INFLUENCE OF DEFORMATION TEMPERATURE ON α_2-PHASE SLIP SYSTEMS OF A Ti_3Al ALLOY

利用透射电子显微镜，采用双倾双束技术和ｇ·ｂ不可见判据，分析了Ｔｉ－２５Ａｌ－１０Ｎｂ－３Ｖ－１Ｍｏ（ａｔ．－％）合金中α_２相（Ｄ０_（１９）结构）在２５—７００℃拉伸形变时的位错类型和滑移系．结果表明：室温拉伸形变主要源于ａ型位错在棱柱面或基面滑移，如〈１１０〉｛１００｝，〈１１０〉｛０００１｝；和少量＋／２型位错对在棱锥面滑移，如〈１１６〉｛２０１｝；＋／２，型位错密度随形变温度提高而减少，４００℃拉伸形变时出现大量孪晶；７００℃形变时没有＋／２型位错对出现，开动的是主要型位错在棱柱面、基面滑移和型位错对在棱锥面滑移，如〈１１０〉｛２１０｝．     

挤压态ZK60镁合金室温拉-压不对称性研究

基于室温轴向拉伸和压缩实验研究了挤压态ZK60镁合金的拉-压不对称性.通过修正黏塑性自洽模型,建立了耦合滑移和孪生的晶体塑性力学模型,模拟了挤压态ZK60镁合金轴向拉、压力学行为,分析了基面、柱面、锥面滑移及{1012}1011拉伸孪生和{1011}1012压缩孪生在塑性变形过程中的激活及演变情况.结合实验与模拟,从微观塑性变形机制角度分析了具有初始挤压态丝织构的镁合金产生拉-压不对称性的机理.结果表明:轴向拉伸过程中拉伸孪生和压缩孪生都较难激活,变形初期以基面滑移为主,由于基面滑移取向因子较低,导致屈服应力较高;随着晶粒转动,基面滑移分切应力降低,应力逐步升高,变形机制转为以柱面滑移为主,辅以锥面c+a滑移,应变硬化率较低,应力-应变曲线较平稳.轴向压缩前期,临界剪切应力较低的拉伸孪生大量激活,导致屈服应力较低;应变达到6.0%后拉伸孪生逐渐饱和,相对活动量快速降低,硬化率迅速提高,由于大量孪晶界对位错滑移形成阻碍,滑移机制未出现大量激活;轴向压缩后期,随着应力的持续升高,压缩孪生启动,相对活动量迅速上升,塑性变形积累的应力得以释放,硬化率降低.因此,挤压丝织构状态决定了镁合金在室温轴向拉、压变形过程中的变形机制存在明显区别,从而导致挤压镁合金产生显著的轴向拉-压不对称性.     

Ti3Al单晶塑性变形行为的晶体塑性有限元模拟

基于晶体塑性理论,建立了滑移变形机制下Ti_3Al单晶晶体塑性的细观本构关系,并利用ABAQUS/UMAT用户子程序接口开发本构关系子程序,将其应用于不同取向Ti_3Al单晶的单向压缩模拟。分析不同取向时晶体滑移系的启动情况,以及滑移系启动与取向的相互关系。结果表明:基面滑移系(0001)1120,柱面滑移系{1010}1120和锥面滑移系{1121}1126均被激活,但由于滑移系之间临界剪切应力和施密特因子的不同,各滑移系的启动情况存在显著差异。基面和锥面滑移系的临界剪切应力较大,仅在施密特因子较大时启动;特别是锥面滑移系,其临界剪切应力最大,因而该滑移系只有在压缩轴接近[0001]方向时才被激活。柱面滑移系的启动较为容易,对塑性变形的贡献也最大。同时与实验结果相比较,模拟结果基本与之吻合。     

面心立方金属{111}〈110〉滑移和{111}〈112〉孪生平面共生变形？…

将Ｂｉｓｈｏｐ－Ｈｉｌｌ最大功原理拓展于ｆｃｃ金属｛１１１｝〈１１０〉滑移和｛１１１｝〈１１２〉孪生两种机制同时起作用的平面共生变形。研究了不同临界剪切应力（ＣＲＳＳ）之比ξ对各理想取向的屈服应力状态及相应活化系的影响。分析结果表明,当ξ〉１／３ｊｆ ,Ｃ,Ｇ和Ｒｃｕ３种取向共同的活化系均为滑移系,不易孪生：其它５种取向共同的活化系均包括滑移系和孪生系,有孪生倾向。同时分析了取向空间里屈服强度各向     

