Effect of thermal spray on the microstructure and adhesive strength of high-velocity oxy-fuel-sprayed Ni-Cr coatings on 9Cr-1Mo steel

Coatings of 80Ni-20Cr and 50Ni-50Cr on a 9Cr-1Mo steel substrate were produced by high-velocity oxy-fuel (HVOF) spraying to protect the steel against steam oxidation in ultrasupercritical (USC) boilers. The oxidation studies on the coated specimens showed good protection against the scale growth on the steel substrate. Both the 80Ni-20Cr and 50Ni-50Cr coatings formed a thin protective oxide film on the coating surface. The 80Ni-20Cr coating showed Fe diffusion from the substrate to the coating and nickel diffusion from the coating to the substrate during the oxidation process. In the case of 50Ni-50Cr coatings, the diffusion process was reduced, but a continuous layer of chromium carbide was observed at the coating/substrate interface during the oxidation. The adhesive/cohesive strength of these coatings was evaluated on aged specimens at 750 °C by using a simple tensile test. The results of the as-coated 80Ni-20Cr specimens showed an adhesive-strength value of 68 MPa. On extended aging, the strength of the coating increased beyond the detection limit of the resin. The nickel diffusion from the coating to the substrate and the iron diffusion from the substrate to the coating caused the increased adhesive strength. In the case of 50Ni-50Cr, the as-coated specimens showed an average adhesive strength of 76 MPa and showed a decreasing trend on the aged specimens. The formation of chromium carbide at the interface caused inferior values in the adhesive/cohesive strength of the 50Ni-50Cr coatings. The chromium carbide formed on the coating/substrate interface was identified as M₂₃C₆-type carbide.     

High-Temperature Behavior of a High-Velocity Oxy-Fuel Sprayed Cr3C2-NiCr Coating

High-velocity oxy-fuel (HVOF) sprayed coatings have the potential to enhance the high-temperature oxidation, corrosion, and erosion-corrosion resistance of boiler steels. In the current work, 75?pct chromium carbide-25?pct (nickel-20?pct chromium) [Cr₃C₂-NiCr] coating was deposited on ASTM SA213-T22 boiler steel using the HVOF thermal spray process. High-temperature oxidation, hot corrosion, and erosion-corrosion behavior of the coated and bare steel was evaluated in the air, molten salt [Na₂SO₄-82?pct Fe₂(SO₄)₃], and actual boiler environments under cyclic conditions. Weight-change measurements were taken at the end of each cycle. Efforts were made to formulate the kinetics of the oxidation, corrosion, and erosion-corrosion. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM)/energy dispersive spectroscopy (EDS) techniques were used to analyze the oxidation products. The coating was found to be intact and spallation free in all the environments of the study in general, whereas the bare steel suffered extensive spallation and a relatively higher rate of degradation. The coating was found to be useful to enhance the high-temperature resistance of the steel in all the three environments in this study.     

HVAF喷涂超细WC-10Co-4Cr粉末涂层的耐腐蚀性研究

对比研究超细和常规粒度WC-10Co4Cr粉末喷涂制备涂层的性能,根据显微形貌、力学性能与电化学特性比较两种涂层的耐腐蚀性并分析机理。在304不锈钢基体上,利用空气助燃高速(High Velocity Air Fuel, HVAF)热喷涂技术制备WC-10Co-4Cr涂层。采用SEM和XRD分析了涂层的物相组成和显微形貌,采用维氏硬度仪和万能拉伸试验机分别测试了涂层的显微硬度与结合强度以表征力学性能,在质量分数为3.5%的NaCl溶液中对涂层进行电化学分析。结果表明：两种WC-10Co-4Cr粉末涂层均具有优异的耐腐蚀性能,超细粉末涂层自腐蚀电位(-0.199 V)高于常规粉末粒径涂层(-0.267 V);超细粉末粒径涂层腐蚀电流密度(1.996×10^-7 A/cm2)小于常规粉末粒径涂层(3.123×10^-6 A/cm²),对基体能起到良好的保护作用。超细粉末与常规粉末WC-10Co-4Cr涂层电位腐蚀的机理主要是WC与粘结相的电偶腐蚀、Cl-对涂层表面钝化膜的破坏引起的孔蚀,腐蚀机理基本一致,主要差异在于,超细粉末涂...     

