节点文献
超细晶铜材的大变形异步叠轧制备技术、组织演变过程与性能研究
【作者】 王军丽；
【导师】 史庆南；
【作者基本信息】 昆明理工大学 ， 材料学， 2007， 博士
【摘要】 超细晶铜材因具有微小的细晶结构而表现出了优异的延展性、导电性以及导热性等性能,已经发展成为了电器仪表、化工、造船、航空、机械等工业部门中的重要原料,具有广阔的应用前景。但由于目前超细晶材料仍无法连续制备在一定程度上限制了它的应用。此外,如何获得组织均匀稳定、性能优异的超细晶材料也是应用中急需解决的一个关键问题。本论文采用大变形异步叠轧法成功地制备出了超细晶铜材,该方法能够实现超细晶带材的连续化工业生产,是一种极具潜力的超细晶材料产业化的生产技术。采用大变形异步叠轧法对粗晶铜带材进行了加工及再结晶退火处理,最终制备出了超细晶铜材。在此基础上,研究了制备过程中超细晶铜材的组织和性能,取得了如下成果:1.研究了大变形异步叠轧及再结晶退火工艺条件对超细晶铜材组织及性能的影响,主要包括等效应变、再结晶退火温度和再结晶退火时间对铜材变形组织、晶粒大小、显微硬度、抗拉强度、屈服强度以及电阻率的影响,获得了制备具有均匀稳定性、高强度和较好电导率的超细晶铜材的最佳工艺条件。（1）对粗晶铜材进行等效应变ε=4.8的异步叠轧,获得的超细晶含有许多亚结构。然后再进行220℃×30～50min的热处理,可以制备出200～500nm的超细晶铜材;（2）制备出的超细晶铜材的抗拉强度σb为424.5MPa,屈服强度σ0.2为323.1Mpa;板面显微硬度为125HV,横截面显微硬度为110HV,纵截面显微硬度为103HV;电导率为76.3 MS/m。2.研究了大变形异步叠轧制备超细晶铜材过程的组织和取向织构变化情况,结果表明:（1）变形等效应变ε≤1.6时,剪切应力的作用使晶粒与晶粒之间发生滑动,部分晶粒内部晶面发生滑移,大晶粒内部转变为许多具有小角度晶界、大小为5个微米的亚晶。此时,异步产生的剪切力在晶粒细化过程中起主要作用;变形等效应变ε在2.4～4.0之间时,随着等效应变的增加,碎化的大角度小晶粒数量增加,包含小角度亚晶的大晶粒内部的位错密度增加;ε≤4.0时,随着变形等效应变的增加,界面逐渐被焊合,在异步叠轧过程中产生的缺陷部分在界面处消失。此时,异步叠轧中性面位置的改变对界面的复合起到主要作用,变形等效应变的增大使晶粒细化程度变大;变形等效应变ε≥4.8时,粗晶铜在变形过程中有两种组织区域组成,分别为细小亚晶区和高密度位错区。增加等效应变ε,高密度位错区减少,亚晶区增大,此时异步叠轧过程形成的界面已经完全焊合;无论等效应变ε有多大,异步产生的剪切力都会使实际中性层与几何中性层位置错开,使其在界面复合中起主导作用;（2）累积叠轧过程和异步叠轧过程在制备超细晶方面的差异在于:异步叠轧细化晶粒过程增加了剪切力的作用,加剧了晶粒间的摩擦,增大了晶界及晶内滑移,同时促进了叠合面的复合;累积叠轧过程大角度晶界的形成由几何变形引起,而异步叠轧过程大角度晶界的形成与位错的塑性滑移有关;（3）经异步叠轧后,样品的变形织构显现出铜式冷轧织构的特征,其中C-{112}<111>取向的晶粒最多,与在早期研究中金属铜的轧制织构基本一致,只是织构位置因剪切力的存在发生偏移;随着异步叠轧等效应变ε的增加,冷轧织构也随之增强;变形主要以位错滑移方式进行。3.对等效应变ε=4.8时获得的超细晶铜材进行再结晶处理,观察再结晶组织及织构演变过程,结果表明:（1）等效应变ε=4.8时,获得的超细晶铜材再结晶过程为:首先发生回复过程,回复机制主要为亚晶规整化,小部分区域发生多边化的回复过程;随着再结晶退火时间的延长,形成新的晶核,形核方式为亚晶转动、聚合形核和亚晶界迁移、亚晶长大形核两种方式;形核过程完成后,在35～50min内形成的晶粒大小在200～500nm之间。再结晶处理后,超细晶较稳定;（2）再结晶初期织构保持再结晶前的轧制织构特征,变形铜材发生很强的回复;随着再结晶退火时间的延长,立方织构组分、退火R织构组分、S组分、B/G组分等织构组分出现,发生不连续的正常再结晶,此时再结晶形成的晶核主要通过大角度晶界的移动来完成;（3）普通轧制获得的铜材再结晶过程中,具有立方取向的再结晶晶核优先生成,在长大过程中会保持优先生长,再结晶退火后主要以立方织构为主;大变形异步叠轧铜材过程中,定向生长机制受到限制,各种再结晶织构组分并存,且已形成的各种取向的晶核在长大过程中共同生长,形成的再结晶织构比较漫散,使铜材的各向异性较普通轧制再结晶退火有很大提高。4.测试了不同等效应变变形铜材、等效应变变形再结晶铜材和对超细晶进行变形加工铜材的显微硬度、力学性能以及导电性能,结合组织研究对其性能的变化进行了分析:（1）在异步叠轧过程中,铜材强度随等效应变的增加而增大,但其延伸率降低;等效应变ε为4.8时的铜材经220℃再结晶退火处理35～50min后,可以获得综合性能较好的超细晶;异步叠轧（ε=4.8）再结晶获得的超细晶铜退火时间大于35min后,残余应力得到消除,但超细晶铜材再进行轧制变形加工,残余应力又开始增加;（2）对于异步叠轧（ε=4.8）再结晶获得的超细晶铜,在晶粒细化到100～500nm时,屈服强度和晶粒尺寸依然较好的符合了传统的Hall-Petch关系;在室温下,超细晶铜具有良好的延展性;（3）等效应变ε增加,超细晶铜材的电阻率增加,电导率降低;经异步叠轧（ε=4.8）和再结晶退火处理后所获得的超细晶铜材的导电性和1#标准退火态铜的导电性相当。5.采用大变形异步叠轧法制备出了组织均匀、高强度、高延展性及良好导电性的超细晶铜材,是本论文的最重要研究成果之一。首次提出采用大变形异步叠轧法制备超细晶铜材,为超细晶材料的制备找到了一种新的途径。关于大变形异步叠轧法制备超细晶铜材组织及织构演变过程的研究以前未见报道,本论文首次开展了这方面的研究工作,同时对晶粒细化机制进行了分析和讨论。6.在最佳工艺条件下,制备出的超细晶铜材的电阻率和1#退火态铜相当;在超细晶铜材加工过程中,电阻率变化不大,与传统理论相悖,其所表现出的这些特性还需进一步探讨和验证。
【Abstract】 The Ultra-Fine-Grained copper（UFG-Copper）with fine structure performs excellent properties,such as ductibility,electrical conductivity and heat conductivity and so on.It has become an important raw material in the following industrial departments as electric apparatus instrument,chemical industry, shipbuilding,aviation and machinery,etc.,and has wide application prospects.At present,that the Ultra-Fine-Grained material is unable to be prepared continuously limits its application in succession.In addition,it is also a key problem need to be solved in application how to obtain uniform and stable UFG material with excellent properties.In this thesis,the UFG-Copper has been prepared by Asymmetrical Accumulative Rolling Bonding（AARB）,which can also realize to the industrial production in succession.for UFG-Copper,therefore,it is an extremely potential technology for UFG-Copper industrialization.The copper with big grains was processed by AARB and treated by recrystallization annealing,UFG-Copper was obtained finally in this thesis.On this basis,the structures and properties of UFG-Copper were researched,and