单晶Ni3Al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Ｎｉ３Ａｌ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     

充氢Ni_3Al｛110｝型解理断裂原位TEM观察SCIEI

利用ＴＥＭ原位观察技术研究了充氢Ｎｉ_３Ａｌ｛１１０｝型解理断裂裂纹萌生、扩展过程。发现｛１１０｝型解理裂纹的萌生是由于｛１１１｝型主裂纹前端位错塞积产生的局部应力集中造成的，且氢的存在降低了｛１１０｝面的解理能。     

Al67Mn8Ti25合金的解理裂纹

利用Ｓｔｒｏｈ 位错塞积模型解释了Ｌ１２ 结构Ａｌ６７ Ｍｎ８Ｔｉ２５ 合金室温解理裂纹的萌生。计算表明,位错塞积优先在与滑移面成３５ ．３°方向诱发微裂纹, 导致解理断裂。经室温弯曲断口解理面取向的电子背散射衍射（ＥＢＳＤ） 测试结果验证表明,Ｌ１２ 结构Ａｌ６７ Ｍｎ８Ｔｉ２５ 合金室温解理断裂裂纹优先在｛１１０｝ 晶面萌生     

双相不锈钢中裂纹尖端塑性变形行为的透射电镜原位观察

在透射电子显微镜下对铁素体-奥氏体双相不锈钢薄膜试样进行了动态拉伸试验,原位观察了裂纹尖端塑性变形过程和位错分布,发现在铁素体相和奥氏体相中,裂尖位错组态有明显差异。在铁素体相中,裂尖无位错区较大,且让错易发生交滑移,在裂纹前端形成较大的塑性区。在奥氏体相中,裂尖无位错区较小,发射的位错在其滑移面内逆塞积。两相中裂尖滑移系的选择都与裂尖Schmid因子有关。但当形变较大时,奥氏体相中裂尖二次滑移系的选择不再为裂尖Schmid因子所支配。     

改性高锰钢裂纹萌生与扩展的原位拉伸研究

借助扫描电镜(SEM)装载的原位拉伸台,观察了经热处理的两种改性高锰钢裂纹萌生与扩展的动态变化过程。结果表明,在改性高锰钢原位拉伸过程中,裂纹源主要为预制缺口处、滑移线密集处、第二相/奥氏体界面及晶界。载荷使奥氏体基体内部形成高密度滑移线,裂纹扩展以向晶内滑移线密集处扩展为主,碳化物/奥氏体界面次之。对于含C和Mn较高的改性高锰钢Mn18,当塑性变形达到一定程度后,由于位错塞积和晶界阻碍效应,碳化物与基体的协同运动受到阻碍,在较大颗粒状碳化物/奥氏体界面产生应力集中,裂纹由此扩展而发生断裂。     

单晶Nb拉伸,压缩及恒应变疲劳后的滑移系和滑移特征

研究了单滑移位向和多滑移位向Ｎｂ单晶在拉伸，压缩及循环变形时的滑移系，根据试样表面滑移线的方向，在极图上确定滑移面，单滑移位向（［３２１］）的单晶，在拉伸时的滑移系为（１０１）［１１１］，在压缩时是（１０１）［１１１］和（２１３）［１１１］．根据ｂｃｃ晶体变形特点，分析了拉伸，压缩和循环变形的滑移系之间的关系，用光学显微镜和透射电镜复型观察了试样的表面形貌，确定了多滑移位向（［１１０］位向）单晶滑     

STRESS CORROSION CRACKING OF 321 STAINLESS STEEL SINGLE CRYSTAL UNDER MODE Ⅱ LOADING

研究了不锈钢Ⅱ型单晶试样在４２％沸腾ＭｇＣｌ＿２溶液中的应力腐蚀。结果表明，对任何晶面取向的试样，其应力腐蚀裂纹均在最大正应力处形核，而在最大剪应力位置并不发生应力腐蚀．在最大正应力位置的周围虽有滑移线，但在裂纹形核的区域并无滑移线，而在有滑移线的地方却没有宏观裂纹。观察表明，有些滑移线上存在很多蚀坑，在蚀坑较轻微的滑移线上，有许多微裂纹，这些裂纹与滑移线成一定角度（约２０°）．在应力腐蚀裂纹的形核与扩展中起作用的是位错局部塞积所形成的应力集中．位错塞积应力与电化学过程的联合作用下导致了应力腐蚀开裂，金属表面的滑移台阶虽然也会发生腐蚀，但并不起主要作用。     

双相层片型NiAl基合金的室温变形及断裂

ＴＥＭ原位拉伸研究表明，尽管双相层片型ＴｉＡｌ基合金中与α２相共存的γ层片相的（１／２）〈１１０］位错具有良好的可滑移性，并在一些γ层片中（１／６）〈１１２］形变孪生也较为活跃，但对变形有贡献的滑移系统及孪生系统数目少是室温塑性差的重要原因。提高多晶体双相ＴｉＡｌ基合金室温塑性的关键在于促使（１／２）〈１１０］｛１１１）以外的滑移系开动。     

