Review of Thermal Spray Coating Applications in the Steel Industry: Part 1—Hardware in Steel Making to the Continuous Annealing Process

This two-part article series reviews the application of thermal spray coating technology in the production of steel and steel sheet products. Part 2 of this article series is dedicated to coating solutions in the continuous galvanizing line. The corrosion mechanisms of Fe- and Co-based bulk materials are briefly reviewed as a basis for the development of thermal spray coating solutions. WC-Co thermal spray coatings are commonly applied to low Al-content galvanizing hardware due to their superior corrosion resistance compared to Fe and Co alloys. The effect of phase degradation, carbon content, and WC grain size are discussed. At high Al concentrations, the properties of WC-Co coatings degrade significantly, leading to the application of oxide-based coatings and corrosion-resistant boride containing coatings. The latest results of testing are summarized, highlighting the critical coating parameters.     

Enhancement of Service Life of Steam Generating Tubes in Oil-Fired Boiler for Power Generation Employing Plasma Spray Technology

The effects of Ni-50 mass% Cr alloy coating, that is plasma-sprayed onto the fire-side of steam generating tubes in a heavy oil-fired boiler, on the high temperature corrosion resistance were examined. One of the severe environments in the industrial manufacturing facilities, where thermal sprayed coatings are employed, is the high temperature corrosion such as the oxidation, sulfidation, and low melting fuel ash corrosion in the fire-side of boiler tubes. In the fossil fuel-fired steam generating boiler facilities, the degradation or failure of steam generating tubes that were derived from the contaminants in a lower grade fuel have often occurred. The situation of degradation of the water evaporator and superheater tubes and corrosion-preventing effects of plasma sprayed coating are described. The enhanced effects of plasma sprayed Ni-50 mass% Cr alloy coating for the suppression of hot corrosion failure of the steam generating tubes of boiler are summarized.     

Characterization of the corrosion performances of as-cast Mg–Al and Mg–Zn magnesium alloys with microarc oxidation coatings

In the present study, corrosion-protective microarc oxidation (MAO) coatings were prepared on AZ31B, AZ80, and ZK60 cast magnesium alloy substrates in an alkaline silicate electrolyte. The corrosion performances of the uncoated and MAO-coated alloys were investigated using electrochemical and salt spray chamber corrosion tests. The microstructure characterization and experimental results show that among the three alloys studied, the ZK60 Mg alloy exhibited the best and AZ31B the least corrosion resistance under the salt spray conditions. The MAO coating provided robust corrosion protection of the Mg substrates and resulted in a significant decrease in the corrosion rate of the alloys by 3–4 orders of magnitude. The MAO coating on ZK60 alloy showed better corrosion protectiveness than that on the AZ series alloys due to the incorporation of different alloying elements in the coating, especially the Zn and Al elements, which are from the Mg substrate. The corrosion performances and mechanisms of the uncoated and MAO-coated Mg alloys are interpreted in terms of the microstructure and phase/chemical compositions of both the substrates and coatings.     

轻水堆包壳锆材服役环境下延寿策略及研究进展

综述了核反应堆用锆合金的涂层研究现状。主要论述了非金属类涂层、金属类涂层以及MAX相涂层。其中MAX相既具有金属的性质,又具有陶瓷的性质。分析了包壳材料服役环境下的腐蚀行为,包括正常工况下的过热水氧化腐蚀和含锂离子的水溶液腐蚀行为,同时也关注了离子辐照行为以及事故工况下的高温蒸汽腐蚀行为。现有涂层材料普遍具有局限性,研究多侧重于高温蒸汽腐蚀。出现了一些新材料,比如可形成致密氧化膜的MAX相、硅涂层等,但是其正常工况下的应用前景不明。相比而言,金属类涂层在抗腐蚀方面更具优势,然而其抗辐照行为和中子经济性尚待研究。目前单一涂层技术在满足抗辐照和中子经济性的基础上尚不足以同时满足正常工况和高温蒸汽下的抗腐蚀性和高稳定性。组合涂层或者多层膜技术逐步受到重视。多元涂层氧化过程中的元素迁移动力学行为以及涂层基体界面的微合金化对结合力的影响具有深远意义,目前该方面的研究有待突破。     

