Effect of extrusion ratios on hardness,microstructure, and crystal texture anisotropy in pure niobium tubes subjected to hydrostatic extrusion

Nb tubes were fabricated through hydrostatic extrusion at extrusion ratios of 3.1 and 6.1 at ambient temperature, and then their microstructure, texture, and Vickers hardness were investigated based on electron back-scattered diffraction (EBSD) data. The fraction of low-angle boundaries (LABs) largely decreased with a sharp decrease in mean grain sizes after hydrostatic extrusion and was not proportional to extrusion ratios, assuming that mixed-asymmetrical junctions forming LABs dissociate at high extrusion ratios from the external stress (>981 MPa) with thermal activation by the generated heat. The correlation between grain size and Vickers hardness followed the Hall?Petch relationship despite the texture gradient of the 〈111〉 cyclic fiber textural microstructure at low extrusion ratios and the 〈100〉 true fiber textural microstructure at high extrusion ratios. The increase in hydrostatic pressure on the Nb tubes contributed to texture evolution in terms of extrusion ratios due to the difference between {110}〈111〉 and {112}〈111〉 components based on EBSD data.     

The effects of die angle on texture and annealing response of ETP copper wire

As-annealed, 2.47 mm ETP copper wire was drawn in five passes to 1.45 mm using carbide dies with nominal included angles of 8, 16 and 24 degrees. A single die, low speed drawing block was used, and the lubricant was fat-based and water soluble. Annealing was undertaken in a box furnace, for six minutes at temperatures ranging from 185 to 230°C. Annealing response and texture evolution were assessed by way of tensile tests, microhardness measurements and x-ray diffraction. Redundant strain accumulation was projected by way of deformation zone geometry, or Δ, analysis.

The as-drawn wire reveals volumes of (111) and (200) fiber texture, as well as a significant volume of essentially randomly oriented grain structure. The ratio of (111) to (200) texture decreases as die angle increases. Increases in die angle and related redundant strain promote the development of random orientation and reduce the sharpness of the (111) and (200) texture components. Increases in die angle and related redundant strain also lower the annealing temperature range and cause non-uniform recrystallization, presumably due to redundant strain and texture gradients. The as-annealed 1.45 mm wire displays a large volume of randomly oriented grain structure for all three die angles. In the case of the as-annealed wire, increases in die angle are associable with a decrease in the volume percent of (111) fiber texture, a decrease in the sharpness of the (200) fiber texture, and an increase in randomly oriented grain structure.     

GRAIN BOUNDARY CHARACTER DISTRIBUTION, TEXTURE AND SUPERPLASTIC DEFORMATION BEHAVIOR OF AN AI-Li ALLOY

The grain boundary character distribution and thetexture of 2091 Al-Li alloy recrystallized at different temperatures were measured by TEM and X-ray techniques respectively. The occurrence frequency of low-energy boundaries decreases with increasing recrystallization temperature, while the frequency of highenergy boundaries increases. The strongest component of recrystallization texture in the test temperature range is {011} <111>. The relative intensity of the texture tends to decrease with increasing recrystallization temperature. The material which contains a high frequency of low-energy boundaries exhibits lower deforming stress and high elongation.     

Effect of annealing temperature on microstructure,texture and properties of molybdenum foil

The microstructure, texture and mechanical properties of 0.06 mm thick molybdenum foil after annealing at different temperatures were studied by micrograph and EBSD analysis. The results show that the grains of the cold-rolled molybdenum foil along the rolling direction are fibrous. As the annealing temperature increasing from 750 °C to 1000 °C, the average layer thickness of these fibrous grains gradually grows. And the relative frequency of low-angle grain boundaries increases, while the relative frequency of high-angle grain boundaries decreases. Also, the main texture of the unidirectional-rolled and annealed molybdenum foils is {112}〈110〉 which content continuously increase to 62% till 1000 °C. Therefore, the strength of RD, TD and 45°RD direction decreases but the elongation increases. During these processes, the mechanism includes classical nucleation and coarsening of subgrain and with annealing temperature rising, the latter dominates the recrystallization process. After annealing at 1050 °C, the molybdenum foil undergoes secondary recrystallization. The grain boundary distribution becomes diffused and the main texture changes into {001}〈110〉, which the fraction is as high as 96%, thus, the mechanical properties of RD, TD and 45°RD exhibit sharp decrease simultaneously.     

