【作者】 林万明；

【导师】 卫英慧；

【作者基本信息】 太原理工大学 ， 材料学， 2011， 博士

【摘要】 纳米晶材料由于其特有的力学性能和物理性能而备受人们的关注,纳米材料性能的提高主要归因于大量的晶界和特殊的晶界结构。表面机械研磨处理(Surface mechanical attrition treatment-SMAT)是通过强烈的塑性变形来制备纳米晶材料的新方法。它能在材料的表面获得纳米级、亚微米级和微米级大小不同的晶粒,该技术已经成功地在许多材料中实现了表面纳米化。面心立方结构的铜及铜合金具有优良的导电性、导热性和耐腐蚀性等优点,广泛应用于电器仪表、航天航空、机械、国防工业等行业。全面系统地了解纳米晶材料的微观结构和性能之间的关系可以为纳米材料的使用提供理论基础。将SMAT技术和传统的表面处理相结合来优化纳米晶材料的性能对纳米材料的应用及研究具有十分重要的意义。本文采用表面机械研磨处理的方法在纯铜、铜钛合金、铜镍合金表面制备了纳米晶组织。采用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、和显微硬度测试仪对SMAT试样的微观组织结构和性能进行了表征。采用电化学极化曲线的方法和电化学阻抗技术,研究了试样在0.05mol/L Na2SO4和0.05mol/L H2SO4混合溶液中的电化学腐蚀行为。将表面改性和纳米化技术相结合可改善材料的综合性能。采用电沉积技术对SMAT纯铜试样表面进行了电沉积镍处理,通过退火处理研究了镍原子在纳米晶铜中的扩散行为及其对性能的影响。采用金属蒸发真空弧(MEVVA)对SMAT处理前后的纯铜进行了钛离子的注入,研究了离子注入钛后试样组织结构的特征及其对性能的影响。主要结论如下：1.经过表面机械研磨处理,纯铜表面产生了强烈的塑性变形,沿表面至基体形成了梯度分布。试样表面的晶粒尺寸随着SMAT处理时间的延长逐渐减小,SMAT处理45min表面晶粒尺寸达到了20nm,晶粒尺寸随着距离表面的深度增加而减小。强烈塑性变形层的厚度随着处理时间的延长而增加,最终达到一稳定值。SMAT处理后纯铜试样表面的显微硬度明显提高,沿深度方向逐渐减小,最终与基体一致。表面显微硬度达到了1.8GPa,比基体提高了1倍。2.固溶Cu-2.wt%Ti合金进行不同时间的SMAT处理后,试样表面的晶粒达到纳米级,SMAT处理60min后晶粒尺寸为30.5nm,变形层的厚度为45μm。SMAT处理后,试样中出现了明显的分层现象及高密度的形变孪晶和交叉孪晶。SMAT处理后试样表面的硬度增大,沿深度成梯度分布。对SMAT试样进行时效处理后,表面硬度变化不大,但距表面40～50μm之间的硬度明显增大。通过热力学计算了Ti含量对铜钛合金层错能的影响。发现随着钛含量的增加,合金层错能降低。3.Cu-10wt%Ni合金经过表面机械研磨处理后,获得了与纯铜类似的具有梯度结构的表面层。表面机械研磨处理90min时,试样表面附近平均晶粒尺寸达到了31.03nm,平均应变为0.0828%。处理时间120min时,表面显微硬度达到2.28GPa,是基体组织的1.52倍。极化腐蚀结果表明,表面机械研磨处理后,Cu-10wt%Ni合金的腐蚀电位产生了负移,钝化能力提高了,但其耐腐蚀性能降低了。4.采用MEVVA对纳米化纯铜表面进行离子注Ti,结果表明：注入离子的浓度服从Gauss分布。和粗晶试样相比,Ti原子在纳米晶铜中更容易扩散。离子注Ti后,试样的耐腐蚀性能明显提高。5.将电沉积技术和SMAT相结合改性纯铜表面性能,通过分析表明：SMAT试样表面纳米晶层内存在着大量的非平衡态缺陷,尤其是晶界数量的增加,降低了镍原子扩散的激活能,提高了扩散系数,加快了镍原子的扩散。在纳米铜试样中,镍原子在100℃下就有明显的扩散现象发生。极化腐蚀的实验结果表明SMAT处理试样的耐腐蚀性能提高。更多还原

