【作者】 刘克明；

【导师】 曾苏民； 周海涛；

【作者基本信息】 中南大学 ， 材料科学与工程， 2012， 博士

【摘要】 微电子、电力、信息、交通及机电等行业的快速发展对高强高导形变Cu基原位复合材料的强度、电导率和塑性提出了更高要求。本文通过合金成分优化、熔铸、大塑性变形及各种热处理,设计并制备了Cu.14Fe.Cu-7Cr和Ag微合金化的Cu-14Fe-0.1Ag.Cu-7Cr-0.1Ag四种实验材料,并采用X射线衍射仪(XRD)、光学显微镜(OM)、扫描电子显微镜(SEM)及透射电子显微镜(TEM)等手段观察和分析了材料的微观组织结构；采用液晶电子拉力试验机、维氏硬度计、数字微欧仪等测试和分析了材料的力学性能和导电性能。系统研究了Ag微合金化在材料凝固、形变及热处理过程中的作用及机理,并引入了定向凝固和强磁场处理技术,详细研究了其对材料组织和性能的影响规律和机制,结合适当的时效工艺,对材料的强度、电导率和塑性进行了有效调控。得出了以下主要研究结果：铸态Cu-Fe合金的Fe相主要以树枝晶的形态分布于Cu基体中,Cu-Cr合金的Cr相绝大部分以树枝晶、少量以细小的共晶形态存在于Cu基体中。微量Ag元素加入后,铸态Cu-Fe.Cu-Cr合金中的初生相和形变Cu-Fe.Cu-Cr原位复合材料中的纤维相平均尺寸和间距减小、分布更加均匀。纤维组织的立体形态为弯曲的薄片状,其轴向形成过程主要经历了枝晶破碎、颗粒扁化与旋转、纤维搭接与合并、纤维细化与均匀化等四个阶段。提出了分段的强化机制物理模型,当冷变形应变量较小时,材料的强度符合修正的混合法则σC=σM fM+σX fX,其中σM=σ+k3m1/2X,对形变Cu-14Fe原位复合材料,当η≤5时,k3=52；随着冷变形应变量的增加,材料的强化机制逐渐偏离混合法则,其强度满足Hall-Petch关系,对形变Cu-14Fe原位复合材料,当5<η≤7.8时,具体的强化数学模型可表示为σC=108+1299λ-1/2;随着冷变形应变量的进一步提高,材料内的位错密度下降,抗拉强度与纤维平均间距之间逐渐偏离Hall-Petch关系,其抗拉强度主要由界面障碍强化模型决定。Ag微合金化使形变Cu-14Fe.Cu-7Cr原位复合材料的强度提高。这主要是因为Ag的加入细化了初生相,使Ag微合金化形变Cu-b.c.c.原位复合材料在更低的变形量下满足Hall.Petch关系,对形变Cu-14Fe-0.1Ag原位复合材料,当4<η≤7.8时,Ag微合金化的强化数学模型可表示为σc=139+1299λ-1/2.通过对不同材料的拉伸断口形貌观察发现,随着冷变形应变量的不断增加,宏观上材料的断口逐渐由杯锥状向剪切形态转变；微观上断口韧窝尺寸逐渐减小、变浅。微量Ag元素加入后,材料出现上述变化的相应冷变形应变量提高,表明微量Ag元素的加入将提高形变Cu-b.c.c.原位复合材料的塑性变形能力。冷变形应变量对形变Cu-b.c.c.原位复合材料电导率的影响主要由Cu基体和纤维相的界面引起的界面散射电阻率决定。界面散射电阻率的数学模型可表示为pint=—0.09+KD(d0/d),对形变Cu-14Fe原位复合材料而言,kD=0.02。微量Ag元素加入后,在相同的冷变形应变量下,形变Cu-14Fe.Cu.7Cr原位复合材料的电导率均有所上升。微量Ag元素对形变Cu-b.c.c.原位复合材料电导率的影响主要是由杂质散射电阻率变化引起的。由于Ag元素与Fe/Cr相比,在Cu基体中具有溶解竞争优势,加入后可进一步促进固溶Fe/Cr原子的析出,而且固溶Ag原子对Cu基体电导率的影响要远远低于固溶Fe/Cr原子。因此,Ag微合金化可降低杂质散射电阻率,从而促使复合材料的电导率上升。微量Ag元素的加入,有利于第二相纤维的细化、纤维／基体的界面能降低以及Fe/Cr等原子在基体中扩散系数的提高,从而导致材料中第二相纤维的热稳定性下降,促使热处理过程中材料的电导率峰值向低温方向偏移；有利于加速第二相粒子的时效析出,促使Cu基体在较低温度下发生脱溶分解,析出细小弥散的第二相粒子,从而导致材料的强度峰值向低温方向偏移。通过Ag微合金化、形变、适当的中间热处理和最终时效处理的协同作用,对形变Cu-14Fe和Cu-7Cr原位复合材料的强度、电导率和塑性进行了综合调控,形成了一种有效的调控工艺。采用合适的强磁场预备热处理,可提高第二相Fe原子在Cu基体中的扩散系数,加速过饱和固溶Fe原子的析出,促使第二相Fe枝晶的球化、细化和均匀化,使形变Cu-Fe原位复合材料的强度和电导率同时获得提高；采用适当的定向凝固处理,有利于铸态组织中初生Cr晶粒形成沿抽拉方向排列的方向性,使第二相长棒状组织的平均尺寸和间距减小、分布更加均匀,从而使形变Cu-Cr原位复合材料在保持高电导率的同时获得强度的大幅提升；结合适当的后续热处理,可对材料的强度、电导率和塑性变形能力进行有效调控。η=7.8的形变Cu-14Fe-0.1Ag原位复合材料经10T强磁场等时时效1h后获得的较好强度/电导率/断后伸长率组合主要有1149MPa/60.3%IACS/3.3%、1093MPa/61.9%IACS/3.5%和1006MPa/63.7%IACS/3.7%等；η=8的形变Cu-7Cr-0.1Ag原位复合材料经等时时效1h后获得的较好强度/电导率/断后伸长率组合主要有1067MPa/74.9%IACS/2.9%、1018MPa/76.0%IACS/3.0%和906MPa/77.6%IACS/3.3%等。更多还原

【Abstract】 The higher strength, better plasticity and conductivity of high-strength and high-conductivity deformation processed Cu-based in situ composites are being required due to the rapid development of microelectronics, electric power, information, transportation and electromechanical industries. Deformation processed Cu-14Fe, Cu-7Cr, Cu-14Fe-0.1Ag and Cu-7Cr-0.1Ag in situ composites were designed and prepared by optimized alloying composition, cast, deformation and heat treatment. Effect of Ag