Characterization and High-Temperature Oxidation Behavior of Cold-Sprayed Ni-20Cr and Ni-50Cr Coatings on Boiler Steels

Microstructure and mechanical properties of cold-spray coatings are usually required in order to explore the potential industrial application of the latter. This article demonstrates the successful formulation of Ni-20Cr and Ni-50Cr coatings on two boiler steels, namely, SAE 213-T22 and SA 516 steel by cold-spray process. The microstructure, coating thickness, phase formation, and microhardness properties of the coatings were evaluated. The coatings were subjected to cyclic heating and cooling cycles at an elevated temperature of 1173.15 K (900 °C) to ascertain their high-temperature oxidation behavior. Moreover, these cyclic exposures can give useful information regarding the adhesion of the coatings with the substrate steels. Of all the coatings, the Ni-50Cr coating on SA 516 steel had a maximum average hardness value of 469 Hv. As observed from the surface field emission–scanning electron microscopy (FE-SEM) analysis, the coatings were found to have nearly dense microstructure with the sprayed particles in interlocked positions. It was concluded that the cold-spray process is suitable for spraying the preceding powders onto the given boiler steels to produce nearly dense and low oxide coatings. The coatings, in general, were found to follow the parabolic rate of oxidation and were successful in maintaining their surface contact with their respective substrate steels.     

Steam oxidation of 80Ni-20Cr high-velocity oxyfuel coatings on 9Cr-1Mo steel: Diffusion-induced phase transformations in the substrate adjacent to the coating

The steam oxidation resistance of 80Ni-20Cr coatings on modified 9Cr-1Mo steel has been evaluated in the temperature range of 600 °C to 750 °C. High-velocity oxyfuel (HVOF) spray was used for the coating process. The steam-oxidized specimens exhibited the diffusion of iron from the substrate to the coating and diffusion of nickel from the coating to the substrate. Nickel diffusion to the substrate adjacent to the coating induced the microstructural changes. Micro X-ray diffraction (XRD) studies and energy-dispersive spectroscopy (EDS) point analysis on these transformed zones revealed that the newly formed phases are the austenite in the high-Ni-concentration region and the martensite in the low-Ni-concentration region. Microhardness studies showed higher hardness values in the martensite zones.     

High-Temperature Erosion-Corrosion Performance of High-Velocity Oxy-Fuel Sprayed Ni-20 Cr Coating in Actual Boiler Environment

The high-velocity oxy-fuel (HVOF) spray technique was used to deposit Ni-20Cr coating on a commonly used boiler steel ASTM A213 347H. The specimens with and without coating were exposed to the super heater zone of a thermal power plant boiler at a temperature of 973 K (700 °C) under cyclic conditions to ascertain their erosion-corrosion (E-C) behavior. High-temperature oxidation behavior of the specimens was also evaluated under cyclic thermal loading conditions at an elevated temperature of 1173 K (900 °C). Mass change data and thickness loss were measured to formulate the kinetics of E-C/oxidation for the specimens. The exposed specimens were characterized by X-ray diffraction (XRD) and field emission–scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS). The uncoated steel suffered higher E-C in comparison with its coated counterpart in terms of mass loss as well as thickness loss. It was observed that overall mass loss was reduced by 31 pct and thickness loss by 44 pct after the application of the coating. The possible formation of Cr₂O₃ phase in the coated substrate may be suggested to contribute to better E-C behavior. During air oxidation exposures, the coating was found to be intact with only marginal spallation of its oxide scales, which is an indicator of good adhesion between the coating and substrate steel. The air oxidation mass change data indicated that the coating enhanced the oxidation resistance of the steel by 85 pct.     

