纯Cu表面Ni-Al梯度涂层的制备

发布时间：2018-06-23 09:16

本文选题：纯Cu表面涂层 + Ni-Al金属间化合物　；参考：《东南大学》2015年硕士论文

【摘要】：采用电镀Ni+粉末包埋渗Al法在纯Cu表面制备CuNi固溶体/Ni/NiAl金属间化合物梯度涂层。在课题组前期的研究中发现,涂层Cu-Ni界面存在较多孔洞,Ni2Al3相转变为NiAl相的临界条件是什么,渗AI层形成的机理是什么,如何设计和实现涂层的结构,如涂层总厚度及各层厚度,这些问题都有待进一步探索。本文在前期研究的基础上,试图解决上述问题,通过采用光学金相显微镜、场发射扫描电镜、X射线衍射图谱、EDS能谱等分析样品的表面形貌和相组成以及截面的元素分布,并测量了涂层的显微硬度、抗高温氧化性能、耐磨性能以及抗热震性能,进一步探索了涂层制备工艺,取得了一些研究成果。在纯Cu表面电镀Ni层,研究了电流密度、pH值和添加剂糖精对Ni沉积速度、镀层表面形貌、硬度以及对后续渗Al过程中的Cu-Ni扩散和渗Al层的影响。结果表明,提高电流密度、降低pH值和加入糖精均使Ni沉积速度提高,电流密度的提高使镀层晶粒细化,高电流密度与低pH值有利于(111)晶面择优取向,糖精的加入有利于(200)晶面择优取向。镀层晶粒的细化和(200)晶面择优取向有利于Cu-Ni、Ni-Al的扩散。通过对镀Ni层样品进行热处理,模拟渗Al过程,探索了温度和时间对Cu-Ni扩散速度及扩散层成分分布的影响以及Cu-Ni界面孔洞形成的原因。结果表明,提高扩散温度,可以显著提高Cu-Ni的扩散速度,Cu-Ni扩散速率随着时间的延长而减小。Cu-Ni界面的孔洞是由于Cu扩散速率大于Ni的可肯达尔效应造成的,要减少孔洞的形成,需要降低Cu扩散速率,制备致密度高、缺陷少的Ni镀层。研究了渗Al工艺对渗AI速度及渗层组织的影响,并分析渗Al层形成过程及机理。结果表明,在600℃-750℃范围内,渗层厚度随着渗Al温度的提高而增加。在1-3h范围内,Ni-Al的扩散反应速率随着时间的延长而减小。CeO2的加入使渗层表面晶粒细小、平整,但渗层内产生了较多空洞,Ce02的加入反而限制了渗A1速度,其影响较为复杂。不同渗Al参数并不影响渗层的相组成,均为单相Ni2Al3。研究了不同温度(850℃-1000℃)氧化过程中Ni2Al3相的相变过程。结果表明,渗层Ni2Al3相在高温氧化过程中会优先转变为Ni3Al相,但随着氧化时间的延长,会逐渐转变为NiAl相,且当温度越高,转变为NiAl相所需要的时间就越短。在高温下,NiAl相比Ni3Al相更稳定。分析了渗Al层形成过程与机理,并发现涂层总厚度约等于镀Ni层厚度与渗Al层厚度之和。采用优化的电镀工艺：电流密度为0.6A/dm2,镀液pH值为5.5,不加任何添加剂条件下电镀2.5h,并在渗Al温度650℃下扩散渗Al1h,制备了总厚度为50μm的CuNi固溶体/Ni/Ni2Al3梯度涂层,测试了涂层的性能。研究结果表明,采用上述工艺基本上解决了课题组前期遗留下来的一系列问题,涂层与基体以及Ni与Ni2Al3之间结合良好,渗Al层的硬度达到了HV900,在800℃下氧化60小时后的氧化增重为1.156mg·cm-2,渗层平均摩擦系数约为0.477,样品在500℃和700℃下的热震次数均达到了20次以上。涂层的硬度、耐磨损性能以及抗高温氧化性能都要明显优于纯Cu以及纯Ni镀层,涂层具有良好的抗热震性能。
[Abstract]:The gradient coating of CuNi solid solution /Ni/NiAl intermetallic compound was prepared on pure Cu surface by electroplating Ni+ powder embedded infiltration Al method. In the previous study of the project group, it was found that there were more holes in the Cu-Ni interface of the coating. What is the critical condition of the transition from Ni2Al3 phase to NiAl phase; what is the mechanism of the formation of the AI layer, and how to design and implement the structure of the coating. These problems, such as the total thickness of the coating and the thickness of each layer, are to be further explored. On the basis of the previous study, this paper tries to solve the above problems by using optical metallographic microscope, field emission scanning electron microscope, X ray diffraction pattern, EDS energy spectrum and so on to analyze the surface morphology and phase composition of the sample and the distribution of elements in the cross section. The microhardness, high temperature oxidation resistance, wear resistance and thermal shock resistance of the coating have been further explored. Some research results have been obtained. The deposition rate of current density, pH value and additive saccharin on Ni, the surface morphology and hardness of the coating, and the Cu-Ni expansion in the subsequent Al process are studied on the pure Cu surface. The effect of dispersion and infiltration of Al layer shows that increasing the current density, reducing pH value and adding saccharin all make the deposition rate of Ni increase, the increase of current density makes the grain refinement of the coating, high current density and low pH value are beneficial to (111) preferred orientation of crystal surface, the addition of saccharin is beneficial to (200) preferred orientation of crystal surface. Grain refinement of the coating and (200) crystal face selection The preferential orientation is beneficial to the diffusion of Cu-Ni and Ni-Al. Through the heat treatment of Ni