异步叠轧中剪切力对超细孪晶铜制备的影响

采用异步叠轧法辅以热处理制备超细孪晶铜材,研究了异步叠轧对晶粒细化的影响.以及再结晶退火时织构转变的情况.结果表明:异步叠轧过程剪切应力的作用形成了搓轧区,它的形成使变形材料经过该区域发生压缩变形和剪切变形,以及累积叠轧的作用,使晶粒细化到约1μm;由于剪切织构积聚了较强的弹性应力,使得再结晶过程中原子定向生长,总的效果相当于剪切织构{001}<110>旋转54.7°变成了退火织构{111}<211>,也就是孪晶组织.     

大变形异步累积叠轧纯铜再结晶退火后的超细孪晶

对纯铜带材进行异步累积叠轧大塑性变形,并辅以再结晶退火处理,制备出了均匀的超细孪晶铜材。利用透射电镜对变形铜材再结晶退火中形成的超细孪晶进行了观察。结果表明,大变形异步累积叠轧铜材在190℃下退火,变形铜材内发生孪晶形核,退火达到30 min时,铜材内形成均匀的超细孪晶,大小为2～3μm;再结晶退火初期,电导率快速上升,随退火时间延长,电导率缓慢升高,最高达59 MS/m。     

异步累积叠轧纯铜再结晶温度、时间对孪晶的影响

采用异步叠轧法辅以热处理制备超细孪晶铜材,研究了不同再结晶退火温度和时间,对退火组织和其中退火孪晶的影响。结果表明:当退火温度在185℃时,随着退火时间的延长,发生再结晶的区域增多,退火孪晶也相应增多,但是再结晶不完全;当退火温度在190℃时,在20～25min退火时间内形成了均匀细小的退火孪晶,退火孪晶大小在2μm左右;当退火温度达到220℃时,退火孪晶的尺寸明显长大,且数量有所减少,达不到所需的超细孪晶铜的要求。     

异步叠轧法制备超细晶铜的组织及性能

室温下对纯铜进行异步叠轧,制备超细晶铜材,研究了异步叠轧过程中纯铜显微组织演变、界面复合以及力学性能的变化。结果表明:搓轧区的存在促进了界面的复合和晶粒的细化;经六道次异步叠轧后可以使纯铜的平均晶粒尺寸从30μm减小到1μm,抗拉强度为450.3 MPa,屈服强度为346.5 MPa,轧制面显微硬度为108.5 HV,横截面显微硬度为66.3 HV,纵截面显微硬度为77.4 HV,伸长率为3%。     

累积叠轧焊制备超细晶组织Mg-Al-Zn合金薄板

采用累积叠轧焊(ARB)工艺制备超细晶组织AZ31镁合金薄板.实验结果表明,进行3道次ARB变形后,AZ31板材晶粒显著细化,平均晶粒尺寸约1.3μm,呈等轴状,材料组织均匀,没有发现孪晶.采用EBSD技术观察组织演变和晶粒的取向差.ARB变形过程中的晶粒细化可归因于累积应变诱导的晶粒细化、累积应变强化回复和再结晶以及ARB变形过程中复杂的界面和剪切应变分布.     

累积叠轧TC4合金制备超细晶组织的研究

通过累积叠轧技术进行TC4合金超细晶组织的制备,考察了TC4合金的热变形特点以及叠轧工艺窗口,研究了叠轧工艺参数和热处理制度对叠轧板材界面结合和微观组织的影响。结果表明：TC4合金的应力-应变曲线表现为动态回复特征,热模拟条件下在加热温度(≥700℃)和变形速率(≤0.1s-1)下能够实现强烈塑性变形。最终TC4合金进行叠轧界面的防氧化处理后,并在加热温度为720℃、轧制速度小于0.5m/s时,获得良好的界面结合和板材质量。累积叠轧变形过程是α/β协同变形和剪切变形综合作用的结果,组织中存在拉长的条带组织以及大量的剪切带。随着叠轧层数的增加,条带组织的间距逐渐变小同时剪切带组织逐渐增加,在叠轧16层(变形量为92.3%)后条带间距为200nm~500nm之间。热处理过程中随着加热温度的增加,溶质扩散和再结晶过程促进了界面结合并最终与基体保持一致,同时叠轧16层的TC4板材在加热温度700℃、保温时间60min的热处理过程中能够实现完全再结晶,获得晶粒尺寸为300nm~600nm的超细晶组织。     

