晶界位错运动与位错反应过程的晶体相场模拟

采用晶体相场模型模拟了小角度对称倾转晶界结构及其在外加应力作用下的晶界演化消失过程,从位错的运动形式和体系自由能的变化,分析晶界的消失过程和位错的反应机理,并计算了位错分解的激活能.研究表明,具有二维三角晶格原于点阵结构形成的小角度对称倾转晶界是由配对的双位错按直线规则排列构成,可以看成由2套位错Burgers矢量组成.晶界的消失演化过程主要分为6个特征阶段,包括如下几方面的特征过程:首先晶界位错攀移,然后发生位错分解,晶界发射位错,位错由攀移运动转化为作滑移运动;接着滑移位错穿过晶粒内部,直到对面晶界上湮没,即被品界吸收与合并:剩余的晶界位错继续作攀移运动,然后又出现位错分解,晶界再次发射位错,使得位错转为作滑移运动,与其它作滑移运动的位错在晶内相遇湮没消失.最后,所有晶界和位错全部消失,双晶结构变成为完整的单晶结构.应用三角晶系的点阵位错的2套基本Burgers矢量的组合,可以有效地表示位错的发射、分解、合并、吸收、湮没的反应过程,并能够揭示出这些反应过程的新Burgers矢量的产生和原有的Burgers矢量的消失,以及Burgers矢量方向发生变化的机理.     

纳米孪晶金属塑性变形机制

本文综述了纳米孪晶金属材料的塑性变形机制.通过分析纳米孪晶二维结构变形时可启动的滑移位错类型,揭示纳米孪晶金属塑性变形的3种位错机制,即位错塞积并穿过孪晶界机制,Shockley不全位错诱导孪晶界迁移机制以及贯穿位错在孪晶片层内受限滑移机制.通过改变加载方向与孪晶界面的相对取向可实现这3类位错机制的可控转变.     

铁镍基合金中蝶状马氏体核胚的研究SCIEI

利用透射电子显微镜(TEM)在Fe-Ni-V-C合金中观察到一些马氏体核胚,核胚的结构为特殊的位错组态:Burgers矢量为1/2[011]fcc,且一端为封闭的发夹型位错,和在发夹型位错内塞税的、Burgers矢量为1/2[110]fcc的位错列。它们分别提供了马氏体相变所必须的二次切变。     

LY12合金在拉伸变形中的微观结构

利用透射电子显微镜观察了不同时效处理的ＬＹ１２铝合金经各拉伸变形度后的亚结构。对于自然时效及１９０℃人工时效的合金，随变形度增大，亚结构由长、直的的位错线变成短、弯的位错线，形成位错条带及位错密度大幅度提高，造成应力一应变曲线上加工硬化率低及屈服强度提高的特征。而３５０℃过时效的合金，随变形度增大，在第二相（Ｓ）周围形成位错环，并与基体位错交互作用，形成位错塞积及高密度位错，造成应力一应变曲线上加工硬化率高、屈服强度低的特征。     

2024-T4铝合金搅拌摩擦焊搅拌区位错及组织性能

采用金相、显微硬度及透射分析方法对2024铝合金搅拌摩擦焊接头搅拌微区的组织性能和位错分布特征进行试验分析,基于位错分析深入了解各微区位错形成与接头组织结构与硬度变化之间的关系。研究表明,WNZ位错主要分布在晶粒内部,大部分是以位错缠结的形式存在,并伴随有大量的沉淀强化析出相Cu_2Mg;而在TMAZ区,大量的位错是以位错塞积的形式存在于晶界或晶粒内部;HAZ区域的位错多以位错塞积的形式存在于晶界附近,并伴随一些典型的Al Cu_3析出相。WNZ和TMAZ区中并未随晶粒细化而造成位错数量和类型的减少,这与FSW特殊的动态回复和动态再结晶过程有关,此外位错分布特征与接头微区硬度分布特征基本吻合。     

