铁硅合金中立方织构的形成

铁硅合金(含硅3.25％)的样品,经过不同的冷轧和中间退火程序,在最后高温退火时,可以通过二次再结晶,或者一次再结晶形成集中的立方织构。通过二次再结晶形成立方织构时,并不包括重新形核的过程。(100)[001]取向的二次再结晶“晶核”,在一次再结晶完成后,就已经存在。通过一次再结晶形成的立方织构,由于样品在冷轧后,得到了较强的加工立方织构,退火时通过同位再结晶,就得到了再结晶立方织构。     

冷轧铜板再结晶織构的形成

电解纯铜经88.7％冷轧后,所形成的轧制织构除稳定的(110)[112]舆(112)[111]外,还存在着一种(3,6,11)[533]织构。在较低温度下退火时,再结晶织构主要为(100)[001]、(358)[352]和舆(100)[001]成孪生取向的(122)[212]织构。随着退火温度的增加,(358)[352]织构逐渐减弱,立方织构(100)[001]则逐渐加强;当退火温度达到900℃时,开成了集中的(100)[001]织构。冷轧铜板在退火的过程中,具有(100)[001]再结晶晶粒首先形成,然后普遍地发生同位再结晶。其中具有(100)[001]取向的晶粒,继续发生选择性的生长,最后形成了集中的立方织构。本支中对轧制织构舆其再结晶织构取向间的关系也进行了分析,再结晶织构一般可认为是原有织构沿某一个[111]轴旋转45°,22°或38°的结果。同时,根据上述几何关系所绘出的理想极图舆实际测定的结果也是符合的。试验结果指出,不同加热速度和不同加热程序对形成最终的再结晶织构,不发生显著的影响,而退火温度对再结晶织构的形成起着主要的作用。     

国产纯铁的轧制与再结晶织构

用极固与金相研究工业纯铁的轧制与再结晶织构和组织。热轧后的试样经过两种冷轧方法：(1)压下率为98.8%,与(2)压下率为64.5%,中间700℃熟炼;二次冷轧和压下率63.5%。试样在氢气中分别于(a)650°和(b)1000℃熟炼。第一类材料的轧制织构经测定为(100)[011]+(112)[110]+(111)[112].试样在a与γ区域熟炼后的主要取向为(100)[011]和(111)[112]。第二类材料的轧制织构与第一类相似,惟偏离角度较大。表面与内部织构不同。第二类材料熟炼后的再结晶织构基本上相似,金相组织显出第二次再结晶现象。     

立方取向镍铁合金的轧制织构

本文用计数器X射线衍射仪测定了立方取向镍铁合金的轧制织构。试样经过不同压延率的冷轧,随着形变程度的增加,逐渐形成了形变織构(112)[111],(110)[112]和共生織构(3,7,11)[9,4,5]。在大于90％压延率的样品中,立方織构仍然保存,应用Rowland点阵转变模型和滑移机理来解释織构转变过程。     

磷对冷轧纯铜再结晶的影响

本文研究了微量磷对冷轧纯铜再结晶的影响。当磷原子主要是溶解在铜中时,大大提高了再结晶温度,增加了再结晶激活能,阻止了立方结构的形成,改变了再结晶结构;但出氧化磷状态存在于铜中时,对以上各方面的影响就不很明显。所有样品的再结晶结构,都与加工结构中的某一种取向相同或接近,并且与主要加工结构间存在着沿<111>相差20—45°的几何关系。分析从金相及X光研究后得到的结果,认为在这种情况下,同位再结晶和选择性生长是再结晶结构形成的过程。 关键词：     

DEFORMATION AND RECRYSTALLIZATION OF(110)[001]SINGLE CRYSTALS OF AN IRON SILICON ALLOY

Plastic deformation and recrystallization were studied in single crystals of an iron siliconalloy with silicon content of 3.25%.The initial orientations were near (110) [001] andthe amount of reduction after rolling was in the range of 5-50%.At an early stageof rolling(2-16%),slip planes were determined to be(101),(101),(011)and(011);twinning planes were determined to be (112)and(112).On the basis of these obser-vations,the origin of cold-rolling texture of single crystals with inital orientations near(110)[001]can be satisfactorily explained. Characteristics of the formation and growth of new grains were studied after successivestages of annealing.It was observed that,in specimens with a reduction of 35%, theformation and growth of new grains along twin boundaries were preferred;while in specimenswith a reduction of 50%,the tendency of preferred growth was not so predominant.Newgrains were found along twinning planes,deformation bands and also at other places witha high concentration of substructures.     