<110>取向银单晶宏/微观裂化及界面失配角分布

以低层错能110取向单晶银为研究对象,采用EBSD和TEM等技术,系统分析了冷拔变形过程中的宏观裂化、微观裂化和界面失配角分布的变化规律与内在机制。研究结果表明,随应变量的增加,冷拔银单晶的宏观裂化不断加剧,变形带数量增加,宽度和间距减小。当应变量大于0.94时,形成了与冷拔方向平行的纤维状组织。与层错能相近的合金相比,纯金属单晶银的交滑移和攀移的被抑制程度降低,除了变形孪晶,在低层错能的单晶银中还出现大量随机捕捉位错界面和几何必须位错界面。界面失配角分析结果表明,低应变下,变形以位错滑移为主;中等应变下,滑移和孪生相互竞争;高应变下,孪生为主要变形机制。     

Analysis of deformation textures of asymmetrically rolled aluminum sheets

Asymmetric rolling, in which the circumferential velocities of working rolls are different, imposes shear deformation and in turn shear deformation textures to sheets through the thickness. A component of ND//〈111〉 in the shear deformation textures can improve the plastic strain ratios of aluminum sheets. In order to understand the evolution of ND//〈111〉, the strain histories and distributions in the sheets and the texture evolution during the asymmetric rolling have been measured and calculated. The shear deformation texture can vary with the ratio of shear to normal strain increments. As the ratio increases from zero to infinity, the texture moves from the plane strain compression texture (β fiber) to the ideal shear deformation texture consisting of {001}〈110〉, {111}〈110〉, and {111}〈112〉. The ratio increases with rolling reduction per pass in asymmetric rolling. However, it is practically difficult to develop a rolling reduction per pass high enough to obtain the ideal shear deformation texture. Imposing the positive and negative shear deformations on the sheet by reversal of the shearing direction can give rise to the ideal shear deformation texture.     

Crystallographic Texture Difference Between Center and Sub-Surface of Thin Cold-Drawn Pearlitic Steel Wires

The texture difference between the center and sub-surface of pearlitic steel wires, which were manufactured by continuous cold drawing, was investigated by orientation distribution function based on electron back-scattered diffraction at different drawing passes. A perfect 〈110〉 fiber texture parallel to drawing direction develops gradually with drawing strain increasing at the wire center, while at the sub-surface, a quasi 〈110〉 fiber texture with the 〈111〉 orientation nearly parallel to the circumferential direction is found. This texture at the sub-surface is softer than the perfect 〈110〉 fiber texture in tension. The reasons for this texture difference and influences on the wire’s mechanical properties are discussed.     

Microstructure and texture characteristics of ZK60 Mg alloy processed by cyclic extrusion and compression

The microstructure and crystallographic texture characteristics of an extruded ZK60 Mg alloy subjected to cyclic extrusion and compression (CEC) up to 8 passes at 503 K were investigated. The local crystallographic texture, grain size and distribution, and grain boundary character distributions were analyzed using high-resolution electron backscatter diffraction (EBSD). The results indicate that the microstructure is refined significantly by the CEC processing and the distributions of grain size tend to be more uniform with increasing CEC pass number. The fraction of low angle grain boundaries (LAGBs) decreases after CEC deformation, and a high fraction of high angle grain boundaries (HAGBs) is revealed after 8 passes of CEC. Moreover, the initial fiber texture becomes random during CEC processing and develops a new texture.     

