Wear and corrosion resistance of laser remelted and plasma sprayed Ni and Cr coatings on copper

Nickel and chromium coatings were produced on the copper sheet using plasma spraying and laser remelting. The sliding wear test was achieved on a block-on-ring tester and the corrosion test was carried out in an acidic atmosphere. The corrosive behaviors of both coatings and original copper samples were investigated by using an impedance comparison method. The experimental results show that the nickel and chromium coatings display better wear resistance and corrosion resistance relative to the original pure copper sample. The wear resistance of the coatings is 8 - 12 times as large as original samples, and the wear resistance of laser remelted samples is better than that of plasma sprayed ones. The corrosion resistance of laser remelted nickel and chromium samples is better than that of plasma sprayed samples respectively. The corrosion rate of chromium coatings is less than that of nickel coatings, and the laser remelted Cr coating exhibits the least corrosion rate.     

激光重熔对电弧喷涂含非晶相铁基涂层性能的影响

目的提高电弧喷涂含非晶相Fe基涂层的抗冲蚀及耐腐蚀性能。方法采用YAG脉冲激光器对电弧喷涂含非晶相Fe基涂层进行激光重熔处理。通过X-ray、SEM、冲蚀磨损和电化学等检测手段,研究该涂层重熔后的组织结构、冲蚀磨损性能和耐腐蚀性能。结果电弧喷涂含非晶相Fe基涂层经激光重熔后发生了晶化,并随着功率的增加,非晶含量降低,硬度也降低。重熔后,涂层与基体的结合方式由之前的机械咬合转变为冶金结合,涂层的致密度明显提高,组织缺陷减少。与喷涂层相比,0.3k W激光重熔涂层的抗冲蚀性能在30°攻角下可提高3倍,在90°攻角下可提高将近6倍。重熔层的冲蚀磨损机制在低冲角时以显微切削为主,高冲角时则以挤压破碎为主。随着激光功率的增加,重熔涂层的抗冲蚀性能降低。同时,在3.5%NaCl溶液中,重熔层的耐蚀性能随重熔激光功率的提高而提高,并且重熔层的腐蚀电流密度比喷涂层明显降低。结论激光重熔不但改善了电弧喷涂含非晶相Fe基涂层与基体间的结合状态,同时也增强了涂层的耐蚀和耐磨性能,是一种有效提升涂层性能的后处理工艺。     

Tribological properties of plasma sprayed zircon-alumina powder mixture with and without laser re-melting

ABSTRACT

This investigation focusses on the wear mechanism of as-sprayed and laser treated mullite based coatings, produced by plasma spraying, under sliding wear condition. First, an alumina powder and zircon sand mixture was plasma sprayed to produce a mullite coating. Selected as-sprayed coatings were subsequently laser treated. The tribological performances of both as-sprayed and laser re-melted coatings were assessed using a pin-on-disc wear apparatus. Hardened steel and WC-Co balls served as rubbing counterparts. A plasma sprayed alumina coating was used for bench marking purposes. Plastic deformation was the dominant wear mechanism under low load-low speed condition for both as-sprayed and laser treated coatings. However, at higher loads and speeds the coatings were found to undergo micro-fracture followed by pulverisation. Wear resistance of the coatings improved following laser treatment.     