高压下ZnO超快极性扩散过程研究

 利用X射线衍射（XRD）、扫描电镜（SEM）等手段，研究了在5 GPa 压力下六方ZnO粉末的结晶过程。系统考查了温度与保温时间对ZnO扩散与结晶过程的影响。结果发现，在高压下ZnO固体的扩散速度大大增加，400 ℃保温0.5 h即可获得理论密度达99%以上的单相、致密的六方相ZnO陶瓷，所有样品均沿晶界开裂，并导致500 ℃以上只能获得单晶与多晶混合的粉末样品；850 ℃保温5 min可制备出平均尺寸超过100 μm、最大尺寸超过350 μm的浅黄色单晶。对实验结果的分析表明：ZnO固体在高压下可能存在一种超快极性扩散机制，这一效应使高压下的ZnO晶粒沿择优方向迅速生长，晶界快速迁移，相邻晶粒生长融合，最后形成单晶；而晶粒在生长过程中沿其它方向发生收缩，促使样品沿晶界开裂。     

γ-α相变中不同晶界特征下铁素体生长形貌的相场模拟

利用多相场模型模拟了奥氏体(γ)-铁素体(α)相变过程中不同晶界特征下铁素体晶粒的形貌与生长动力学.模型中通过能量梯度系数和耦合项系数的协同变化定量表达晶界能与晶界迁移率的各向异性,同时固定相场界面宽度来保证计算精度.模拟结果显示:随着原奥氏体晶界能与铁素体-奥氏体晶界能比值σ_(γ,γ)/σ_(α,γ)的增加,三叉相界面处的平衡角β减小,铁素体晶粒沿原奥氏体晶界与垂直于奥氏体晶界方向的生长速率差变大.铁素体与奥氏体晶粒间的晶粒取向越接近,铁素体生长越缓慢.模拟结果可描述铁素体晶粒生长形貌的多样性,与实验结果符合.     

多晶金刚石薄膜硅空位色心形成机理及调控

金刚石硅空位色心在量子信息技术和生物标记领域有重要应用前景.本文对硅衬底上多晶金刚石生长过程中硅空位色心形成机理及调控方法进行研究.通过改变金刚石生长氛围中的氮气和氧气比例,实现了对硅空位色心发光强度的有效调控,所制备系列多晶金刚石样品的光致发光光谱显示,硅空位色心荧光峰与金刚石本征峰的比值最低为1.48,最高可达334.46,该比值与金刚石晶粒尺寸正相关.进一步用光致发光面扫描和拉曼面扫描分析样品可知,多晶金刚石中的硅应来自于硅衬底,在多晶金刚石生长过程中,衬底硅单质先扩散至金刚石晶粒处,随着金刚石晶粒生长,硅单质再扩散并入金刚石晶体结构中形成硅空位色心.不同样品硅空位发光强度的差异,是由于生长过程中氮气和氧气对金刚石硅空位色心的形成分别起到促进和抑制的作用.     

