【作者】 陈小红；

【导师】 刘平； 井晓天；

【作者基本信息】 西安理工大学 ， 材料学， 2009， 博士

【摘要】 高脉冲强磁场技术和高速电气化铁路的发展,对磁场导体和电力接触线材料的性能提出了新的要求,需要高强度、高导电性和高导热性的材料,本文开发出的Cu-Cr系原位形变复合材料可以满足上述材料的性能要求。本文采用感应加热熔炼、旋转锻、线拉变形及中间热处理制备了Cu-15Cr-0.1Zr、Cu-15Cr-0.2Zr、Cu-15Cr-0.1Zr-RE三种形变原位复合材料,借助扫描电镜(SEM)和透射电镜(TEM)高分辨电镜(HREM)和抗拉强度测试、导电率测试等手段研究了合金化元素Zr、微量的RE元素、应变量、中间退火工艺等对合金组织和性能的影响。以余氏固体与分子经验电子理论和程氏改进的TFD理论为基础,通过对原位复合材料中纤维相和界面的研究,进一步阐释了界面结合因子与界面性能的的关系。主要的研究结果如下：采用冷变形结合中间热处理技术研制出新的具有超高强度、高导电、高热稳定性的Cu-15Cr-0.1Zr和Cu-10Cr-0.1Zr原位复合材料,应变量η=6.43时,材料的强度／导电率分别为：1212MPa/71.5%IACS,1096MPa/76.3%IACS,抗软化温度均达550℃。合金元素Zr的加入促进Cr的析出,保持了微合金化Cu-15Cr复合材料的高导电性；添加0.1wt%Zr可使Cu-15Cr-0.1Zr的抗拉强度提高约15%；同时,Zr的加入使复合材料的抗软化温度提高了50℃左右。在Cu-15Cr-0.1Zr合金中加入微量的RE会使合金的导电性略有提高,但强度降低。合金的铸态组织由Cu基体、粗大的Cr枝晶、少量的Cu-Cr共晶组成。在冷拉拔过程中,热锻并经固溶处理后的Cr相沿拉拔方向伸长,在较低的应变量下纤维保持着与铸态树枝晶相同的bcc单晶结构,在较高的应变量下,单根Cr纤维被分隔为一些由亚晶界组成的亚结构,相邻亚晶的偏差角在5°～30°之间。随着应变量的增大,逐渐形成横截面为弯曲薄片状的Cr纤维,对界面的观察发现,Cu/Cr界面在η=6.43条件下显示完全共格或波纹图衬度。对两次中间退火制备的Cu-15Cr-0.1Zr合金的研究发现,中间退火在不严重影响材料强度的同时显著提高了材料的导电率。第一次中间退火对合金的最终性能起关键作用。拉拔至最终尺寸时,第一次中间退火温度为450℃的合金能获得最好的抗拉强度。第一次中间退火温度为500℃的合金能获得最好的导电性能。测定了形变Cu-Cr原位复合材料的强度并分析其强化机理,认为是界面作用的结果。可用几何协调位错强化模型和界面位错源强化模型描述。对Cu-15Cr-0.1Zr合金的热稳定性研究表明：合金的抗软化温度达到了550℃左右,满足性能指标。合金在400℃～600℃退火,导电率随着退火温度的升高逐渐增大,在600℃达到最大值(约78%IACS),并随着退火温度的继续升高迅速下降。在不同的温度条件下,研究大变形Cu-15Cr-0.1Zr原位复合材料中Cr纤维的断裂行为。用SEM及TEM观察了Cr纤维形态的变化,测定了Cr纤维的断开直径,并进行了数值模拟。观察结果显示,纤维高温下断裂过程是逐步形成空洞、纵向开裂、柱状化、断开和球化。模拟结果表明：纤维断裂受界面扩散控制,并分析了其计算模型,经比较,计算值和实验结果具有很好的一致性。对Cu-Cr原位复合材料中的Cu/Cr界面的界面结合因子的计算结果表明：Cu(111)／Cr(110)异相界面的电子密度差Δρ最大,同时该界面电子密度保持连续的原子状态组数σ′也大,其符合更高强度级别的强韧化。更多还原

