纳米等离子涂层制备—整体加热重熔及其点蚀特性研究

发布时间：2018-02-25 16:29

本文关键词： 团聚体纳米等离子涂层孔隙及裂纹重熔点蚀钝化　出处：《上海大学》2016年博士论文　论文类型：学位论文

【摘要】：本文以Cu、FeCr、NiAl、FeSi四种纳米粉体为原料,制备Cu、FeCr、NiAl、FeSi四种纳米等离子涂层,并对四种纳米等离子涂层进行重熔处理。本文主要开展的工作如下:本文首先通过喷雾造粒法及等离子喷涂技术,制备出Cu、FeCr、NiAl、FeSi四种纳米等离子涂层,并对其内部结构及相关性能进行初步测试分析;为了进一步优化四种纳米等离子涂层内部结构、耐腐蚀性能及机械性能,将Cu、FeCr、NiAl、FeSi四种纳米等离子涂层分别在850℃、900℃、950℃、1000℃,1050℃、1100℃、1150℃、1200℃,650℃、700℃、750℃、800℃,1100℃、1150℃、1200℃、1250℃温度进行氢气气氛下整体加热重熔处理,并分别对四种纳米等离子涂层在内部微观形貌及结构、耐腐蚀性能及机械性能方面进行测试分析,以期得到具有更好内部结构及性能的等离子涂层;此外,为了进一步研究纳米等离子涂层在3.5%(wt.)NaCl溶液中的腐蚀机理,通过扫描电化学显微镜(SECM)对四种涂层微观点蚀性能进行测试分析,从而揭示纳米等离子涂层在腐蚀溶液中的点蚀过程及机理;另外,对四种纳米等离子涂层在硼酸缓冲液中的钝化现象及钝化膜性能进行了研究;最后,通过materials studio软件对四种纳米等离子涂层热处理工艺进行了模拟,从而在分子动力学及表面能的层面对纳米等离子涂层在热处理过程中的结构及性能的变化,以及对涂层内部结构对涂层晶粒弛豫现象的影响进行理论研究,通过以上几个方面的研究,主要得到的结论如下:通过喷雾造粒法对四种纳米粉体进行了团聚处理,团聚体具有良好的质量及流动性,适宜直接作为等离子喷涂的喷涂材料;通过等离子技术直接将团聚体作为喷涂材料喷涂至Q235低碳钢表面,制备出四种纳米等离子涂层,通过对涂层微观形貌及性能的研究发现,纳米等离子涂层内部结构表现出明显的双重特性,即纳米等离子涂层由未熔化的纳米级颗粒及熔化部分构成,未熔化的纳米级颗粒之间及纳米级颗粒与熔化部分界面处存在细小缝隙,这些细小缝隙在纳米等离子涂层中形成孔隙及裂纹,所以,纳米等离子涂层中存在孔隙及裂纹的原因是由于涂层中未熔化纳米级颗粒的存在。将Cu、FeCr、NiAl、FeSi四种纳米等离子涂层分别在850℃、900℃、950℃、1000℃,1050℃、1100℃、1150℃、1200℃,650℃、700℃、750℃、800℃,1100℃、1150℃、1200℃、1250℃温度进行氢气气氛下重熔处理发现,Cu、FeCr、NiAl、fesi四种纳米等离子涂层分别在950℃、1150℃、700℃、1200℃下进行重熔处理后,涂层内部纳米级颗粒被消除,涂层内部形成单一致密的结构,从而使涂层中的孔隙及裂纹明显减少甚至消除,涂层的耐腐蚀性能及机械性能显著提高。四种纳米等离子涂层在3.5%(wt.)nacl溶液中发生点蚀现象的主要原因是由于涂层中存在孔隙及裂纹,涂层结构不致密所致,溶液通过纳米等离子涂层中的孔隙及裂纹进入涂层内部并对低碳钢基体进行腐蚀,从而在样品表面形成点蚀;纳米等离子涂层在3.5%(wt.)nacl溶液中的腐蚀包括两种腐蚀行为,即点蚀及均匀腐蚀,均匀腐蚀是由于涂层本身被腐蚀产生的,而这种腐蚀产生的电流远小于点蚀所产生的电流,且均匀腐蚀产生的电流并不随着重熔温度的不同及浸泡时间的不同而发生明显的变化,说明纳米等离子涂层在不同温度重熔处理后及在溶液中不同浸泡时间所表现的耐腐蚀性能的强弱主要是由于点蚀行为的不同;纳米等离子涂层在3.5%(wt.)nacl溶液浸泡过程中,涂层中孔隙及裂纹较大的地方点蚀程度容易随着浸泡时间的延长逐渐增强,而一些孔隙及裂纹较小的地方,点蚀现象容易随着浸泡时间的延长减弱甚至消失,这主要是点蚀产生的不溶性生成物会将孔隙及裂纹堵塞所致;cu、fecr、nial、fesi四种纳米等离子喷涂样品分别在950℃、1150℃、700℃、1200℃温度下重熔处理后具有最好的耐点蚀性能,这主要是由于在这些温度下重熔处理后涂层孔隙及裂纹较少,涂层致密性及均匀性较好。对低碳钢基体及分别在950℃、1150℃、700℃、1200℃温度下重熔处理后的cu、fecr、nial、fesi纳米等离子涂层在硼酸缓冲液中进行动电位极化曲线、恒电位阳极钝化及mott-schottky进行研究可知,四种纳米等离子涂层在硼酸缓冲液中均出现钝化现象,且四种经过以上温度重熔处理后的涂层维钝电流均较低碳钢偏小;四种纳米等离子涂层在硼酸缓冲溶液中恒电位阳极钝化过程中产生较为致密的钝化膜,这种钝化膜可以有效屏蔽电荷的通过,而低碳钢则形成较为疏松多孔的钝化膜,这种钝化膜不能有效的对电荷产生屏蔽作用,四种纳米等离子涂层在硼酸缓冲溶液中形成p型半导体,而低碳钢则形成n型半导体,且四种纳米等离子涂层钝化膜载流子密度均较低碳钢明显偏小。对cu、fecr、nial、fesi四种纳米等离子涂层分别在850℃、900℃、950℃、1000℃,1050℃、1100℃、1150℃、1200℃,650℃、700℃、750℃、800℃,1100℃、1150℃、1200℃、1250℃温度下重熔进行materials studio模拟发现,Cu、FeCr、NiAl、FeSi四种纳米等离子涂层分别在950℃、1150℃、700℃、1200℃温度下重熔处理后其表面能最小。说明四种纳米等离子涂层分别在950℃、1150℃、700℃、1200℃温度下重熔处理后涂层最稳定,涂层内部缺陷最少;将模拟实验与重熔实验进行对比分析可以看出,模拟状态下的四种最佳热处理温度与重熔实验中最佳重熔温度吻合,这说明经过最佳重熔处理后,纳米等离子涂层内部未熔化纳米级颗粒被消除,涂层致密度增强,从而有效降低了涂层内部晶粒的弛豫现象。
[Abstract]:In this paper, Cu, FeCr, NiAl, FeSi four nano powder as raw materials, preparation of Cu, FeCr, NiAl, FeSi four nano coating, and four kinds of nano coating of plasma remelting. The main work is as follows: firstly, by spray granulation and plasma spraying technology, preparation Cu, FeCr, NiAl, FeSi four nano coating, and the performance of its internal structure and preliminary test analysis; in order to further optimize the internal structure of four kinds of nano coating, corrosion resistance and mechanical properties, corrosion resistance to Cu, FeCr, NiAl, FeSi four nano plasma coating respectively at 850 C, 900 C, 950 C, 1000 C, 1050 C, 1100 C, 1150 C, 1200 C, 650 C, 700 C, 750 C, 800 C, 1100 C, 1150 C, 1200 C, 1250 C temperature under hydrogen atmosphere heating remelting, and