the results were as follows:1.Effects of process conditions of AARB and recrystallization annealing on structures and properties of UFG-Copper were studied,including effects of equivalent strain,recrystallization annealing temperate and recrystallization annealing time on deformed structure,grains sizes,micro hardness,tensile strength, yield strength and electrical conductivity of UFG-Copper.The best process conditions and parameters prepared for uniform and stable UFG-Copper with high strength and good electrical conductivity,have been obtained.（1）The Copper with big grains was processed by AARB and the equivalent strain（ε）was equal to 4.8,the UFG obtained is composed of lot of sub-structure.Then these UFG was heat-treated at 220℃for 30～50min and the UFG-Copper with the grain sizes of 200～500nm has been prepared.（2）Tensile strength（σb）of UFG-Copper is 424.5Mpa,yield strength(σ0.2)is 323.1Mpa,the micro hardness on normal plane,transition plane,rolling plane is 125HV,110HV,103HV respectively and the electrical conductivity is 76.3 MS/m.2.The structures and orientation texture evolution of UFG-Copper during AARB were studied and the results were as follows:（1）Whenεis lower or equal to 1.6,the slips happen on grain boundaries and crystal planes owing to the shearing force.There occur many sub-grains possessing small angle boundaries and 5μm grains sizes within the big grains. At this moment,the shearing force by asymmetrical rolling plays a main role in the course of grain refinement.Whenεis between 2.4 and 4.0,the amounts of small grains which have big angle boundaries and the density of dislocation in big grains containing many sub-grains increase with the rise ofε.When e is lower or equal to 4.0, with increasingε,the interface are bonded gradually and some defects produced by AARB have disappeared on interface.At this moment,that the change of neutral plane position plays a main role in the course of interface bonding,the grain refinement degree heightens whenεincreases.When e is higher than 4.8,the copper with big grains is made up of two kinds of structure regions in the course of deforming,namely fine sub-grains region and high density dislocation region.The high density dislocation region reduces and the sub-grains region increases with the rise ofε,the interfaces produced by AARB have bonded completely at this moment.No matter what e is,the shearing force brought by asymmetrical rolling plays a main role in interface bonding,which leads to the position difference of real neutral plane and the geometric neutral plane.（2）The difference in preparing UFG used by AARB and ARB lies in:the shearing force is added in AARB process,which enhances the friction of grains,improves the slips of boundaries and crystal plane,and promotes the bonding of interfaces.The formation of big angle boundaries is caused by geometric deformation during ARB process,while the formation of big angle boundaries is related to plastic slips of dislocations during AARB process.（3）The deformed texture of the samples prepared by AARB shows the characteristic of cold-rolled texture-Copper texture,the number of grains with C orientation is the largest,which is the same to some research on that of the rolling copper early,but the texture position deviates owing to the existing of shearing stress.The strength of rolling texture becomes stronger with increasingε.The deformation goes on by means of the dislocation slip.3.UFG-Copper was treated by recrystallization annealing whenεwas equal to 4.8,and then the reerystallization structure and texture were observed,the results were as follows:（1）Whenεwas equal to 4.8,the recrystallization course of UFG-Copper