模拟位错斑图的元胞自动机与分子动力学模型

建立了一个模拟位错斑图形成的元胞自动机-分子动力学模型，该模型考虑了在相同或不同滑移面上具有相反Burgers矢量方向的刃型位错间的长程与短程相互作用，采用分子动力学方法处理长程相互作用，采用元胞自动机方法处理短程相互作用，应用这个模型，模拟了在没有外加应力和存在外加循环应力条件下的Cu单晶的位错结构。     

不同调制波长Cu/Ag多层膜硬度分析

用直流电沉积双槽法在纯铜基体上制备了不同调制波长的Cu/Ag多层膜,研究了多层膜硬度与调制波长之间的关系.实验结果表明,当调制波长位于600～300nm时,Cu/Ag多层膜的硬度与调制波长之间较好地符合基于位错塞积模型的Hall-Petch关系;当调制波长小于300 nm时,硬度与调制波长的关系偏离了HaU-Petch关系.由实验结果分析得出了Cu/Ag多层膜的位错稳定存在极限晶粒尺寸约为25 nm,与基于程开甲等人的位错稳定性理论得出的Ag晶体极限晶粒尺寸27 nm接近,验证了程开甲等人的位错稳定性理论.     

MoS2中的位错

给出了具有层状结构的硫化钼(MoS_2)中位错的透射电镜(TEM)观察结果在基面上,位错和位错网络常分解成不全位错和不全位错网络利用衍衬效应分析了这些位错的Burgers矢量、材料的层错能可由扩展结估算出     

单晶Ni_3Al裂纹扩展的TEM原位观察

利用透射电镜（ＴＥＭ）原位拉伸在室温下对（１１０）［１１０］取向 Ｎｉ３ＡＩ合金单晶中裂纹的萌生与扩展进行了研究结果表明：裂纹沿之字形路径扩展且裂纹的总体扩展路径与拉伸轴平行迹线分析表明,首先激活的是（１１１）和（１１１）两个主滑移面上的滑移系;其后在 Ｓｃｈｍｉｄ因子为零的两个滑移面上的滑移系激活．为了解释所观察到的现象而建立了一个位错塞积模型位错应力场的计算表明,塞积位错列所产生的应力场导致了第二滑移系的启动,并使得裂纹扩展路径平行于拉伸轴的方向     

时效析出对2E12铝合金疲劳断裂行为的影响

测试等屈服强度条件下190℃,1h欠时效和190℃,46h过时效状态Al-Cu-Mg系2E12铝合金的疲劳寿命,并分别采用扫描电镜和透射电镜观察了疲劳断口形貌及时效析出特征,并在此基础上解释时效析出对2E12铝合金疲劳断裂行为的影响。结果表明;疲劳裂纹主要萌生于试样表面的粗大残留相位置;由于过时效试样晶内析出大量的S平衡相降低疲劳变形时的位错滑移可逆性,加剧晶界处位错塞积程度;同时晶界上较宽的无析出带和沿晶界析出的粗大针状S相进一步促进晶界集中变形和开裂,从而降低过时效试样的疲劳寿命。     

Interior dislocation behavior in superplastic deformation of 8090 Al-Li alloy

1lNTRODUCTl0NInteriordislocationslipisoneoftheimpor-tantaccomodationmechanisminsuperplasticde-f....ti..[1~10J,inwhichthegrainsarerefinedbydynamicrecrystallization.Butthesuperplas-ticdeformationprocessleadstodifferentgrainsizesatvariousstagesandcausesachangeingrainboundaryslidingquantity,italsomakestlieaccommodatingmechanismsatvariousstagesshowdifferentfunctions,especiallydislocationslipmechanism.Therefore,itissignificantf0rthisinvestigationtoreplenishthecurrenttheoryofsuperplasticdeformati…     

Partial dislocation configurations in a low-angle boundary in α-Al2O3

The dislocation structures of a low-angle tilt grain boundary in alumina bicrystal were investigated by transmission electron microscopy. The grain boundary was found to consist of two regions: an area with pairs of partial dislocations and an area with groups of odd numbered partial dislocations (multiple-partial-structure). Eight kinds of multiple-partial-structures were found in the fabricated grain boundary. The Burgers vectors of each partial dislocation in the grain boundary can be distinguished by dark-field imaging, and thus the arrangement of partial dislocations in the multiple-partial-structures are determined. It is concluded that a slight twist component of the boundary is the origin of the characteristic multiple-partial-structures.     