respectively to four kinds of nano coating in micro plasma the morphology and The structure, properties and mechanical properties of corrosion resistance are analyzed in order to get better performance with plasma coating structure and internal; in addition, in order to further study the nano coating on the plasma 3.5% (wt.) corrosion mechanism in NaCl solution, by scanning electrochemical microscopy (SECM) were tested on four kinds of coating micro pitting the performance, so as to reveal the pitting corrosion process and mechanism of nano coating in corrosion solution; in addition, the performance of four kinds of nano coating passivation in borate buffer solution and passivation film were studied; finally, through the simulation of four kinds of nano coating heat treatment process of Materials Studio software, so as to change the face of the structure and properties of nano coating during heat treatment in molecular dynamics and surface energy of the coating layer, and the internal structure of the coating grain relaxation Theoretical study of the phenomenon, through the researches above, the main conclusions are as follows: by spray granulation of the reunion of four kinds of nano powder, aggregates with quality and good fluidity, suitable as spraying material for plasma spraying; by plasma technology directly to the aggregates as spraying materials to spray Q235 low carbon steel surface, prepared four kinds of nano coating, through the study on Microstructure and properties of the coatings, the internal structure of nano plasma coating showed double features obvious, namely nano plasma coating consists of nano particles and melting part of unmelted, there are tiny gaps between the nano particles and unmelted nano particles and melting part of the interface, the small gap formation of cracks and pores in the nano coating, so nano plasma Causes of cracks and pores in the coating is due to sub unmelted nano particles in the coating. The Cu, FeCr, NiAl, FeSi four nano plasma coating respectively at 850 C, 900 C, 950 C, 1000 C, 1050 C, 1100 C, 1150 C, 1200 C, 650 C, 700 C, 750 C, 800 C, 1100 C, 1150 C, 1200 C, 1250 C temperature under hydrogen atmosphere remelting treatment, Cu, FeCr, NiAl, FeSi four nano plasma coating respectively at 950 C, 1150 C, 700 C, 1200 C after remelting treatment, coating with nanometer particles by eliminating the internal structure of the coating, to form a single compact, so that the pores in the coating and the crack was reduced or even eliminated, corrosion resistance and mechanical properties of the coating significantly improved. Four kinds of nano plasma coating (wt.) in 3.5% main causes of pitting in the solution of NaCl is due to the presence of cracks and pores in the coating. Coating The dense solution through the pores caused by nano plasma coating in coatings and corrosion and crack into the low carbon steel substrate, resulting in the formation of pitting corrosion on the surface of the sample; in the 3.5% coating nano plasma (wt.) corrosion in NaCl solution includes two kinds of corrosion behavior, namely pitting corrosion and uniform corrosion, uniform corrosion is due to the coating itself the corrosion current and corrosion, this is far less than the current generation of pitting, and uniform corrosion is