MIDRIB AND LEDGE OF BAINITE IN A Cu-Zn-Al-Mn ALLOY

The bainitic transformation in a Cu-Zn-Al-Mn alloy has been examined with TEM.The re-sults show that the stacking faults and also the bainitic midrib are found at the beginning ofbainite formation in the alloy.The stacking fault planes can pass continuously through themidrib in bainite.The growth ledges occur at the broad faces and rims of bainite.The broadand narrow faces of th ledges are parallel to the fault plane and habit plane respectively.Boththeir Miller indices are {110}_(B2).The moving direction of ledges is parallel to the fault plane.It may be deduced that the bainite in alloy are initially formed by shear and the process ofgrowth are go verned by propagation o f fault planes.     

Cu-Zn-Al-Mn合金的贝氏体中脊和台阶SCIEI

用透射电镜详细地研究了Cu-Zn-Al-Mn合金的贝氏体相变。观察结果表明:该合金中贝氏体在形成初期已存在层错。同时观察到贝氏体中脊,贝氏体内部的层错面能够连续地通过中脊。在贝氏体宽面及端部存在长大台阶,台阶的宽面和窄面分别平行于贝氏体层错面和惯习面,其晶面指数均属{110}_(B2)晶面族,长大台阶的推进方向平行于层错面。由此推测,Cu-Zn-Al-Mn合金贝氏体在相变初期首先以切变方式形成,而其长大过程是由其层错面的扩展所控制。     

钢中贝氏体形核初期微观形貌及精细结构的TEM观察

利用ＴＥＭ研究了８Ｍｎ８ＳｉＭｏ钢贝氏体晶核初期篚过程中的微观组织及精细结构。实验观察到初期贝氏体具有应力变促发亚单元形核特征，相变单元的三维形貌呈薄片状；贝氏体／奥氏体相界面可形成缺陷面，为母相奥氏体塑性协调变形亚结构。实验结果表明贝氏体的初期形成具有切变特征。     

EFFECT OF SELF-ACCOMMODATION FOR TWINNED MARTENSITE AND INVARIANT HABIT PLANE

The shear components of strain tensors for matrix and twin crystal of (?)winned martensite wereroughly opposite after calculation,and the strain energy would be reduced.The growth ofmartensitic plates along the normal direction of the twin plane may depend upon the effect ofself-accommodation between the matrix and twin crystals.Based upon the analysis on thedisplacement vectors of the normals for different habit planes,the{10,3,15}_f plane could formthe macroscopic invariant habit plane;but the(5(?)5)_f,(2(?)2)_f,and(1(?)1)_f planes aredifficult to become the invariant planes.     

孪晶马氏体的自协作效应及不变惯习面SCIEI

本文计算了孪晶马氏体基体和孪生部份的应变张量,发现二者的切变分量大致相反,故应变能降低。马氏体片可依靠基体和孪晶间的自协作效应沿孪晶面的法问长大。根据对不同惯习面法线的位移矢量的分析,{10,3,15}f面可构成宏观的不变惯习面,而{575}f,{252}f和{111}f面则难以构成。     

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。     

化学气相沉积钨单晶管材表面电解蚀刻形成的{110}晶面形貌

报导了具有<111>晶向(轴向)的管状钼单晶基体化学气相沉积(CVD)钨单晶涂层的电解蚀刻工艺及形成的{110}晶面形貌。实验发现,通过电解蚀刻,表面的{110}晶面可以完全被蚀刻出来。蚀刻出来的{110}晶面呈台阶结构,并同<111>晶轴相平行。蚀刻出来的{110}晶面在圆管的表面分成均等六个区。每个区内{110}晶面的台阶面的宽度呈现周期性的变化,开始台阶面较宽,逐渐变窄,然后通过一过渡区后,进入下一周期,{110}晶面的台阶面的宽度又逐渐变宽。     

Refinement of edge-to-edge matching model and its application in the Mg17Al12/α-Mg and α-Y/α-Mg systems

A refined version of the edge-to-edge matching model is described here. In the original model, the matching directions were obtained from the planes with all the atomic centers that were exactly in the plane, or the distance from the atomic center to the plane which was less than the atomic radius. The direction-matching pairs were the match of straight rows–straight rows and zigzag rows–zigzag rows. In the refined model, the matching directions were obtained from the planes with all the atomic centers that were exactly in the plane. The direction-matching pairs could be the match between any two matching directions. Four eighths of the predicted orientation relationships (ORs) were consistent with the experimental OR in the Mg₁₇Al₁₂/α-Mg system using the original model, but four sixths of the predicted ORs were consistent with the experimental ORs using the refined model. The refined model also successfully interpreted the grain refining mechanism of α-Y in the magnesium alloys.     