【Abstract】 Nanocrystalline materials attract particular interest because of their unique mechanical and physical properties. The property variation in these materials are frequently attributed to either the numerous amount of grain boundaries and/or the specific grain boundary structure that was claimed to differ fundamentally from that of the conventional grain boundary.Surface mechanical attrition treatment (SMAT) is a promising way to produce nano-grained microstructures by imposing intense plastic deformation into metals and alloys. It enables one to obtain ultrafine-grained structures from nanometer-sized grains to submicrometer-sized and micrometer-sized crystallites within the deformed surface layer. This technique has been successfully applied in achieving surface nanocrystallization in a variety of materials.Copper and copper alloy have wide application in industry, especially, electric meter manufactrere, aerospace and aviation, car manufacturing, due to excellent electrical conductivity, thermal conductance and corrosion resistance. Understanding of the relationship between microstructures of nanocrystalline materials and their properties is necessary. Optimizing the properties of nanocrystalline materials and understanding their essential behaviors become significant for actual application and scientific study.Nanostructured surface layers were produced in pure copper, Cu-Ti alloy and Cu-Ni alloy respectively by means of surface mechanical attrition treatment (SMAT). The microstructure features and properties of the surface layer of SMATed samples were characterized in detail by using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and microhardness testing machine.The electrochemical corrosion behavior of the samples was investigated through the potentiodynamic polarization method and the electrochemical impedance spectroscopy (EIS) technique in0.05mol/L Na2SO4+0.05mol/L H2SO4solution.The combination of surface modification and nanotechnology was applied to modify the surface properties of metal materials. The SMATed copper samples surface was cleaned and electroplated with a layer of pure nickel and Scanning electron microscope (SEM), GDS, X-ray diffractometer (XRD), etc. were used to analyze diffusion behavior of Ni atoms in the pure copper. In addition, Titanium (Ti) ions were implanted into the surface nanocrystalline copper samples by using metal vapor vacuum arc (MEVVA). The surface microstructure and concentration distribution of implanted ions were characterized by using X-ray diffractometer (XRD), transmission electron microscope (TEM), Auger electron spectroscopy (AES). The main conclusions can be drawn as follows:1. The surface layer of pure copper was severely deformed after SMAT, and such a gradient structure was formed from the top surface to the matrix. Particularly, the severely deformed layer can be further divided to nanostructured layer and layer with superfine structure.The grain sizes in the top surface of samples decreased with the prolonging of treatment time. The grain size in the top surface of the samples treated for45min was20nm. The grain size decreased when away from the top surface.The depth of the severely deformed layer increased with the prolonging of SMAT treatment time and finally reached a plateau at about250μm, while the depth of the whole strained layer could be as deep as450μm.Microhardness of the surface layer was obviously elevated after SMAT and it decreases gradually to the level of the matrix along the direction away from the top surface. The microhardness of the top surface could be2times as high as that of the matrix.2.Surface nanocrystallization layer was produced on solid solution treated Cu-2wt%Ti alloy by means of surface mechanical attrition treatment. The grain size in the top surface of the samples treated for60min was30.5nm.The stratification phenomena occurred on the Cu-2wt%Ti alloy samples. High density deformation twin and crossover twin were observed in the samples.After surface mechanical attrition treatment, the micro-hardness of the stratified interface began to keep stabilization, but after aging treatment, the micro-hardness of interface increased rapidly.With the introduction of Ti, Stacking fault energy of copper was brought down.3. Nanocrysitalline surface lauer was achieved in Cu-10wt%Ni alloy after SMAT. When the treatment time was90min, the average grain size on the surface of the sample achieved the smallest size of31.03nm, the mean micro-strain was0.0828%correspondingly. Experimental evidences also indicated that the SMAT treatment played an important role in the strength of the alloy. Its micro-hardness on the surface was2.28GPa when the sample was processed for120mins, which was1.52times harder than that of the matrix.The result showed that the corrosion potential of Cu-10wt%Ni Alloy shifted to a more negative value and its passivity behavior enhanced with respect to the coarse grain alloy. As a result, the corrosion behavior of Cu-10wt%Ni Alloy decreased after SMAT.4. Titanium ions were implanted into the surface nanocrystalline copper by using metal vapor vacuum arc (MEVVA). Ti distribution is measured by using Auger electron spectroscopy (AES). The results showed that after the surface mechanical attrition treatment (SMAT), the concentration of implanted ions followed Gauss distribution. The specimens after ion implantation have a remarkable enhancement of corrosion resistance with respect to the specimens without the surface treatment. 5. The combination of electrodeposition and SMAT was applied to modify the surface properties of metal materials.It concluded that the increase of diffusion rate was attributed to lower diffusion activation energy and higher coefficient which was induced by the non-equilibrium defects in nanocrystaline (such as high density dislocations and dislocation cells), especially, a large number of grain boundaries.The diffusion phenomenon of Ni atoms in the SMAT copper can be obviously observed at100℃.更多还原