IFHANAL-3 Inhibited Chromate-Free Conversion Coatings on V95T2 Aluminum Alloy

Alloys in the Al–Cu–Mg–Zn system are known to be characterized with high corrosion resistance in both atmospheric and aqueous media. It was earlier demonstrated that the alkaline chromate-free converting composite IFHANAL-3 enabled one to produce coatings with protective properties not inferior to those of conventional chromate coatings on a number of aluminum alloys, including that of grade V95 with different thermal treatment. The present work was devoted to studies of the effect of different complexing agents on the oxidation process and protective properties of coatings on V95T2 alloy. The studied modifying dopants decrease the concentrations of different oxides in the composition of conversion coatings, thus facilitating the adsorption of corrosion inhibitors and improvement of their protective properties. The decrease of the oxidation temperature in the solution of IFHANAL-3 modified with inhibitors of the azol type does not ly affect protective properties of the formed coatings.     

Submicron free-chromate chemical conversion coatings on AMg-3 aluminum alloy

Coatings obtained in solutions of permanganates are known alternatives to thin chromate conversion coatings on aluminum alloys. However, permanganate ion is an insufficiently effective corrosion inhibitor for aluminum in the acidic medium, and, therefore, modified additives are introduced into converting solutions based on it. The present research is devoted to studying the corrosive characteristics of coatings produced by chemical oxidation in the IFKhANAL-2 permanganate composition and its modifications on AMg-3 aluminum alloy. It is shown that iron and nickel salts are most effective as modified additives and subsequent filling of produced coatings in corrosion inhibitor solutions increases their protective properties up to the level of standard chromate coatings. The researched coatings provide protection for 1.5 years under conditions of a humid tropical climate.     

Deposition of protective coatings from aqueous solutions of silicates of tertiary ammonium bases

The possibility of using aqueous solutions of organic ammonium base silicates to produce protective adhesive films for paint and varnish coatings on a steel surface is examined. It is established that the protective ability and moisture resistance of films do not depend on the magnitude of a silicate modulus of tertiary ammonium bases, solution concentration, and temperature. The optimal concentration (10 g/L) and temperature range (45–50°C) of the working solution, as well as the time for its processing, are determined. It is shown that the following treatment of the organosilicon coating with the solution bearing cerium (III) ions improves its protective potency. It is revealed that the protective ability of the coatings increases with the reduction of the length of a hydrocarbon radical.     

Electrochemical corrosion behaviour and surface morphology of electrodeposited zinc,zinc–cobalt and their composite coatings

Abstract

The electrochemical behaviour as well as the surface morphology characteristics of electrodeposited Zn and Zn-Co (≈3 wt-%) alloy coatings on low carbon steel samples, with and without included nanoparticles of organic co-polymers in their structure, are discussed. Their corrosion resistance and protective properties were studied in a model corrosion medium, 5 wt-% NaCl, using electrochemical methods such as polarisation resistance (R _p) measurements and potentiodynamic (PD) polarisation curves. Scanning electron microscopy (SEM) was performed to examine the surface morphology changes of the samples before and after the corrosion treatment. Some conclusions are drawn about the influence and importance of the organic nanoparticles on the corrosion behaviour of the coatings presented.     

热镀锌层柠檬酸改进型铈盐转化膜的生长机理

将热镀锌钢板浸入含有25 g/L Ce(NO3)3·6H2O、4~6 g/L H2O2(30%)、15~20 g/L H3Cit的处理液中,在70℃下处理10 s~240 min,从而在其表面获得铈盐转化膜。采用中性盐雾试验(NSS)和电化学极化曲线来分析膜层耐蚀性能,确定最佳成膜时间范围。采用扫描电镜(SEM)观察膜层的微观形貌,利用能谱仪(EDS)、X射线光电子能谱仪(XPS)、红外吸收光谱仪(IR)分析膜层的化学组成。结果表明:处理时间为10 min左右的铈盐转化膜耐腐蚀性能最优,最佳工艺条件下得到的铈盐转化膜的耐蚀性能与铬酸盐转化膜的相当;随着处理时间的延长,膜的厚度增加,膜层的裂纹变宽;处理时间超过10 min后膜层逐步产生脱落,耐腐蚀性能也随之降低;转化膜的生长过程中,前期以柠檬酸铈吸附膜的沉积为主,后期以Ce(OH)3/Ce2O3及Ce(OH)4/CeO2的沉积占主导。     

