High-Pressure Cold-Sprayed Ni and Ni-Cu Coatings: Improved Structures and Corrosion Properties

Cold spraying is a promising technique for the production of dense metallic coatings. In cold spraying, coating formation is through high velocity impacts of solid particles with high kinetic energy. During impact, particles deform plastically and adhere to the substrate, gradually building-up the coating. This makes it possible to form pure and dense coating structures. These impermeable coatings are advantageous in many applications such as those where corrosion protection is required. Nickel and nickel-copper alloys have good corrosion resistance and therefore, as dense coatings, have high potential for employment as corrosion barrier layers. In this study, the structural and corrosion properties of high-pressure cold-sprayed (HPCS) Ni and NiCu coatings are characterized. NiCu alloys are known to have good corrosion resistance in sulphuric and hydrochloric acids, whereas Ni is resistant to caustic soda and alkaline salt solutions. This study also shows the effect of heat treatments on coating properties. FESEM studies of cross-sectional samples reveal structural details of the HPCS coatings while corrosion properties are evaluated with polarization measurements. The corrosion behavior of both the bulk and substrate material is determined in order to assess the real corrosion protection potential of the coatings.     

Effect of Ceramic Particles on Properties of Cold-Sprayed Ni-20Cr+Al2O3 Coatings

Cold spraying is a thermal spray process enabling the production of metallic and metal-ceramic coatings with low porosity and low oxygen content, capable of, e.g., resisting corrosion. The aim of this study was to characterize the microstructural and mechanical properties of cold-sprayed Ni-20Cr+Al₂O₃ coatings and to clarify the effect of the hard particles on different coating properties. Accordingly, the research focused on the microstructure, denseness (impermeability), adhesion strength, and hardness of the coatings. Scanning electron microscopy (SEM) analysis and corrosion tests were run to gain information on the through-porosity. Ceramic addition in cold-sprayed Ni-20Cr+Al₂O₃ coatings improved their quality by lowering their porosity. Moreover, hardness was slightly higher than those of cold-sprayed Ni-20Cr coating, indicating a hardening effect by the ceramic particles. The addition of Al₂O₃ also made it possible to use high gas temperatures without nozzle clogging, which affects coating properties, such as coating thickness, denseness, and hardness.     

Corrosion Properties of Cold-Sprayed Tantalum Coatings

Cold spraying enables the production of pure and dense metallic coatings. Denseness (impermeability) plays an important role in the corrosion resistance of coatings, and good corrosion resistance is based on the formation of a protective oxide layer in case of passivating metals and metal alloys. The aim of this study was to investigate the microstructural details, denseness, and corrosion resistance of two cold-sprayed tantalum coatings with a scanning electron microscope and corrosion tests. Polarization measurements were taken to gain information on the corrosion properties of the coatings in 3.5 wt.% NaCl and 40 wt.% H₂SO₄ solutions at room temperature and temperature of 80 °C. Standard and improved tantalum powders were tested with different spraying conditions. The cold-sprayed tantalum coating prepared from improved tantalum powder with advanced cold spray system showed excellent corrosion resistance: in microstructural analysis, it showed a uniformly dense microstructure, and, in addition, performed well in all corrosion tests.     

Effect of Process Parameters and Heat Treatments on Properties of Cold Sprayed Copper Coatings

Cold gas dynamic spraying or cold spray is specifically suitable to obtain high-conductivity copper coatings for a variety of applications. Copper coatings at different coating parameters were deposited and subjected to various post treatments. The effect of process parameters and the treatment conditions on coating properties such as electrical conductivity, porosity, microhardness etc., was studied. The as-coated specimens exhibited low conductivities and conductivity was found to improve with heat treatment. Treatments were carried out in vacuum at different temperatures and for different durations and conductivities close to bulk annealed copper were achieved. Good correlation was observed between the conductivity, porosity and hardness of the as-coated and heat-treated specimens. Similar correlations were observed between conductivity-porosity and hardness-porosity of the coatings and the relative influence of cold work and porosity on coating properties was determined.     

