Al20Cu2Mn3相中孪晶的高分辨电子显微术研究

2024铝合金中的弥散相Al_(20)Cu_2Mn_3普遍由孪晶组成,通过高分辨像的观察分析,发现其孪晶间的界面不是镜面,而是滑移面;孪晶两部分不是反映(或旋转)对称,而是滑移反映对称,“金刚石”滑移面是(101),滑移矢量(1/4)(a-c),组成孪晶的各晶体组元呈棱柱体形状,各侧棱都平行于[010],棱柱侧面是{010}和{100}。     

Detailed Structures and Formation Mechanisms of Well-Known Al_(10)RE_2Mn_7 Phase in Die-Cast Mg-4Al-4RE-0.3Mn Alloy

The detailed structures and the corresponding formation mechanisms of the well-known Al_(10)RE_2Mn_7 phase in the conventional die-cast Mg–4Al–4RE–0.3Mn alloy were thoroughly investigated using transmission electron microscopy(TEM). The results indicate that the Al_(10)RE_2Mn_7 phase ordinarily contains both normal (111) twins and orientation twins.Both detailed TEM observations and density functional theory calculations indicate that the Al_(10)RE_2Mn_7 phase is transferred from the Al_8REMn_4 phase following an orientation relationship as [010]_(Al_8REMn_4)//[101]_(Al_(10)RE_2Mn_7) and (101)_(Al_8REMn_4)//(110)_(Al_(10)RE_2Mn_7). Moreover, forming orientation twins in the Al_(10)RE_2Mn_7 phase is attributed to the blurry regions at incoherent twin boundaries in the Al_8REMn_4 phase. Finally, these formed orientation twins result in the (111) twins in the Al_(10)RE_2Mn_7 phase.     

Phase and structural transformations in U and U-Nb alloy upon severe deformation and heat treatments

Transmission electron microscopy was used to analyze the twin and dislocation structure of samples of commercial uranium in the initial (undeformed) state and after severe deformation using explosive loading by plane and spherical waves of various intensity. It has been shown that an increase in the intensity of explosive loading by a plane wave leads, first, to an increase in the density of randomly distributed dislocations and twins and, then, to the development of polygonization processes with the formation of a subgrain structure of the α phase. Crystallographic analysis of the initial and deformation-induced twins in uranium has shown the presence of predominantly {130} twins of mixed type and, in singular cases, {172} and {176} twins of the second kind. It has been established that the retained spherical shells have a distinctly pronounced zonal structure, which contains information on the forward and reverse martensitic phase transformations of uranium (α ? β(γ) ? L, etc.) that occur under shock-wave loading by spherical waves. Conditions are determined for the manifestation of structural heredity in the U-6 wt % Nb alloy with recovery of the size and shape of grains of the initial high-temperature γ phase during the forward γ → α″ martensitic transformation upon cooling and during reverse α″ → γ transformation upon heating. Elimination of the structural heredity with significant grain refinement of the high-temperature γ phase occurs in the process of repeated quenching from 700°C after one type of preliminary treatments (cold deformation of α″ martensite, recrystallization of the deformed α″ phase, high-temperature aging of the initial α″ martensite, and eutectoid decomposition).     

Types of twins and the dislocation structure of α uranium in the initial and explosion-deformed states

Transmission electron microscopy is used to study and analyze the twin and dislocation structures of commercial-purity uranium samples in the initial (undeformed) state and after severe deformation induced by shock loading by plane waves with various intensities. As the shock loading intensity increases, the density of chaotically distributed dislocations and twins first increases, and, then, polygonization processes develop and result in a subgrain structure. Crystallographic analysis of the initial and deformation twins in uranium reveals predominant twins of the compound type {130} and rare {172} and {176} second-type twins.     

密排六方金属的塑性变形

综述了密排六方金属可能的滑移和孪生变形方式。滑移面包括：（０００１）基面，（１１００）柱面和〈ｃ〉型及〈ｃ＋ａ〉型锥面。（１０１２）、（１１２１）和（１１２２）是其主要的孪生类型，在Ｔｉ和Ｚｒ中还可能出现（１０１１）、（１１２４）和（１１２３）型孪晶。进一步分析了塑变过程中滑移和孪生之间的关系。着重讨论了Ｔｉ和Ｚｒ的滑移方式与试验温度之间的关系，其滑移面开动按由易到难的排列顺序为：柱面、锥面和基面     

Atomistic simulation of kink-pairs of screw dislocations in body-centred cubic iron

The nudged elastic band method is used to calculate the activation paths connecting jumps between the two degenerate states A and B of the screw dislocation core in body-centred cubic (bcc) iron. Kink-pairs are found to be involved in all such jumps. By comparing the activation energies, it is shown that the jump from state A to state B on the {101} plane is not the same as that from B to A, and whichever is easier depends on the direction of the applied stress. This asymmetry results in a characteristic zigzag pattern of slip, and forms the basis of an explanation for pencil glide at elevated temperatures. The activation energy of the rate-determining jump is found to decrease with increasing stress, but the predicted flow stress is about three times greater than the experimental value at all temperatures.     