Mg-4Zn合金表面掺锶羟基磷灰石涂层：物理化学性质及体外细胞响应

生物可降解镁合金由于具有高比强度、低弹性模量和优良生物相容性而受到广泛关注。然而,其过高的腐蚀速率却限制了其潜在的临床应用。因此,具有高生物相容性的羟基磷灰石(HA)涂层常被用于阻碍镁基体和周围生物环境的相互作用。采用电化学沉积法在Mg-4Zn合金表面制备了HA和掺锶(Sr)HA涂层。利用扫描电子显微镜(SEM)、能谱(EDS)、透射电子显微镜(TEM)、三维激光扫描显微镜(3D LSM)和亲水角监测系统对材料表面性质进行表征。本研究还探讨了材料动态离子释放、蛋白吸附、细胞吸附、增殖与成骨分化行为。结果显示,HA中引入Sr导致了晶格畸变和结晶度下降。涂覆掺SrHA的样品中镁离子释放量比其他样品更低,说明耐腐蚀性更好。掺Sr样品表面蛋白吸附与初始细胞吸附的改善是由于其具有更高的表面粗糙度和亲水性。Sr的引入并未显著改变细胞的增殖,却明显提高了成骨分化效果。综上所述,掺SrHA涂层是一种非常有前景的镁合金保护性生物相容涂层。     

钛酸铁钠晶须/FEVE复合涂层的制备及其耐磨防腐性能

目的为提升氟碳涂层的耐磨和防腐性能。方法采用KH550对钛酸铁钠晶须进行改性,并将改性晶须分散于氟碳树脂(FEVE)中,制备钛酸铁钠晶须/FEVE复合涂层。采用红外光谱、接触角、光学显微镜、金相显微镜和扫描电镜等表征方法,分析了改性前后钛酸铁钠晶须的变化及其在树脂中的分散性。采用电化学交流阻抗研究了涂层在模拟海水中的电化学腐蚀行为。采用摩擦磨损试验机研究了涂层的摩擦学性能。结果钛酸铁钠晶须经改性后,接触角由14.5°增大为111°,呈现出优异的疏水性,能够均匀分散于FEVE中。交流阻抗测试结果表明,复合涂层的防护性能随晶须含量的增加呈现先提升后降低的趋势,当晶须质量分数为10%时,复合涂层的电化学阻抗高达1011?·cm2,优于纯氟碳涂层,呈现出优异的耐腐蚀性能。晶须含量过高时,因晶须交联形成网络结构而降低了涂层的防腐性能。钛酸铁钠晶须的添加同时大幅提升了FEVE涂层的耐磨性能,晶须质量分数为5%的复合涂层表现出最优的摩擦学性能,体积磨损量低至0.0164mm3,较纯FEVE涂层提升11.2倍。结论钛酸铁钠晶须/FEVE复合涂层具备优异的耐磨防腐性能,能有效降低实际工况中的涂层损伤,延长涂层的使用寿命。     

The effects of microstructural features on the performance gap in corrosion resistance between bulk and HVOF sprayed Inconel 625