Mechanical properties of cold-sprayed and thermally sprayed copper coatings

The present investigation compares the mechanical properties of cold-sprayed and thermally sprayed copper coatings. The mechanical properties of the Cu-coatings are determined by in plane tensile test using micro-flat tensile specimen technique. A deeper view into the type of obtained defects, their stability and their influence on coating performance, is supplied by subsequent failure analyses and the comparison to annealed copper coatings. The results demonstrate that cold-sprayed coatings, processed with helium as propellant gas, show similar performance as highly deformed bulk copper sheets and respective changes in properties after annealing. In the as-sprayed condition, cold-sprayed coatings processed with nitrogen and thermally sprayed coatings show rather brittle behavior. Whereas subsequent annealing can improve the properties of the cold-sprayed coating, processed with nitrogen, such heat treatments have only minor influence on the tensile properties of thermally sprayed copper coatings. The investigation of failure modes for the as-sprayed states and after different heat treatments provided further information concerning particle–particle bonding and the effect of oxides on mechanical properties.     

300M钢表面冷喷涂锌镍复合涂层性能研究

目的 研究300M高强钢表面的冷喷涂锌镍复合涂层的涂层性能.方法 采用机械混合的方式将锌粉和镍粉进行混合,利用低温气动喷涂技术在300M高强钢表面制备锌镍复合涂层,采用扫描电子显微镜、能量色散谱和显微硬度测试仪研究涂层的微观组织结构.采用普通中性盐雾加速实验、涂层破损盐雾加速试验及户外暴晒试验,对冷喷涂锌镍涂层的抗腐蚀性能进行综合评价.考核冷喷涂对300M钢基材疲劳性能的影响.结果 根据SEM的表面及截面图片分析,冷啧涂锌镍复合涂层十分致密,且无孔隙及裂纹,涂层的孔隙率平均为0.4％,结合强度40 MPa左右.根据EDS结果分析,锌镍复合涂层中锌的质量分数为85％左右,镍的质量分数为15％左右.锌镍复合涂层的显微硬度为70.8HV0.49.锌镍复合涂层中镍粒子的强化作用,提高了涂层的硬度.冷喷涂锌镍复合涂层具有非常好的抗腐蚀性能,盐雾实验超过770h,即使涂层破损也可以达到600h.户外暴晒实验12个月表面无明显腐蚀,并且冷喷涂对300M钢基材的疲劳性能没有影响.结论 冷喷涂锌镍复合涂层作为抗腐蚀涂层,可以对300M高强钢提供保护.     

Corrosion behavior of HVOF-sprayed and Nd-YAG laser-remelted high-chromium,nickel-chromium coatings

Thermal spray processes are widely used to deposit high-chromium, nickel-chromium coatings to improve high temperature oxidation and corrosion behavior. However, despite the efforts made to improve the present spraying techniques, such as high-velocity oxyfuel (HVOF) and plasma spraying, these coatings may still exhibit certain defects, such as unmelted particles, oxide layers at splat boundaries, porosity, and cracks, which are detrimental to corrosion performance in severe operating conditions. Because of the process temperature, only mechanical bonding is obtained between the coating and substrate. Laser remelting of the sprayed coatings was studied in order to overcome the drawbacks of sprayed structures and to markedly improve the coating properties. The coating material was high-chromium, nickel-chromium alloy, which contains small amounts of molybdenum and boron (53.3% Cr, 42.5% Ni, 2.5% Mo, 0.5% B). The coatings were prepared by HVOF spraying onto mild steel substrates. A high-power, fiber-coupled, continuous-wave Nd:YAG laser equipped with large beam optics was used to remelt the HVOF-sprayed coating using different levels of scanning speed and beam width (10 or 20 mm). Coating that was remelted with the highest traverse speed suffered from cracking because of the rapid solidification inherent to laser processing. However, after the appropriate laser parameters were chosen, nonporous, crack-free coatings with minimal dilution between coating and substrate were produced. Laser remelting resulted in the formation of a dense oxide layer on top of the coatings and full homogenization of the sprayed structure. The coatings as sprayed and after laser remelting were characterized by optical and electron microscopy (OM, SEM, respectively). Dilution between coating and substrate was studied with energy dispersive spectrometry (EDS). The properties of the laser-remelted coatings were directly compared with properties of as-sprayed HVOF coatings.     