Post-treatment of thermal spray coatings on magnesium

Magnesium alloys have a beneficial combination of high strength to weight ratio, good machinability and high recycling potential. Despite this, the application of magnesium still is behind that of other constructive materials mainly due to low wear and corrosion resistance. For more demanding applications, a large amount of surface treatment methods are developed to overcome this problem. Thermal spraying is an efficient and flexible method of coating deposition and is widely used for protection of different materials against corrosion and wear. Nevertheless, the bonding of thermal spray coatings on magnesium alloys is not sufficient, so the following post-treatment processes are needed. One of such possibilities is high energy beam treatment of thermally sprayed coatings. During the heat treatment of magnesium substrates with coating the remelting of coating and a thin surface layer of substrate occurs. Depending on the combination of applied coating system and treatment method, different processes can be realised in modified layers: the alloying of magnesium substrate with other elements to improve corrosion properties, redistribution of hard particles from composite coating and new phases formation during the processing to improve the wear resistance of magnesium alloys. In the present work some examples concerning the laser and electron beam treatment of aluminium based composite coatings as well as infra red irradiation of zinc based coatings are described. Coatings are deposited on magnesium substrates (AM20, AZ31, AZ91) by arc spraying with Zn, ZnAl4 and ZnAl15 solid wires and cored wires in aluminium core with powder filling containing different hard particles, such as boron, silicon and tungsten carbide or titanium oxide. Remelting of thermal spray coatings is carried out by means of continuous irradiation of СО₂-laser in nitrogen or argon atmosphere, electron beam in vacuum and focused tungsten halogen lamp line heater in atmosphere. Microstructure of sprayed coatings as well as that of modified surface layers is investigated by metallographic methods. Corrosion properties are estimated by electrochemical measurements. Abrasion wear resistance of the modified layers is determined by scratch test, corundum grinding disk test and Rubber wheel test. It is shown that all methods applied for processing of thermal spray coatings lead to formation of modified surface layers in magnesium substrate with improved wear and corrosion properties. Different mechanisms of microstructure formation such as redistribution of chemical composition of composite coating components, partial remelting of hard phase particles, and new phases formation are discussed. Electrochemical behaviour of modified surface layers is mostly improved due to alloying, homogenization of element distribution and strong decrease of as-sprayed coating porosity. Abrasion wear resistance of processed magnesium substrates strongly depends on the microstructure and usually is 5 to 20 times higher compared with base material.     

The effect of Mo content in plasma-sprayed Mo-NiCrBSi coating on the tribological behavior

NiCrBSi is a material popularly used as a hard thermal sprayed coating. The coating performs well as a wear resistant coating under low stress. At higher stress in metal-to-metal sliding wear condition, however, the NiCrBSi starts to experience surface deformation, which will inevitably lead to seizure as the stress increases. In order to improve the tribological properties of the NiCrBSi plasma-sprayed coating, Mo is added to the coating to reduce the friction between the coating and other metal contacting surface, thus, improving its dry sliding wear resistance. In this study, various amounts of Mo were mixed with NiCrBSi at 0, 25, 50, 75 and 100 wt.%. The powders were sprayed using an air plasma spraying technique onto stainless steel samples to form coatings, which were ground to achieve flat surfaces and a thickness of 350-400 μm. The mechanical properties of the coatings were determined. The coating samples were then tested using a reciprocation ball-on-flat tribometer. It was found that as the Mo/NiCrBSi ratio increases, the wear mechanism changes. Coatings containing 75%Mo and 25%NiCrBSi exhibit the highest wear depths corresponding to the cracking of the thin NiCrBSi splats. On the other hand, coatings containing 25%Mo and 75%NiCrBSi possess the lowest wear depths with no surface cracks. The presence of Mo covering the coating surface hinders the metal seizure between NiCrBSi and steel counter surface.     

Metal Coatings on Steel at Lighthouse Beach,Lagos

Abstract

Trials are reported of zinc, lead and aluminium coatings exposed for 8·7 years at Lighthouse Beach, Lagos. Sprayed aluminium coatings gave good results. Zinc coatings applied by hot-dipping or electrodeposition were also successful but, after 8·7 years, sprayed zinc coatings were beginning to fail. Electrodeposited lead coatingscould not be recommended. The thickness of coating applied to the steel specimens was only 50–80 μm.     

激光熔敷Ni基合金涂层的腐蚀磨损性能研究

系统研究了２１－４Ｎ阀门钢表面激光敷Ｎｉ基ＷＣ合金,Ｎｉ基ＷＣ稀土（ＣｅＯ２）合金涂层,在不同冲击速度和腐蚀介质浓度下的动腐蚀、动磨损和腐蚀磨损性能。试验结果表明,激光熔敷层的腐蚀磨损性能优于２Ｃｒ１３钢,Ｎｉ６０＋２０％ＷＣ＋０．５％ＣｅＯ２具有最佳的抗腐蚀磨损性能。根据试验结果,用多元回归分析方法分别建立了冲击速度,介质浓度与腐蚀磨损速率之间,动腐蚀速率,动磨损速率与腐蚀磨损速率间的定量关系,     