电弧喷涂Zn-Al伪合金涂层耐腐蚀性能研究进展

通过在钢基体表面制备涂层可以很好地延长钢铁材料的服役时间,减少因腐蚀造成的重大事故和人员伤亡。相较于传统的纯Zn涂层、纯Al涂层以及Zn-Al合金涂层,Zn-Al伪合金涂层能够为基体材料提供长久有效的腐蚀防护,在钢铁材料的腐蚀防护中具有巨大的应用潜力。简述了Zn-Al伪合金涂层电弧喷涂制备工艺的特点;介绍了Zn、Al、Zn-Al合金及Zn-Al伪合金涂层在模拟海洋环境下的腐蚀防护原理;在此基础上从组分、喷涂工艺参数(喷涂距离、喷涂电流和喷涂电压)、元素掺杂(Mg、Si及Re)及后处理工艺(封孔、激光重熔)等角度,论述了其对Zn-Al伪合金涂层耐蚀性的影响;讨论了Zn-Al伪合金涂层防腐体系在桥梁、海洋钢结构件、地下运输管道中的应用现状;最后总结了目前研究工作中存在的挑战,提出了电弧喷涂Zn-Al伪合金涂层尚需深入研究的重点问题,为提高钢铁材料使用寿命提供了参考。     

Application of HVOF thermal spraying to solve corrosion problems in the petroleum industry—an industrial note

Commercially available thermal spray coatings have seen limited use in corrosion applications due to the presence of interconnecting porosity and oxide networks. Use of vacuum chambers or post-treatments can eliminate most defects, but these methods are costly and impractical on a large scale. The ability to produce such high-quality coatings by thermal spraying in atmosphere and without post-treatments would offer important advantages as a means of building and repairing process equipment. A modified HVOF process using unique inert gas shrouding has resulted in highly dense, low-oxide coatings of metallic alloys. These coatings were extensively evaluated for severe petroleum industry corrosion applications in laboratory and plant testing, with exposures as long as 5 years. Coatings of corrosion-resistant alloys, such as type 316L stainless steel and Hastelloy C-276, were shown to act as true corrosion barriers. They were protective to underlying base metals in severe environments and in most cases exhibited corrosion resistance comparable to the corresponding wrought alloy. The process was scaled up for on-site plant use and successfully applied to numerous corrosion problems in petroleum industry plant equipment. Significant technical and economic advantages can be realized by use of thermal spray coatings to solve plant equipment problems.     

掺杂镍对镁合金表面冷喷涂锌基涂层性能的影响

目的研究镍添加对冷喷涂锌基涂层耐蚀性的影响,为镁合金提供有效的防护涂层。方法采用低压冷喷涂技术在镁合金基体表面分别制备锌基和锌/镍基复合涂层,通过微观观察、摩擦磨损实验、电化学极化法和电化学阻抗谱测试及全浸泡腐蚀试验,研究镁合金表面冷喷涂涂层的结构、摩擦磨损行为和耐蚀性。结果镁合金表面冷喷涂锌基涂层后,其硬度和耐磨性得到显著提高,掺镍后的锌/镍基涂层具有更高的硬度和耐磨性。锌基和锌/镍基涂层均能为镁合金提供腐蚀防护,锌/镍基涂层比锌基涂层具有更好的耐蚀性。相对镁合金来说,锌基涂层和锌/镍基涂层的自腐蚀电位分别正移了260 mV和560 mV;长期腐蚀后锌/镍基涂层形成了更致密的腐蚀产物膜,腐蚀电阻显著高于锌基涂层。结论冷喷涂锌基和锌/镍复合涂层均能对镁合金提供防护作用,掺杂镍后的锌/镍基复合涂层具有更高的硬度、耐磨性和耐蚀性。     