累积叠轧焊法制备超细晶纯铝的研究

采用累积叠轧焊方法在室温下对1060纯铝进行剧烈塑性变形，并分析1060纯铝变形前后内部微观组织结构的演变和力学性能的变化。实验结果表明，随着累积叠轧道次的增加，层界面复合越来越紧密，5道次后出现母材基体的相互渗透；材料的抗拉强度和硬度得到大幅度提高，伸长率在1道次时急剧下降，然后基本保持不变；晶粒尺寸急剧细化，等效真应变为6．4的条件下得到了平均晶粒尺寸为400nm的超细晶组织。     

预退火时间对累积叠轧超细晶铜室温拉伸断裂行为的影响

对采用严重塑性变形方法制备的超细晶金属进行退火处理,是提高该类材料综合性能的常见方法。为保证晶粒不发生明显长大,对累积叠轧(ARB)方法制备的超细晶纯铜在100℃(低于再结晶温度)时进行退火处理,研究保温时间对ARB超细晶铜室温拉伸断裂行为的影响以及样品的微观结构、力学行为、断口形貌,并对其力学性能和断裂机制进行分析。结果表明:当退火时间为30 min时,ARB超细晶铜的屈服强度和抗拉强度都达到退火态的极大值。断口的大量韧窝表明:退火时间30 min时的材料具有一定的塑性变形能力,断裂机制以韧性断裂为主,因此,退火时间为30 min时,ARB超细晶铜的强度与塑性达到最佳匹配。     

大变形异步叠轧法制备超细晶铜材的再结晶研究

采用大变形异步叠轧法制备了超细晶铜材,研究了再结晶过程中铜材的组织演变过程、织构变化过程以及晶界特征分布情况.结果表明:经过220℃×35min和220℃×60min退火处理,分别获得0.1-0.2μm和0.5～1.0μm范围的超细晶铜材,主要晶界类型均属于低能晶界;六道次叠轧后的无氧纯铜板材在退火初始阶段仍为轧制织构,但由于剪切力的作用织构强点位置发生偏移、强度有所降低;随着退火时间的延长,织构组分发生变化,C取向发生孪晶转变,流向B/G取向.     

累积叠轧焊AZ31镁合金微观组织和织构演变的EBSD研究

对AZ31镁合金热轧板在350℃进行了累积叠轧焊(ARB)变形,采用EBSD技术研究了AZ31镁合金的微观组织和织构演变.结果表明,ARB可以显著细化AZ31镁合金的晶粒组织,经过3道次变形后平均晶粒尺寸为2.18μm,后续的ARB变形使AZ31镁合金的微观组织更均匀,但晶粒不会再显著细化,说明存在临界ARB变形道次,使晶粒细化和晶粒长大之间达到动态平衡.AZ31镁合金在ARB变形过程中的晶粒细化机制为连续动态再结晶,尤其还观察到了旋转动态再结晶.动态再结晶的形变储存能来源于多道次累积的剧烈应变和沿厚度方向分布复杂的剪切变形.ARB变形过程中旋转动态再结晶和剪切变形使新晶粒c轴发生旋转,导致基面织构弱化.     

Recrystallized microstructural evolution of UFG copper prepared by asymmetrical accumulative rolling-bonding process

Copper sheet with grain size of 30-60μm was processed by plastic deformation of asymmetrical accumulative rolling-bonding(AARB)with the strain of 3.2.The effects of annealing temperature and time on microstructural evolution were studied by means of electron backscattered diffraction(EBSD).EBSD grain mapping,recrystallization pole figure and grain boundary misorientation angle distribution graph were constructed,and the characteristics were assessed by microstructure,grain size,grain boundary misorientation and texture.The results show that ultra fine grains(UFG)are obtained after annealing at 250℃ for 30?40 min.When the annealing is controlled at 250℃for 40 min,the recrystallization is finished,a large number of small grains appear and most grain boundaries consist of low-angle boundaries.The character of texture is rolling texture after the recrystallization treatment,but the strength of the texture is faint.While second recrystallization happens,{110}1ī2+{112}11ī texture component disappears and turns into{122}212cube twin texture component.     

极薄带多层复合轧制中的界面现象

复合材料是国家重点支持的新材料高新技术领域之一,而轧制法是最为广泛应用的层状复合材料的生产方式。利用异步轧制的剧烈塑性变形能力,在室温下进行了多道次多层复合叠轧试验,在没有中间退火和热处理的情况下,轧后的试样表现出了与普通轧制复合不同的特点。基于试验结果,描述了多层复合极薄金属带材的界面形貌演化、变形诱导扩散及金属间化合物生成等现象。     

异步叠轧辅助退火制备超细晶铜材的形成机制及组织控制(英文)

