显微术(TEM)观察表明,超塑变形过程中形成了大量亚晶界网络,且随变形量增大,亚晶界及小角晶界比例不断增加。亚晶界由位错墙和位错网络构成,不稳定的亚晶界在超塑性变形过程中不断吸收晶内滑移和攀移位错,亚晶界位错密度不断增加,取向差不断增大。伴随亚晶界的滑移和迁移及亚晶的转动,部分亚晶界转变为小角度晶界,并进而转变为大角度晶界,即在超塑性变形过程中发生了连续动态回复与再结晶(CDRR)。     

大晶粒含钛Fe—36.5Al基合金的超塑性研究

通过对未加Ｔｉ及加有不同量Ｔｉ的Ｆｅ－３６．５Ａｌ基合金的高温变形行为的研究，发现加Ｔｉ的合金在９００－１０００℃，初始应变速率为２．０８×１０＾－４－８．３３×１０＾－２ｓ＾－１范围内比未加Ｔｉ的ＦｅＡｌ合金的延伸率有较大幅度提高，且应变速率敏感性指数ｍ值普遍超过０．３。     

DYNAMIC RECRYSTALLIZATION AND SUPERPLASTICITY IN Al-Li ALLOY

The behavior of dynamic recrystallization in the superplastic deformation of 8090 and 2091 aluminum-lithium alloys have been investigated.TEM observations indicated that dynamic recrystallization occurs at thetriple junction of grain boundaries.The measurement of grain boundary angle showed that recrystallization indynamic equilibrium exists in the process of superplastic deformation of 8090 Al-Li alloy.It is also indicatedthat,besides the role of refining grains and the grain boundary sliding,dynamic recrystallization playsconcurrently a role of stablizing microstructure.Thus dynamic rccrystallization can be used to induce metalssuperplasticity,which leads to a simplification of pretreatment for superplastic deformation.     

SUPERPLASTICITY IN SiCw／ZK60 COMPOSITE

The superplastic deformation behavior of SiCw/ZK60 composite was investigated at temperatures ranging from 573K to 723K and at initial strain rates ranging from 8.3x10-4s-1 to 8.3x10-2s-1. A maximum elongation of 200% with a m-value of 0.35 was obtained at 613K and a initial strain rate of 1.67x 10-2s-1. The apparent activation energy (98kJ/mol) approximates that for grain boundary diffusion (92kJ/mol) in magnesium. It is proposed that the dominant mechanism of superplastic deformation in the present composite is grain boundary sliding accommodated by diffusional transport, besides, interfacial sliding plays an important role in the superplastic deformation.