Cold Spray Al-5% Mg Coatings for the Corrosion Protection of Magnesium Alloys

Poor corrosion resistance is a significant limitation of magnesium alloys as structural materials. To address this problem, the objective of this study was to apply to a magnesium alloy a corrosion-resistant barrier coating that has galvanic compatibility with magnesium and a hardness value no less than that of magnesium. Aluminum coatings were applied to ZE41A-T5 Mg by the cold spray process. A custom-made high-purity Al-5 wt.% Mg powder was produced by spray metal forming for the coating evaluation. In addition, coatings of commercially pure Al (99.5 wt.%), high-purity Al (99.95 wt.%), AA5356, and AA4047 were used for comparison. Coating evaluation included mechanical testing (hardness and adhesion strength) and corrosion testing (salt spray, galvanic coupling, and crevice corrosion). The Al-5% Mg powder resulted in the best overall performance, including a high hardness, 125 H_v100, and an adhesion strength, over 60 MPa, when treated for over 1000 h in a salt spray chamber and with a low galvanic current.     

镁合金表面冷喷涂层防护研究进展

镁合金作为最轻质的金属结构材料,由于其密度低和比强度高等优良的物理和力学性能,在航空、航天、汽车以及电子等领域引起广泛关注。然而,镁合金化学性质活泼、耐腐蚀和耐磨损性差等缺点严重制约其进一步应用。近些年发展起来的冷喷涂技术,在固态下制备涂层,涂层致密且与基体结合良好,因此可为镁合金表面防护提供一种新的有效方法。主要综述了镁合金表面冷喷涂耐腐蚀涂层(纯铝、铝合金和复合材料涂层)和耐磨损涂层(合金和复合材料涂层),论述了影响冷喷涂层耐腐蚀、耐磨损以及其他力学性能(硬度和涂层/基体结合强度)的主要因素,包括杂质元素含量、合金种类以及复合材料涂层中陶瓷颗粒含量、尺寸和形貌等。对比了几种常用表面处理技术制备的纯铝涂层的耐腐蚀性能,并阐述了冷喷涂技术在镁合金表面防护方面的优势。此外,还分析了热处理对冷喷涂纯铝和复合材料涂层耐蚀性的影响。最后提出了目前冷喷涂技术在镁合金防护方面的局限性以及发展难题,对未来研究趋势进行了展望。     

挤压镁合金腐蚀与防护研究进展

随着挤压镁合金的广泛应用,如何改善其较差的耐蚀性自然成为无可回避的重要研究课题。通过综合分析国内外挤压镁合金腐蚀研究领域的相关研究成果,从腐蚀行为与防护技术两个方面进行了讨论。挤压镁合金易于受到多种腐蚀形式的破坏,其腐蚀行为、性能和机理受到材料特性和腐蚀环境等多种因素的影响,表现出多样性和复杂性,特别是应力和腐蚀协同所用下的挤压镁合金失效行为,尚需开展深入研究。通过优化制备工艺参数、合金化和热处理等技术进行组织和成分优化,基于应力条件、不同的腐蚀环境,开发新型耐腐蚀挤压镁合金,对于提高挤压镁合金抗腐蚀性能,扩大其应用领域具有实用价值。电化学镀、化学转化膜、自修复涂层等涂层技术在合金表面形成钝化膜、陶瓷膜以及释放缓蚀剂,对挤压镁合金提供了有效防护。其中,自修复涂层能够有效解决涂层破损产生的局部腐蚀问题,极大地改善了膜层的防护性能,拥有良好的应用前景,是涂层研发的新方向。     