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。     

Zr-4合金双轴疲劳行为及其微观变形机理Ⅱ.双轴循环变形亚结构及其织构的发展

用透射电镜分别观察了Zr-4合金比例和非比例双轴疲劳变形亚结构.结果表明:等效应变幅为0.8%,不同主应变比下,Zr-4合金比例双轴疲劳后典型的位错组态是{1010}柱面滑移产生的平行位错线.随着等效应变幅提高,从平面状向波纹状滑移转化,有形成位错胞的趋势.非比例加载过程中,随着相位角从30°增大到90°,位错组态从平行位错墙变化成位错胞.相位角为90°时,随着等效应变幅提高,位错保持位错胞结构,但位错密度增高.非比例变形前后织构分析表明:随着相位角提高,{1010}极点密度减弱,{1011}锥面极点密度增强,表明合金塑性变形从以{1010}柱面滑移为主向柱面滑移加锥面滑移多系滑移转化.Zr-4合金非比例附加强化一方面是由于部分柱面滑移被锥面滑移取代后,滑移系本身临界分切应力提高;另一方面由于多滑移导致〈a/a〉和〈c+a〉/〈a〉位错与位错之间交互作用力提高.     

钛合金板材辊弯成形特性及显微组织和织构演化规律

以TB5、TC4钛合金板材为研究对象,研究了辊弯成形工艺对钛合金板材显微组织、织构和力学性能的影响。结果表明：对于TB5钛合金板材,单道次实验中,随成形角度增大,回弹角度逐渐增大,主要原因为单道次成形存在少量{332}〈113〉孪生变形,导致塑性变形量降低,弹性回复增大;在成形角度30°多道次成形实验中,随道次数增加,回弹角度随孪生变形量先增后减。对于TC4钛合金板材,单道次实验中,随成形角度增大,回弹角度逐渐增大,这是由于基面〈a〉滑移比柱面〈a〉更容易开动,产生〈0112〉//ND织构;多道次实验柱面〈a〉滑移系引起塑性变形,织构转变为〈1234〉//TD,回弹角度逐渐减小。在多道次成形中,TB5、TC4两种板材滑移方向均改变,但相比于单道次30°成形,TB5多道次成形回弹角度增大,而TC4回弹角度减小。     

高温终轧工艺对初始织构不同的AZ31镁合金板材组织的影响

以初始织构不同的AZ31镁合金板材为研究对象进行了高温终轧和最终退火,结合转靶X射线衍射仪和电子背散射衍射分析手段分析了不同板材基面织构的变化情况以及滑移和孪生对形变织构的影响规律。结果表明,高温终轧后,两种板材的宏观织构存在着单峰和倾斜的双峰基面织构区别;最终退火后,两种板材的织构强度都得到弱化,但弱化程度存在差异,并且再结晶织构在一定程度上遗传了形变织构的特征。对于初始织构强度较高的板材,高温终轧时锥面滑移活性增强,柱面滑移受到抑制,从而表现出带状变形集中区域,以此来弥补由于位错滑移受限引起的变形能力不足,此时形变织构的变化主要受到滑移和孪生的共同作用的影响。对于初始织构强度较弱的板材,高温终轧时非基面滑移活性得到增强,滑移和孪生相互竞争,孪生活动受到了明显抑制,此时形变织构的变化主要受到滑移的影响。     

初始织构对AZ31镁合金中温塑性变形的影响

采用光学显微镜和XRD宏观织构分析,研究了具有不同初始织构的AZ31镁合金在中温热模拟压缩变形中组织和织构的演变行为。结果表明:以柱面织构为主的试样较基面织构试样有更好的变形能力,其塑性在210~230℃温度区间内显著改善,取决于柱面a滑移能协调样品应变;压缩过程中由于主要变形机制由{1012}孪生转变为柱面滑移,基面组分先增强后减弱,柱面组分先减小后增强;以基面织构为主的试样脆韧转变发生在230~250℃,取决于c+a滑移启动和DRX;压缩过程中基面组分减弱,柱面组分增强。温度升高促进非基面滑移系和DRX的激活,使初始织构的影响减弱。     

形变温度对Ti3Al基合金α2相滑移系的影响

利用透射光电显微管，采用双倾双束技术和ｇ．ｂ不可见判据，分析了Ｔｉ－２５Ａｌ－１０Ｎｂ－３Ｖ－１Ｍｏ（ａｔ．－％）合金中α２相（Ｄ０１９结构）在２５－７００℃拉伸形变时的位错类型和滑移系，结果表明：室温位伸形变主要要源于α型位错在棱柱面或基面滑移，如（１１２０）（１０１０），（１１２０）（０００１）；和少量Ｃ＋ａ／２型位错对在棱锥面滑移，如（１１２６）（２０２１）；Ｃ＋ａ／２，型位错密度随形变温提     

