高压扭转纳米结构Al-Mg铝合金的微观结构演变和位错组态

利用透射电镜（TEM）和高分辨透射电镜（HRTEM）研究高压扭转大塑性变形纳米结构Al-Mg合金的微观结构演变和位错组态。结果表明：对尺寸小于100 nm的晶粒,晶内无位错,其晶界清晰平直;而尺寸大于200 nm的大晶粒通常由几个亚晶或位错胞结构组成,其局部位错密度高达10^17 m^-2。这些位错是1/2〈110〉型60°位错,且往往以位错偶和位错环的形式出现。在高压扭转Al-Mg合金的超细晶晶粒中,用HRTEM同时观察到分别由0°纯螺型位错和60°混合位错分解产生的Shockley部分位错而形成的微孪晶和层错。这些直接证据证实,通常存在于FCC纳米晶中由晶界发射部分位错而产生孪晶和层错的变形机制,同样可以存在于超细晶FCC金属中。基于实验结果,分析了高压扭转Al-Mg合金中的局部高密度位错、位错胞、非平衡晶界、层错和孪晶等对晶粒细化的作用,提出了相应的晶粒细化机制。     

高压扭转大塑性变形对Al-Zn-Mg-Cu-Mn铝合金组织和织构的影响

对不同高径比的Al-Zn-Mg-Cu-Mn铝合金试样进行了高压扭转大塑性变形,并应用X射线衍射(XRD)与电子背散射衍射(EBSD)分析了合金大塑性变形时的微观组织变化。结果表明:合金在高压扭转大塑性变形后,Mg Zn2相进入到Al基中,初始组织在高压扭转剪切变形下发生拉长并细化。随着合金高径比的降低,其受到的扭转剪切效果不断上升。在高径比等于0.25时,小角度晶界的最大比例为0.522。合金(220)晶面具有最强的衍射峰,(111)晶面衍射峰比初始合金试样的衍射峰值更强。最大极密度值随高径比的降低而减小。     

纯W高压扭转显微组织演化过程TEM分析

在相对较低温度下完成了纯W不同扭转圈数高压扭转实验,通过EBSD、TEM及HRTEM观察了纯W高压扭转过程中的显微组织形貌及微观结构。结果表明,随着等效应变增大,纯W材料显著细化,位错密度增加,非平衡晶界增多。高压扭转过程中小角度晶界向大角度晶界转化现象明显,且位错结构逐渐转移至晶界,细小晶粒内部无明显缺陷。当等效应变增大至5.5时,由于部分晶粒尺寸与位错平均自由程相近,晶粒变形方式由晶内滑移向晶界滑移转变。     

IF钢高压扭转过程中不均匀塑变特征的仿真模拟

采用有限元软件DEFORM-3D对IF钢试样高压扭转过程进行计算机仿真模拟,研究高压扭转试样不均匀塑性变形特征,对硬度和显微组织分布进行研究。结果表明:试样在进行高压扭转两个阶段(压缩、扭转)的过程中,均发生了显著的不均匀塑性变形,在扭转初期阶段,其不均匀变形程度尤其显著;在试样径向,IF钢试样的塑性变形程度从中部到边缘逐步增大;在试样的轴向,试样的塑性变形程度随距试样下表面距离的增加而逐渐减小;硬度分布和显微组织检测结果均验证了模拟结果的可靠性。     

电子束辐照对多壁碳纳米管的影响（英文）

在室温下采用透射电子显微镜中汇聚的电子束辐照多壁碳纳米管。结果表明,在能量为100 keV的电子束辐照下除了碳纳米管管壁有一些弯曲外没有其他结构被破坏;当电子能量增加到200 keV时,纳米管有明显的损伤,可以观察到纳米管的无定型化、纳米管外壁的凹坑和缺口。200 keV的电子束辐照还能形成碳洋葱和2根多壁纳米管的焊接。多壁碳纳米管的离位阀能为83~110 keV。能量超过阀能的电子束可以很轻易地损伤纳米管而低于阀能的电子束则很难损坏纳米管,其损伤机理为溅射和原子离位。     

