等通道热挤压变形对奥氏体不锈钢组织与性能的影响

在500℃～1000℃温度区间,对00Cr19Ni10奥氏体不锈钢进行了ECAP热挤压变形,利用金相显微镜与透射电镜对变形后的组织进行了微观组织观察。发现ECAP变形的组织演变过程与孪晶带和剪切变形带的形成及演变有关,同时发现随着变形温度的升高,组织逐渐从以孪生变形为主向以滑移带变形为主转变。对变形后金属的力学性能进行了测定。结果表明,等通道热挤压变形能显著提高材料的综合力学性能。     

等通道挤压对纯铜组织与性能的影响

等通道挤压作为强烈塑性变形方法的一种,可使材料的晶粒尺寸细化到纳米级.对纯铜试样进行了不同道次的等通道挤压变形,并对其组织和硬度进行了测试.结果表明,纯铜在进行等通道挤压变形时,先形成条带状亚结构,随着挤压道次增加,这些亚结构逐渐细化,亚界面逐渐转化成小角度晶界,进而转化为大角度晶界.经过等通道挤压变形8道次后,纯铜可细化至40～120 nm大小的纳米晶结构.经等通道挤压后纯铜的硬度显著上升,随着等通道挤压道次的增加,硬度增长趋于平缓,6道次后逐渐趋于饱和.     

等通道转角挤压工艺制备块体超细晶纯铜的研究

利用等通道转角挤压(EqualChannelAngularPressing,简称ECAP)工艺制备超细晶块体纯铜,并研究了其微观组织和硬度的变化.结果表明:纯铜塑性优良,在室温下能够顺利进行ECAP挤压,累积翅性变形量大于100%:经过两道次C形路线挤压可将纯铜晶粒细化至10μm以下,达到超细晶,同时硬度提高4倍以上:ECAP工艺制备的超细晶纯铜可用于制作较高强度的连接受力部件.     

等通道转角挤压制备超细晶GCr15钢研究

研究了GCr15钢等通道转角挤压(ECAE)的原理与技术实施手段。通过设计ECAE模具的几何结构,研究了剪切应变累积效应的计算方法。通过对GCr15钢单道次ECAE加工后光学微观组织的观察,讨论了模具几何结构条件(转角与背转角大小)对GCr15钢微观组织变化的影响。结果表明:GCr15钢的ECAE变形组织形态较好地符合理论预测结果;多道次ECAE加工显著改善了GCr15钢的微观组织;通过ECAE工艺,也能够制备出大尺寸致密的细晶材料。     

圆形挤压件等通道多弯角挤压变形机理研究

等通道弯角挤压工艺是制备块体超细晶粒材料的重要方法之一.由于等通道弯角单道次挤压获得的挤压件变形分布不均匀,因此,在等通道弯角挤压细化晶粒工艺中必须寻求较好的工艺路线,以避免挤压件变形的不均匀性.通过设计复杂模具型腔模拟了多弯角挤压变形过程,获得了挤压工艺载荷-行程曲线,得出了等通道弯角挤压在不同工艺路线下对应挤压件的变形分布均匀程度,为实验研究圆形挤压件等通道弯角挤压工艺提供可靠的工艺参数和较好的工艺路线.     

纯铜纳米晶切屑的等通道转角挤压块体成形工艺北大核心CSCD

通过有限元和试验相结合的方法,探究等通道转角挤压试验中挤压道次对由挤压纳米晶纯铜切屑制备的纯铜棒料所受的等效应变、挤压载荷和平均等效应力的影响规律,研究在热压协同作用下挤压道次对纳米晶细化和纳米成形块体致密性的影响。结果表明:随着挤压道次的增加,试样的平均等效应变和等效应力逐渐增大,变形区的等效应变分布的均匀性降低,试样的硬度先增大后降低;随着挤压道次的增加,在低道次(<4道次)下挤压后试样的固化成形效果越好,在高道次(>4道次)下由于挤压试样受热和高压的作用,晶粒间难以融合固结,且材料出现的孔隙和裂痕增多,试样的变形抗力下降。     

等通道转角挤压制备超细晶材料的最新研究进展

等通道转角挤压(Equal channel angular pressing,ECAP)方法是制备性能优异超细晶材料最常见的大塑性变形方法之一。模角、挤压路径、挤压道次、挤压温度和挤压速度等因素都会影响等通道转角挤压制备超细晶材料的性能;等通道转角挤压的模具也在不断地优化,如背压-等通道转角挤压(Back pressure ECAP,BP-ECAP)模具、可加热的模具以及在等通道转角挤压基础上形成的板材连续剪切技术等,这些新的模具可以改变ECAP变形过程中的组织均匀性。本文综述了等通道转角挤压制备超细晶材料的最新研究进展,并指出了几个需要深入研究的问题及方向。     