It is commonly observed that there is a performance gap between the corrosion resistance of thermally sprayed coatings and the equivalent bulk material. This is attributed to the significantly modified microstructure of the sprayed coatings. However, currently there is no detailed understanding of which aspects of microstructural modification are primarily responsible for this performance gap. In this work several deliberately microstructurally modified versions of the Ni-based superalloy Inconel 625 were produced. These were subjected to potentiodynamic electrochemical testing in 0.5 M H₂SO₄ to investigate the links between specific microstructural features and electrochemical behaviour. Samples were prepared by high-velocity oxy-fuel (HVOF) thermal spraying, laser surface remelting using a high power diode laser and conventional powder sintering. Microstructural features were examined by optical and scanning electron microscopy and X-ray diffraction. Potentiodynamic testing was carried out on the following forms of Inconel 625: wrought sheet; HVOF sprayed coatings; sintered powder compacts; laser melted wrought sheet and HVOF sprayed coatings. Using the corrosion behaviour, i.e. passive current density, of the wrought sheet as a baseline, the performance of different forms of Inconel 625 was compared. It is found that a fine dendritic structure (with associated microsegregation) produced by laser remelting wrought sheet has no significant effect on corrosion performance. Up to 12% porosity in sintered powder samples increases the passive current density by a factor of only around 2. As observed previously, the passive current density of HVOF sprayed coatings is 20-40 times greater. However, HVOF coatings subjected to laser surface remelting are found to have a passive current density close to that of wrought material. It is concluded that, whilst porosity in coatings produces some decrease in corrosion resistance, the main contributing factor is the galvanic corrosion of localised Cr-depleted regions which are associated with oxide inclusions within HVOF sprayed samples.     

Corrosion properties of in situ laser remelted NiCrBSi coatings comparison with hard chromium coatings

This study aims at evaluating the effect of an in situ laser remelting treatment of NiCrBSi coatings, deposited by plasma spraying. Life Cycle Assessment (LCA) method was used to estimate the environmental impacts of coating processes. It was demonstrated with this LCA that the in situ remelting process was clean. Microstructural results were also evaluated. A good metallurgical bond was formed at the remelted coating interface. Scanning electron microscopy observation revealed also that laser treatment induces a change of the microstructure from lamellar to columnar dendritic. The dependence between the microstructure of NiCrBSi coatings, which was modified by laser treatment, and corrosion resistance has been evaluated by potentiodynamic polarization curves. Results show that, the corrosion resistance was increased because of a finer structure and higher densities of the coatings, but corrosion mechanisms occurring in all cases were different. From the electrochemical experiments in NaCl solution it can be deduced that laser remelting of as-sprayed coatings does not affect their corrosion rate. Corrosion evolves due to a progressive penetration of the electrolyte through the disturbed structure of the as-sprayed samples, whereas the substrate surface of remelted coating is not reached, because of a higher density. But ClMO intermediate species were formed on the surface, because Cl⁻ can destroy the protective film on the coating. The hybrid plasma/laser process was cleaner than hard chromium plating and its corrosion behavior is superior too.     

Effect of Heat Treatment on the Microstructure and Properties of HVOF-Sprayed Co-Cr-W Coating

Co-Cr-W HVOF-sprayed protective coatings are used for their high oxidation and wear resistance. Apart from the oxidation resistance, the stability of their mechanical properties in relation to thermal loading is crucial with respect to the most common high-temperature application areas. This work is focused mainly on evaluation of the heat-induced changes in the phase composition and related mechanical properties. It was shown that the original powder, composed fully from face-centered cubic Co-based alloy, partly changes its phase composition during spraying to a hexagonal close-packed (hcp) structure. The annealing further increases the ratio of the hcp phase in the structure. The heat-induced phase changes are accompanied by an increase in the coatings’ hardness and cohesion strength. The abrasive and adhesive wear behavior was evaluated. While the coatings’ heat treatment had a positive effect on the coefficient of friction, the abrasive and adhesive wear resistance of annealed coating was lower compared to as-sprayed coating.     

Deposition and Properties of Phosphate Coatings on Galvanized Steel

It is shown that protective films on galvanized steel can be obtained from alkaline phosphate solutions in the presence of phosphorus-containing ligands. The samples are suggested to be treated in these solutions prior to application of crystalline phosphate coatings. The films obtained are compared with crystalline phosphate coatings by using scanning electron microscopy (SEM) and x-ray diffraction (XRD) methods.     