Microstructure and plastic deformation of orthorhombic titanium aluminides Ti<Subscript>2</Subscript>AlNb. IV. Formation of the transformation twins upon the α<Subscript>2</Subscript> → <Emphasis Type="Italic">O</Emphasis> phase transformation

X-ray diffraction transmission electron microscopy, and measurements of microhardness and resistivity were used to study the formation of the orthorhombic O phase upon the α₂ → O phase transformation. It has been found that the orthorhombic O phase is formed by the diffusion mechanism in the form of thin lamellar precipitates (domains). Upon subsequent growth, these domains form packets of twins with a twinning plane {110}. It is shown that the (130) twinning plane is not realized directly, but it appears as a result of joining of twin packets. No formation of an intermediate metastable phase was observed upon this transformation.     

生长铜膜中孪晶形成与出现几率的分子动力学模拟

运用分子动力学和静力学方法对(111)生长铜膜中孪晶形成的原子过程与能量进行了模拟研究.所用的原子间相互作用势为Finnis-Sinclair型镶嵌原子法(EAM)势.模拟和计算分析结果表明,(111)生长铜膜表面沉积原子在不同局部可形成正常排列的fcc畴或错排的hcp畴;沉积原子处于hcp位置时体系的能量比fcc位置时要高,其增量决定了孪晶面出现几率.沉积原子错排能还受相邻{111}孪晶面的影响,其间距小于3个原子层厚时,沉积原子错排能与不形成孪晶的Al晶体表面沉积原子错排能相当,此时形成孪晶面的几率极低;随间距的增加,表面沉积原子错排能迅速降低,在间距达到约12个原子层厚以后,降到略低于完整Cu晶体{111}表面的沉积原子错排能,这表明此时出现孪晶面的几率比在完整晶体表面形成一个新的孪晶面的几率要大.     

Crystallographic aspects of deformation twinning and consequences for plastic deformation processes in γ-TiAl

Mechanical twinning is an important deformation mechanism in the γ-phase of near-γ-TiAl alloys at room temperature as well as at high temperature. The present work examines the crystallography of twinning in the ordered L1₀ structure of the γ-phase and quantifies the resulting deformation for different crystallographic directions. In addition, the open question is addressed whether twin interfaces represent obstacles for glide dislocations. It is shown that one part of the possible glide dislocations remains completely unaffected by the twin interface because their Burgers vectors lie in the twin plane. The other part of the dislocations has to change its glide directions while passing the interface, which can occur by suitable dissociation processes. Prerequisite is a sufficiently high applied stress. The reoriented twin may be more favorably oriented for some glide directions than its parent crystal and thus promote further dislocation plasticity. The impact of this effect on ductility depends on the volume fraction of twins.     

钢中贝氏体长大方式的TEM研究

利用ＴＥＭ考察了钢中贝氏体铁素体／奥氏体相界面台阶结构及奥氏体精细结构。用ＴＥＭ温台发现在贝氏体增厚过程中新形成的贝氏体中存在奥氏体预存孪晶；在贝氏体铁素体／奥氏体相界面存在台阶结构，但台阶阶面可对应于母相奥氏体中孪晶面或层错面，表明台阶的阶面为共格的滑移界面。因而贝氏体铁素体／奥氏体相界面可通过界面台阶沿面缺陷进行保守滑移，贝氏体长大具有滑移切变特征。根据实验结果提出了贝氏体二次层错切变模型及组织形貌示意图。     

〈111〉生长铜膜中孪晶形成与出现几率的分子动力学模拟

运用分子动力学和静力学方法对〈111〉生长铜膜中孪晶形成的原子过程与能量进行了模拟研究.所用的原子间相互作用势为Finnis-Sinclair型镶嵌原子法(EAM)势.模拟和计算分析结果表明,〈111〉生长铜膜表面沉积原子在不同局部可形成正常排列的fcc畴或错排的hcp畴;沉积原子处于hcp位置时体系的能量比fcc位置时要高,其增量决定了孪晶面出现几率沉积原子错排能还受相邻{111}孪晶面的影响,其间距小于3个原子层厚时,沉积原子错排能与不形成孪晶的Al晶体表面沉积原子错排能相当,此时形成孪晶面的几率极低;随间距的增加,表面沉积原子错排能迅速降低,在间距达到约12个原子层厚以后,降到略低于完整Cu晶体{111}表面的沉积原子错排能,这表明此时出现孪晶面的几率比在完整晶体表面形成一个新的孪晶面的几率要大.     