基于等通道角挤压工艺制备超细晶中碳钢

将马氏体相变与强塑性变形工艺相耦合,开发了在马氏体形态下通过等通道角挤压强塑性变形工艺快速制备亚微米级中碳钢.研究表明:马氏体钢快速加热到923K并保温适当时间后进行等通道角挤压,在位错分割、动态再结晶、应变诱导相变的共同作用下,可使过饱和铁素体组织快速细化到0.5μm以内,同时应变诱导使过饱和的碳以碳化物的形式在晶内或晶界以质点的形态弥散析出.通过控制回火温度及时间,可得到最佳铁素体晶粒尺寸以及碳化物分布.试验表明,采用这种工艺制备出的中碳钢超细晶材料具有很高的热稳定性.     

等通道转角挤压制备超细晶镁合金腐蚀行为研究进展

镁合金较差的耐蚀性制约着其应用进程,等通道转角挤压(ECAP)可实现镁合金的组织超细化,有望在提高镁合金力学性能的同时改善其耐蚀性。综述了当前ECAP制备超细晶镁合金腐蚀行为的研究进展,通过对纯镁、Mg-Al合金、Mg-RE合金等典型镁材腐蚀行为与机理的分析,初步探索了借助ECAP同时实现镁合金强韧化和耐蚀化的可能途径。     

AZ31镁合金等横截面通道角温挤压变形机理分析与实验研究

采用有限元模拟和实验研究相结合的方法对AZ31镁合金等横截面通道角温挤压变形进行了研究,确定了优化的模具几何形状,选择了合理的工艺参数.结果表明,在挤压过程中,适当减少摩擦,选择挤压温度为250℃左右时,可以降低挤压载荷,使挤压件顺利挤出,同时提高模具使用寿命.给出了凸模和预应力组合凹模等关键零件的设计方法,实现了多道...     

Corrosion behaviour of nanocrystalline 304 stainless steel prepared by equal channel angular pressing

Effect of microstructure change on the corrosion behaviour of equal channel angular pressed (ECAPed) 304 stainless steel (SS) was investigated. Nanostructure (80–120 nm) was obtained after 4 and 8 passes ECAP and exhibited a higher corrosion resistance than as-received SS. However, thickness and composition of the passive film formed in air at room temperature on both as-received and 8-pass samples show little difference, indicating that Cr diffusion is not enhanced by the formation of nanostructure. The improved corrosion resistance of ECAPed SS is not caused by thickness or composition change, but by compactness and stability improving of the passive film.     

Deformation twins in pure titanium processed by equal channel angular pressing

The structure of $\text{{1}\text{0}\text{1}\text{̄}\text{1}}$ deformation twins in commercially pure titanium processed by equal channel angular pressing was examined by high resolution electron microscopy in an attempt to explain the accommodation of shear strain imposed by the pressing. The results indicate that various twinning dislocations were activated to produce twins that accommodated the imposed shear strain.     

Refinement and consolidation of pure Al particles by equal channel angular pressing and torsion

Consolidation of pure Al powder was conducted at 200 °C by equal channel angular pressing and torsion (ECAPT) method. The grain refinement and consolidation behavior were deeply investigated by scan electronic microscopy (SEM) and transmission electronic microscopy (TEM). The density, hardness and room temperature compression properties of the deformed samples were measured. The experiment results show that ECAPT is an effective method of consolidating powders at relatively low temperatures. Pure Al particles are successfully consolidated into dense bulk material after 4 passes of ECAPT at 200 °C. The consolidated material possesses fine grain structure and excellent mechanical properties. The refinement and consolidation mechanisms were analyzed. ECAPT is a promising method to produce the high-performance bulk materials from particles.     