Effects of strain rate on mechanical properties,microstructure and texture of Al—Mg—Si—Cu alloy under tensile loading

The effects of strain rate on the mechanical properties, microstructure and texture of Al—Mg—Si—Cu alloy were investigated through tensile test, microstructure and texture characterization. The results show that strain rate has some influences on the mechanical properties and microstructure, but a slight influence on the texture. Overall, yield strength, ultimate tensile strength and elongation increase first, then remain unchanged, and finally increase with increasing strain rate. Independent of strain rate, microstructure in the vicinities of the fracture regions of all the specimens is composed of the slightly elongated grains. However, some differences in misorientation angle distributions can be observed. As strain rate increases, the low angle grain boundaries (LAGBs) increase first, and then decrease. Textures in the vicinities of the fracture regions are almost identical with increasing strain rate.     

MICROSTRUCTURE AND TEXTURE EVOLUTIONS OF AA1050 ALUMINUM ALLOY COLD ROLLED TO HIGH STRAINS

采用ECC和EBSD技术研究了AA1050铝合金冷轧到大应变量下微观组织和织构的演变规律. 结果表明, AA1050合金冷轧到 大形变量时, 微观组织由低应变下的胞块组织结构转变成典型的层片状界面 (LBs)结构, 其内部的LBs基本与轧向 (RD) 平行; 主要存 在两种转变机制, 即由于轧制变形 (机制I) 和借助于S--bands结构的剪切作用 (机制II),从而导致GNBs逐渐旋转到与RD平行, 且以 机制I为主. 变形过程中, 由于晶粒的分裂形成大量的大角度界面, 随应变的增加, 大角度界面的间距逐渐减小、 数目逐渐增多; 当冷轧到90%应变量时, 除原始晶界外, 约为47%的大角度界面起源于变形诱导的界面. 冷轧变形主要形成典型的Brass+S+Copper轧制织构, 且强度随应变的增加而逐渐增加.     

PHOSPHORUS SEGREGATION AND ANNEALING TEXTURE IN A LOW CARBON STEEL SHEETS

The present work is to study the effect of phosphorus on the annealing texture of a low carbonsteel at different cold rolling and annealing condition by means of pole-figure,inverse-polefigure and orientation distribution function(ODF)method.The microstructure and distribu-tion of phosphorus in steel sheet are studied by means of metallography,scanning electron mi-croscope(SEM)and electron probe microanalysis(EPMA).The results show that phos-phorus promotes the formation of the fiber texture of〈011〉parallel to the rolling direc-tion and〈111〉normal to the sheet surface.The texture was found to be affected mainlyby preannealing temperatures,promoted at 390 or 590℃,and retarded at 490℃.At thepreannealing temperature promoting the formation of texture,phosphorus segregation to theinterior of grains was observed.It seems that the formation of the fiber texture may be associ-ated with the segregation of phosphorus.     

退火温度对冷拔钢丝织构与性能的影响

采用精确的线材织构测定方法分析了冷拔钢丝在450、550和650 ℃退火过程中织构变化,并采用光学显微镜和显微硬度计研究了此过程中钢丝的显微组织和显微硬度。 结果表明：冷拔钢丝在不同温度下退火过程中,随着退火温度的升高,显微组织由纤维状转变为等轴晶,硬度显著下降;不同温度退火后的织构与拉拔态的织构类型相同,以<110>丝织构为主,且沿着线材径向呈现一定梯度分布。 但是随着退火温度的升高,<110>丝织构强度下降。另外,退火过程中,冷拔钢丝的硬度与<110>丝织构强度具有相似的变化趋势。     

Evolution of Annealing Twins and Recrystallization Texture in Thin-Walled Copper Tube During Heat Treatment