Molecular Dynamics Simulation of Micro Mechanisms in Slip Deformation Theory of Crystals

Based on the discussion that there should be a micromechanism that causes a macroscopic slip of mono-crystal copper, molecular dynamics simulations with the analytical displacement feld around a crack tip have been carried out. The result of the simulation shows that macroscopic shear slip in an f.c.c. mono-crystal copper occurs as discrete time events. This is because cross-slips occur in many places in a material such that a macroscopic shear slip is blocked until some critical state of deformation. A macroscopic shear slip then occurs suddenly at the critical state in which the area of disordered atomic arrangement has stretched from one end of a crystal to the other end. The reason why macroscopic shear slips occur in the directions of the slip planes of a crystal is attributed to the fact that the areas of disordered atomic arrangement develop only along those directions.     

薄W(111) 和W(110) 晶面熔化的原子模拟

根据改进分析型嵌入原子法(MAEAM),利用分子动力学(MD)模拟研究含表面薄W(111)和W(110)晶面熔化机制。首先研究温度对晶面表层原子均方位移(MSD)的影响,表明表面和非谐效应对晶面结构和性质影响明显,且原子振动呈现各向异性的特点。在此基础上进一步分析其原子密度函数(ADF)和结构因子(SF)随温度变化,发现薄W(111)和W(110)晶面熔化机制不同,对于W(111)晶面,表面在其熔化转变过程中起主要作用,在3700K完全熔化,拟合无序原子分数随温度变化表明W(111)晶面预熔-熔化转变温度为3550K;而W(110)晶面则出现过热,直到4000K完全熔化,非谐效应在其熔化转变中起主要作用。     

单晶硅裂纹尖端的位错发射行为

利用透射电镜原位观察了单晶硅压痕裂纹尖端位错及位错偶沿滑移面的发射行为,考察了滑移面取向,外荷对发射位错及塑性区的影响,结果表明：在I型载荷作用下,滑移面与裂纹面夹角要影响从裂纹尖端发射的位错数量及塑性区,发射出的位错可沿最大切应力方向改变运动方向或交换滑移面运动,实验观察的位错宽度平均值为22．0nm,与Peierls位移框架模型计算的23．6nm相近。     

Crystal Structure Peculiarities of Martensite in the Ni<Subscript>47</Subscript>Mn<Subscript>42</Subscript>In<Subscript>11</Subscript> Alloy that Underwent Forward and Reverse Phase Transformations

The martensite structure of the Ni₄₇Mn₄₂In₁₁ alloy has been studied, and crystallographic peculiarities of the structure realized after ten cyclic forward and reverse phase transformations have been shown. Each cycle includes the heating to a temperature corresponding to the existence of austenite and subsequent cooling to cryogenic temperatures. It was found that (107)-twinned martensite crystals can contact not only on the (10\(\bar 7\)) plane, which, being the symmetry axis for the crystals, is not among the close-packed planes, but also on the (12\(\bar 7\)) plane, which is among close packed planes but is not the symmetry axis.     

Torsional Fatigue Cracking and Fracture Behaviors of Cold-Drawn Copper:Effects of Microstructure and Axial Stress

The fatigue cracking and fracture behavior of cold-drawn copper subjected to cyclic torsional loading were investigated in this study.It was found that with increasing stress amplitude,the fracture mode of cold-drawn copper gradually changes from a shear fracture on transverse maximum shear stress plane to a mixed shear mode on both transverse and longitudinal shear planes and finally turns to the shear fracture on multiple longitudinal shear planes.Combining the cracking morphology and the relationship between torsional fatigue cracking and the grain boundaries,the fracture mechanism of cold-drawn copper under cyclic torsional loading was analyzed and proposed by considering the effects of the microstructure and axial stress caused by torsion.Because of the promotion of the grain boundary distribution on longitudinal crack propagation and the inhibition of axial stress on transverse crack grown,the tendency of crack propagation along the longitudinal direction increases with increasing stress levels.     