micro-alloying, directional solidification and high magnetic field on the microstructure and properties of Cu-Fe/Cr during the solidification, cold drawing and heat treatment were investigated by using X-Ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), LCD electronic tensile-testing machine, Vickers hardness tester and micro-ohmmeter. The main results of the research are as follows.The as-cast microstructure of Cu-Fe alloys included Cu matrix and Fe dendrite, and that of Cu-Cr alloys was made of Cu matrix, Cr dendrite and a small quantity of Cu-Cr eutectic. Ag micro-alloying refined the Fe and Cr dendrites in Cu-Fe and Cu-Cr alloys, which decreased the average size and spacing of the filaments in deformation processed in situ composites. During the cold deformation, the formation of the curved lamelliform filaments experienced the following four main steps in the longitudinal section, namely breaking of dendrites, flattening and rotating of particles, lapping and merging of filaments, refining and homogenizing of filaments.Sectionalized physical model of strengthening mechanism was developed. With small cold deformation strain, the strength of the composites can be calculated by the modified rule of mixing <σC=σMfM+σXfX, where σM=σ+k3m1/2X, and k3=52for deformation processed Cu-14Fe in situ composite at η≤5. As the cold deformation strain increasing, the strengthening mechanism deviated from the rule of mixing gradually, and the strength agreed with Hall-Petch relation. The mathematical model can be expressed as σC=108+1299λ-1/2for Cu-14Fe composite at5<η≤7.8. As the cold deformation strain further increasing, the dislocation density in the composites decreased, so that the strengthening mechanism disobeyed Hall-Petch relation gradually, and the strength can be forecasted by the interface obstacle strengthening model. Ag micro-alloying increased the strength of Cu-14Fe and Cu-7Cr composites. This is attributed to the microstructure refinement which makes Ag micro-alloying deformation processed Cu-b.c.c. in situ composites conform to Hall-Petch relation in smaller cold deformation strain. The strengthening mathematical model of Ag micro-alloying can be expressed as σC=139+1299λ-1/2for Cu-14Fe-0.1Ag composite at4<77<7.8.The fracture surface analysis of the samples showed that the macroscopic fracture morphology of the composites gradually changed into shear fracture from cup and cone shape with the cold deformation strain increasing, and the dimples size in the microstructure gradually decreased. The shear fracture was delayed to bigger cold deformation strain after the addition of trace Ag, which indicated that Ag micro-alloying could improve the plastic deformability of deformation processed Cu-b.c.c. in situ composite.The influence of cold deformation strain on the conductivity of the