ON THE M_7C_3 IN Cr27 CAST IRON

Determination of(Fe,Cr)_7C_3 in Cr27 cast iron results about 30 v.-%.Minor Si and Mn arepresent.Sectional area of the M_7C_3 grains is 1—50μm~2.Combining matrix analysis of elec-tron diffraction pattern with calculated angle between plane traces,{011}twins and also{013}twins producing local environment for Ru_7B_3 are observed in the orthorhombic M_7C_3.A crystallographic model for M_7C_3 is proposed.     

Structure of As-Cast Hafnium

The structure of a hafnium crystal grown by the method of floating zone melting which underwent upon cooling the β → α (bcc → hcp) polymorphic transformation has been studied using the metallography, EBSD analysis, and electron microscopy. It has been shown that the α-phase structure of as-cast hafnium consists of lath-shaped crystals grouped into packets. As a rule, the α-phase grains contain several packets of different orientations from 12 orientations that can arise according to the Burgers orientation relationships. The boundaries of the α-phase grains and packets differ significantly. The grains have smooth boundaries, whereas the boundaries of packets are wavy. The misorientations between separate laths in a packet are less than 1°. Extended twins with a \({\left\{ {10\;\bar 1\;2} \right\}_\alpha }\) twinning plane have been discovered in the structure of hafnium. The presence of twins in the hafnium crystal is due to the influence of the total internal stresses caused by the temperature gradient that arise upon zone melting and by the β → α phase transformation. The fracture of the hafnium crystal at room temperature occurs along the basal (0001) plane. The typical fracture is brittle-viscous with a predominance of the brittle component.     

晶体取向及析出相对Al-Cu-Li单晶腐蚀行为的影响（英文）

通过扫描电子显微镜、透射电子显微镜、光学显微镜、剥落腐蚀溶液浸泡实验和电化学测试研究晶体取向和析出相对Al-Cu-Li单晶腐蚀行为的影响。结果表明,时效态Al-Cu-Li合金不同取向的腐蚀速率按(001)<(101)<(111)的顺序增加,与淬火态合金的腐蚀速率按(111)<(001)<(101)的顺序增加明显不同。T₁相的析出恶化了Al-Cu-Li合金的耐蚀性,且不同晶面取向的恶化程度不同。时效态合金的严重局部腐蚀沿着晶体学方向扩展,并以腐蚀带的形式沿{111}_Al面扩展。     

高纯钛压缩孪生行为研究

利用背散射电子衍射(EBSD)技术对高纯钛形变组织中同一个晶粒内部出现的{1122}和{1124}压缩孪生进行了研究。结果表明:{1124}孪晶总是伴随{1122}孪晶在同一晶粒中产生,在变形组织中没有发现单独存在的{1124}孪晶;这种极少出现的{1124}压缩孪晶主要由{1122}孪晶与传统晶界或{1122}孪生变体之间交互作用改变了局部应力状态而诱发的。在同一个晶粒中,由{1122}孪晶诱发的{1124}孪晶更倾向于同其中一个{1122}孪生变体具有相同的转轴。此外,根据晶体对称性及相同晶粒中{1122}和{1124}孪晶之间的取向关系,{1122}和{1124}孪晶之间可发生孪晶反应并形成4种不同类型的孪晶反应界面。     

{112} 〈111〉 Twins or Twinned Variants Induced by Martensitic Transformation?

Twinned substructure in lath martensite was induced in the interstitial free (IF) steel via a high pressure thermal cycle (heating up to 1100 ℃ and holding for 30 min, cooling at 10 ℃/s to room temperature under a pressure of 4 GPa). Experimental observations and theoretical simulation confirm that the twinned substructure has the origin related to the twinned variants rather than the bcc {112} 〈111〉 twins, while extra diffraction spots were caused by crystal overlapping rather than any extra phase. The differences in crystallography and electron diffraction behavior between twinned variants and {112} 〈111〉 twins were discussed in detail.     