Effect of ammonia concentrations on SCC of α-brass under mode III loading

Stress corrosion cracking (SCC) of α-brass in ammonia solution was studied under mode III loading. The results showed that SCC occurred on the principal stress planes where shear stresses are zero. No SCC occurred on the maximum shear stress plane. Ammonia concentration affected fracture behaviour. When the concentration was low, many cracks with spacing of 10–150 μm were found on 45 ° planes, i.e., the principal stress planes. When the concentration was high, the cracks on 45 ° planes were not clearly visible because of serious general corrosion.     

倾斜平面对焊缝超声探伤结果的影响

对与主波束中心轴线成一定夹角的加工刀角在横波声场中的反射特点进行了研究,得出了横波声场中倾斜平面区别于体积型缺陷的一些反射特征,并给出了相应的结论.     

Dislocation motions in 5-fold planes of icosahedral Al-Pd-Mn

Dislocations moving in 5-fold planes of icosahedral AlPdMn have been observed in in situ heating TEM experiments. Similar dislocations forming a deformation band in the as-grown material have been analyzed in bright field and in LACBED conditions. Their Burgers vectors are translations of the 6-dimensional hyperlattice, with components in the physical space along 2-fold directions out of the plane of motion. Dislocations have accordingly moved by climb, presumably with a difficult jog-pair nucleation.     

Elastic fields of (774)γ[4 4 \overline {14} ]γ crystons and the formation of a lath structure of bainitic ferrite

An analysis has been performed for elastic fields of crystons that simulate the carriers of shear deformation on planes close to the habit plane of the additional-to-{558}_γ component of the bimodal distribution of ferrite habits in a bainite macroplate. The conclusion has been drawn that the additional component arises according to the same mechanism as the main component, but in the region of austenite with a twin orientation.     

The effect of strain path on the development of deformation structures in severely deformed aluminium alloys processed by ECAE

Equal channel angular extrusion (ECAE) has been used to investigate the formation of submicron grain structures in Al-alloys deformed to ultra-high plastic strains by different strain paths. The different strain paths were obtained by rotating billets through 0, 90, and 180° between each extrusion cycle. High resolution EBSD analysis has been employed to measure the boundary misorientations within the deformation structures. This has highlighted great differences in the evolution of the deformed state, as a function of the strain path, even after effective strains as high as 16. It has been demonstrated that the most effective method of forming a submicron grain structure by severe plastic deformation is to maintain a constant strain path. Processing routes involving a 180° rotation reverse the shear strain every second pass and this prevents the build up of significant numbers of new high angle boundaries. When a sample is processed with an alternate clockwise and anticlockwise 90° rotation, between each extrusion cycle the billet is deformed on two shear planes, each of which experiences half the total strain, compared to the single shear plane when there is no rotation. This reduces the rate of formation of high angle boundaries. With a constant clockwise 90° rotation the sample is also deformed on two alternate shear planes, but the total strain becomes redundant every fourth extrusion cycle. However, in this case each shear is reversed out of sequence after first deforming the billet on the alternate shear plane. This appears to be a much more effective means of forming new high angle boundaries than 180° rotation, where the shear strain is immediately reversed each alternate cycle, but is still less efficient than deformation with a constant strain path.     

扭转试样的氢致滞后开裂

无裂纹扭转试样充氢后在恒定的扭矩作用下能产生氢致滞后开裂。顺时针扭转时裂纹面和扭转轴成45°;反时针扭转则沿-45°面产生裂纹。计算表明,如果氢原子在α-Fe中的应变场是非球对称的,则氢原子的应变场和扭转应力场之间存在有互作用能,而且在45°面(顺时针扭转时)上具有极小值。这就将导致氢原子向45°面扩散和富集,当其浓度达到临界值时就会引起氢致滞后开裂。对于充氢的缺口或预裂纹扭转试样(即Ⅲ型裂纹)上述结论也成立。     

高氮奥氏体钢低温断面的晶体学分析

用扫描电镜对18Cr-18Mn-0.7N高氮奥氏体钢的组织及低温脆断断面的晶体学特征进行了分析.结果表明:低温脆断断口上有退火孪晶界断面、沿晶断面及穿晶断面3种断裂刻面.退火孪晶界断面为一光滑、平坦的{111}面,上有折线状台阶,其它3组{111}面上的形变组织在退火孪晶界断面上形成3组交角为60°的直线状平行迹线;沿晶断面为一光滑曲面,{111}面的形变组织在其上形成几组不同交角的曲线状平行迹线;穿晶断面粗糙不平,显示平行于{111}面的台阶、河流花样或棱状花样,它们是不同{111}面上的裂纹在扩展中合并形成的.