高压扭转对AZ91D镁合金中第二相析出行为的影响

对铸态商用AZ91D镁合金固溶处理后进行高压扭转,再进行时效处理,利用光学显微镜,扫描电镜及X射线衍射对其微观结构和力学性能进行了详细研究。结果表明高压扭转大塑性变形使合金的晶粒尺寸由固溶态的～100μm细化到纳米晶,同时使基体中长杆状和块状的β-Mg_(17)Al_(12)析出相转变为颗粒状和椭圆块状。虽然经过高压扭转大塑性变形后的试样在时效处理过程中显微硬度呈下降趋势,但其硬度值较只经T6处理的试样相比有很大提高。只经高压扭转大塑性变形处理后的固溶态试样显示了最高显微硬度,其值为128 HV0. 1。     

Mg-7Gd-4Y-1Nd-0.5Zr合金热轧过程中的组织与织构演变

采用金相显微镜、扫描电镜和X射线衍射仪,对Mg-7Gd-4Y-1Nd-0.5Zr合金铸锭在450℃条件下轧制变形过程中的微观组织和织构演变规律进行研究。结果表明:该合金在轧制过程中存在着两种织构组分:基面织构和棱柱面织构。随变形程度的增加,基面织构不断增强,棱柱面织构不断减弱。在450℃条件下轧制时,棱柱面滑移系启动协调晶粒的塑性变形形成棱柱面织构,形成的棱柱面织构组分在后续变形过程中通过{1012}1011孪生及退火过程中孪生区域的静态再结晶而不断被削弱。     

锆合金剧烈塑性变形组织演变的研究进展

综述了锆合金剧烈塑性变形行为的研究进展,系统阐述了锆合金剧烈塑性变形技术,包括等径转角挤压、高压扭转、累积叠轧、扭转挤压及多向锻造。重点介绍以上方法在纯锆、Zr-Nb系合金及Zr-Sn-Nb系合金中的应用。详细介绍锆了合金微观组织及性能演变行为的研究现状,全面描述了锆合金组织和织构的演变。     

电子束诱导非晶GaAs晶化的形核与长大

利用高分辨电子显微镜对电子束辐射诱发非晶GaAs晶化过程现象进行了原位观察。结果表明，具有几个原子大小的原子簇在辐射初期产生，并作为晶化的核心在随后的辐射过程中不断长大；大部分结晶晶粒保持相同的晶体取向，其余少量不同取向的晶粒也与前者保持孪晶关系。电子束辐照诱发非晶GaAs晶化的速率与电子束流密度有关；电子束辐照非晶GaAs结晶不是电子束诱发材料温度升高的结果，而与电子能量有关。本文对辐照晶化的机制和结晶过程进行了讨论。     

铸造缺陷对ZL101合金断裂行为的影响

通过扫描电子显微镜和光学金相显微镜观察ZL101合金断口及附近组织中的铸造缺陷,使用ANSYS软件分析了加载过程中铸造缺陷附近的应力场分布。结果发现:铸件在拉伸过程中由铸造缺陷附近的共晶组织内产生初始裂纹,裂纹沿着共晶区向外扩展,最终导致合金断裂。铸造缺陷附近形成的应力集中使Al基体发生局部塑性变形,大量位错塞积使Si相断裂。     

高压扭转变形Mg-Zn-Y合金的组织演化和时效行为

采用透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)仪和显微硬度计研究了高压扭转(HPT)变形Mg-Zn-Y合金的微观组织演变和时效行为。结果表明,在HPT变形前后,合金中的第二相颗粒是W相和Mg₂₄Y₅相,且在HPT处理后没有观察到任何新沉淀物的形成,说明HPT变形并未导致合金发生相变。同时,发现HPT变形过程是伴随着形变孪晶的产生和大量位错增殖而进行的,其中形变孪晶在HPT处理过程中被第二相颗粒所细分。与未变形合金相比,HPT变形可以加速时效进程,即在更短的时效时间达到相对高的峰值硬度。对HPT变形7圈的试样进行175 ℃×8 h时效处理后,峰值显微硬度达到约114 HV0.1。经过时效处理后,析出相优先在位错和孪晶界处形核,说明位错和孪晶界充当析出相优先形核位点。     

