【作者】 喻辉；

【导师】 戴品强；

【作者基本信息】 福州大学 ， 材料学， 2005， 硕士

【摘要】 电沉积法是制备全致密的纳米晶材料最有前途的方法之一。本文采用脉冲电沉积法,在铜基上制备块体的纳米晶体镍。探索脉冲电沉积纳米晶体镍的制备技术,研究了脉冲电流密度、糖精添加剂浓度对纳米晶体镍的组织结构及晶粒尺寸的影响,并用正交法寻求纳米晶体镍脉冲参数的最佳配方。在此基础上,采用差热分析(DTA 及 DSC)、XRD 及 TEM 等手段研究纳米晶体镍的热稳定性;利用静态浸泡、阳极极化曲线等方法研究纳米晶体镍的耐蚀性能;采用宏观拉伸的方法考察了纳米晶体镍的力学性能,并用 TEM 原位拉伸法观察纳米晶体镍形变与断裂过程的微观过程。实验结果表明: 1.在瓦特型镀液中添加糖精添加剂,采用脉冲电沉积法可以获得纳米晶体镍;提高糖精浓度和脉冲电流密度,能有效地细化纳米晶体镍的晶粒尺寸;糖精浓度升高,促进纳米晶体镍(111)面择优生长,而提高脉冲电流密度则促进了纳米晶体镍 (200)面择优生长;通过正交试验发现:纳米晶体镍显微硬度最高的脉冲参数为:占空比为 20%,平均电流密度 30A/dm2,周期 100ms;最佳电流效率的脉冲参数为:占空比为 60%,平均电流密度 30 A/dm2,周期50ms。 2.纳米晶体镍加热过程的晶粒长大可分为三个阶段:晶粒稳定阶段(室温-200℃)、低温晶粒异常长大阶段(200℃-300℃)和晶粒正常长大阶段(300℃-500℃);其中纳米晶体镍的晶粒开始明显长大温度约为 270℃,其晶粒长大激活能约为 208kJ/mol;纳米晶体镍在晶粒稳定阶段保持原有的(200)面织构,而在低温异常晶粒长大阶段转变为(111)和(200)面双织构,在晶粒正常长大阶段又转变为弱的(111)面织构;纳米晶体镍的显微硬度在晶粒稳定阶段略有升高,随后随温度的升高而降低。 3.在 NaCl溶液和 HCl溶液中,不同晶粒尺寸的纳米晶体镍的耐蚀性能比瓦特镍和多晶镍板差;阳极极化曲线中,纳米晶体镍有钝化区出现;在HCl 溶液中,纳米晶体镍的自腐蚀电位和腐蚀电流密度随着晶粒尺寸减小分别减小和增大;纳米晶体镍和瓦特镍在 NaCl 溶液和 HCl溶液中腐蚀后形貌为局部点蚀,其中在 HCl中形成的腐蚀坑密度远远大于在 NaCl溶液中。 4.纳米晶体镍拉伸断裂为脆性断裂。晶粒尺寸为 27.8nm 的纳米晶体镍断裂强度约为 986MPa,屈服强度约为 624 MPa,延伸率约为 1.3%,变形强化指数 n 为 0.18;纳米晶体镍形变断裂过程中,裂尖发射位错,位错迅速离开裂尖向前运动,在裂尖前方有无位错区(DFZ) 形成,纳米晶晶界既是位错阱,能吸收位错,又是位错源,能向其它晶粒发射位错;微裂纹扩展有连续扩展和不连续扩展两种方式。更多还原

【Abstract】 The electrodeposition is one of the most promising methods for preparingfull dense nanocrystalline materials. In the present work, the pulseelectrodeposition was adopted to prepare bulk nanocrystalline nickel on thecopper base. The effect of pulse current density and saccharin concentration onthe microstructure as well as the grain size of nanocrystalline nickel wasinvestigated and the orthogonal method was employed to find the optimumresult of parameter for nanocrystalline nickel. The differential thermal analysis(DTA and DSC), X-ray diffraction (XRD), transmission electron microscopy(TEM) and so on, were applied to investigate the thermal stability ofnanocrystalline nickel. The corrosion resistance of nanocrystalline nickel wascompared with that of Watt nickel and polycrystalline nickel plate in thesolution of NaCl and HCl by the methods of static soak and polar anodicpolarization curve and the mechanism of corrosion was analyzed. Themechanical property of nano- crystalline nickel was evaluated by macroscopictension and the microscopic process of deformation and fracture was observedby in-situ tension test under TEM. The experimental results were shown asfollows. 1. The nanocrystalline nickel can be obtained by using pulseelectrodeposition with the addiction of saccharin into Watt-type solution. Theincrement of saccharin concentration and pulse current density can cause thegrain size of nanocrystalline nickel decrease. In the nanocrystalline nickel, theincreasing of saccharin concentration is beneficial to the preferential growth ofthe (111) planes, however, preferential growth of the (222) planes are enhancedwith the increasing of pulse current density. It was found by orthogonalexperiment that the optimum pulse parameter for the maximum micro-hardnessof nanocrystalline nickel can be 20% for duty ratio, 30 A/dm2 for averagecurrent density and 100ms for period. The optimum pulse parameter for currentefficiency can be 60% for duty ratio, 30A/dm2 for average current density and50ms for period. II<WP=4>2. The growing process of grains for nanocrystalline nickel during heatingcan be clarified as three stages: the stage ?, grains kept stabilizing (roomtemperature-200℃), the stage ? , grains growing abnormally at low temperature(200℃-300℃) and the stage ? , grains growing normally(300℃-500℃). Thetemperature of grain starting to grow significantly is about 270℃ and the activeenergy about 208 KJ/mol. The original (200) plate textures are kept in the stage? , howerer, the plane textures turn into (111) and (200) double texture in thestage ? , and again the plane textures turn into weak (111) ones in the stage ofgrains growing normally.The micro-hardness increases slightly in the stage ?and decreased with the increment of temperature after stage ?. 3. In the solution of NaCl and HCl, corrosion resistance of nanocrystallinenickel with varied grain sizes are lower than that of Watt nickel andpolycrystalline nickel plate. There are passivating areas in the curve of anodepolarization. In the HCl solusion, the corrosion potential decreases whilecorrosion current density increases as the grain size decreases. The local spotcorrosion occurs after etching in the NaCl and HCl solution and the density ofcorrosion pit in the HCl solution was much more than that in the NaCl solution. 4. The nanocrystalline nickel displays very high strength but very poorductility. The strength of fracture with grain size 27.8nm is about 986MPa, theyield strength about 624MPa, the elongation about 1.3%, deformation hardeningexponent n about 0.18. In the process of fracture in nanocrystalline nickel, thedislocations were emitted from the crack tip and moved forward, and then adislocation free zone (DFZ) formed in the front of crack tip. The dislocation canbe absorbed by the grain boundary or emitted from the grain boundary. Themicro-crack propagates from crack tip continually or discontinually.更多还原