CVD法制备ZnO薄膜生长取向和表面形貌

利用具有特定温度梯度的CVD设备,以锌粉和氧气为原料,在Si(100)衬底上制备了ZnO薄膜。研究发现,锌粉中加入某些氯化物后可以改变ZnO薄膜的生长取向。用FESEM观察ZnO薄膜的表面形貌,发现Zn和氯化物的量比为1∶1时,生长的ZnO薄膜表面晶粒呈菱形或三角形({101}面),当二者的量比为10∶1时薄膜表面晶粒呈六棱台形({001}面)。XRD分析结果证实,前者只观察到(101)和(202)衍射峰,而后者出现(002)衍射峰且其强度大于(101)衍射峰。改变衬底或温度后得到的结果相同。因此,作者认为氯化物改变薄膜生长取向的现象与衬底和生长温度无关,添加的氯化物起到降低ZnO{101}面表面能的作用,随着氯化物浓度的增加,薄膜从沿[001]方向生长逐渐转向沿[101]方向生长。     

Dislocations in Fe-3% Si alloy single crystals deformed at a higher rate

The method of etching dislocations is used to study the distribution of dislocations and twins in Fe-3% Si alloy single crystals prepared from the melt after plastic deformation with higher speed. The crystals are deformed by twinning in the 〈111〉 directions along the {112} planes and by slip in the 〈111〉 directions along the {110} planes. The results prove that the dislocations causing plastic deformation move in the {110} planes during both fast and slow deformation. The difference in the slip surfaces during fast and slow deformation is explained by the different number of cross slips per unit dislocation path.     

Characterization of twinning in electrodeposited Ni–Mn alloys

Twinning is ubiquitous in electroplated metals. Here, we identify and discuss unique aspects of twinning found in electrodeposited Ni–Mn alloys. Previous reports concluded that the twin boundaries effectively refine the grain size, which enhances mechanical strength. Quantitative measurements from transmission electron microscopy (TEM) images show that the relative boundary length in the as-plated microstructure primarily comprises twin interfaces. Detailed TEM characterization reveals a range of length scales associated with twinning beginning with colonies (～1000?nm) down to the width of individual twins, which is typically <50?nm. We also consider the connection between the crystallographic texture of the electrodeposit and the orientation of the twin planes with respect to the plating direction. The Ni–Mn alloy deposits in this work possess a {110}-fiber texture. While twinning can occur on {111} planes either perpendicular or oblique to the plating direction in {110}-oriented grains, plan-view TEM images show that twins form primarily on those planes parallel to the plating direction. Therefore, grains enclosed by twins and multiply twinned particles are produced. Another important consequence of a high twin density is the formation of large numbers of twin-related junctions. We measure an area density of twin junctions that is comparable to the density of dislocations in a heavily cold-worked metal.     

Structure and stability of Σ3 grain boundaries in face centered cubic metals

Σ3 grain boundaries form as a result of either growth twinning or deformation twinning in face centered cubic (fcc) metals and play a crucial role in determining the mechanical and electrical properties and microstructural stability. We studied the structure and stability of Σ3 grain boundaries (GBs) in fcc metals by using topological analysis and atomistic simulations. Atomistic simulations were performed for Cu and Al with empirical interatomic potentials to reveal the influence of stacking fault energy on the morphology of the twinned grains. Three sets of tilt Σ3 GBs were studied with respect to the tilt axis parallel to ?111?, ?112?, and ?110?, respectively. We showed that Σ3{111} and Σ3{112} GBs are thermodynamically stable and the others will dissociate into terraced interfaces regardless of the stacking fault energy. The morphology of the nano-twinned grains in Cu is predicted from the above analysis and found to match with experiments.     

Special misorientations in localized deformation regions in Fe-3%Si alloy single crystals

Extended regions located at an angle of 20° to the rolling plane are observed inside deformation bands in a (110)[001] Fe-3%Si alloy single crystal at a high strain (～60%). These regions were interpreted earlier as shear bands. The lattice orientation in these bands is close to (110)[001], and their habit plane is parallel to the {112} planes of the deformed {111}〈112〉 matrix. The misorientations between the bands and the matrix group around special misorientations Σ9, Σ19a, Σ27a, and Σ33a, which are characterized by close angles of rotation about axis 〈110〉. During primary recrystallization, the (110)[001] grains growing from the bands retain segments of the corresponding special boundaries with the deformed matrix.     