Thin-walled copper tubes are usually produced by multi-pass float-plug drawing deformation. In general, the annealing treatment subsequently is necessary to release the stored energy and adjusts the microstructure. In this study, an investigation on the evolution of annealing twins as well as textures in the thin-walled (Ф6 mm×0.3 mm) copper tube underwent holding time-free heat treatment was reported. Electron backscattered diffraction analysis reveals that a large number of Σ3 boundaries (60° 〈111〉 twin relationship) are produced at the early stage of heat treatment, which is due to the lower boundary energy. With the recrystallization proceeding, the migration rate of grain boundaries decreases on account of the grain growth; meanwhile, the unique Σ9 boundaries (38.9° 〈110〉 relationship) are formed due to the interaction of the Σ3 boundaries. As a result, the number fractions of Σ3 boundaries and high-angle grain boundaries decrease rapidly. During the grain growth stage, a strong recrystallization texture was formed due to the fact that the grains of Goss orientation have a growth advantage over the others. As a result, the initial copper texture was transferred into the Goss texture in domination.     

Hot working of AA1050—relating the microstructural and textural developments

An aluminum alloy AA1050 was deformed in plain strain at different hot working conditions. An increase in temperature or a decrease in strain rate reduced the relative drop in cube {001}〈100〉 and the relative increase in rolling texture components of Cu {112}〈111〉 and S {231}〈346〉, especially apparent at the higher strain. Along with such textural changes, significant differences in hot worked microstructures were observed. The two distinct microstructural features, as observed by polarized light optical microscopy, were grain boundary serrations (GBS) and in-grain inclined lines (IIL), typically observed at an approximate angle of 35° with rolling direction (RD). At higher temperatures and lower strain rates, and correspondingly lower Zener–Holloman factors (Z≈10⁹−10¹⁰ s⁻¹), coarse but nearly equiaxed grain interior substructures and GBS were observed. Interestingly, orientation imaging microscopy (OIM) clearly showed insignificant/non-noticeable differences between the substructures of different orientation components. An increase in Z aligned the grain-interior low angle boundaries at an angle of approximately 35° with RD and at higher Z (Z≈10¹²−10¹³ s⁻¹) the main microstructural feature was the IILs. Development of in-grain long range misorientation (LRM) was estimated to be the mechanism behind the optical visibility of the IILs. The appearance of IILs had two apparent effects—first the substructures of different orientation components were different, and secondly the stability of cube grains dropped noticeably. Generalizing the IILs or 35° inclined cell walls as plastic instabilities or strain localizations, the observed differences in their relative appearance at different deformation conditions and/or texture components could be explained. When formation of such strain localizations are considered as “necessary” for the reorientation of grain segment(s), the cube stability at low Z deformation could also be understood.     

AZ21镁合金降温多向压缩过程中的组织和微观织构演化

对AZ21镁合金进行了降温多向压缩变形,利用OM及SEM/EBSD技术观察和分析了其显微组织和微观织构的演化.结果表明,随着变形道次的增加,晶粒尺寸迅速减小,经4道次的变形晶粒可细化至0.8μm.高温变形时生成的相互交叉的扭折带可将原始晶粒有效地分割而细化.673 K第1道次变形至ε=1.2时,几乎所有的晶粒都发生了90°的转动,基面由变形前平行于压缩方向转至与压缩方向垂直,基面织构强度先减小后增大;第2道次变形时,织构变化与第1道次基本一样,表现为与变形温度无关,仅取决于变形程度.第2道次变形后织构强度低于第1道次,变形道次的增加可以弱化织构.     

Deformation and Recrystallization of Silicon Iron

A study of the orientations and microstructure of 3 pct Si-Fe alloys after deformation and recrystallization has been made. The components found after deformation agreed with recently published work on single crystals, being primarily (001) [110], (111) [110], and (111) [112]. A pronounced effect of temperature of recrystallization was found on microstructure and orientation. Low temperature recrystallization was interpreted in terms of low angle boundaries which resulted in the retention of a large amount of the deformation texture. High temperature recrystallization was interpreted in terms of high angle boundaries which gave rise to new components. No simple angular relation between the deformation and high temperature recrystallization textures could be detected.     