Nano- and microvoid formation in ultrafine-grained martensitic Fe-Ni-Mn steel after severe cold rolling

Severe cold-rolling was applied on solution annealed Fe-Ni-Mn steel with fully lath martensite structure to obtain ultrafine-grained structure. Field emission scanning electron microscopy and high resolution transmission electron microscopy (HRTEM) were employed to investigate the microstructural evolution after severe cold-rolling. HRTEM images showed the typical deformed structure consisting of lamellar dislocation cell blocks. HRTEM study also revealed strain-induced reverse martensitic transformation (activated during grain refinement). It was assumed that severe plastic deformation route and related deformation mode were responsible for microstructural evolutions. X-ray diffraction (XRD) diagram revealed 7% (volume fraction) reverted austenite after final deformation pass. Moreover, HRTEM images revealed nano-void nucleation at the interface of severely deformed martensite and reverted austenite presumably due to high strain energy of misfit and molar volume difference between the austenite and the martensite. It seems that the coalescence of nano-voids could lead to the formation of microvoids in the microstructure.     

Structure and phase transformations in TiNiFe ternary alloys subjected to plastic deformation by high-pressure torsion and subsequent heat treatment

The results of a complex study of ternary TiNiFe alloys with a low-temperature shape-memory effect subjected to megaplastic deformation by high-pressure torsion (HPT) with subsequent heat treatment are presented. Investigations have been performed using X-ray diffraction, transmission and scanning electron microscopy, and measurements of electrical properties. It has been established that, at moderate degrees of reduction, the plastic deformation in the Ti₅₀Ni₄₉Fe₁ alloy induces a B2 ? B19′ thermoelastic martensitic transformation and the formation of a developed banded dislocation and twin structure in the B19′ martensite; in the Ti₅₀Ni₄₇Fe₃ alloy, a mainly analogous dislocation substructure is formed, but in the B2 austenite. The megaplastic deformation by HPT at room temperature leads to the amorphization of the Ti50Ni49Fe1 alloy and to the high-angle nanofragmentation of the Ti50Ni47Fe3 alloy. Specific features of the evolution of the structure and martensitic transformations in the TiNiFe ternary alloys after plastic deformation and heat treatment have been established. It has been found that the heat treatment of both alloys after HPT at temperatures of 553–773 K results in the formation of a nanocrystalline or mixed nano-submicro-crystalline structure.     

Enhanced microhardness in nanocomposite Ti60Cu14Ni12Sn4Ta10 processed by high pressure torsion

Nanostructured Ti₆₀Cu₁₄Ni₁₂Sn₄Ta₁₀ alloys have been obtained by (i) arc-melting (AM) the pure elements and (ii) AM followed by severe plastic deformation induced by high pressure torsion (HPT). Scanning electron microscopy (SEM) reveals that the AM specimen consists of a dendrite–eutectic structure. After the HPT, the center of the disks exhibits a microstructure similar to the AM specimen but with strongly deformed dendrites and the lamellae become refined and intermixed as the distance from the disk center increases. At the edge of the HPT disks the dendritic/eutectic morphology is no longer observed by SEM. The Vickers microhardness is higher in the HPT disks as compared to the AM samples. This result is discussed in terms of the peculiar morphologies and nanostructures achieved after each processing route.     

Influence of niobium and yttrium on plastic deformation energy and plasticity of Ti-based amorphous alloys

Many amorphous alloys have been developed to date,but the low plasticity has limited their application.To achieve an amorphous alloy with high plasticity,a series of(Ti₄₀Zr₂₅Cu₉Ni₈ Be₁₈)_100-xTM_x(x=0,1,2,3,4 at.%,TM=Nb,Y)alloys were designed to study the influence of Nb and Y addition on the plasticity.The amorphous samples were prepared using the vacuum melting and copper mold casting process.The microstructures,glass forming ability and mechanical properties of the alloys were investigated by X-ray diffractometry(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HRTEM),depth-sensitive nanoindentation,and uniaxial compressive test.The plasticity of different bulk amorphous alloys was investigated by measuring the plastic deformation energy(PDE)during loading.The relationship between the PDE value and plasticity in bulk amorphous alloys was explored.Results show that Nb addition decreases the PDE value and promotes the generation of multiple shear bands,which significantly increases the fracture strength and plasticity,while the addition of Y element reduces the fracture strength and plastic strain of the alloy.     