composites depends on the interface scattering resistivity generated by the interface between Cu matrix and filaments. The mathematical model of the interface scattering resistivity can be expressed as ρint=-0.09+kD(d0/d), where kD=0.02for Cu-14Fe composite. Ag micro-alloying improved the conductivity of Cu-14Fe and Cu-7Cr composites. The effect of trace Ag on the conductivity of the composites depends on the impurity scattering resistivity. Ag micro-alloying promoted the solid solution Fe/Cr atoms to precipitate due to the solid solution advantage of Ag in Cu matrix, and solid solution Ag has relatively little damage to the conductivity of Cu matrix contrast to Fe/Cr. Therefore Ag micro-alloying reduced the impurity scattering resistivity to improve the conductivity of the composites.Ag micro-alloying reduced the thermal stability of Fe/Cr filaments due to refined filaments, decreased the interface energy between Cu matrix and filaments, and increased the diffusion coefficient of Fe/Cr atoms in Cu matrix, which promoted the peak conductivity to migrate to lower temperature during heat treatment. Moreover, it also contributed to promote precipitation decomposition of Cu matrix at lower temperature, and accelerate aging precipitation of Fe/Cr atoms to form dispersed precipitates, which led to the peak strength to migrate to lower temperature during heat treatment.The combination of the strength, conductivity and plasticity of Cu-14Fe and Cu-7Cr composites was optimized by using Ag micro-alloying, deformation, intermediate heat treatment and aging treatment. A new micro-alloying thermo-mechanical treatment process was developed. The prior heat treatment under high magnetic field enhanced the diffusion coefficient of Fe atoms in Cu matrix, accelerated the precipitation of supersaturated solid solution Fe atoms, and promoted Fe dendrites spheroidizing, refining and homogenizing, which made both strength and conductivity of the Cu-Fe composites increase. Directional solidification technology made primary Cr phase arrange along the drawing direction, decreased the average size and spacing of rod-like Cr phase, and made Cr distribute more uniform, which improved the strength of Cu-Cr composites significantly and retained the relatively high conductivity. Combining optimized subsequent heat treatment processes made the composites obtain good combination property of strength, conductivity and elongation. The strength/conductivity/elongation of Cu-14Fe-0.1Ag composite reached1149MPa/60.3%IACS/3.3%,1093MPa/61.9%IACS/3.5%and1006MPa/63.7%IACS/3.7%at η=7.8after isochronic aging treatment1h under10T magnetic intensity; The strength/conductivity/elongation of Cu-7Cr-0.1Ag composite reached1067MPa/74.9%IACS/2.9%,1018MPa/76.0%IACS/3.0%and906MPa/77.6%IACS/3.3%at η=8after isochronic aging treatment1h.更多还原