不锈钢Ⅱ型单晶试样的应力腐蚀

研究了不锈钢Ⅱ型单晶试样在４２％沸腾ＭｇＣｌ＿２溶液中的应力腐蚀。结果表明，对任何晶面取向的试样，其应力腐蚀裂纹均在最大正应力处形核，而在最大剪应力位置并不发生应力腐蚀．在最大正应力位置的周围虽有滑移线，但在裂纹形核的区域并无滑移线，而在有滑移线的地方却没有宏观裂纹。观察表明，有些滑移线上存在很多蚀坑，在蚀坑较轻微的滑移线上，有许多微裂纹，这些裂纹与滑移线成一定角度（约２０°）．在应力腐蚀裂纹的形核与扩展中起作用的是位错局部塞积所形成的应力集中．位错塞积应力与电化学过程的联合作用下导致了应力腐蚀开裂，金属表面的滑移台阶虽然也会发生腐蚀，但并不起主要作用。     

镍基单晶裂纹扩展路径研究

采用紧凑拉伸（CT）试样研究了3种不同温度（950，850，760℃）和3种不同晶体取向（[001]，[011]，[111]）下镍基单晶合金DD3的断裂特征，采用光学显微镜和扫描电子显微镜观察分析了裂纹扩展路径及断口形貌。采用率相关晶体滑移有限元程序对试件裂纹尖端三维分切应力场结构、裂纹启裂和扩展机制以及滑移系激活规律进行了模拟计算分析。结果表明：晶体取向和环境温度对裂纹启裂和扩展以及断裂强度和断裂形式有较大的影响，低温下裂纹扩展沿着特定的滑移带方向，与裂纹平面成一斜角，[001]裂纹取向下为45°，[011]裂纹取向下为53．7°，[111]裂纹取向下为90°，这使得宏观上裂纹扩展路径呈现Z字形外观。而温度较高时，发生的Ⅰ型裂纹扩展与加载方向垂直。并且随着温度的升高，断裂形式逐步由脆性断裂转化为韧性断裂。     

STUDY ON FRACTOGRAPHY OF TRANSGRANULAR SCC OF 70Cu-3OZn IN AN AMMONIACAL SOLUTION

1.IntroductionThemechanismsofstresscorrosioncracking(SCC)havenotyetbeenresolved,andthisproblemremainsasignificalltengineeringconcernandisofacademicillterest.Ofparticularinterestisthecaseoftransgranularstresscorrosioncracking(TSCC)oftheductileface-centeredcubic(FCC)metalsandalloyssincethesematerialshavemultipleslipsystemsandarecharacterizedbyhighdislocationvelocities.SinceSCCisacrackingphenomenon,thepropagationmechanismsmustbeabletofullyexplainthedetailsonthefracturesurfacesproducedbyanddu…     

EBSD Analysis of Fatigue Crack Growth of 2124 Aluminum Alloy for Aviation

运用电子背散射衍射(EBSD)分析技术对2124-T851铝合金板材的疲劳裂纹扩展进行了分析研究。结果表明,疲劳裂纹扩展以穿晶为主,随晶粒取向的不同而呈现一定的择优性。当裂纹扩展到晶界时,由于相邻晶粒间存在的取向差,裂纹会偏离其正常扩展路径而发生偏转,而晶内的裂纹偏转则更多是因为粗大第二相粒子在循环应力作用下协调变形能力差引起的。裂纹扩展过程中发生裂纹分叉与特定的晶体学方向有关,是由于裂纹尖端多个等效{111}<110>滑移系的同时开动造成的。     

Molecular dynamics simulation on mechanisms of plastic anisotropy in nanotwinned polycrystalline copper with {111} texture during tensile deformation

Based on molecular dynamics (MD) simulation, the mechanisms of plastic anisotropy in nanotwinned polycrystalline copper with {111} texture during tensile deformation were systematically studied from the aspects of Schmid factor of the dominant slip system and the dislocation mechanism. The results show that the Schmid factor of dominated slip system is altered by changing the inclining angle of the twin boundaries (TBs), while the yield stress or flow stress does not strictly follow the Schmid law. There exist hard and soft orientations involving different dislocation mechanisms during the tensile deformation. The strengthening mechanism of hard orientation lies in the fact that there exist interactions between the dislocations and the TBs during plastic deformation, which leads to the dislocation blocking and reactions. The softening mechanism of soft orientation lies in the fact that there is no interaction between the dislocations and the TBs because only the slip systems parallel to the TBs are activated and the dislocations slip on the planes parallel to the TBs. It is concluded that the plastic anisotropy in the nanotwinned polycrystalline copper with {111} texture is aroused by the combination effect of the Schmid factor of dominated slip system and the dislocation mechanism.     