【Abstract】 With the development of the high pulse and high field magnets technology and the high speed electric railway, there is a new urgent need by the magnetic field conductor and the electric contact wire, which needs the best combination of high strength, high electrical conductivity and high thermal conduction. Thus, deformed Cu-Cr in-situ composites were developed.Deformation processed Cu-15Cr-0.1Zr, Cu-15Cr-0.2Zr and Cu-15Cr-0.1Zr-RE in situ composites were manufactured by inductive melting, casting, swaging, appropriate wire drawing and intermediate annealing. Effect on the microstructure and properties of Cu-Cr in situ composite caused by the content of Zr, the addition of RE, intermediate annealing of alloys were studied through scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution electron microscopy(HREM), tensile test, and resistivity measurement, on the basis of the combination of Yu’s empirical electron theory in solid and molecules (EET) and Cheng’s improved Thomas-Fermi-Dirac (TFD) theory. The relationship between the valence electron structure of a biphase interface and its properties is explained further through the research on the effect of the fiber phase and Cu/Cr interface in in-situ composites. The main results of the research are listed below:A new type of high strength and high conductivity Cu-15Cr-0.1Zr and Cu-lOCr-0.1Zr in situ composites were successfully prepared using the cold drawing and intermediate heat treatment, When alloy was drawn to 6.43 the strength/conductivity can reach 1212MPa/71.5%IACS and 1096MPa/76.3%IACS respectively, and all the softening temperatures are up to 550℃.The addition of 0.1wt%Zr accelerate the precipitation of Cr in the matrix and keep the conductivity of the micro-alloying Cu-15Cr composite; the ultimate tensile strength of Cu-15Cr-0.1Zr can increases about 15% and the soften temperature of Cu-15Cr-0.1Zr can improves 50℃with addition the trace Zr. The addition of Zr about 0.2% in Cu-15Cr alloy could promote alloy work hardening in the process of alloy deformation, and against to the deformation of alloy, and reduced the conductivity of alloy. The addition of RE in Cu-15Cr-0.1Zr alloy improved electrical conductivity. But, at the same time it also reduced the strength.As cast, the alloy include of Cu matrix, gross Cr dendrite and a small quantity of Cu-Cr eutectic. In the process of alloy deformation, Cr phases with heat forged and solution treatment were elongated along the direction of drawing. At lower drawing strains, some of Cr fibers have the same bcc single crystal structure as that of dendrites in the as cast state. At higher drawing strains, a single fiber was divided into sub-grains. These sub-grains were separated by sub-grain boundaries. Relative angle differences across the sub-grain boundaries are about 5°～30°.With the increasing of strain, Cr phases formed fibers and Cr ribbons were curl and fold in cross section, observation at the interface showed that the interface of Cu/Cr were coherent or shows moire pattern contrast atη=6.43.The study on Cu-15Cr-0.1Zr alloy prepared by two times intermediate annealing showed appropriately intermediate annealing and obviously improved the electrical conductivity, and the strength did not terribly reduced. The first intermediate annealing was very important for the properties of alloy. When the alloy was drawn to 6.43, the alloy prepared by the first intermediate annealing at 450℃can obtain best strength, and the alloy prepared by the first intermediate annealing at 500℃can obtain best electrical conductivity. In this paper, the relationship of three times intermediate annealing and the properties of Cu-15Cr-0.1Zr alloy were also studied. The results showed that when alloy prepared by three times intermediate annealing was drawn to 6.43, the strength of alloy was smaller than the alloy prepared by two times intermediate annealing, but the electric conductivity had a little increasing.The strength of deformation-processed Cu-Cr in-situ composite was measured. The results showed to be anomalously higher than those predicted by rule of mixture equations. The strength increased with increasing of the deformation. The strengthening mechanism was discussed. The analysis indicate that the sub-structural especially phase boundary strengthening plays the crucial role. The experimental data are in good agreetment with the predictions of the geometrically-necessary dislocation model and interface as dislocation source model.The results of thermal stability test for Cu-15Cr-0.1Zr alloy showed that the softening temperature of the alloy exceed about 550℃, and achieved the performance figure. When alloy was annealed during 400℃～600℃, electric conductivity gradually increased with the increasing of annealing temperature. The electric conductivity of alloy reached maximum value (about 78%IACS) when alloy was annealed at 600℃. At last, with the continuous increasing of annealing temperature, the electric conductivity rapidly reduced. Investigate the fracture behavior of Cr fibers in heavily drawn Cu-15Cr-0.1Zr in-situ composite wires as a function of temperature. Results of SEM and TEM show the fibers undergo interfacial diffusion shape change from cavitation, longitudinal spliting plus, cylinderization plus, breakup to complete spheroidization failure. Predicted result showed the fracture behavior of the Cr fibers were consistent with interfacial diffusion, Experimental results were compared with existing models and the appropriate physical model for breakup of filaments were provided.The interface conjunction factors of the Cu/Cr interface of Cu-Cr in-situ composites show that:the electron density of Cu(lll)/Cr(110) interface Ap is the largest in other interface, and the number of atom state groupsσ’ which keeps continuous interface electron density is larger, according to the theory of Yang Zhilin, The larger theΔρof Cu/Cr interface, the larger the stress on the interface is, if the larger theσ’ or a, that is the steady combine at the higher stress station, so that accord with strength and toughness at higher strain.更多还原