六角密排金属主滑移面选择的电子结构研究

运用基于局域密度泛函近似的离散变分Ｘα原子簇方法计算了六角排金属的电子结构及其相互作用参数,讨论了相互作用参数与其宏观性能间的内在联系。以相互作用参数Ｔ（ｈ,ｋｊｌ）为基础,提出了基于电子结构理论的六角密排金属主滑移面选择的判据,所得结论与实验观测相符。     

LOW CYCLE FATIGUE BEHAVIORS AND MICROSTRUCTURES OF Ti–2Al–2.5Zr WITH FINE GRAIN AT RT AND 77 K

对细晶Ti--2Al--2.5Zr合金进行了室温/低温(77 K)疲劳实验及微观组织观察. 结果表明: 室温低应变幅Δε_t/2(=0.5%, 1.0%)下,合金表现为循环软化; 室温高应变幅(1.5%, 2.0%)下, 则表现为循环应力饱和; 77 K时, 不同应变幅下均表现为循环硬化, 且随应变幅升高, 循环硬化程度增强. 疲劳寿命测试结果表明: 低温疲劳寿命始终高于室温. 断口SEM观察表明, 室温和低温下, 疲劳裂纹扩展区均有明显的疲劳条纹,疲劳裂纹以穿晶方式扩展, 室温下伴随有大量二次裂纹, 低温下的二次裂纹数量明显减少. TEM观察表明: 低温下孪生是合金主要的变形方式, 包括{1011}和{1121}型孪晶. 疲劳变形位错组态为: 室温较低应变幅(0.5%, 1.0%)下, 形成位错线和局部位错缠结; 室温下应变幅提高到1.5%和2.0%时,\{1010}柱面和{1121}锥面滑移同时开动, 位错组态演化为亚晶和明显的位错胞. 77 K下, 应变幅2.0%时形成沿 柱面平行分布的位错带; 77 K下应变幅升高到4.5%时, 多滑移形成相互垂直的位错线. 低温诱发形变孪晶是Ti--2Al--2.5Zr低温疲劳寿命升高的原因.     

Deformation Mechanisms of Alpha-Uranium Single Crystals

The operative deformation elements in α-uranium single crystals under compression at room temperature have been determined as a function of the compression directions. The deformation mechanisms noted may be arranged with respect to their frequency of occurrence and ease of operation in the following order: 1—(010)-[100] slip, 2—{130} twinning, 3—{~172} twinning, and 4—under special conditions of stress application, kinking, cross-slip, {~176} twinning, and {011} slip. The composition planes of the {172} and {176} systems were found to be irrational. Cross-slip was shown to be associated with the major (010) slip system, coupled with localized interaction of slip on the (001) planes. The mechanism of kinking was found to be similar to that observed in other metals in that it occurred chiefly when the compression direction was nearly parallel to the principal slip direction [100] and was associated with a lattice rotation about an axis contained in the slip plane and normal to the slip direction: the [001] in the uranium lattice. The resolved critical shear stress for slip on the (010)-[100] system was found to be 0.34 kg per mm². In a single test it was shown that under compression in suitable directions twinning on the {130} also occurs at 600°C     

PRECIPITATION AND MICROSTRUCTURE OF Cr MODIFIED Al3Ti

1. IntroductionThe tetragonal D022 compound A13Ti has recently received attention as a possible structural material because of its low density, 3.4g/cm', and its good oxidation resistanced'2].However, D0zz-AlsTi has the disadvalltages, that it is a line compound and is extremelybrittle at room temperature, presumably due to the lack of slip systems associated withthe crystal symmetry[2]. It is known that partially replacing some of the aluminum atomsin AlsTi with Cr[31, Ni[4], or Ag['] etc…     

金属间化合物Al_(67)Mn_8Ti_(25)合金解理能和解理面

用ＥＥＴ 计算了Ｌ１２ 结构Ａｌ６７ Ｍｎ８Ｔｉ２５ 合金的键结构, 键能和主要解理面的解理能。结果表明几种低指数晶面的解理能以｛１１０｝ 晶面为最低, 其值为３ ．１２Ｊ·ｍ － ２ ; 其次为｛１００｝ 和｛１１１｝ 型晶面, 解理能分别为４ ．１７ 和４ ．８７Ｊ·ｍ － ２ 。用电子背散射衍射技术对合金室温弯曲断口解理刻面的晶体学位向进行了测定, 在所测刻面中,｛１１０｝ 刻面约占５４ ％ ,｛１００｝ 和｛１１１｝ 约占３１ ％ 和８ ％ , 其结果与ＥＥＴ 计算结果相一致。可以认为, 解理能低是Ａｌ６７ Ｍｎ８Ｔｉ２５ 合金室温脆性解理的主要原因之一。     