Dependence of thermoelectric behaviour on severe plastic deformation parameters: A case study on p-type skutterudite DD0.60Fe3CoSb12

High-pressure torsion (HPT), a severe plastic deformation technique, can effectively improve the thermoelectric performance of skutterudites, resulting in ZT values higher than for ball-milled and hot-pressed (BMHP) samples. In this paper the influence of the HPT parameters, i.e. the number of revolutions (equivalent to the applied strain), the processing temperature and the hydrostatic pressure on the microstructural and thermoelectric properties of the skutterudite DD_0.60Fe₃CoSb₁₂ are evaluated and compared with the BMHP samples before HPT processing. Whilst the three parameters have specific effects on (i) the crystallite size, (ii) the density of lattice defects and (ii) the density of cracks, a suitable combination thereof allows for an increase of the figure of merit by at least 20%.     

冷轧时效对新型Ti-Nb-Zr合金组织和性能的影响

利用X射线衍射仪(XRD)、光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和拉伸测试等手段,研究形变热处理对新型β(Ti-25Nb-25Zr)钛合金组织演变和力学性能的影响。结果表明:由于合金具有较高的β稳定性,冷轧过程没有应力诱发α″相的形成,合金的变形机制以位错滑移为主。随着冷轧变形量的增加,加工硬化速率和弹性模量逐渐降低。经过相同的时效处理(300℃、2 h),固溶态和冷轧态的合金相组成分别为β+等温ω和β+α相。冷轧产生的位错缺陷和晶界有效抑制ω相,促进了α相的析出。冷轧时效相比固溶时效能更好地得到较高的强度和理想的弹性模量,满足医用材料的性能要求。     

High-pressure torsion, a new processing route for thermoelectrics of high ZTs by means of severe plastic deformation

High-pressure torsion (HPT) is a type of severe plastic deformation (SPD) that is highly suited to produce bulk ultrafine-grained and nanocrystalline materials, as it introduces many grain boundaries as well as dislocations and point defects. In this paper, HPT-mediated nanocrystallization was used to reduce the thermal conductivity and enhance the Seebeck coefficient of skutterudites. Both p- and n-type skutterudites have been processed by HPT with 4 and 5 GPa at temperatures up to 773 K, resulting in a strongly strengthened nanocrystalline structure, revealing oriented, lamellar-shaped crystallites with a size of ∼50 nm and an enhanced dislocation density. In comparison with ball-milled plus hot-pressed skutterudites, the HPT-processed samples show a reduction of the thermal conductivity up to 40%. This and the slightly higher Seebeck coefficient are the reasons why HPT proved to enhance the figure of merit (ZT) values up to a factor of 2, in spite of a markedly enhanced electrical resistivity.     

镍钛形状记忆合金在局部包套压缩下的塑性屈服

作为一种崭新的尝试,局部包套压缩被应用于实现镍钛形状记忆合金在室温下的大塑性变形。基于主应力法和塑性屈服准则,分析了镍钛形状记忆合金局部包套的压缩塑性力学。采用透射电镜、高分辨透射电镜和扫描电镜研究镍钛形状记忆合金在局部包套压缩下的显微组织演变和变形行为。静水压力随着包套外径的增加而增加,有效地抑制了显微裂纹的萌生和扩展,有助于提高镍钛形状记忆合金的塑性,避免了脆性断裂的发生。在0．15～0．50的真实应变范围内,镍钛形状记忆合金在三向压应力状态下的塑性变形满足密席斯塑性屈服准则。在更大的塑性应变下,由于非晶相的出现,镍钛合金不能满足密席斯塑性屈服准则。