Comparison of a cold-sprayed and plasma-sprayed Fe25Cr20Mo1Si amorphous alloy coatings on 40Cr substrates

The purpose of this paper is to examine whether cold spraying is capable of manufacturing high-quality ferrous-based amorphous alloy coatings by comparing the performance of a cold-sprayed with a plasma-sprayed Fe25Cr20Mo1Si amorphous coating on a 40Cr substrate. The hardness, microstructure, wear resistance, and corrosion resistance of the two coatings were determined with potentiodynamic polarization curves, neutral salt spray tests, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction and their performance differences were examined. The results show that the cold-sprayed Fe25Cr20Mo1Si coating has an amorphous content of 97.63%, which is slightly higher than that for the raw powder (97.24%) and plasma-sprayed coating (96.55%). The coating hardness ranges from 720 HV to 1,030 HV, which is higher than plasma-sprayed coating (590–610 HV) and decreases the wear rate to about 2/3. The average porosity is 2.97 ± 0.59%, which is lower than that of the plasma-sprayed coating (4.95 ± 0.13%). The cold-sprayed Fe25Cr20Mo1Si coating can pass the 3,000 hr neutral salt spraying test, while the plasma-sprayed coating fails within 120 hr. The corrosion current in 3.5% NaCl solution reached to its stable value about 1.66 A/cm², which is about 1/4 of the plasma-sprayed coating (5.81 A/cm²). Upon analyzing the properties and the anticorrosion performance, it was found that there are no through-thickness pores in the cold-sprayed coating that impact its long-term anticorrosion performance. Cold spraying can be used to fabricate ferrous-based amorphous coatings instead of traditional thermal spraying technologies to obtain high-quality ferrous-based amorphous coatings.     

A Comparative Study on Ni-Based Coatings Prepared by HVAF,HVOF, and APS Methods for Corrosion Protection Applications

Selection of the thermal spray process is the most important step toward a proper coating solution for a given application as important coating characteristics such as adhesion and microstructure are highly dependent on it. In the present work, a process-microstructure-properties-performance correlation study was performed in order to figure out the main characteristics and corrosion performance of the coatings produced by different thermal spray techniques such as high-velocity air fuel (HVAF), high-velocity oxy fuel (HVOF), and atmospheric plasma spraying (APS). Previously optimized HVOF and APS process parameters were used to deposit Ni, NiCr, and NiAl coatings and compare with HVAF-sprayed coatings with randomly selected process parameters. As the HVAF process presented the best coating characteristics and corrosion behavior, few process parameters such as feed rate and standoff distance (SoD) were investigated to systematically optimize the HVAF coatings in terms of low porosity and high corrosion resistance. The Ni and NiAl coatings with lower porosity and better corrosion behavior were obtained at an average SoD of 300 mm and feed rate of 150 g/min. The NiCr coating sprayed at a SoD of 250 mm and feed rate of 75 g/min showed the highest corrosion resistance among all investigated samples.     

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。     

Effects of Spark-Plasma Sintering Treatment on Cold-Sprayed Copper Coatings

Cold-spray is well known as an effective coating technique to make thick metallic coatings. However, cold-sprayed metallic coatings usually have low tensile strengths due to low adhesion strength between particles, and low ductility due to low adhesion strength between particles and work hardening. Spark-plasma sintering (SPS) is a pressure-sintering technique that employs a large pulsed direct current. Compared to annealing heat treatment (AHT), SPS is expected to effectively improve the adhesion strength between particles in cold-sprayed metallic coatings. In order to investigate the effects of SPS, cold-sprayed Cu coatings were treated by both SPS and AHT under a wide range of temperatures. The microstructures and mechanical properties of the treated specimens were investigated primarily by scanning electron microscopy, electron backscatter diffraction analysis, hardness tests, and tensile tests. Despite comparable values for porosity, crystal grain size, plastic strain distribution, hardness, and yield stress, the tensile strength and ductility of the specimen treated by SPS at 400 °C (SPS400) were significantly higher than those of the specimen treated by AHT at 450 °C. Based on these results, it was determined that SPS treatment is more effective in improving the adhesion strength between the particles in cold-sprayed Cu coatings than AHT.     