obtained is that the recovery course happens firstly and its recovery mechanism is mainly sub-structures regularity and polygonization recovery at a small region.The new grain cores form gradually with the longer annealing time,which are two nucleation formations during recrystallization course,one is sub-grains turning and aggregating to nucleate,and the other is transferring of sub-grain boundaries and growing up to nucleate for sub-grain.The grains with the sizes of 200～500nm come into being when the recrystallization annealing time is controlled between 35min and 50min. UFG-Copper is uniform and stable after recrystallization.（2）At the beginning of recrystallization,the texture sustains the characteristics of rolling texture and the strong recovery happens in deformed copper.With the longer annealing time,there appear some component textures,such as cube texture,R texture,S texture and B/G texture,and the discontinuous recrystallization takes place,at this moment,the formation of crystal nucleus is completed by the transferring of big angle boundaries.（3）During the course of recrystallization for copper prepared by common rolling,crystal nucleus with cube orientation come into being preferentially, which will sustain the priority of growth during the growing up,the main texture is cube texture after recrystallization annealing.While during the course of recrystallization for copper prepared by AARB,the directional growth mechanism is limited and there are all kinds of recrystallization textures existing,the crystal nucleus having been formed with all kinds of orientation grows up together,so,the recrystallization texture is diffuse,which makes the anisotropy of the copper by AARB is better than that of the copper by common rolling and recrystallization.4.The micro hardness,tensile properties and electrical conductivity of UFG-Copper under the different conditions were determined and the change of properties was analyzed.（1）During the course of AARB,the strength of copper increases with the rise ofε,but its elongation rate decreases.UFG-Copper with good properties（ε= 4.8）can be obtained when recrystallized annealing at 220℃for 35～50 minutes.When the recrystallization annealing time is longer than 35 minutes, the remaining strain is banished,but the remaining strain of UFG-Copper begins to increase when deformed again.（2）The yield strength and grains sizes of the recrystallization UFG-Copper prepared by AARB withε=4.8,still meet to traditional Hall-Petch relation,the UFG-Copper has good ductibility at room temperature.（3）Electrical resistivity of UFG-Copper increases and electrical conductivity decreases with the rise of equivalent strain.Electrical conductivity of UFG-Copper prepared by AARB withε=4.8 and recrystallization is the same to that of annealing copper of No.1.5.UFG-Copper possessing uniform structure,high strength and ductibility, good electrical conductivity has been prepared by AARB and recrystallization annealing,which is one of the most important research achievements of this thesis. UFG-Copper prepared by AARB was proposed firstly,this can provide a new method for preparing UFG materials.The structure and texture evolution in the course of UFG-Copper prepared by AARB have not been reported yet,but this work was researched here,in the meantime,the mechanism of grain refinement was analyzed and discussed too.6.Electrical resistivity of UFG-Copper prepared by AARB at the optimal process conditions is the same to that of annealing copper of No.1.The electrical resistivity has little change during the process of UFG-Copper,which are different to traditional theory,but above characteristics need to be investigated further.