not different with the remelting temperature and soaking time of different change shows that the nano plasma coating after remelting treatment at different temperatures and different soaking time in solution showed corrosion the performance of the strength is mainly due to the different Pitting Behavior; in the 3.5% coating nano plasma (wt.) NaCl solution soaking process, the pores and cracks of large The local pitting degree easily with the increase of immersion time increased, while some smaller pores and cracks, pitting phenomenon easily with the extension of soaking time, weaken or even disappear, this is mainly pitting corrosion of insoluble material will generate cracks and pores blockage caused by Cu, FeCr, NiAl; FeSi, four kinds of nano plasma spraying the samples were at 950 C, 1150 C, 700 C, at a temperature of 1200 DEG C after the remelting treatment has the best corrosion resistance, which is mainly due to the temperature in the coating after remelting treatment of cracks and pores small, compact coating and good uniformity. The low carbon steel substrate and respectively at 950 degrees, 1150 degrees. 700 C, Cu, after the remelting treatment at a temperature of 1200 DEG C FeCr, NiAl, potentiodynamic polarization curves of FeSi nano coating in boric acid buffer, potentiostatic anodic passivation and Mott-Schottky study shows that the four kinds of nano etc. The passivation phenomenon appeared ion coating in boric acid buffer, and the four kinds of coating after the passivation current temperature after remelting treatment are low carbon steel is small; passivation coating is dense four kinds of nano coating in borate buffer solution of potentiostatic anodic passivation process, the passivation film can effectively shield charge through, and low carbon steel is more porous passivation film formed on the passivation film, can not effectively to charge the shielding effect, the formation of four kinds of P type semiconductor nano coating in boric acid buffer solution, and the formation of low carbon steel is n type semiconductor, and the four kinds of nano carrier density plasma coating passivation film of low carbon steel obviously too small. For Cu, FeCr, NiAl, FeSi four nano plasma coating respectively at 850 C, 900 C, 950 C, 1000 C, 1050 C, 1100 C, 1150 C, 1200 C, 650 C, 700 C, 750 C, 800 C, 1100 C, 1150 C, 1200 C, 1250 C temperature materials studio remelting simulation, Cu, FeCr, NiAl, FeSi four nano plasma coating respectively at 950 C, 1150 C, 700 C, 1200 C temperature after remelting treatment on its surface. The smallest shows four kinds of nano plasma coating respectively at 950 DEG C, 1150 C, 700 C, 1200 C temperature after remelting coating is the most stable, the internal defects of the coating will be at least; simulation experiment and remelting experiments were analyzed as can be seen, the four best fit the best heat treatment temperature and remelting remelting experiments in the simulation condition, indicating that the best after remelting treatment, nano plasma coating internal unmelted nano particles is eliminated, coating density enhanced, thereby effectively reducing the internal coating grain relaxation phenomenon.

【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG174.4

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