梯度NiCrAlY涂层的1000和1100℃氧化行为研究

采用电弧离子镀技术及后续热处理工艺在镍基高温合金上制备了均匀NiCrAlY涂层和梯度NiCrAlY涂层,分析了2种涂层的组织结构,对比研究了2种涂层静态空气下1000和1100℃恒温氧化行为以及1100℃的循环氧化行为.结果表明:均匀NiCrAlY涂层由γ′/γ相和少量β-NiAl相、α-Cr相组成,成分分布均匀;梯度NiCrAlY涂层具有外层富Al和内层富Cr的结构,其中外层由β-NiAl相和少量γ′/γ相、α-Cr相组成.一方面,梯度涂层的初始Al含量较高;另一方面,氧化过程中其富Cr区两侧出现了对富Al区的Al向基体扩散起阻碍作用的Cr(W)析出带.这两方面使梯度涂层长时间维持更多的Al存储相,提升了氧化膜的迅速生成及再生成能力,从而使涂层具有较好的抗氧化性能.     

Application of High Temperature Corrosion-Resistant Materials and Coatings Under Severe Corrosive Environment in Waste-to-Energy Boilers

Corrosion-resistant materials (CRMs) and coatings are key technologies to increase power generation efficiency and reduce maintenance in waste-to-energy (WTE) plants. Corrosion environment became severe as steam temperatures have increased. The steam condition of more than 400 °C/3.9 MPa became possible in WTE boilers by using highly durable corrosion-resistant coatings, such as thermal spray of Al/80Ni20Cr alloy, HVOF-sprayed NiCrSiB alloy, Alloy 625 weld overlay for waterwall tubes and also superheater tubes. Also, the use of 310S type stainless steels and high Cr-high Mo-Ni base and high Si-Cr-Ni-Fe alloys have progressed because of a better understanding of corrosion mechanisms. Furthermore, high durability coatings using cermet and ceramic materials were applied to high temperature superheaters. This paper describes the major developments and the application of CRMs and coating technologies in the last 30 years in WTE plants, the corrosion mechanisms of alloys, the deterioration mechanisms of spray coating layers, and future subjects for the development of corrosion-resistant materials and coatings.     

Erfahrungen mit Hochtemperatur-Korrosionsschutzschichten in stationären Gasturbinen

Experience with hot corrosion protective coatings in stationary gas turbines The article reviews the hot corrosion phenomena occurring in stationary gas turbines, shows up the requirements for coatings, and discusses the properties of diffusion and overlay coatings. Based on laboratory and field experience guidelines are given which coating system and what coating composition would be the optimum choice under given corrosion conditions. The problems to be solved for coating developments at highest temperatures, i.e. above about 1000 °C, are outlined.     

Oxidation-resistant coatings for ultra-high-temperature refractory Mo-based alloys

The synthesis of robust coatings that provide protection against environmental attack at ultra-high temperatures is a difficult challenge. In order to achieve this goal for Mo-based alloys the fundamental concepts of reactive diffusion pathway analysis and kinetic biasing are used to design a multilayer coating with a phase sequencing that provides for structural and thermodynamic compatibility and an underlying diffusion barrier to maintain coating integrity. The coating structure evolution during high-temperature exposure facilitates a prolonged lifetime as well as a self-healing capability. Both borosilicide and aluminide coatings that can be synthesized by a pack cementation process are demonstrated to yield superior environmental resistance on Mo-based systems at temperatures up to l,700°C and can be adapted to apply to other refractory metal systems.     

Identification of degradation mechanisms in coatings for supercritical steam applications

The development and qualification of coatings for materials used in modern steam power plants stems from the increased demand for higher efficiency, and hence higher operating temperatures. Within the EU funded project ‘SUPERCOAT’, several coatings, both overlay and diffusion type, were investigated. Seven different coatings are presented in this work. They included two commercially available HVOF coatings (Ni–20Cr and Ni–50Cr), an aluminium‐based slurry coating (IPCOTE), together with two further variations of this slurry coating containing sputter‐coated inter‐layers. An overlay slurry coating consisting of silica particles embedded in a matrix of alumina and chromia was also examined. The final coating to be investigated was a pack‐aluminised sample of P92. All the coating systems examined showed superior oxidation resistance compared to the 9%Cr steel substrate (P91 or P92) in extended exposures to a steam environment at 650 °C. However, in service component lifetime will be limited by degradation of the coating, therefore it is essential that the mechanisms controlling this behaviour are understood. This paper reviews several degradation mechanisms that have been observed during long‐term exposure of these coatings. The mechanisms that have been observed include depletion of active alloying elements, diffusion of aluminium into the substrate from the coating, formation of Kirkendall porosity and mechanical failure of the coatings. Examples of each of these mechanisms will be presented. Possible processing routes to avoid these degradation mechanisms will also be discussed.     