热喷涂技术应用及研究进展与挑战

热喷涂作为重要的表面工程技术之一,是通过在材料表面制备材料保护涂层与功能涂层,赋予基体材料没有,但服役环境所必须的表面性能的方法。由于热喷涂可以制备从超过50%孔隙缺陷含量到接近完全致密的任意材料的涂层,基于缺陷控制可满足从可磨耗、耐高温隔热、耐磨损与耐腐蚀等不同服役要求,经过100余年的发展已经形成了包括等离子喷涂、超音速火焰喷涂、电弧喷涂、普通火焰喷涂等一系列方法,已经成为在众多产业领域,包括航天航空、交通运输、石油化工、电力能源、冶金钢铁、纺织与造纸、机械制造等,提高产品寿命与竞争力不可或缺的技术。制备可以提供耐磨损、耐环境腐蚀防护、耐高温隔热防护等保护涂层是热喷涂尤为重要的应用方面,热喷涂作为可显著提升结构零件耐磨损的涂层制备方法应用非常广泛,但在动载如冲蚀、空蚀、疲劳磨损、或高应力磨料磨损条件下,涂层材料的耐磨性能尚不能完全发挥;由于涂层总是存在一定的孔隙,难以以制备态直接用作长效耐腐蚀防护涂层,适当的封孔处理成为其用作耐腐蚀涂层的必要条件;包括以燃气轮机热障涂层为代表的耐高温隔热涂层等在航空与地面重型燃机中的应用,在欧美热喷涂市场中约占比60%,随着我国燃气轮机技术的发展,该市场潜力有望逐步得到发掘。热喷涂耐磨损涂层性能的进一步提升不仅需要开发新型硬质耐磨材料以及宽温域自润滑材料,还需要结合材料开发,发展可使粒子间结合充分的涂层制备方法,其次,基于涂层结构特征与服役性能关系控制磨损服役条件,防止源于粒子间脱落的加速磨损是确保长效磨损保护的基础。如何制备在喷涂态即可满足腐蚀介质不浸渗的致密涂层依然是热喷涂耐腐蚀涂层制备需要攻克的挑战。冷喷涂、等离子喷涂、物理气相沉积、液料热喷涂等新方法近年来发展迅速,与这些方法相配套的材料制备技术的发展将是这些新方法得到广泛应用的基础。新能源、医疗、民生、半导体等对导电、催化、生物活性、绝缘、耐刻蚀等功能涂层的需求也将有力推动热喷涂技术的发展。本文将结合目前热喷涂技术在国内外的应用现状与存在的问题,展望热喷涂技术进一步发展过程中有待解决的主要挑战性技术问题,为本领域技术人员合理认识热喷涂技术的特点,直面挑战,深入开展开发与基础研究,推动技术提供参考。     

舰船海水阀门Ni基合金喷熔层的性能研究

在分析海水阀失效机理的基础上,采用粉末火焰喷熔工艺制备了海水阀Ni45Mo涂层,采用SEM、EDS、XRD方法分析了涂层的组织结构;评价了Ni45Mo涂层的抗腐蚀和耐磨损性能,并与2Cr13、QAl9-2、QAl10-3-1.5材料进行了对比。研究结果表明:Ni45Mo涂层具有优良的抗腐蚀和耐磨性能,最后探讨了Ni45Mo涂层抗腐蚀和耐磨机理。     

喷涂工艺对MCrAlY涂层组织影响

采用超音速、爆炸喷涂工艺制备钢铁炉辊用MCrAlY涂层,借助XRD、SEM和EDS等手段分析了涂层组织。结果显示：超音速制备涂层中Cr元素含量比粉末成分偏高,Al、Y元素降低,可能在喷涂过程中元素烧损,形成的氧化物在喷涂沉积过程被吹飞,未沉积到涂层中。XRD分析结果显示涂层由Co基固容体、Al,Co、Cr7C3、TaC等相组成。涂层致密,孔隙率低,显微硬度大,结合强度高。相对超音速工艺制备涂层,爆炸喷涂工艺制备的涂层中除铝元素外,分布较均匀,涂层致密度较低,涂层相对显微硬度较高,结合强度二者一致。     