冷喷涂Cu402F涂层激光重熔表面改性后摩擦学行为

目的研究激光重熔后冷喷涂Cu402F涂层在腐蚀介质中的摩擦学行为。方法采用冷喷涂技术在镍铝青铜9442合金上制备了厚度约为882.11μm的Cu402F涂层,并使用激光重熔技术对冷喷涂涂层进行表面改性。使用OM、SEM观察涂层截面与表面的微观形貌;使用XRD、X射线残余应力测试仪、多功能表面性能测试仪、多频直线往复磨蚀实验机,重点表征测试了涂层的组织、表面残余应力、摩擦学性能与磨蚀行为。结果激光重熔后的涂层分为表面重熔层、多孔的重熔过渡层以及冷喷涂遗传层。激光重熔前后,涂层的物相、残余应力均未发生较大变化。在20、50、100 N条件下,激光重熔态涂层的平均摩擦系数呈递增趋势,磨损率分别为1.01×10~(-2)、1.17×10~(-2)、1.34×10~(-2) mm~3/(N·m);由磨蚀实验可知,磨蚀是涂层表面产生钝化膜与钝化膜被破坏的此消彼长的过程,反映着摩擦与腐蚀的协同作用,涂层在磨蚀过程中,开路电位与摩擦系数呈正相关,说明激光重熔态涂层表面钝化膜产生的速度快于钝化膜被坏的速度。结论激光重熔保留了冷喷涂技术制备的Cu402F涂层的优点,同时激光重熔涂层上产生钝化膜的速度更快,有利于提高涂层的耐磨蚀性能。     

Tribological behavior and wear mechanisms of TiN/TiCN/TiN multilayer coatings

This work employs the PVD process to deposit coatings of single layer TiN, binary layer TiN/TiCN, multilayer TiN⇔⇔N, and sequenced TiN⇔CN⇔N multilayer coatings with variable individual TiN-layer and TiCN-layer thicknesses on tungsten carbide disks and inserts. Also investigated are the fracture mechanisms and the influence of sequence and thickness of these coatings on cylinder-on-disk, line-contact wear mode and ball-on-disk, point-contact wear mode through SRV reciprocating wear tests. Actual milling tests identify wear performance. Experimental results indicate that the coating with a total thickness of 7 Μm and layer sequence TiN/TiCN/TiN exhibits good wear resistance on SRV wear test and milling test. The thickest multilayer TiN/Ti/TiN coating, although having the highest hardness, has the worst wear resistance for all tests. No-tably zero-wear performance was observed for all coating disks under cutting fluid lubricated condition due to the transferred layers formed between the contact interface.     

Influence of Plasma Remelting on the Microstructure and Cavitation Resistance of Arc-Sprayed Fe-Mn-Cr-Si Alloy

Surface remelting is an important technique for modifying the microstructure of thermally sprayed coatings as it reduces the porosity and promotes a metallurgical bond between substrate and coating. Many studies have been carried out in the field of materials selection and surface engineering in an attempt to reduce cavitation damage. In this work, an Fe-Mn-Cr-Si alloy was deposited by arc spraying and then remelted by a plasma-transferred arc process. The base metal was a soft martensitic stainless steel. The influence of remelting current on coating and base metal microstructure and cavitation resistance was studied. The use of a lower mean current and a pulsed arc reduced the thickness of the heat-affected zone. In specimens remelted with constant arc current, dendrites were aligned parallel to the path followed by the plasma torch; while in those remelted with a pulsed plasma arc, the alignment of the microstructure was disrupted. The use of a higher peak current in pulsed-current plasma transferred arc remelting reduced mass loss due to cavitation. Fe-Mn-Cr-Si coatings exhibited cavitation-induced hardening, with martensite formation during cavitation tests. This transformation helps to increase the cavitation resistance of the remelted coating compared with the soft martensitic stainless steel base metal.     

激光重熔对Al2O3-40% TiO2等离子喷涂层耐冲蚀性能的影响

利用等离子喷涂方法制备Al₂O₃-40% TiO₂涂层,对涂层进行激光重熔处理.分别对等离子喷涂层和激光重熔涂层进行耐冲蚀磨损性能试验,研究了激光重熔对Al₂O₃-40% TiO₂等离子喷涂层耐冲蚀性能的影响.结果表明,激光重熔消除了Al₂O₃-40% TiO₂等离子喷涂层的层状结构,使得等离子喷涂层中γ-Al₂O₃转变为α-Al₂O₃,形成了α-Al₂O₃+TiAl₂O₅稳定结构.激光重熔后的涂层组织致密均匀、硬度高,具有冶金结合特征,使得耐冲蚀性能得到极大提高,其磨损特征为冲蚀粒子冲击作用下产生的裂纹、破碎与块状剥落.     