镁合金表面腐蚀防护技术研究进展

镁合金较差的耐腐蚀性能限制了其大规模应用。利用表面腐蚀防护技术可以有效改善镁合金的耐蚀性能,延长镁合金的服役寿命。因此,可靠的表面腐蚀防护技术是突破镁合金应用瓶颈的关键。从镁合金表面腐蚀防护技术的分类入手,阐述了各种防护技术的基本原理。在此基础上,综述了近年来镁合金腐蚀防护技术的研究进展,包括电化学方法、化学方法及其他表面腐蚀防护方法等,阐明了各种技术的优缺点及适用范围,并对镁合金表面防护技术的发展趋势进行了展望。经过多年的发展,镁合金表面防护技术的理论研究和应用日臻完善,现有的表面防护方法一定程度上都能为镁合金基体提供腐蚀防护作用。然而,随着镁合金应用范围的扩展,相关结构件常会面临恶劣的服役环境。因此,单一的表面腐蚀防护技术已经很难满足工业领域对镁合金材料的迫切需求,多种表面处理技术联合制备的复合涂层具有广阔的应用前景。镁合金表面防护技术当前正朝着功能化和智能化的复合涂层方向发展,同时对制备工艺的安全环保性也提出了更高要求。未来除了保证高耐蚀性外,开发多功能智能涂层对提升防护层的长效防护能力、拓宽镁合金的应用范围具有重大的现实和长远意义。     

Mo含量对FeCoCrNiMox高熵合金等离子喷焊层组织与性能的影响

目的 研究不同Mo元素添加量对FeCoCrNiMox(x=0、0.5、1、1.5)高熵合金等离子喷焊层组织和性能的影响,以期望获得一种高硬度、耐腐蚀的喷焊层,用于改善传统工模具表面防护与使用寿命的问题。方法 采用等离子喷焊技术在Q235A低碳钢表面制备了不同Mo含量的高熵合金喷焊层,通过X射线衍射仪(XRD)、光学显微镜(OM)、扫描电子显微镜(SEM)、能量色散X射线光谱仪(EDS)表征其微观组织与相结构,借助显微硬度计和电化学工作站对喷焊层的硬度和耐腐蚀性能进行测试。结果 随着Mo含量x从0逐渐增加到1.5,喷焊层的晶界胞状枝晶组织(枝晶内为白色富Mo相,枝晶间为灰色富Fe、Ni相)逐渐增加,合金微观组织变得细小;喷焊层的硬度由204.4HV0.2增加至706.8HV0.2;喷焊层在3.5%NaCl溶液中呈现出明显的钝化行为,腐蚀电位由?0.753 V增大到?0.412 V,腐蚀电流密度由1.23×10^?4 A/cm²减小到3.80×10^?6 A/cm²,点蚀电位由?0.642 V增大到?0.371 V,具有优异的耐腐蚀性能。结论 所设计的FeCoCrNiMox合金及相应的等离子喷焊工艺,满足对喷焊层高耐磨以及耐腐蚀性的要求,有望应用于传统工模具的表面防护与修复。     

Development of thermal sprayed layers for high temperature areas in waste incineration plants

Corrosion and wear in the hot gas area of thermal energy plants are severe problems, which often cause premature damage of components. In general, the most components of plants are made of materials, which are not stable under corrosive conditions. For corrosion protection (and also wear protection) and lifetime extension of these components, coatings with more resistant materials are applied. Because of the high concentration of corrosive species and the alternating composition of the atmosphere near to the components, the waste incineration plant is the “worst case” of high temperature corrosion. Nowadays, the most usual coating process to protect pipes in the waste incineration plants is cladding. In the last few years, alternative processes are under investigation because cladding is very cost‐intensive. The specific costs of thermal spraying are much lower than those of cladding. In addition, the coating by thermal spraying reduces the risk of the dilution of substrate and coating material, different materials can be combined (e.g. metal alloys, ceramics) and the thickness of the layer for an acceptable resistance according to corrosion and wear can be drastically reduced. Thermal spraying has the potential to create cost‐efficient coatings to protect components in the critical zones of incineration plants. Since many years, ATZ Entwicklungszentrum is involved in the development and/or advancement of materials, technologies and applications of thermal spraying for corrosion and/or wear protection in thermal energy plants. The main focuses of the investigations are layers for components in high temperature areas of waste incineration plants. On the basis of the present results, different coatings (metal alloys, ceramics) and different spray technologies (e.g. HVOF, APS) have been tested by different strategies (corrosion tests under laboratory scale, air cooled material probes inside the hot gas area of an incineration plant and coated pipes in operation as part of the superheater of incineration plants). This paper will give an overview about the current results of these corrosion tests, in which the focus are the investigations with material probes. First results showed that with the combination of different thermal sprayed layers a significant corrosion protection can be achieved.     