Oxidation Behavior of Pt–Ir Modified Aluminized Coatings on Ni-base Single Crystal Superalloy TMS-82+

The oxidation resistance of Pt–Ir modified aluminized coatings, prepared by magnetron sputtering, was investigated. Cyclic oxidation tests revealed that Pt–30 at%Ir and Pt–50 at%Ir modified aluminide coatings demonstrated a smaller mass change compared with Pt, Pt–80 at%Ir and Ir modified aluminide coatings. Cross-sectional analyses following cyclic oxidation tests showed that the TGO layer formed on the Pt modified aluminide coating surface is almost twice as thick as those on the Pt–30 at%Ir and Pt–50 at%Ir coatings. In addition, the Pt–30 at%Ir and Pt–50 at%Ir samples had a much smoother surface than the Pt modified coatings after cyclic oxidation, and the latter suffered from severe surface rumpling. However, when the Ir content exceeded 80 at% in Pt–Ir modified coatings, internal voids formed during cyclic oxidation. These results show that the addition of 30–50 at%Ir to Pt-modified aluminized coatings is most effective in enhancing oxidation resistance.     

Corrosion inhibitors in conversion coatings. IV

This review covers main approaches to development of inhibited conversion formulations for chemical oxidation of aluminum alloys. A mechanism explaining the formation of conversion coatings on aluminum alloys from chromate conversion baths is proposed; the protective properties of the resulting coatings are characterized. It is demonstrated that various modified methods for the preparation of chromate conversion coatings on aluminum enhance their protective properties, however, without solving ecological problems. Among alternative corrosion inhibitors used in chemical oxidation of aluminum alloys, molybdate-containing formulations are worth noting and have been much investigated. The most promising approach is to develop corrosion inhibitors for use during both the formation of a conversion coating and its subsequent filling with compounds chemisorbable at the modified oxide. Original Russian Text ? S.V. Oleinik, Yu.I. Kuznetsov, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 4, pp. 421–428.     

Corrosion inhibitors in PEO-coatings on aluminum alloys

The corrosion properties of coatings obtained by plasma-electrolytic oxidation (PEO) in silicate and borate electrolytes on AMg-5 and D17 aluminum alloys are studied. An increase in PEO-coating thickness on AMg-5 alloy obtained in borate electrolyte does not provide an increase in their corrosion resistance in chloride media. The greatest contribution to increasing the corrosion resistance of such coatings is made by filling them with corrosion inhibitors. Additional hydrophobization by low molecular fluoroplast increases the protective action of such inhibited coatings.     

SOFCs金属连接体表面改性Mn-Co尖晶石涂层研究现状

Fe-Cr铁素体不锈钢是中低温固体氧化物燃料电池(SOFCs)的理想连接体材料，但其在高温有氧环境中表面易被氧化，且会引起阴极“Cr毒化”现象，致使电池工作效率降低。Mn-Co尖晶石因其较高的高温导电性和抗氧化性，被广泛应用于连接体保护涂层以提高连接体的抗氧化性，并减少Cr的扩散。但Mn-Co尖晶石涂层在长期服役过程中仍存在Cr元素扩散导致Cr₂O₃过渡氧化层不断增厚、涂层导电性能下降的现象，研究发现通过对Mn-Co尖晶石涂层进行掺杂改性可有效改善上述问题。本文结合近年来Mn-Co尖晶石涂层研究进展，简述了典型的Mn-Co尖晶石晶体结构及其导电机制，总结了改性元素在Mn-Co尖晶石中可能的掺杂位点及对尖晶石晶体结构的影响，重点阐述了稀土元素Y、La、Ce，以及过渡族元素Cu、Fe改性对Mn-Co尖晶石涂层抗氧化性、导电性、黏附性，以及热膨胀系数相容性的影响，详述了改性元素作用机理，总结对比了不同元素对Mn-Co尖晶石涂层改性的侧重点。最后，对当前研究中Mn-Co尖晶石涂层存在的问题及今后改性Mn-Co尖晶石涂层的研究方向进行了展望。     