coating, the influence of temperature and time on the diffusion velocity of Cu-Ni and the distribution of the composition of the diffusion layer and the formation of the pores in the Cu-Ni interface are explored. The results show that the diffusion temperature of the Cu-Ni can be increased and the diffusion speed of Cu-Ni can be improved significantly. The diffusion speed of Cu-Ni can be significantly improved. With the prolongation of time, the hole in the.Cu-Ni interface is caused by the Kendal effect of the Cu diffusion rate greater than Ni. To reduce the formation of the hole, it is necessary to reduce the Cu diffusion rate and prepare the Ni coating with high density and less defects. The effect of the infiltration of the Ni on the infiltration rate and the microstructure of the infiltrated layer is studied, and the formation process of the infiltration Al layer is analyzed and the formation process of the infiltration Al layer is analyzed. The results show that the thickness of the permeation layer increases with the increase of Al temperature in the range of 600 C -750. In the range of 1-3H, the diffusion reaction rate of Ni-Al decreases with time, and the addition of.CeO2 makes the surface grain of the permeable layer fine and smooth, but there are more holes in the layer, but the addition of Ce02 restricts the velocity of the permeation A1, and the influence of the infiltration rate is limited. The different Al parameters do not affect the phase composition of the permeable layer. The phase transition process of Ni2Al3 phase in the oxidation process at different temperatures (850 C -1000 C) is studied for the single-phase Ni2Al3.. The results show that the Ni2Al3 phase in the permeation layer will change to Ni3Al phase in the process of high temperature oxidation, but with the prolongation of the oxidation time, it will gradually change into NiAl phase, and when the oxidation time is prolonged, the phase will be gradually transformed into NiAl phase. The higher the temperature, the shorter the time needed to transform into the NiAl phase. At high temperature, NiAl is more stable than the Ni3Al phase. The formation process and mechanism of the Al layer are analyzed, and the total thickness of the coating is equal to the sum of the Ni layer thickness and the thickness of the infiltrated Al layer. The optimized electroplating process: the current density is 0.6A/dm2, the pH value of the plating bath is 5.5, without any addition. Under the condition of electroplating 2.5h and diffusion of Al1h at the temperature of 650 C, the CuNi solid solution /Ni/Ni2Al3 gradient coating with a total thickness of 50 m was prepared, and the performance of the coating was tested. The results show that the above process has basically solved a series of problems left over by the project group, and the combination of coating and matrix, and the combination of Ni and Ni2Al3. The hardness of the permeable Al layer reached HV900. The oxidation weight increased to 1.156mg. Cm-2 at 800 C for 60 hours. The average friction coefficient of the layer was about 0.477. The thermal shock times of the samples reached more than 20 times at 500 and 700. The hardness, wear resistance and high temperature oxidation resistance of the coating were obviously better than pure Cu and pure Ni plating. The coating has good thermal shock resistance.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

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