对原始晶粒大小为60～100μm的铜材进行六道次大变形异步叠轧并辅助退火处理,获得晶粒大小为200nm的超细晶铜材,研究超细晶铜材的微观组织结构和性能。结果表明:六道次大变形异步叠轧后的超细晶铜材组织中存在大量的亚结构,也存在特定织构C组分,其强度和显微硬度高但伸长率和电导性下降。经220°C、35min退火处理后,亚结构消失,晶界由大角度晶界组成,织构由多种织构组分组成,也出现部分孪晶。与六道次大变形异步叠轧的超细晶铜材相比,经220°C、35min退火处理的超细晶铜材的抗拉强度和屈服强度略有下降,但伸长率和导电性明显提高。     

Texture,microstructure and mechanical properties of equiaxed ultrafine-grained Zr fabricated by accumulative roll bonding

The texture, microstructure and mechanical behavior of bulk ultrafine-grained (ufg) Zr fabricated by accumulative roll bonding (ARB) is investigated by electron backscatter diffraction, transmission electron microscopy and mechanical testing. A reasonably homogeneous and equiaxed ufg structure, with a large fraction of high angle boundaries (HABs, ∼70%), can be obtained in Zr after only two ARB cycles. The average grain size, counting only HABs (θ > 15°), is 400 nm. (Sub)grain size is equal to 320 nm. The yield stress and UTS values are nearly double those from conventionally processed Zr with only a slight loss of ductility. Optimum processing conditions include large thickness reductions per pass (ε ∼ 75%), which enhance grain refinement, and a rolling temperature (T ∼ 0.3T_m) at which a sufficient number of slip modes are activated, with an absence of significant grain growth. Grain refinement takes place by geometrical thinning and grain subdivision by the formation of geometrically necessary boundaries. The formation of equiaxed grains by geometric dynamic recrystallization is facilitated by enhanced diffusion due to adiabatic heating.     

LZ91合金在累积叠轧焊合过程中的界面焊合研究

采用金相显微镜和扫描电境观察了LZ91镁锂合金在累积叠轧焊(ARB)过程中的界面焊合现象。结果表明：道次压下量为50%的ARB工艺可以使LZ91板材获得良好的界面焊合,板材的抗拉强度和维氏硬度得到明显的改善。后续的ARB变形可以有效改善界面焊合质量,ARB轧制后退火可以使板材界面焊合强度增加。LZ91合金累积叠轧焊变形中的界面焊合机制是：合金表面硬化层先发生破裂,新鲜金属暴露,然后在轧制压力的作用下一起流动、相互接触,最终形成冶金结合。     

Bulk texture evolution of Cu-Nb nanolamellar composites during accumulative roll bonding

A combination of accumulative roll bonding (ARB) and rolling is used to fabricate nanolamellar Cu-Nb multilayers with individual layer thicknesses (h) of 600 μm ? h ? 10 nm with a total strain imposed between 0.5 and 11.6. Neutron diffraction, scanning electron microscopy and transmission electron microscopy are used to characterize the microstructures and measure orientation distribution functions of both phases as a function of layer thickness. Fiber plots are calculated from the orientation distribution functions in order to understand the texture evolution in the Cu and Nb layers with increasing strain. Results are compared with rolling studies of single phase Cu, single phase Nb, and cast Cu-20 wt.% Nb composite. Results indicate that textures develop in the Cu and Nb layers during ARB that are distinct from classical rolling textures frequently observed both in their single-phase counterparts and in rolled composites. The atypical texture that develops shows a preferential strengthening of specific β fiber components at the expense of others in Cu and a strengthening of the α fiber at the expense of the γ fiber in Nb. No dynamic recrystallization is observed in Cu, even at strains above 99.99%, further delineating the behavior from single phase and composite behavior previously observed. Viscoplastic self-consistent (VPSC) polycrystal simulations were carried out to provide an understanding of the texture evolution in accumulative roll bonding. Enforcing planar slip in Cu leads to texture evolution for VPSC consistent with observations. A reasonable fit for Nb could be produced via the selection of specific {1 1 0} and {1 1 2} slip systems.     

Texture evolution of high purity tantalum under different rolling paths

Deformation behavior and texture evolution of the material can be significantly affected by strain path change. For this reason, two rolling methods, unidirectional rolling (UR) and clock rolling (CR), were employed to manufacture tantalum plates. Texture evolution during unidirectional rolling and clock rolling was studied respectively by orientation distribution function (ODF). Related annealed microstructures were investigated by orientation image map (OIM). Usually, unidirectional rolling led to a strengthening of the main texture component with increasing strain, but for tantalum dominant texture component {0 0 1} θ-fiber was stable after 70% deformation, while minor texture component {1 1 1} γ-fiber was enhanced with increasing strain. In clock rolling, both of the two fibers were not stable any more for their intensity varied with rolling pass. After the final deformation, a similar texture was produced by the two rolling methods. However, recrystallization texture revealed a big difference. Such different texture development was contributed to microstructural change resulted from rolling path change.