循环压缩载荷下Ni3Al基合金单晶体的疲劳开裂

采用两种晶体取向的单边缺口试样，在循环压缩载荷下对Ｎｉ３Ａｌ基合金单晶体的疲劳裂纹萌生和扩展行为进行了研究。在循环压缩载荷下，第一阶段的晶体学开裂在缺口根部同时沿着两个或更多的（１１１）面发生。     

B2结构Fe3Al单晶在室温拉伸过程中的取向转动

借助于ＥＢＳＤ方法，研究了８个位向Ｂ２结构Ｆｅ３Ａｌ单晶室温拉伸变形时晶体取向的转动。结果表明，无论原始取向如何，在拉伸过程中晶体拉伸轴总会向着〈１１０〉方向转动，也即〈１１０〉为稳定取向。当晶体拉伸轴转向取向三角形中部的软取向时，晶体表现为几何软化，相应的加工硬化率较低。反之，当晶体拉伸轴转向〈００１〉－〈１０１〉对称线时，晶体表现为几何硬化，相应的加工硬化率较高。当拉伸轴处于软取向时，单晶试样     

Effects of Crystal Orientations on the Low-Cycle Fatigue of a Single-Crystal Nickel-Based Superalloy at 980 °C

The influence of crystal orientations on the low-cycle fatigue(LCF) behavior of a 3Re-bearing Ni-based single-crystal superalloy at 980 °C has been investigated. It is found that the orientation dependence of the fatigue life not only depends on the elastic modulus, but also the number of active slip planes and the plasticity of materials determine the LCF life,especially for the [011] and [111] specimens. The [011] and [111] specimens with better plasticity withstand relatively concentrated inelastic deformation caused by fewer active slip planes, compared to the [001] specimens resisting widespread deformation caused by a higher number of active slip planes. Additionally, fatigue fracture is also influenced by cyclic plastic deformation mechanisms of the alloy with crystal orientations, and the [001] specimens are plastically deformed by wave slip mechanism and fracture along the non-crystallographic plane, while the [011] and [111] specimens are plastically deformed by planar slip mechanism and fracture along the crystallographic planes. Moreover, casting pores,eutectics, inclusions and surface oxide layers not only initiate the crack, but also reduce the stress concentration around crack tips. Our results throw light upon the effect of inelastic strain on the LCF life and analyze the cyclic plastic deformation for the alloy with different orientations.     

Crystallographic and macroscopic orientation of planar dislocation boundaries—correlation with grain orientation

A novel geometric analysis method for determination of the three-dimensional orientation of extended planar dislocation boundaries in polycrystals based on TEM measurements is presented. The analysis is applied to data for tensile deformed aluminium, revealing that the boundaries have a strong preference for certain crystallographic planes, depending on the crystallographic orientation of the grain. The crystallographic boundary planes are distributed around, but do not coincide with, the most stressed macroscopic planes inclined 45° to the tensile axis. The strong correlation between the crystallographic boundary planes and the grain orientation shows that the boundary orientation is closely linked to the active slip systems. The observed correlation can be explained by a Schmid factor analysis assuming activity on the five most stressed slip systems.     

Role of Crystallographic Textures on Failure Behavior in HSLA Grade-420 Steel During Cold Rolling

The microstructural and textural evolution was analyzed during rolling at room temperature to obtain detailed information about the failure behavior in HSLA grade-420 steel. Electron backscatter diffraction measurements were carried out in both non-cracked and cracked areas after cold rolling to find a correlation between microstructural parameters (i.e., grain orientation, grain boundary characteristics and Taylor factor) and crack propagation. The results showed that the crack tended to propagate along grains oriented with {001} planes parallel to the normal direction with high Taylor factor value. The special boundaries associated with the {111}, {110} and {221} planes were indicated as crack resistance, while ∑ 5, 13a and 17a, which related to the {001} planes, were crack-susceptible. Transgranular cracking was subjected within grains with high Taylor factor, while mismatch in Taylor factor between neighboring grains could provide an easy path for intergranular crack propagation.     

Stress corrosion failure of Zircaloy-2 sheets in methanolic HCl solution: Role of crystallographic texture

The stress corrosion cracking (SCC) characteristics of Zircaloy-2 sheets in methanol-0.4 vol. pct. hydrochloric acid have been studied in the annealed and cold-rolled conditions using longitudinal and transverse specimens. The times to failure for annealed longitudinal specimens were longer than those for similarly tested transverse specimens at stress levels below ～45% UTS. The cold-rolled specimens developed resistance to SCC, but failed totally by cleavage when notched, unlike annealed specimens which failed by intergranular initiation followed by cleavage. The crystallographic texture developed by cold rolling is such that the crack initiation is difficult because of quicker passivation characteristics of the crack initiating plane. The texture also gives unfavourable orientation of slip and twinning planes with respect to tensile axis. The crack initiating planes are identified with the help of X-ray pole figures. The apparent activation energy is found to be texture dependent at a given stress level. On the basis of apparent activation energy measurements, dynamic tests at constant cross-head speeds and electrochemical measurements, the mechanism of SCC is identified to be the one involving stress-aided anodic dissolution.