Ti-6Al-3Nb-2Zr-1Mo钛合金在低温高应变速率下的变形行为

在变形温度为193~298 K、应变速率为2000~3000 s^-1的范围内,对Ti6321钛合金进行动态压缩试验,研究温度和应变速率对材料力学性能和变形行为的影响。采用光学显微镜（OM）、透射电子显微镜（TEM）和电子背散射衍射（EBSD）表征和分析了合金的微观结构演变。结果表明,随着温度的降低和应变速率的增加,Ti6321钛合金的动态屈服强度和平均流动应力均增大,而断裂应变明显降低。采用Johnson-Cook本构方程预测了Ti6321钛合金在低温高应变速率下的力学行为,拟合结果与实验结果吻合较好。微观结构分析表明,随着变形温度的降低,｛112｝和｛101｝2种孪晶的含量明显增加,即变形机制逐渐由孪晶的辅助作用转变为孪晶占主导地位。     

Calculations of intersection cross-slip activation energies in fcc metals using nudged elastic band method

The nudged elastic band (NEB) method is used to evaluate activation energies for dislocation intersection cross-slip in face-centered cubic (fcc) nickel and copper, to extend our prior work which used an approximate method. In this work we also extend the study by including Hirth locks (HL) in addition to Lomer–Cottrell locks and glide locks (GL). Using atomistic (molecular statics) simulations with embedded atom potentials we evaluated the activation barrier for a dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane when intersecting a 120° forest dislocation in both Ni and Cu. The initial separation between the screw and the intersecting dislocation on the (1 1 1) glide plane is varied to find a minimum in the activation energy. The NEB method gives energies that are ∼10% lower than those reported in our prior work. It is estimated that the activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120° intersection forming GL in Ni and Cu are ∼0.47 and ∼0.65 eV, respectively, and from the fully cross-slip plane state to the partially cross-slipped state forming LC are ∼0.68 and ∼0.67 eV. The activation energies for cross-slip from the fully glide plane state to the partially cross-slipped state at the 120° intersection forming HL in Ni and Cu are estimated to be ∼0.09 and ∼0.31 eV, respectively. These values are a factor of 3–20 lower than the activation energy for bulk cross-slip in Ni and, a factor of 2–6 lower than the activation energy for cross-slip in Cu estimated by Friedel–Escaig analysis. These results suggest that cross-slip should nucleate preferentially at selected screw dislocation intersections in fcc materials and the activation energies for such mechanisms are also a function of stacking fault energy.     

镁合金温变形过程中的孪生及孪晶交叉

对AZ31镁合金在3种温度(523,573和673 K)下进行了单向压缩变形.在523 K,当真应变ε达到0.22时真应力-真应变曲线出现尖锐的应力峰值,在应力峰值之前先后经历了缓慢加工硬化(0.02≤ε<0.06)和急剧加工硬化(0.06≤ε<0.22)2个阶段.利用SEM/EBSD技术分析了这2个阶段对应的显微组织.结果表明,在缓慢加工硬化阶段(ε=0.03),仅有少量孪晶出现;在急剧加工硬化阶段(ε=0.06),产生了大量{101~-2}孪晶,孪晶间的相互交叉导致材料产生急剧加工硬化.AZ31镁合金{101~-2}孪晶间交叉有5种可能存在的形式,孪晶的形成和交叉与压缩应力方向有密切关系.在基体应力方向分别为近似<112~-0>和<101~-0>方向时确认了(101~-2)-(011~-2)和(101~-2)-(01~-12)2种交叉形式.     

交叉预压缩对轧制态AZ31镁合金拉压不对称性的影响

通过对轧制态AZ31镁合金板材进行多向预压缩,运用塑性变形的方式,产生了{1012}一次拉伸孪晶和{10 1 2}-{10 1 2}二次拉伸孪晶,并结合EBSD表征和XRD分析,对预压缩后材料的拉伸压缩实验的结果表明,预压缩对镁合金拉压不对称性的降低和强度的提高有明显效果。交叉预压缩之后,由于产生了孪生,材料组织晶粒细化,使得材料在再变形时,屈服强度和最大强度均明显增强。产生的拉伸孪晶片层可以有效地改变晶粒的取向,在一定程度上削弱了基面织构,在{1012}一次拉伸孪晶中产生了{1012}-{1012}二次拉伸孪晶,二者结合作用,改善了材料的再变形行为,从而降低了镁合金板材的拉压不对称性。