Comparative Study of Micro- and Nano-structured Coatings for High-Temperature Oxidation in Steam Atmospheres

For many high-temperature applications, coatings are applied in order to protect structural materials against a wide range of different environments: oxidation, metal dusting, sulphidation, molten salts, steam, etc. The resistance achieved by the use of different kind of coatings, such as functionally graded material coatings, has been optimized with the latest designs. In the case of supercritical steam turbines, many attempts have been made in terms of micro-structural coatings design, mainly based on aluminides, and other diffusion coating systems in order to consider alternatives, nano-structured coatings based on Cr and Al compositions and deposited by a physical vapor deposition technique, were assessed to high-temperature oxidation resistance in steam environments. The oxidation kinetics where analyzed for up to 2,000 h at 650 °C by means of gravimetric measurements. The evaporation behavior was also analyzed by thermogravimetric-mass spectrometry. Excellent results where observed for some of the nano-structured coatings tested. Those results where compared to results obtained for micro-structured coatings. Based on that comparison, it was deduced that the nano-structured coatings have a potential application as protective systems in high-temperature steam environments.     

Ultrafine Particulate Dispersed High-Temperature Coatings by Hybrid Spray Process

Oxide dispersion strengthened alloys (ODS), although not commonly used in coating applications, have long been used for high-temperature structural applications due to their superior creep properties. In this paper, we present the design, synthesis, and characterization of a new class of functionally engineered high-temperature coatings in which ultrafine oxide particulates are dispersed in the matrix alloy to achieve superior creep resistance along with improved high-temperature corrosion and erosion resistance. These coatings were fabricated using a novel technique called “hybrid spray process”. Hybrid spray technique combines arc spray and high-velocity oxy fuel (HVOF) spray processes; the metallic matrix alloys are fused by the wire arcing component of the process, whereas the ultrafine particles are synthesized in-flight by the HVOF component from liquid precursors. These particulate dispersed high-temperature composite coatings were fabricated using liquid precursors for SiO₂, Cr₂O₃, Al₂O₃, and wire feed stock of 55/45 NiCr, in one step. The coatings were then characterized using electron microscopy (SEM/TEM) and thermogravimetric analysis (TGA). High-temperature erosion, oxidation, and corrosion performance of these coatings were also evaluated and compared with 304 stainless steel, arc sprayed NiCr coatings as well as Alloy 625 overlay cladding. The hybrid spray process produced dense coatings with uniform dispersion of the ultrafine oxide particles. Further, these coatings also demonstrated superior corrosion, erosion, and oxidation resistance; SiO₂ particulate dispersion being most effective in terms of high-temperature corrosion resistance.     

高功率脉冲磁控溅射制备金属氮化物涂层EI北大核心CSCD

高功率脉冲磁控溅射(HiPIMS)作为目前研究热门的物理气相沉积方法之一,已经在刀具材料、不锈钢、聚合物、复合材料等基体上实现硬质涂层、生物涂层、耐腐蚀涂层、耐高温氧化涂层、绝缘涂层等多种类型涂层制备。通过高功率脉冲磁控溅射与复合方法及后续热处理等工艺方法复合,调节高功率脉冲磁控溅射的脉冲频率、峰值功率、占空比、多脉冲和双极性实现对靶材离化率、等离子体空间分布、涂层沉积速率、相结构、微观结构、元素成分、内应力等等离子体参数和涂层物相结构的调整,以提高基体材料的硬度、耐磨损、耐腐蚀、耐高温氧化及生物相容性等综合使役性能。特别是在应用于金属氮化物涂层的制备及性能研究方面,具有巨大的工程应用价值。结合目前硬质涂层材料的应用现状,探讨高功率脉冲溅射技术沉积涂层的特性和技术优势,介绍20多年来高功率脉冲磁控溅射技术在制备单元单层、多元多层、纳米多层与多元复合、高熵合金及含Si、O、C等金属氮化物硬质涂层工艺及性能等方面应用的研究进展。     