The Effect of Post-Heat Treatment on Microstructure of 316L Cold-Sprayed Coatings and Their Corrosion Performance

The combined effects of process gases and post-heat treatment temperature on the microstructure of 316L cold-sprayed coatings on Al5052 substrates have been investigated in this study. The stainless steel coatings were subjected to heat treatment at four different temperatures (250, 500, 750, and 1000 °C) to study the effect of heat treatment. In addition, the corrosion performances of the coatings at different process temperatures have been compared using the potentiodynamic scanning technique. Microstructural characterization of the coatings was carried out using scanning and transmission electron microscopy and x-ray diffraction. The results of present study showed that cold-sprayed stainless steel coatings processed with helium exhibited higher corrosion resistance than those of coatings sprayed with nitrogen process gas. This could partially be attributed to the reduction in porosity level (4.9%) and improvement of particle-particle bonding. In addition, evaluation of the mechanical and microstructural properties of the coatings demonstrated that subsequent heat treatment has major influence on the deposited layers sprayed with He process gas.     

Deposition Behavior of Copper Fine Particles onto Flat Substrate Surface in Cold Spraying

Cold spray is a promising process to fabricate high-quality metallic coatings. However, it is necessary to improve some properties, especially the adhesive strength of the coating to the substrate to clarify deposition mechanism of the solid particles onto substrate surface. In this study, deposition behavior of the cold sprayed copper fine particles was observed precisely and the adhesive strength of the coating was evaluated. The deposition behavior of the sprayed individual copper particles on mirror polished stainless steel substrate was fundamentally investigated. The interface microstructure between sprayed particle and substrate revealed that an amorphous-like band region was recognized at interface during coating fabrication at high power conditions. For the deposition mechanism of the cold sprayed particles onto substrate surface, it was indicated that the deformation of the particles initially induce the destruction of its surface oxide and an appearance of the active fresh surface of the material may enhance the bonding between particles and substrate. On the other hand, in coating fabrication at high power condition, bonding between particle and substrate may be possibly formed via oxygen-rich amorphous-like layer at interface.     

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.     

Electrodeposition of multi-layer Pd–Ni coatings on 316L stainless steel and their corrosion resistance in hot sulfuric acid solution

Pd–Ni coating shows good corrosion resistance in strong corrosion environments. However, in complex aggressive environments, the performance of the coatings is limited and further improvement is necessary. The effects of the applied plating current density on the composition, structure and properties of Pd–Ni coatings were studied. By changing the current density in the same bath, multi-layer Pd–Ni coatings were prepared on 316L stainless steel. Scanning electronic microscopy, weight loss tests, adhesion strength, porosity and electrochemical methods were used to study the corrosion resistance of the films prepared by different coating methods. Compared with the single layer Pd–Ni coating, the multi-layer coatings showed higher microhardness, lower internal stress, lower porosity and higher adhesive strength. The multi-layer Pd–Ni coating showed obviously better corrosion resistance in hot sulfuric acid solution containing Cl^?.     

Air plasma sprayed metallic coatings for sour environments

Abstract

Among protective coatings for components used in petrochemical applications, plasma sprayed alloys containing chromium, nickel, and molybdenum have potential to provide functional surfaces with good resistance to corrosion and wear. They could offer a cost effective solution by limiting the use of expensive bulk materials such as Inconel or Hastelloy superalloys or highly alloyed chromium stainless steels, since a low cost base material could be selected to give the required mechanical strength combined with suitable corrosion resistance from its modified surface. To limit fabrication costs of coating deposition, air plasma spraying techniques can be proposed, but proper optimisation of the plasma processing parameters is required to increase coating performance. In this paper, coatings based on Ni–Cr–B–Si and Mo alloys have been deposited following a design of experiment methodology. Results of characterisation tests for preliminary spraying trials (metallographic, tribological, and corrosion tests) are reported and discussed. Following analysis of numerical results, a coating obtained by the codeposition of two commercial powders (Metco 505 and Metco 16C) was sprayed on carbon steel substrates. Sulphide stress corrosion cracking tests, according to the NACE TM 0177-90 standard, at up to 90% of the yield stress of the coated specimens did not induce any damage for test durations of up to 720 h. Tribological properties have also been evaluated in terms of the slurry abrasivity response number (SAR), friction coefficients, and mass loss after ASTM standard ball on disc tests. Good resistance to erosion damage was obtained with a final SAR number of 37.     