热喷涂Ni基复合涂层重熔处理的研究现状

热喷涂Ni基复合涂层因具有耐磨、耐腐蚀及耐高温等特点,被广泛应用于机械零件的表面修复和保护。但是,热喷涂层为典型的层状结构,具有微缺陷含量较高、与基体结合强度低等特点,难以适应苛刻的工作环境,其应用和发展受限。重熔处理可以消除热喷涂层的层状结构,消除或部分消除孔隙、裂纹等微缺陷,使涂层与基体形成冶金结合,提高涂层的使用性能。本文首先介绍了几种适用Ni基复合涂层的重熔技术(即激光重熔、火焰重熔、感应重熔等),随后介绍了重熔处理对Ni基复合涂层表面完整性(即微缺陷、结合强度和硬度)的影响,接着分析了重熔处理对Ni基复合涂层两种服役性能(即耐磨性、耐腐蚀性能)的影响,最后总结了目前在关于Ni基复合涂层重熔技术研究中存在的问题,进而探讨了相应的解决方案,并指出挖掘新的表面重熔技术和对不同的材料体系进行针对性研究是未来重点发展的方向。     

Laser remelting of plasma-sprayed yttria partially stabilized zirconia coatings

A plasma-sprayed 8 wt.% yttria partially stabilized zirconia coating doped with 3 wt.% SiO₂ was remelted by laser. The microstructure of the as-sprayed and laser-remelted coatings was characterized by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and x-ray diffraction (XRD). The effect of laser remelting on the hardness, wear resistance, and thermal shock resistance of the coatings was also studied. The laser-remelted coating consists of fine solidification grains without the presence of pores and cracks. The elements are uniformly distributed in the laser-remelted coating. Nontransformable tetragonal (t′) phase is predominant in the laser-remelted coating with a small amount of cubic phase. Laser remelting greatly enhanced the hardness, wear resistance, and thermal shock resistance of the coatings, and should find more applications.     

Properties and tribological performance of ceramic-base chromium and vanadium carbide composite coatings

In the current study, the surface of AISI D2 steel was coated with the powder blends of ferro-vanadium (Fe-V) and ferro-chromium (Fe-Cr). The coatings were performed using a thermo-reactive diffusion (TRD) treatment by the pack cementation method at three different temperatures (900 °C, 1000 °C, and 1100 °C) and three different durations (1 h, 2 h, and 3 h). The structural and mechanical characteristics of the coatings were compared between the treatment groups. For this aim, the types of the formed phases, the microstructure, the microhardness, the surface roughness, and the wear and friction performance of the coated samples were examined. XRD analysis found composite carbide coatings including chromium carbide (Cr-C), vanadium carbide (V-C), and chromium vanadium carbide (Cr-V-C). The coatings' thickness was 11.3–23.2 μm, hardness was 2100–2500 HV, and average surface roughness (R_a) was 0.286–0.550 μm, depending on the treatment condition. The vanadium containing phase contents of the coatings increased with the elevating coating temperatures. The formed composite coating layers caused a change in the appearance of wear track and wear mechanism on the material surface. After the coating process, there found to be a decrease in the friction coefficient as well as an improvement in the wear resistance up to 7 times. In the composite coating layers, the increase in V-C content in comparison to Cr-C led to an enhancement in wear resistance on the material surface.     

等离子喷涂氧化锆涂层及激光重熔涂层的摩擦磨损性能

采用等离子喷涂制备了常规氧化锆涂层和纳米氧化锆涂层,并对制备的纳米氧化锆涂层进行了激光重熔处理,系统地研究了3种氧化锆涂层(常规、纳米和激光重熔涂层)在常温和高温下的摩擦磨损性能.结果表明,纳米氧化锆涂层耐磨性能明显优于常规氧化锆涂层,而激光重熔处理后的纳米氧化锆涂层在常温和高温下,都表现出最低的摩擦系数和最好的耐磨性能.这3种涂层的表面粗糙程度、涂层孔隙率和裂纹状况明显不同,从而表现出不同的摩擦磨损特性;说明纳米粉末等离子喷涂结合激光重熔技术是提高氧化锆涂层性能的有效方法.     