Relationships between deformation mechanisms and initial textures in polycrystalline magnesium alloys AZ31

1　INTRODUCTIONMagnesiumisthelightestmetallicstructuralma terialwithhighspecificstrengthandisusedinauto motive ,electronicsandaerospacefield[1,2 ] .Howev er ,magnesiumoftenshowspoorformabilityatroomtemperatureduetoitshexagonalstructurewithlessindependentslipsystems ,whichlimitsitsuse .Dif ferentslipsystemshavebeendetectedinmagnesiumsuchasbasalslipof { 0 0 0 1}〈112 0〉 ,prismslipof{ 10 10 }〈112 0〉[3,4 ] andpyramidslip (includingthea typeof {hkil}〈112 0〉andthea +ctypeof {hkil}〈112 3〉[…     

Dependence of Microstructure Evolution and Mechanical Properties on Loading Direction for AZ31 Magnesium Alloy Sheet with Non-basal Texture During In-Plane Uniaxial Tension

In-plane uniaxial tension of AZ31 magnesium alloy sheet with non-basal texture has been conducted in order to demonstrate the effects of loading direction on the microstructure evolution and mechanical properties at ambient temperature. Loading axes are chosen to be along five directions distributed between rolling direction (RD) and transverse direction (TD), allowing various activities in involved slip and twinning modes to take place. As for twinning modes, electron backscattered diffraction observations confirm that the contribution of ${{\{ 10\overline{1}1\} }}$ compression twinning is minimal to the plastic deformation of all deformed samples. By comparison, ${{\{ 10\overline{1}2\} }}$ extension twinning (ET) not only serves as an important carrier on sustaining and accommodating plastic strain but also contributes to the emergence of TD-component texture with the progression of plastic strain. In terms of slip modes, analysis on Schmid factor demonstrates that the increasing tilted angle between loading direction and RD of sheet is unfavorable to the activation of basal <a> slip, whereas it contributes to the activation of prismatic <a> slip. These observations consequently explain the increasing tendency of 0.2% proof yield stress. Moreover, the activations of basal <a> slip and ${{\{ 10\overline{1}2\} }}$ ET collectively contribute to the concentration of two tilted basal poles toward normal direction. With increasing angle between loading direction and RD, the activations of basal <a> slip and ${{\{ 10\overline{1}2\} }}$ ET are gradually weakened. This leads to a weakening tendency about concentration of two tilted basal poles, a generally increasing tendency about Lankford value (r-value) and a generally decreasing tendency about strain-hardening exponent (n-value).     

Tailoring Texture to Highly Strengthen AZ31 Alloy Plate in the Thickness Direction via Pre-tension and Rolling-Annealing

Conventional wrought Mg alloys, such as AZ31 and ZK60 rolled plates, usually exhibit significantly low tensile yield strength in the thickness direction. This can be attributed to the high activity of {10-12} tension twinning due to the strong basal texture (< 0001 > //ND, normal direction). In this work, the tensile yield strength in the ND of the as-rolled (AR) AZ31 plate increased from 50 to 150 MPa (increased by 200%) via simple processing, i.e., pre-tension and rolling-annealing (PTRA) treatment. The strong basal texture (< 0001 > //ND) of the AR plate was changed into a weakened fiber texture (< 0001 > ⊥ND). The evolution of microstructures during PTRA treatment and the activated deformation modes during uniaxial tension were studied quantitatively and statistically by the means of intergranular misorientation (IM) and in-grain misorientation axes (IGMA) analysis. The results indicate that various twin variants, as well as {10-12}-{10-12} secondary twins, were activated during pre-tension and rolling, and most residual matrix was consumed by twins after annealing. The dominated deformation modes in tension changed from {10-12} tension twinning (the AR sample) to prismatic slip (the PTRA sample) in the early tensile deformation. The underlying formation mechanism of the fiber texture and corresponding strengthening mechanism were discussed.     

Ti-2Al-2.5Zr单道次皮尔格轧制过程中显微组织和织构的演化

研究了单道次皮尔格轧制过程中Ti-2Al-2.5Zr材料的变形行为和织构的演变规律。结果表明,在轧制过程中,｛102｝孪晶和柱面滑移是最容易被激活的2种变形模式,｛102｝孪晶的产生使得晶粒在轴向上的位向从<100>转向<110>。并且,在不同瞬时Q值和等效应变量下,滑移和孪生导致｛0001｝极图中最大极密度点在切向上发生变化。     

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。