High Pressure Cold Sprayed (HPCS) and Low Pressure Cold Sprayed (LPCS) Coatings Prepared from OFHC Cu Feedstock: Overview from Powder Characteristics to Coating Properties

Cold spraying enables high quality Cu coatings to be deposited for applications where high electrical and/or thermal conductivity is needed. Fully dense Cu coatings can provide an effective corrosion barrier in specific environments. The structure of cold-sprayed Cu coatings is characterized by high deformation which imparts excellent properties. Coating properties depend on powder, the cold spray process and post treatments. First of all, powder characteristics have a strong influence on the formation of pure coatings. Secondly, cold spraying provides dense, adherent, and conductive coatings by using HPCS and LPCS. Furthermore, an addition of Al₂O₃ particles to the Cu powder in LPCS process significantly improves coating properties. Also, heat treatments improve electrical conductivity. This study summarizes optimal characteristics of Cu powder optimized for cold spraying, achieving high coating quality and compares properties of HPCS Cu, LPCS Cu and Cu+Al₂O₃ coatings prepared from the same batch of OFHC Cu powder.     

铜基体上等离子体喷涂钨涂层性能研究

介绍了铜基体上等离子喷涂1 mm钨涂层核聚变试验装置壁材料的制备,并对真空和大气等离子体喷涂钨涂层性能进行了比较研究,内容主要包括微观形貌、气孔率、杂质含量、结合强度和热负荷性能.结果表明,气孔率和氧杂质含量差异是大气和真空等离子体喷涂钨涂层热负荷性能差异的主要原因.     

Microstructure of Interfacial Region Between Cold-Sprayed Copper Coating and AlN Substrate Coated with Sputtered Titanium and Copper

Cold spraying has been developed as a high-quality coating technique. In this article, copper is deposited on an AlN substrate coated by the sputtering of titanium and copper at a low pressure of less than 1.0 MPa, making this approach suitable for a wide range of engineering applications. In order to understand the adhesion mechanism at the atomic scale, the interfacial regions are carefully observed in thin foil samples from the cross sections of the specimens with a HREM. We find a unique wavy boundary between the sputtered titanium and the sputtered copper. It is assumed that the shear-instability phenomenon occurs due to the cold-spraying process and influences the adhesive strength. Furthermore, the cold-sprayed copper particles are connected directly without any oxidation layer due to the appearance of new metallic surfaces during the impact process. The TEM data clearly reveal the phenomena and mechanisms related to the impact of powder sprayed on the substrate.     

Duplex coating of electroless nickel and HVOF (high-velocity oxygen fuel) sprayed WC-Co

The porosity of thermal sprayed coatings is usually a problem when coatings are used in wet corrosion application. The porosity allows media to penetrate to the surface of the base material. Corrosion spreads rapidly and the coating loses contact with the substrate and delaminates. This problem can be initiated by impregnating different polymers into the pores. An alternative approach has been tested in the present work to prevent corrosion of cemented carbide coated carbon steel in wet corrosion environments. Carbon steel substrates were coated with a thin film of electroless nickel (electroless nickel plating) and then HVOF (High-Velocity Oxygen Fuel) sprayed with cemented carbide. Reference specimens without electroless nickel were sprayed at the same time. The microhardness of the specimens was measured and the coating structure examined using optical microscopy and X-ray diffractometry (XRD). The bond between the layers and the base material was examined by means of a bend test. A salt chamber test was also performed for the specimens. The structure of the electroless nickel layer was crystalline as a result of the HVOF spraying. There were no cracks in the nickel layer, if the layer was about 20 μm thick. According to the results of the bend test, the adhesion between coatings and substrate was good, and there was no difference between the duplex-coated specimen and the reference specimen. A sample with a thin nickel layer under an HVOF sprayed cemented carbide did not exhibit corrosion after 8 h in the salt chamber test.