Chemical oxidation of lithium-containing aluminum alloy 1424

The possibility of obtaining protective conversion coatings on the surface of lithium-containing aluminum alloy 1424 in chromate-free conversion solutions IFKhANAL-1 and IFKhANAL-3 is shown. The kinetics of formation, composition, and protective properties of these coatings are studied. It is shown that the introduction of modifying additives and corrosion inhibitors into the IFKhANAL-1 oxidizing solution significantly increases the resistance of formed coatings to pitting corrosion in chloride-containing environments.     

A Study of the Corrosion Resistance of Pump–Compressor Pipes with a Diffusion Zinc Coating under the Complicated Conditions of Gas-Producing Wells

The results of corrosion tests of diffusion zinc coatings under the complicated corrosion and erosion conditions of gas-production wells are presented. The slowdown of the anodic process of the solution of a coating and its salt passivation in model solutions was shown by the electrochemical research. It was established that the corrosion rates of diffusion zinc-coated 36G2F steel samples were 4.1–6.1 times lower than those of samples without coating. The corrosion resistance and the operational reliability of pump–compressor pipes can be increased by using protective duplex system combining a diffuse zinc coating (protective layer) and an upper layer of a polymer coating (barrier layer).     

不同涂层对304不锈钢高温防护效果的对比研究

采用溶胶凝胶法在304不锈钢表面上分别制备了SiO2、Al2O3、ZrO2防护涂层。通过X射线衍射(XRD)、扫描电镜(SEM)对不同氧化物涂层进行了结构和形貌的表征。对比了不同氧化物涂层保护样品的高温抗氧化性、抗热冲击性以及在3.5wt%NaCl溶液中的耐电化学腐蚀性。结果表明Al2O3涂层具有很好的高温抗氧化性和耐电化学腐蚀性,而ZrO2涂层具有良好的抗热冲击性能。     

Influence of WC addition in Co-Cr-W-Ni-C flame sprayed coatings on microstructure, microhardness and wear behaviour

In present paper the influence of the tungsten carbide (WC) particle addition on the microstructure, microhardness and abrasive wear behaviour of flame sprayed Co-Cr-W-Ni-C (EWAC 1006) coatings deposited on low carbon steel substrate has been reported. Coatings were deposited by oxy-acetylene flame spraying process. Wear behaviour of coatings was evaluated using pin on flat wear system against SiC abrasive medium. It was observed that the addition of WC particle in a commercial Co-Cr-W-Ni-C powder coating increases microhardness and wear resistance. Wear behaviour of these coatings is governed by the material parameters such as microstructure, hardness of coating and test parameters (abrasive grit size and normal load). Addition of WC in a commercial powder coating increased wear resistance about 4-9 folds. WC modified powder coatings showed better wear resistance at high load. Heat treatment of the unmodified powder coatings improved abrasive wear resistance while that of modified powder coating deteriorated the wear resistance. SEM study showed that wear of coatings largely takes place by microgroove, crater formation and scoring. Electron probe micro analysis (E.P.M.A.) of unmodified and WC modified powder coating was carried out for composition and phase analysis.     

Microarc Oxidation of Carbon-Graphite Materials (Review)

The review is devoted to microarc (or plasma-electrolytic) oxidation (MAO) of carbon-graphite materials with the purpose of protecting their surfaces from oxidation, primarily, high-temperature oxidation. It is found that the formation of protective coatings on graphite under certain conditions occurs in accordance with trends similar to the formation of oxide layers on valve metals. The phenomenological model of the mechanism of formation of MAO coatings on graphite is given. In particular, the results of our own studies are described, as well as the data on the achieved level of characteristics of obtained MAO coatings are given.