【作者】 胡斌梁；

【导师】 谭援强；

【作者基本信息】 湘潭大学 ， 一般力学与力学基础， 2013， 博士

【摘要】 Ni-P合金镀层具有镀液稳定、操作简单、耐磨耐蚀性能优良以及性价比高等特点,在电子、机械、化学化工等工业领域中获得了广泛应用。但是,随着现代科学技术的快速发展,单一镀层材料难以满足复杂恶劣工况条件下对材料性能的要求,多元多功能Ni-P复合镀层材料正日益引起人们的重视。本文研究工作以纳米三氧化二铝和六方氮化硼为分散相,采用脉冲电沉积方式制备Ni-P复合镀层,利用SEM、XRD以及EDS等手段分析镀层的结构,同时采用Tafel线性外推法、电化学交流阻抗以及摩擦磨损实验等手段对镀层的耐蚀及摩擦学性能进行评价。为了探索复合镀层的失效机理,本文对Ni-P/纳米Al₂O₃复合镀层划痕过程进行了有限元模拟,分析了涂层中应力分布规律,获得了涂层可能产生裂纹的位置和模式。采用脉冲电沉积方法制备Ni-P复合镀层的适宜工艺条件为：pH值4.0,脉冲频率1500Hz,占空比0.2,电流密度5A/dm2,镀液温度50℃,镍磷镀液中分散相Al₂O₃或BN（h）悬浮量为20g/L,表面活性剂为聚乙烯醇。Ni-P复合镀层热处理前为非晶态结构,经200℃热处理后镀层内析出少量的Ni₅P₄和Ni₁₂P₅等亚稳相,镀层结构仍为非晶态,300℃热处理80分钟后镀层内开始析出少量稳定的Ni₃P相,镀层为非晶态与晶态混合组织,400℃热处理80分钟后,镀层中Ni₁₂P₅等亚稳相消失,主要为Ni₃P相,镀层已完全晶化。与Ni-P合金镀层对比,Al2O3、BN（h）固体颗粒阻滞了镀层中第二相的析出速度,使晶化时间延长。当热处理温度不变时,随着热处理时间的延长,Ni-P复合镀层的显微硬度先增大后减小,出现一个硬度峰值；提高镀层的热处理温度,达到硬度峰值所需要的热处理时间缩短。载荷为30N,转动速度为100r/min时,Ni-P/纳米Al₂O₃和Ni-P/BN（h）复合镀层与淬火45钢对摩时的摩擦因数分别为0.2、0.08,2种复合镀层的耐磨性能比Ni-P合金镀层显著提高,Ni-P复合镀层具有优异的摩擦学性能。在低载荷和低转速条件下,复合镀层的磨损机理为轻微磨粒磨损,在高载荷和高转速条件下,表现为疲劳磨损与磨粒磨损的混合磨损机理。2种Ni-P复合镀层在3.5%NaCl和10%H₂SO₄腐蚀介质中的耐蚀性能均优于Ni-P合金镀层；热处理后复合镀层在3.5%NaCl溶液中的耐蚀性能发生了改变,300℃热处理后的复合镀层耐蚀性能最好,而400℃热处理后的耐蚀性能降低,出现了轻微的点蚀；随着浸泡时间的延长,Ni-P/BN（h）复合镀层的耐蚀性先升高后降低。铝液与Ni-P/纳米Al₂O₃复合镀层的湿润性较差。铝液在Ni-P/纳米Al203复合镀层表而只发生界面反应,产生较薄的金属化合物AlP或Al₃Ni层,不利于铝液在复合镀层上的铺展。因此,Ni-P/纳米Al203复合镀层表现出良好的耐铝侵蚀性能。划痕过程可以分为划针尖端压入涂层表面、划针在涂层表面上滑动和划针升高等三个阶段。前两个阶段由于划针尖端对涂层表面的作用,在涂层表面形成划痕,在涂层中产生局部高应力;划针升高后在涂层中留下了较大的残余应力。应力分析表明当划针尖端压入涂层后,由于基底的塑性变形,在划针尖端周边的接触边缘区域会产生堆积变形,在堆积的顶点,径向应力和第一主应力具有最大拉应力；在接触中心之下,涂层/基底界面上的对应点,径向应力、第一和第二主应力会出现最大拉应力：划针尖端压入涂层后在涂层表面滑动时,划针尖端的前面,涂层会产生最大的堆积,在堆积区域的顶点,沿滑动方向的正应力和第一主应力出现了最大拉应力；划针尖端压入涂层深度越大,基底塑性变形越大,堆积就会越高,在堆积区沿着滑动方向的正应力和第一主应力就会越大;对于涂层为弹性变形,基底为弹塑性变形的涂层结构,划痕过程产生的残余应力主要集中在划痕结束时划针尖端之下的涂层/基底界面区域,以及划针尖端前面的堆积区,残余应力的最大值主要存在于涂层表面和基底/涂层界面的涂层中,这些最大残余应力均是拉应力。根据应力的分布规律,在划痕过程中涂层产生裂纹主要会出现在划针尖端前面堆积区的表面和划针与涂层接触区之下的涂层/基底界面上,这些区域内最大应力都是拉应力,相应地会产生第一型裂纹。由于在划痕后,在涂层中存在较大的残余应力,即使划痕结束后,在涂层中仍然有可能引起新裂纹和原有裂纹扩展。更多还原