激光表面重熔对热喷涂铝涂层微观结构及其阻氢性能的影响

采用Ｘ射线衍射仪、扫描电镜及热充氢等方法,研究了激光重熔对不锈钢表面热喷涂铝涂层的微观结构及其阻氢性能的影响。结果表明,激光重熔后涂层组织均匀、致密,主要由ＡｌＦ３（Ｎｉ,Ｃｒ）固溶体、ＣｒＦｅＮｉ奥氏体等相组成,而且涂层与基体形成了良好的冶金结合。此外,激光表面重熔后涂层的阻氢性能亦得到改善。     

激光重熔Cr等离子喷涂层的组织及其导电性的研究

用5kW CO2激光器对铜排表面的Cr等离子喷涂层进行重熔，并对激光熔覆层组织、硬度、导电性能进行了研究。结果表明，激光熔覆层的组织致密、均匀，与基体结合很好。涂层平均显微硬度为HV200，是基体的3倍左右。激光熔覆层和等离子喷涂层在0．35mm处的电导率分别为70.4％IACS和53，5％IACS．对于3mm厚的铜排，激光熔覆和等离子喷涂铜排的整体电导率则分别为96．2％IACS和92．6％IACS。激光熔覆层和激光熔覆后铜排的整体电导率均高于相应的等离子喷涂层及其铜排。     

Electroless deposition of Ni-P composite coatings containing kaolin nanoparticles

Abstract

The ability to codeposit particulate matter in a matrix of electroless nickel has led to a new generation of composite coatings with unique properties, such as high hardness wear, abrasion, corrosion and high temperature oxidation resistance. In this paper, the authors report on the development of electroless Ni–P–kaolin composite coating, and the characteristic properties of the selected deposits were evaluated by scanning electron microscopy, energy dispersive X-ray and X-ray diffraction techniques. A good rate of deposition of 12 μm h^?1 was observed for the optimised concentration of 6 g L^?1 of kaolin in the bath. For the optimised bath composition and operating conditions, the composite deposit was found to contain 81·7%Ni, 9·8%P and 10·5%kaolin. Heat treatment at 400°C for 1 h results in an increase in the hardness and wear resistance of the composite coating. The corrosion resistance is also highly enhanced by the incorporation of kaolin in the nickel–phosphorus matrix. The crystallite size of the composite coating is 20 nm, and the codeposition of kaolin follows the Langmuir adsorption isotherm.     

Microstructures and mechanical properties of FeCoCrNi high entropy alloy/WC reinforcing particles composite coatings prepared by laser cladding and plasma cladding

FeCoCrNi HEA coatings with 20% mass fraction of WC reinforcing particles were prepared by two different cladding methods, laser cladding (LC) and plasma cladding (PC). The microstructure of HEA matrix and WC particles of LC and PC coatings were discussed respectively. For HEA matrix, dendritic morphology was observed in both coatings. For WC particles, a few granular (Cr,W)₂C carbides around WC particles in LC coatings, and a large number of crystal and fishbone Fe₃W₃C carbides around WC particles in PC coatings. Mechanical properties as hardness and wear resistance of the two kinds of coatings were also investigated. The interstitial solution strengthening effect of C element is stronger in PC coating, and the hardness of HEA matrix in LC coatings is twice that of in PC coating, which shows a strong retention force on WC particles. The friction coefficient of LC coating is lower and stable, with the volume wear rate of 0.7 × 10⁻⁵ mm⁻³/N·m, showing high wear resistance. PC coatings have poor wear resistance due to decarbonization and oxidation of WC particles and reduction of retention force of HEA matrix, with the volume wear rate of 8.29 × 10⁻⁵ mm⁻³/N·m. The wear mechanism of both coatings were also discussed.     

镁合金表面冷喷涂铝涂层的热处理研究

使用冷喷涂方法在铸态AZ91D镁合金基体上沉积了纯Al涂层,所得涂层组织致密,厚度均匀,与基体结合良好,孔隙率小于1%.随后用机械减薄的方法使Al涂层的厚度减薄到135 μm,对减薄后的试样在真空加热炉中分别进行了400℃×20 h和400℃×40 h的热处理.结果显示随着保温时间的延长,Al涂层全部转化为较高硬度和较...