【作者】 李学磊；

【导师】 朱荻；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 电铸技术是一种利用电沉积原理制造零件的精密特种加工方法,它具有加工时无切削应力变形、无热影响区、无工具损耗、成形精度高等优点,主要用于传统工艺难以加工的金属零件的制造,已在航空、航天、兵器、汽车等领域获得重要的应用。但是,传统的电铸技术在生产应用中仍然存在着一些难以解决的问题,例如,具有复杂型面的零件在电铸时,其外表面质量差,容易产生麻点、针孔和结瘤等问题;镍锰合金电铸时,除了有外表面质量的问题,还存在因元素成分分布不均而导致电铸层开裂的问题;电铸铬层中因内应力的存在,将会产生微裂纹。这些问题的存在一直制约着电铸技术的发展。为了解决传统电铸技术在实际生产应用中存在的技术问题,本文利用一种新型的电铸技术——游离粒子磨擦辅助电铸技术,分别对金属镍、镍锰合金和铬进行了电铸试验研究。其具体研究内容包括以下几个方面:1.提出了阴极平动式游离粒子磨擦辅助电铸技术,解决了复杂型面零件电铸成形问题,并进行了相关的试验研究。对游离粒子磨擦辅助电铸技术的作用机理进行了深入分析。试验结果和理论分析得出,在电沉积过程中,通过游离粒子的磨擦、挤压和碰撞阴极表面能够有效去除副反应所带来的针孔、麻点等缺陷,强化沉积层;在阴极周围作随机运动的游离粒子能够使阴极表面的电场分布呈现动态效果,起到脉冲电沉积的作用,可以细化晶粒,改善沉积层的性能。2.研制了精密电铸设备和平动机构,采用上下进给机构、旋转主轴和平动装置的复合设计方式,并根据实际需求,设计了平动量和平动频率均可在较大范围内调节的平动装置,使机床操作方便,并可用于不同形状和尺寸零件的精密电铸成形。3.获得了阴极平动式游离粒子磨擦辅助电铸技术在不同工艺参数下,对镍电铸层的表面形貌、组织结构和性能的影响规律。结果表明,使用阴极平动式游离粒子磨擦辅助电铸技术可以显著提高电铸层外表面质量,所制备镍电铸层的外表面光亮,表面粗糙度低于Ra0.056μm。与传统电铸技术所制备电铸层相比,磨擦辅助电铸技术所制备镍电铸层各晶面的衍射强度降低,择优程度发生改变,晶粒尺寸显著减小,在一定工艺参数范围内晶粒小于150 nm;显微硬度和抗拉强度都提高了将近一倍。并成功电铸成形了形状复杂、表面光亮、显微硬度在380HV-400HV之间的电解工具电极。4.针对火箭发动机推力室身部外壁镍锰合金电铸时存在的表面质量、沉积速度和沉积均匀性问题,开展了游离粒子磨擦辅助电铸试验。获得了工艺条件对电铸层的锰含量、微观组织结构及性能的影响规律。结果表明,在较低锰盐浓度和较高温度时,可以在较高电流密度时进行电铸,电铸层的锰含量在0.5wt%以内,在此条件下,可以相应的提高电铸速度;所得到的电铸层表面光亮,平整,无任何缺陷的电铸层,其表面粗糙度低于Ra0.05μm,晶粒得到了明显的细化。与传统电铸相比,其组织结构也发生了明显的改变,(200)面取代了(220)面成为主要择优取向面;显微硬度和抗拉强度都得到了明显提高,电铸层中锰含量分布均匀性得到了提高。并成功制备了表面光亮的火箭发动机推力室身部外壁,对其测试与分析表明,电铸层达到了较好的厚度及成分分布均匀性。5.针对飞机起落架“渗气”现象,开展了无裂纹电铸铬的基础试验研究。对电铸铬层中微裂纹产生的机理进行了深入的研究,利用游离粒子的扰动来提高析氢过电位,改变组织结构,减小内应力,从而达到根除裂纹的目的。研究了工艺参数对电铸层的耐蚀性、耐磨性、显微硬度和结合力的影响规律。结果表明:在一定工艺参数下能够得到无裂纹的电铸铬层,经336h盐雾试验后不出现任何腐蚀,显微硬度达到了600HV以上,表面粗糙度在Ra0.1μm以下,结合强度满足要求。更多还原

【Abstract】 Electroforming is a nontRaditional machining technology in which a metallic part is produced by the electrodeposition of metal onto a cathode mandrel in an electrolytic bath. It has high fidelity of shape reproduction without heat affected zones, cutting force and tool wear, which is mainly used for the metallic parts that are difficult to manufacture for tRaditional machining. Now it has been successfully employed in the areas of aviation, aerospace, weapon, automobile and so on.However, there are still some disadvantages in applications of tRaditional electroforming that are difficult to be overcome. For example, poor surface with pinholes and nodules usually appears in the electroforming of complex parts with thin wall. In the process of Ni-Mn alloy electroforming, there is cRack problem due to the nonuniform distribution of element composition besides poor surface. Because of internal stress, micro cRacks will appear in the tRaditional chromium electroforming. As a result, the development of electroforming is seriously restricted.A novel electroforming technique named AbRasion-assisted Precision Electroforming (APEF) is utilized to resolve the problems of tRaditional electroforming in the area of applications. Electroforming of nickel, Ni-Mn alloy and chromium is respectively researched in the dissertation. The main works focused on the research and application of APEF as follows:1. In order to resolve existing electroforming problems of complex parts with thin wall, APEF with orbital movement cathode was put forward. The mechanism of APEF has been studied by experimental and theoretical analysis. The results showed that the polishing, extruding and impacting with free particles could effectively eliminate the pinholes, pits and nodules caused by hydrogen evolution. Simultaneously, free particles that touch tightly the cathode surface move in Random