【Abstract】 Due to its simple process, good performance and economy, Ni-P alloy coating has been widely used in industries, such as mechanical, electronics and chemical engineering, etc. However, with the development of the science and technology, the alloy coating cannot meet the complicated environment. Thus, multifunctional Ni-P composite coating materials have been paid more and more attention to. The hexagonal boron nitride [BN(h)] particles have excellent lubrication performance, high thermal stability and corrosion resistance, so preparation Ni-P/BN(h) composite coating by adding BN(h) particles to Ni-P base plating solution, can further improve the corrosion resistant wear-resisting performance of Ni-P alloy coating, and have much significance.Ni-P/BN(h) composite coating was prepared by electroplating, evaluated by the organization structure of the coating, microhardness and deposition rate of the coating, to study the process of Ni-P/BN(h) composite coating. Results show that the best technology for pulse frequency was1500Hz, occupies empties compared was0.2, pH was4.0, electroplating temperature was50℃, current density was5A/dm2, the content of BN(h) particle in plating solution was20g/L, and surface active agent was poval.The effect of technology for heating processing on organization structure and microhardness of Ni-P/BN(h) composite coating was studied. Results show that as-deposited Ni-P/BN(h) composite coating was amorphous structure; a small amount of Ni5P4and Ni12P5etc. metastable phases were precipitated from coating, and the coating was still amorphous structure after200℃heat treatment; but after300℃heat treatment in80minutes, the precipitated phases were a lot of unsteady phases and a small amount of Ni3P stable state phase, the composite coating was amorphous structure and crystalline state mix organize; after heat treatment of400℃in80minutes, the composite coating was crystallized to great degree. Compared to Ni-P alloy coating, BN(h) particles could lead to reduce the precipitated speed of the second phase and extend crystallization time. At given heat treatment temperature, the microhardness of Ni-P/BN(h) composite coatings increase at the beginning, then decrease with the extension of heat treatment time, which have a maximum microhardness; The time of reaching the maximum microhardness of composite coating was short, as the heat treatment temperature rises.Friction factor of Ni-P/BN(h) composite coating reduced with the suspension quantity of BN(h) increased; when suspension quantity of BN(h) was20g/L, the friction factor was minimum, about0.08, wear loss was just as a quarter of Ni-P alloy plating, Ni-P/BN(h) composite coating showed excellent tribological properties. The friction factor of composite coating increased with loads and rotation speed increased, the wear mechanism of composite coating was slight particle attrition when load and rotation speed were low. However, the wear mechanism of composite coating was fatigue wear and particle attrition synergy when load and rotation speed were high. The corrosion resistance performance of Ni-P/BN(h) composite coating was researched by SEM, tafel polarization curves and electrochemical impedance spectroscopy. The experimental results show that the corrosion resistant performance of Ni-P/BN(h) was superior to Ni-P alloy plating when immersed in3.5%NaCl and10%H2SO4solution for240h. This research concluded that corrosion resistance performance of Ni-P/BN(h) composite coating after heat treatment in3.5%NaCl solution were changed, the best corrosion resistance performance was at300℃heat treatment; and after400℃heat treatment of corrosion resistant performance was reduced, a little corrosion would appear, and the polarization resistance was least; And, the corrosion resistance of Ni-P/BN (h) composite coating were first increased, then decreased as for the extension of immersed time.In order to explore the mechanism of coating failure, the work had simulated scratching process on coating surface of TiN hard material deposited on strain hardening steel substrate with finite element method; next, it analyzed stress field in coating; finally, it predicted positions and modes that crack might initiate. Scratch process may be divided into three phases, i.e. a stylus tip indenting coating surface, the stylus tip slipping on coating surface and the stylus tip rising over coating surface. During former two phases, the stylus tip has coating surface formed a groove due to its acting on coating surface, and induces local stress concentration. There are residual stresses in coating after the stylus tip rises over the coating surface. Stress analyses have showed that after the stylus tip indents the coating surface, pile-up deformation appears near the edge of contact zone due to the plastic deformation of substrate, and radial stress and first principal stress reach the maximum tensile stresses at the vertex of pile-up deformation; likewise, radial stress and first and second principal stresses reach the maximum tensile stresses at the corresponding point of the substrate/coating interface underneath the contact center. When the stylus tip slips continuously on the coating surface after it indents the coating surface, the coating surface takes place the highest pile-up deformation front the stylus tip. At the vertex of pile-up deformation, the normal stresses along slipping direction and first principal stress have the maximum tensile stress. The deeper the stylus tip indents the coating surface, the heavier the substrate generates plastic deformation, the higher the coating surface take place the pile-up deformation, the larger the stresses are induced. For the coating system in which the coating material is deformed by elastic deformation and the substrate material is deformed by elastic and plastic deformation, biggish residual stresses induced during scratch process mainly occur on the coating surface and in the coating of the substrate/coating interface, and those residual stresses all are tensile.Based on the analysis of stress distributing rules in the scratch process, the crack initiating in the coating may mainly occur on the surface of the pile-up zone front stylus tip and on the coating/substrate interface underneath the contact region between stylus tip and coating. In the zones, the maximum stresses induced by scratching are tensile; accordingly, the cracks induced by the maximum stresses are mode. Moreover, because there are biggish residual stresses in coating after scratching, they may still induce fresh crack generation and original crack propagation.更多还原