冷喷涂铬锆铜涂层在海水中的耐蚀性能

采用冷喷涂技术在普通碳钢基体上制备了厚度为300μm的铬锆铜涂层,用扫描电子显微镜(SEM)观察涂层的组织形貌。用开路电位（OCP）、电化学阻抗谱和动电位极化曲线等电化学方法研究冷喷涂铬锆铜涂层在天然海水中的耐蚀性能。研究表明,铬锆铜涂层组织致密,在海水环境中,涂层表面形成一层致密的腐蚀产物膜,能有效阻止腐蚀介质向涂层内部渗透,对基体起到良好的保护作用。     

Aqueous Corrosion Behavior of Micro Arc Oxidation (MAO)-Coated Magnesium Alloys: A Critical Review

Magnesium (Mg) and its alloys, in the current era of persistently growing engineering demands, have become the most promising materials finding widespread industrial applications. Numerous processes are available for surface protection of Mg and its alloys to potentially minimize corrosion damage. The micro arc oxidation (MAO), a fairly recent and eco-friendly coating process, emerged as a novel means to provide an adherent, hard, scratch-resistant, wear-resistant, and corrosion-resistant coatings on Mg alloys. However, the successful utilization of such coatings demands a thorough understanding of the influence of a relatively large number of process parameters such as electrolytic composition, presence of insoluble additives in the electrolyte, electrical parameters employed, and the composition of the Mg alloy substrate on the corrosion resistance. The detailed influence of all the above parameters on the corrosion behavior of Mg alloys is critically reviewed and presented in this article. In addition, this article also reviews the recent trends in terms of duplexing the MAO process using different techniques/processes such that the composite coatings are produced with enhanced corrosion resistance.     

Resistance of thermal-sprayed duplex coating composed of aluminum and 80Ni-20Cr alloy against aqueous corrosion

The development of corrosion-resistant sprayed coatings without sealing is required to increase the reliability of the thermal spray coating method and to expand the field of application for wet corrosion environments. The conventional wire flame-sprayed aluminum coating on steel without sealing has poor resistance against aqueous corrosion and has restricted practical use. A duplex coating composed of sprayed aluminum on an 80Ni-20Cr alloy undercoat exhibited sufficient resistance in a hot, near-neutral aqueous environment through a trial use in a vegetable oil process. In this paper, the mechanism of corrosion resistance of the duplex coating is investigated by electrochemical polarization measurements and electron probe microchemical analysis (EPMA) to examine the individual role of each layer and the change of the microstructure with time.     

High-Temperature Corrosion in Waste-to-Energy Boilers

There are 88 waste-to-energy (WTE) plants in the U.S. and over 600 worldwide. In total, they combust close to 143 million metric tons of municipal solid wastes (MSW) and generate about 45 billion kW · h of electricity and an equal amount of thermal energy for district heating and industrial use. The presence of various impurities, especially HCl and chloride salts, in the combustion gases results in much higher corrosion rates of boiler tubes and has led to the development of special alloys and also metal protection techniques, including high velocity oxygen fuel (HVOF) sprayed coatings. This study examines the corrosion mechanisms in WTE boilers and summarizes the findings of a corrosion survey of several WTE facilities in the U.S. The study also examines existing and potential methods for reducing corrosion problems.