铝—硅涂层防护性能的研究

采用静态高温氧化、热腐蚀试验以及多种物理分析方法研究了镍基合金上的铝—硅涂层的防护性能。揭示了硅在涂层中的分布形式及其在高温曝置期间的变化情况。指出铝—硅涂层的防护性能明显优于渗铝涂层,而且在本试验范围内随硅含量的增加而提高。这是由于: (a) 铝—硅涂层减轻或防止涂层中“MC碳化物缺口”的出现; (b) 含硅的γ′-相具有优良的抗氧化性能; (c) 1100℃短时间曝置后在Al—Si涂层与基体界面处形成的连续的富硅M_6C“隔层”起扩散屏障的作用。     

Terahertz dielectric properties of plasma-sprayed thermal-barrier coatings

We investigated the electromagnetic wave transmittance and dielectric properties of yttria partially stabilised zirconia thermal-barrier coatings by terahertz time-domain spectroscopy in which the samples were irradiated by a pulsed THz wave in the frequency range of 0.1-6.3 THz. The coating microstructure was varied by changing the spray conditions and the THz transmittance and dielectric constants were examined as functions of frequency. The coatings exhibited a high transmittance of 20%-80% at frequencies below 0.5 THz and almost zero transmittance above 1.5 THz. The refractive index n for different coatings ranges from 4 to 6, depending on the coating microstructure. For any given coating, n increases to some extent with increasing frequency. Unlike the imaginary part of the dielectric constant, the real part of the dielectric constant is strongly correlated with the porosity of the coatings, which suggests that terahertz spectroscopy may potentially be used to non-destructively evaluate the porosity of ceramic coatings.     

Some Features of High-Temperature Oxidation of Aluminide Coatings on Alloy TsNK-7P

Special features of high-temperature oxidation of aluminide coatings (slip-deposited Al – Si and ion-plasma-deposited VSDP-11) on alloy TsNK-7P are considered. The kinetics of the oxidation process, the element composition, and the microhardness of coatings with different thicknesses are described. Results of thermal fatigue tests of alloy TsNK-7P with aluminide diffusion coatings are presented. It is shown that the VSDP-11 coating ensures a higher heat resistance and thermal fatigue strength on alloy TsNK-7P than the Al – Si coating and can replace the latter on turbine vanes of gas compressor units.     

含纳米Ni粉高温陶瓷涂层/GH202合金界面反应的研究

涂层失效一般是由涂层与基底界面的显微组织演变引起的,对高温下含纳米Ni粉的陶瓷涂层与合金组织的演变进行了研究,结果表明:陶瓷涂层/合金试样在900℃下进行真空扩散退火后,合金基底内在靠近界面的附近依次出现了Al2O3的晶间氧化物和针状TiN氮化物析出层;在长时间扩散过程中,纳米镍粉逐渐聚集长大,与合金基底在界面处融为一体,形成涂层与基体的咬合,使涂层与基体的结合趋向于冶金结合,具有抑制涂层失效的作用。     

Oxidation protection of NiCoCrAlY coatings on γ-TiAl

The effect of NiCoCrAlY overlay coatings on the oxidation resistance of γ-TiAl was studied at 900 ℃ in static air. To hinder the interdiffusion of the elements, the Al/Al2O3 layer was added between the coating and the alloy. The results show that the TiAl alloy exhibits poor oxidation resistance. NiCoCrAlY coating can not effectively protect the γ-TiAl substrate from high temperature oxidation because of the serious interdiffusion between the coating and the substrates. With Al/Al2O3 diffusion barrier, the NiCoCrAlY coating exhibits excellent oxidation protection on γ-TiAl alloy.     

沉积偏压对AlCrTiN纳米复合涂层力学与抗高温氧化性能的影响

沉积偏压对涂层的结构与性能具有重要影响,为研究其对AlCrTiN纳米复合涂层成分、组织结构、力学与抗高温氧化性能的影响规律,采用磁控溅射技术,改变沉积偏压(-30、-60、-90、-120 V)制备四种AlCrTiN纳米复合涂层。利用X射线衍射仪、扫描电子显微镜、纳米压痕仪等仪器表征涂层的组织结构、成分、力学性能和抗高温氧化性能。研究结果表明：不同偏压下制备的AlCrTiN纳米复合涂层均为NaCl型fcc-(Al,Cr,Ti)N相结构。随着沉积偏压增大,涂层由沿(111)晶面择优生长转变为无明显的择优生长取向,晶粒尺寸降低,残余应力和硬度增大。偏压为-90 V与-120 V时,涂层表面更加致密,具有更高的硬度和弹性模量。在800℃与900℃氧化1 h后,所有涂层表面均生成一层连续致密的Al₂O₃膜。随着沉积偏压增加,氧化膜厚度逐渐降低,表明抗高温氧化性能逐渐增强,这是因为高偏压下涂层组织更致密,且晶粒更细小。研究成果对AlCrTiN纳米复合涂层的综合性能提升与工程化应用具有一定指导意义。     