单晶铜纳米线屈服机理的原子模拟研究

采用分子静力学方法模拟了〈100〉单晶铜纳米线的拉伸变形过程,研究了纳米线屈服的机理. 结果表明：1） 纳米线初始屈服通过部分位错随机激活的{111}〈112〉孪生实现,后继屈服通过{111}〈112〉部分位错滑移实现;2） 纳米线变形初期不同滑移面上的部分位错在两面交线处相遇形成压杆位错,变形后期部分位错在刚性边界处塞积,两者都阻碍位错滑移,引起一定的强化作用. 关键词： 纳米线 屈服 位错 分子静力学     

Statistical analyses of deformation twinning in magnesium

To extract quantitative and meaningful relationships between material microstructure and deformation twinning in magnesium, we conduct a statistical analysis on large data sets generated by electron backscattering diffraction (EBSD). The analyses show that not all grains of similar orientation and grain size form twins, and twinning does not occur exclusively in grains with high twin Schmid factors or in the relatively large grains of the sample. The number of twins per twinned grain increases with grain area, but twin thickness and the fraction of grains with at least one visible twin are independent of grain area. On the other hand, an analysis of twin pairs joined at a boundary indicates that grain boundary misorientation angle strongly influences twin nucleation and growth. These results question the use of deterministic rules for twin nucleation and Hall–Petch laws for size effects on twinning. Instead, they encourage an examination of the defect structures of grain boundaries and their role in twin nucleation and growth.     

Grain-boundary faceting at a = 3, [110]/{112} grain boundary in a cubic zirconia bicrystal

The atomic structure of a = 3, [110]/{112} grain boundary in a yttria-stabilized cubic zirconia bicrystal has been investigated by high-resolution transmission electron microscopy (HRTEM). It was found that the grain boundary migrated to form periodic facets, although the bicrystal was initially joined so as to have the symmetric boundary plane of {112}. The faceted boundary planes were indexed as {111}/{115}. The structure of the {111}/{115} grain boundary was composed of an alternate array of two types of structure unit: {112}- and {111}-type structure units. HRTEM observations combined with lattice statics calculations verified that both crystals were relatively shifted by (α/4)[110] along the rotation axis to form a stable grain-boundary structure. A weak-beam dark-field image revealed that there was a periodic array of dislocations along the grain boundary. The grain-boundary dislocations were considered to be introduced by the slight misorientation from the perfect = 3 orientation. The fact that the periodicity of the facets corresponded to that of the grain-boundary dislocations must indicate that the introduction of the grain-boundary dislocations is closely related to the periodicity of the facets. An atomic flipping model has been proposed for the facet growth from the initial = 3, {112} grain boundary.     

强流脉冲电子束作用下纯镍表层中织构及结构缺陷的演化行为

利用强流脉冲电子束(HCPEB)装置对金属纯Ni进行轰击,采用X射线衍射及透射电子显微镜(TEM)技术详细分析了受轰击样品的变形结构和缺陷。X射线衍射分析表明,经强流脉冲电子束处理后,在{111}和{200}晶面出现了择优取向。TEM表层微观结构分析表明:强流脉冲电子束轰击1次和5次后,晶粒内部形成了大量的(111)[112]型波状条带结构,在波状条带内部包含大量平行的(200)[110]型微条带;10次轰击后,样品变形结构发生变化,除大量的条带状结构外,变形孪晶的数量明显增多。这些变形微结构不仅影响表层的织构演化行为,而且还能细化晶粒,强流脉冲电子束技术为制备表面纳米材料提供了一条有效的途径。     

High resolution transmission electron microscope observation of zero-strain deformation twinning mechanisms in Ag

We have observed a new deformation-twinning mechanism using the high resolution transmission electron microscope in polycrystalline Ag films, zero-strain twinning via nucleation, and the migration of a Σ3{112} incoherent twin boundary (ITB). This twinning mechanism produces a near zero macroscopic strain because the net Burgers vectors either equal zero or are equivalent to a Shockley partial dislocation. This observation provides new insight into the understanding of deformation twinning and confirms a previous hypothesis: detwinning could be accomplished via the nucleation and migration of Σ3{112} ITBs. The zero-strain twinning mechanism may be unique to low staking fault energy metals with implications for their deformation behavior.