directions, which can effect the electric field distribution of cathode surface just like pulse electroforming. As a result, bright layers with finer gRains and better properties were obtained.2. A new precision electroforming machine and orbital movement device have been developed. Feeding mechanism, rotated main axis and orbital movement device were assembly designed to make the machine easily be opeRated. Particularly, orbital movement device with larger orbital moving amplitude and frequency was designed to expand the scope of electroforming objective.3. Nickel electroforming by APEF with orbital movement cathode has been researched. The morphology, microstructure and properties of nickel electroformed with various processing paRameters were studied. The results showed that the APEF can observably improve the surface quality, and produce a bright nickel deposit with surface roughness of less than Ra 0.056μm. The degree of preferential orientation notably decreased and each preferential orientation changed, the gRain size obviously decreased less than 150nm. Both micro hardness and tensile strength of the deposits could be increased by double in contRast with the sample produced by tRaditional electroforming methods. Based on the experimental results, complex blade cathodes with smooth surface and higher micro hardness Ranging from 380HV to 400HV were produced successfully.4. In order to resolve the existing problems of surface quality, electroforming Rate and nonuniform distribution of element composition on the outer shell of thrust chamber of rocket engine, experiments of Ni-Mn alloy electroforming using APEF were carried out. The manganese contents, microstructure and properties of the Ni-Mn deposits electroformed with various processing paRameters were studied. The experimental results showed that higher current density could be used and the manganese content could be controlled less than 0.5wt% under the condition of low concentRation manganese salt and high tempeRature. The sample produced by APEF was bright and smooth without any defects; the surface roughness was less than Ra 0.05μm and the gRain sizes were refined. Compared with the sample electroformed with tRaditional method, the microstructure changed obviously among which the crystal of (200) is preferential orientation instead of (220) preferential orientation. The micro hardness and tensile strength could be increased too. The bright deposition layers of electroforming Ni-Mn alloy used for the outer shell of thrust chamber of rocket engine were produced successfully with better thickness and uniform distribution of element composition.5. Experimental research of cRack-free chromium electroforming was carried out aimed to permeability gas phenomenon. The geneRation mechanism of micro cRacks was carefully studied. The disturbing of free particles can increase the overpotential of hydrogen evolution, change the microstructure and decrease the internal stress. Therefore micro cRacks in the coating can be eliminated. The corrosion resistance, wear resistance, micro hardness and bonding strength of the chromium coating electroformed with various processing paRameters were studied. The experimental results showed that cRack-free chromium coating without any corrosion after 336 hours neutRal salt fog spRay test can be obtained, the micro hardness was above 600HV, the surface roughness was less than Ra 0.1μm and the bonding strength met the requirement.更多还原