Orientation relationship between primary and secondary recrystallized texture in electrical steel

Cube ({100}〈001〉) texture is developed through secondary recrystallization when rolling direction is changed towards the transverse direction at the final stage of cold-rolling of grain-oriented electrical steel. The development of the cube texture is discussed stressing the role of high-energy boundary having the misorientation angle between 20 and 45°, which was used for the explanation of the development of Goss ({110}〈001〉) texture in our previous works. The high-energy boundary has more structural defects, which are linked to high mobility and high grain boundary diffusion rate. Quicker coarsening of precipitates enables high-energy boundaries to move earlier than other boundaries during final annealing. A texture component that has the highest frequency of high-energy boundary can be a main component through selective growth during secondary recrystallization. Textures different from Goss can also be predicted by analyzing the frequency of high-energy boundaries in the primary recrystallized texture. The growth model based on Coincident Site Lattice (CSL) boundaries and another model based on Orientation Pinning (OP) are tested, but these models cannot provide a consistent explanation in the present experiment.     

高锰TWIP钢的冷轧变形行为

研究了低层错能奥氏体TWIP钢的冷轧组织和织构的演变。随着应变的增加,孪晶变形机制被激活。TEM、XRD等观察结果显示:随着应变量的增加,孪晶增加。在不同应变水平上,G{011}<100>织构都占主要位置。变形初始时,B{011}<211>织构强度较低,随着应变增加其强度显著增加。而E{111}<011>、Y{111}<112>、RG{011}<011>、Cu{112}<111>、CuT{552}<115>等织构在不同应变水平呈不同变化趋势。与其他织构相比,Cube{001}<100>织构强度相当低。     

Structure and Thermal Stability of High-Strength Cu–18Nb Composite Depending on the Degree of Deformation

The microstructure and thermal stability of multifiber in situ Cu-18Nb composites with a true strain (e) of 10.2 and 12.5 have been studied by the methods of scanning and transmission electron microscopy and X-ray diffraction analysis. It has been established that niobium dendrites in the copper matrix acquire the shape of ribbons with thicknesses of less than 100 nm under strong plastic deformation. As the strain grows, the thickness of niobium ribbons decreases, and the degree of axial texture 〈110〉Nb║〈111〉Cu║DA (drawing axes) and the macrostresses in the crystal lattice of niobium increase. Interplanar distances between adjacent {110}Nb planes are stretched in the longitudinal section of the composites and reduced in their transversal section under the action of macrostresses. It has been shown that, as a result of the annealing of these composites, niobium fibers sustain coagulation, which begins at 300°C, actively develops with increasing temperature, and leads to the appreciable softening of a composite at 700°C. The softening of a composite after the annealing is accompanied by the relaxation of macrostresses in niobium and the recovery of its unit cell parameters to standard values.     

冷轧压下率对连续退火Ti-IF钢组织和深冲性能的影响

以工业生产的Ti-IF钢热轧板为研究材料,结合连续热镀锌线的工艺特点,采用实验室冷轧、盐浴退火方法和金相、X射线织构测试和力学性能检测等分析手段,研究了冷轧压下率对组织、织构和深冲性能的影响规律。试验结果表明,随着冷轧压下率从60%提高到90%,冷轧态α取向线上的取向密度不断增强,主要形成了{223}〈110〉和{114}〈110〉织构,γ取向线上的{111}〈011〉和{111}〈112〉织构亦有所增强;退火后铁素体晶粒尺寸从9.0级细化到10.5级,导致强度(特别是屈服强度)有所增加,η_(90°)值有所降低。试验钢退火后仍具有较强的{223}〈110〉和{114}〈110〉织构,此外,随着冷轧压下率从60%提高到80%,{111}〈110〉和{111}〈112〉织构有增强的趋势,且{111}〈110〉织构比{111}〈112〉织构强,r_(90°)值有所提高;当冷轧压下率进一步提高到90%时,{111}〈112〉织构明显增强,但{111}〈110〉织构变化较小,导致{111}〈112〉织构比{111}〈110〉织构强,使r_(90°)值反而有所降低,这与γ织构分布变化导致制耳分布曲线由典型的4制耳特征转变为6制耳特征有关。