多尺度复合层状纳米晶镍的制备及其力学性能研究

发布时间：2018-03-06 09:47

本文选题：电沉积　切入点：层状纳米晶　出处：《上海电力学院》2017年硕士论文　论文类型：学位论文

【摘要】：纳米晶材料在力学性能方面表现出高强度,但在变形过程中通常展现出令人失望的较低的塑性,这也严重限制了纳米晶材料在工程上的应用。纳米晶材料的低塑性也是归因于其本质上缺乏有效地位错运动,这使得纳米晶材料在变形时不能形成较大的加工硬化能力来维持塑性变形。研究表明,通过构造含有晶粒尺寸呈现双峰或多峰分布的复合结构可以有效地改善纳米晶材料的应变硬化能力。基于上述思路,本文通过采用大电流密度(23A/dm2)和小电流密度(1.5A/dm2)交替变化的直流电沉积法,制备出了由大晶粒层和小晶粒层交替变化的块体层状纳米结构镍。通过X射线衍射仪(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM)对镀层的晶体结构和形貌进行了分析。结果表明,在1.5A/dm2电流密度下,镀层具有(200)择优生长织构,晶粒尺寸约为267nm,处于超细晶范畴;在23A/dm2电流密度下,镀层无生长织构,晶粒呈现随机生长,晶粒尺寸约为45nm,处于纳米晶范畴。通过持续拉伸模式,在拉伸速率4.17×10-2s-1下,层状纳米晶镍的抗拉强度(ζUTS)和延伸率(δETF)达到1290MPa,12.5%。与纳米晶和超细晶Ni相比,延伸率显著提高,且保持一个适中的强度。加工硬化速率被保持到8%的真应变,说明层状纳米晶Ni的加工硬化能力得到加强。扫描电镜结果显示,层状纳米晶镍与超细晶和纳米晶Ni的形貌分别相对应,表现出层状的韧窝和隆起结构。为了研究层厚比对层状纳米结构Ni的力学性能影响,制备了一系列不同层厚比的层状纳米晶Ni。通过拉伸数据表明,当硬层和软层的比值为1:1时(即时间间隔为1h-4min),此时有最佳的力学性能,抗拉强度和延伸率达到1415MPa,12.3%,加工硬化速率维持到真应变9.2%。通过在一个宽的应变速率持续拉伸模式下(0.417s-1-4.17×10-5s-1),层状纳米晶Ni(时间间隔1h-4min)表现出强的应变速率敏感性(m:0.018,V:19b3)。对制备的层状纳米结构Ni进行间歇应力释放拉伸实验(应变速率4.17×10-2s-1),延伸率提高到14.6%,说明不同的变形模式,对纳米晶材料的力学性能有很大的影响。间歇的应力释放缓解了在持续拉伸过程中局部的应力集中从而提高了纳米层状晶Ni均匀变形的能力。
[Abstract]:Nanocrystalline materials exhibit high strength in mechanical properties, but in the process of deformation usually shows a disappointingly low plasticity, which severely limits the application of nanocrystalline materials in engineering. With low plasticity of nanocrystalline materials is also attributed to the nature of the lack of effective dislocation motion, which makes the in the deformation of nanocrystalline materials can form when work hardening ability to maintain large plastic deformation. The results show that the grain size is constructed containing composite structure of Shuangfeng or multi peak distribution can effectively improve the strain hardening ability of nanocrystalline materials. Based on the above ideas, this paper adopts the high current density (23A/dm2) and small the current density (1.5A/dm2) DC electrodeposition method alternately, prepared by the large grain layer and small grain layer alternating blocks of layered nanostructured nickel. By means of X ray diffraction (XRD), scanning electron The electron microscope (SEM), transmission electron microscopy (TEM) morphology and crystal structure of the coatings were analyzed. The results show that in the current density of 1.5A/dm2 coating, with (200) preferred growth texture, grain size is about 267nm, in the ultrafine grained category; in the current density of 23A/dm2 coating, no growth texture, grain show the random growth, the grain size is about 45nm, in the nanocrystalline category. Through continuous stretching mode, the stretching rate of 4.17 * 10-2s-1, the tensile strength of layered nanocrystalline nickel (zeta UTS) and elongation (delta ETF) reached 1290MPa, 12.5%. and nano crystal compared and ultra-fine Ni, elongation significantly increased and maintain a moderate strength. The work hardening rate is maintained until the true strain of 8%, that the work hardening ability of layered nanocrystalline Ni was strengthened. Scanning electron microscopy showed that the morphology of nanocrystalline nickel layer with ultrafine grained and nanocrystalline Ni respectively Should exhibit a layered dimple and uplift structure. In order to influence the mechanical properties of the layer thickness ratio of layered nano structure of Ni, the preparation of a series of different thickness ratios of layered nanocrystalline Ni. by tensile data show that when the ratio of the hard layer and the soft layer is 1:1 (i.e. the time interval is 1h-4min). This is the best mechanical properties, tensile strength and elongation reach 1415MPa, 12.3%, to maintain the true strain hardening rate of 9.2%. through a wide strain rate tensile mode (0.417s-1-4.17 * 10-5s-1), layered nanocrystalline Ni (interval 1h-4min) exhibited strong strain rate sensitivity (m:0.018. V:19b3). The layered nanostructured Ni prepared by intermittent release of stress (tensile strain rate of 4.17 * 10-2s-1), the elongation rate increased to 14.6%, indicating the different deformation modes, have great influence on the mechanical properties of nanocrystalline materials. Intermittent The stress release relieves the local stress concentration in the continuous stretching process and thus improves the ability of the homogeneous deformation of the nanocrystalline Ni.

【学位授予单位】：上海电力学院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1;TQ138.13

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