ECAP温变形制备亚微晶钢中渗碳体变形特征

采用透射和扫描电子显微镜研究了ECAP变形中渗碳体的变形特征。结果表明:片状渗碳体相主要以弯曲变形、剪切变形、拉伸变形、扭折变形和剪断变形5种方式协调ECAP剧烈塑性变形,这表明在本实验ECAP纯剪切变形条件下钢中硬而脆的渗碳体相具有良好的塑性变形能力。渗碳体片层的变形方式主要是取决于渗碳体所处的应力状态,而渗碳体所处的应力状态是与渗碳体的片层取向和片层厚度密切相关,其中渗碳体的片层厚度起决定性作用。     

Microstructural evolution in a commercial low carbon steel by equal channel angular pressing

In the present investigation, both macroscopic and microscopic microstructural changes in a plain low carbon steel with a mixed structure of ferrite and pearlite were examined during equal channel angular pressing . During equal channel angular pressing, the sample was rotated 180°around its longitudinal axis between the passages. By repeating the pressing up to the accumulated effective strain of ∼4, ferrite grains with a submicron size of 0.2–0.3 μm were obtained. Optical observation revealed that hard pearlite phase deformed macroscopically in a similar manner to soft ferrite phase due to a considerable capability of pearlitic cementite for plastic deformation under the present equal channel angular pressing conditions. An examination of micrographs taken by transmission electron microscopy showed that the microstructural change in ferrite phase was similar to those in single phase Al solid solution alloys in that the non-equilibrium configurations of grain boundary were observed. In pearlite phase, the morphological change of cementite lamellar plates was represented by the existence of either severely necked fragments parallel to each other or curled wavy fragments. Microstructural evolution in a plain low carbon steel subjected to equal channel angular pressing was discussed by comparing it to that of equal channel angular pressed Al solid solution alloys and heavily cold drawn pearlitic steel wire, which exhibited similar microstructural change.     

GCr15钢等径弯曲通道变形后的组织特性

在650℃采用等径弯曲通道变形（ECAP）方法对原始组织为层片状珠光体的GCr15钢进行了Bc方式的多道次变形。采用透射电镜和洛氏硬度等实验方法,对不同道次下的组织特性和硬度进行了分析。结果表明：冷变形和温变形都能使渗碳体片层发生球化,但一道次温变形情况下渗碳体球化程度明显高于冷变形一道次,硬度值由原始态（层片状珠光体）的42 HRC分别降至38 HRC（冷变形）、27 HRC（温变形）,温变形二道次后,铁素体基体接近等轴状,平均晶粒尺寸约为0.4μm,球化完全的渗碳体颗粒粒径约为0.1μm,硬度值由27 HRC（温变形一道次）增至32 HRC左右。     

等径角挤压过程的计算机模拟

等径角挤压可以在不改变材料横截面的情况下使其反复产生严重的塑性变形,从而降低材料的晶粒尺寸,是制备块体超细晶材料的新工艺。该文采用DEFORM程序对等径角挤压过程进行了模拟,分析了挤压过程中材料的应力、应变、挤压力等的变化及其分布,为今后的研究打下了基础。     

镁合金等通道转角挤压过程中的晶粒细化机制

采用金相显微镜、背散射电子衍射(EBSD)和透射电子显微镜(TEM)分析ZK60镁合金在等通道转角挤压(ECAP)过程中不同部位的显微组织特征。结果表明:ZK60镁合金经240℃ECAP变形1道次后,合金的晶粒得到明显细化,但组织仍不均匀。剪切变形前,合金组织主要为粗大晶粒并伴有大量孪晶,剪切区的组织主要为剪切变形带和少量再结晶组织;剪切变形后,合金的晶粒组织主要为再结晶组织;合金ECAP过程的晶粒细化主要为机械剪切和动态再结晶的综合作用。     

等径弯曲通道变形力的研究

本文利用上界定理计算等径弯曲通道变形 (ECAP)的挤压力 ,为ECAP的模具设计、挤压力的计算提供了一种可行的方法     

A modified die for equal channel angular pressing

Tensile stress occurs in the vicinity of upper surface of the specimen in the severe plastic deformation zone, which increases the cracking and fracture tendency of the specimen and impedes the further ECAP processing. In this paper, the conventional ECAP die (Ψ = 16° and Φ = 90°) was modified to eliminate the tensile stress and enhance the compressive stress in the severe plastic deformation zone, therefore reducing the cracking and fracture tendency of the specimen. Finite element analysis demonstrated that the stress state changes from tensile to strongly compressive when using the modified die. A modified die was made and employed to extrude the commercially pure aluminum to verify its effectiveness experimentally. The billet was successfully extruded for 20 passes without obvious surface defects with the modified die, compared to 13–14 passes at most for the conventional die. Consequently, much more fine and uniform microstructure was obtained with the average grain size of 200–300 nm, while the average grain size is ～500 nm in the case of using the conventional die.