镁合金化学镀Ni-Cu-P/Ni-P复合镀层及腐蚀防护机理研究

目的为提高镁合金化学镀Ni-P合金镀层的腐蚀防护性能。方法在AZ31B镁合金表面,先化学镀Ni-Cu-P,再化学镀Ni-P,制备Ni-Cu-P/Ni-P复合镀层。研究复合镀层的表面形貌、成分、厚度和腐蚀电流密度随镀液硫酸铜浓度的变化规律,表征1.0 g/L硫酸铜质量浓度下,复合镀层的截面形貌、成分和晶态结构。结合动电位极化曲线和盐雾试验,分析复合镀层的耐蚀性能和腐蚀防护机理。结果复合镀层中的铜含量随硫酸铜浓度的增加而升高,铜对复合镀层的结构和性能影响很大。通过抑制镀层表面胞状物的生长和增加形核点数量,铜的共沉积能够大幅提高复合镀层的致密性。随硫酸铜浓度的增加,样品表面的催化活性下降,镀液稳定性升高,由此导致复合镀层的厚度随硫酸铜浓度的增加而明显下降。硫酸铜质量浓度为1.0 g/L时,复合镀层均匀致密,并具有可钝化性,按照ISO 9227,其耐盐雾腐蚀时间超过180 h。结论化学镀Ni-Cu-P/Ni-P复合镀层能够赋予镁合金表面优异的耐蚀性能,复合镀层所具有的可钝化性和均匀致密的镀层结构,是镀层腐蚀防护性能提升的主要原因。     

2A12 铝合金硬质阳 极氧化及膜层性能研究

目的对混合酸电解液体系中2A12铝合金硬质阳极氧化膜层的制备及性能进行研究。方法采用以硫酸为主的混合酸电解液体系,对2A12铝合金进行硬质阳极氧化,研究混合酸电解液主要成分对2A12硬质阳极氧化膜层性能的作用和影响。结果在硫酸的溶解、有机酸吸附以及添加剂的耦合作用下,混和酸电解液避免了2A12铝合金硬质阳极氧化膜制备过程中存在的烧蚀现象,膜层平均硬度达到400HV0.05以上。WX添加剂能够明显改善2A12铝合金硬氧化膜层的耐蚀性能,经过168 h的中性盐雾试验,仅出现了5%的白霜,但与相同厚度的7A04铝合金硬质阳极氧化膜层相比,耐蚀性较差。结论建议制备有耐蚀性要求的硬质阳极氧化膜层时选用铜含量较低的铝合金材料。     

Study of the HVOF Ni-Based Coatings’ Corrosion Resistance Applied on Municipal Solid-Waste Incinerators

Oxidation of exchanger steel tubes causes important problems in Municipal Solid-Waste Incinerator (MSWI) plants. The present paper shows a possible solution for this problem through High-Velocity Oxygen Fuel (HVOF) thermal spray coatings. A comparative study was carried out between powder and wire Ni-based thermal spray coatings (with the same composition). These optimized coatings were compared based on their microstructure, wear properties (ASTM G99-90, ASTM G65-91), and erosion-corrosion (E-C) resistance. An E-C test designed in the Thermal Spray Centre was performed to reproduce the mechanisms that take place in a boiler. Studying the results of this test, the wire HVT Inconel coating sprayed by propylene appears to be the best alternative. A commercial bulk material with a composition similar to Ni-based coatings was tested to find the products of the oxidation reactions. The protective mechanisms of these materials were assessed after studying the results obtained for HVOF coatings and the bulk material where the presence of nickel and chromium oxides as a corrosion product can be seen. Kinetic evolution of the Ni-based coatings can be studied by thermogravimetric analysis. The protection that Inconel coatings give to the tube through the difference of the gain mass can be seen. Ni-based HVOF coatings by both spray conditions are a promising alternative to MSWI protection against chlorine environments, and their structures have a very important role.