Improving corrosion properties of high-velocity oxy-fuel sprayed inconel 625 by using a high-power continuous wave neodymium-doped yttrium aluminum garnet laser

Thermal spray processes are widely used to protect materials and components against wear, corrosion and oxidation. Despite the use of the latest developments of thermal spraying, such as high-velocity oxy-fuel (HVOF) and plasma spraying, these coatings may in certain service conditions show inadequate performance,e.g., due to insufficient bond strength and/or mechanical properties and corrosion resistance inferior to those of corresponding bulk materials. The main cause for a low bond strength in thermalsprayed coatings is the low process temperature, which results only in mechanical bonding. Mechanical and corrosion properties typically inferior to wrought materials are caused by the chemical and structural inhomogeneity of the thermal-sprayed coating material. To overcome the drawbacks of sprayed structures and to markedly improve the coating properties, laser remelting of sprayed coatings was studied in the present work. The coating material was nickel-based superalloy Inconel 625, which contains chromium and molybdenum as the main alloying agents. The coating was prepared by HVOF spraying onto mild steel substrates. High-power continuous wave Nd:YAG laser equipped with large beam optics was used to remelt the HVOF sprayed coating using different levels of power and scanning speed. The coatings as-sprayed and after laser remelting were characterized by optical microscopy and scanning electron microscopy (SEM). Laser remelting resulted in homogenization of the sprayed structure. This strongly improved the performance of the laser-remelted coatings in adhesion, wet corrosion, and high-temperature oxidation testing. The properties of the laser-remelted coatings were compared directly with the properties of as-sprayed HVOF coatings and with plasma-transferred arc (PTA) overlay coatings and wrought Inconel 625 alloy.     

钼基体表面二硅化钼涂层的制备及其高温抗氧化性能

以工业废弃硅化钼棒为原料,采用浆料涂刷法在钼表面制备MoSi2基抗氧化涂层.研究涂层的显微组织、相组成及在1500℃的高温氧化行为.结果表明,以废弃硅化钼棒和纯MoSi2粉末为原料制备的涂层和基体之间形成明显的连接层.纯MoSi2制备的涂层(PM)在烧结后出现少量裂纹,而以废弃硅钼棒为原料制备的涂层(SM)在烧结后没有...     

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.     

An Overview of Using Small Punch Testing for Mechanical Characterization of MCrAlY Bond Coats

Considerable work has been carried out on overlay bond coats in the past several decades because of its excellent oxidation resistance and good adhesion between the top coat and superalloy substrate in the thermal barrier coating systems. Previous studies mainly focus on oxidation and diffusion behavior of these coatings. However, the mechanical behavior and the dominant fracture and deformation mechanisms of the overlay bond coats at different temperatures are still under investigation. Direct comparison between individual studies has not yet been achieved due to the fragmentary data on deposition processes, microstructure and, more apparently, the difficulty in accurately measuring the mechanical properties of thin coatings. One of the miniaturized specimen testing methods, small punch testing, appears to have the potential to provide such mechanical property measurements for thin coatings. The purpose of this paper is to give an overview of using small punch testing to evaluate material properties and to summarize the available mechanical properties that include the ductile-to-brittle transition and creep of MCrAlY bond coat alloys, in an attempt to understand the mechanical behavior of MCrAlY coatings over a broad temperature range.     

镍基合金上Pt-Al涂层的高温氧化行为研究

采用电镀铂之后渗铝的方法在GH586镍基高温合金上制备铂铝(Pt-Al)涂层,采用扫描电子显微镜(SEM)、X射线衍射仪、电子能谱仪等方法研究分析其高温抗氧化性能。结果表明,Pt-Al涂层具有优良的抗高温氧化性能,Pt的加入,在涂层与基体的互扩散中起到了扩散障的作用,抑制了基体合金元素向外层扩散,优化了材料的选择性氧化。同时,对Pt元素在其中的作用机制进行探讨     

High—temperature protective coatings on superalloys

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