Wetting of the low-angle grain boundaries

It is demonstrated that the classical Read–Shockley model of the low-angle grain boundary fails to predict quantitatively the misorientation angle, at which the grain boundary wetting phase transition occurs. This is because the wetting transition at the low-angle grain boundary is associated with the low value of the solid/liquid interfacial energy. For sufficiently low interfacial energies, the dislocation cores are unstable against the substitution by the pipes of the liquid phase (wetted core dislocation). The energy of the low-angle grain boundary composed of the array of wetted core dislocations is calculated under the assumptions of the circular cores. The grain boundary wetting transition occurs at the misorientation θ≈0.19b/R_F, where b and R_F are the Burgers vector of dislocation and the Frank's radius, respectively. The impact of wetted core dislocations on the mechanical behavior of the material is discussed.     

弹性交互作用下直刃型位错的稳态构型及其滑移稳定性

从各向同性连续介质中直线位错之间的弹性交互作用能出发，推导具有任意Ｂｕｒｇｅｒｓ矢量夹角的两平行直刃型位错之间弹性交互作用的滑移力攀移力表达式。指出两平行直刃型位错的弹性交互作用存在三个滑移平衡位置：ｕ１＝１，ｕ２＝－１，ｕ３＝ｔｇφ，并确定了三滑移平衡位置成为滑移稳定平衡位置的条件，还得到滑移，攀移共同运动情况下两平行直刃型位错在弹性交互作用下的稳态构型，分别讨论了紧束缚，弱束缚情况下位滑移的稳     

Dislocation–grain boundary interaction in 〈1 1 1〉 textured thin metal films

The interaction of lattice dislocations with symmetrical and asymmetrical tilt grain boundaries in 〈1 1 1〉 textured thin nickel films was investigated using atomistic simulation methods. It was found that the misorientation angle of the grain boundary, the sign of the Burgers vector of the incoming dislocation and the exact site where the dislocation meets the grain boundary are all important parameters determining the ability of the dislocation to penetrate the boundary. Inclination angle, however, does not make an important difference on the transmission scenario of full dislocations. Only limited partial dislocation nucleation was observed for the investigated high-angle grain boundary. The peculiarities of nucleation of embryonic dislocations and their emission from tilt grain boundaries are discussed.     

Stress fields and geometrically necessary dislocation density distributions near the head of a blocked slip band

We have examined the interaction of a blocked slip band and a grain boundary in deformed titanium using high-resolution electron backscatter diffraction and atomic force microscopy. From these observations, we have deduced the active dislocation types and assessed the dislocation reactions involved within a selected grain. Dislocation sources have been activated on a prism slip plane, producing a planar slip band and a pile-up of dislocations in a near screw alignment at the grain boundary. This pile-up has resulted in activation of plasticity in the neighbouring grain and left the boundary with a number of dislocations in a pile-up. Examination of the elastic stress state ahead of the pile-up reveals a characteristic “one over the square root of distance” dependence for the shear stress resolved on the active slip plane. This observation validates a dislocation mechanics model given by Eshelby, Frank and Nabarro in 1951 and not previously directly tested, despite its importance in underpinning our understanding of grain size strengthening, fracture initiation, short fatigue crack propagation, fatigue crack initiation and many more phenomena. The analysis also provides a method to measure the resistance to slip transfer of an individual grain boundary in a polycrystalline material. For the boundary and slip systems analysed here a Hall–Petch coefficient of K = 0.41 MPa m^½ was determined.     

同位相热机械疲劳形变后γ／γ′相界面上的位错网分析

DD8单晶镍基高温合金经过同位相热机械疲劳（TMF）后，在垂直于应力轴的γ/γ′相界面上存在着大量的六角形位错网。对位错网中的位错进行的分析表明，六角形位错网中的位错都是刃型位错，而且这些位错的Brugers矢量都不与滑移过程开始的滑移系相对应。利用双交滑移模型说明了位错网的形成机制。