Corrosion behavior of plasma-sprayed coatings on a Ni-base superalloy in Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-60 Pct V<Subscript>2</Subscript>O<Subscript>5</Subscript> environment at 900 °C

The shrouded plasma spray process was used to deposit NiCrAlY, Ni-20Cr, Ni₃Al, and Stellite-6 metallic coatings on a Ni-based superalloy (62Ni-23Cr-1.48Al-0.80Mn-0.37Si-0.10Cu-0.025C-bal Fe). NiCrAlY was used as a bond coat in all cases. Hot corrosion studies were conducted on uncoated as well as plasma-spray-coated superalloy specimens after exposure to molten salt at 900 °C under cyclic conditions. The thermogravimetric technique was used to establish the kinetics of corrosion. X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDAX) and electron-probe microanalysis techniques were used to analyze the corrosion products. The uncoated superalloy suffered accelerated corrosion in the form of intense spalling of the scale. The NiCrAlY coated specimen showed a minimum weight gain, whereas the Stellite-6 indicated a maximum weight gain among the coatings studied. All the coatings were found to be successful in developing resistance against hot corrosion, which may be attributed to the formation of oxides, and spinels of nickel, aluminum, chromium, or cobalt.     

Y2O3对NiCr-Cr3C2金属陶瓷涂层热腐蚀性能影响行为研究

本文利用超音速火焰喷涂技术(HVOF),在20G钢表面制备了掺杂1wt.%、3wt.%、5wt.%三种不同含量Y2O3的NiCr-Cr3C2金属陶瓷复合涂层,并探究了其在650℃,Na2SO4/K2SO4熔盐环境中的热腐蚀性能。利用扫描电镜(SEM)、显微硬度计、拉伸试验机等对涂层的微观结构和力学性能进行了表征,利用X射线衍射仪(XRD)、拉曼光谱、X射线能谱仪(EDS)对复合涂层热腐蚀产物形貌、物相进行分析。结果表明掺杂1wt.%Y2O3的NiCr-Cr3C2复合涂层结构致密、孔隙率低、结合强度高,显微硬度达到801HV。热腐蚀过程中掺杂Y2O3的NiCr-Cr3C2复合涂层表面均生成耐蚀性良好且致密的Cr2O3膜。随着Y2O3掺杂量的增加,涂层的耐热腐蚀性能先升高后下降,当Y2O3掺杂量为1wt.%时,复合涂层表现出最佳的耐热腐蚀性能。     

前驱体碳化粉末反应火焰喷涂制备TiC增强金属复合涂层

采用前驱体碳化复合技术制备了Ti-Fe-C和Ti-Ni-C两种体系的反应热喷涂复合粉末,通过氧乙炔火焰喷涂原位合成并沉积了TiC增强Fe基和Ni基复合涂层.利用XRD、SEM和EDS研究了复合粉末、涂层的相组成和组织结构,考察了TiC/Fe、TiC/Ni复合涂层的硬度和耐磨性.结果表明: 复合粉末在喷涂过程中反应充分,可分别生成以Fe和Ni为粘结相的TiC增强涂层;两种涂层都是由TiC颗粒均匀分布的复合强化片层和TiC聚集片层叠加而成,TiC/Fe复合涂层的片层较薄,而TiC/Ni涂层中TiC的聚集片层较少;TiC/Fe涂层的硬度高于TiC/Ni涂层,两者的耐磨性能分别约为Ni60涂层的11倍和6倍.     

超音速火焰喷涂工艺对WC-CoCr涂层的力学性能影响研究

采用超音速火焰喷涂（HVOF）在调质45钢表面制备WC-CoCr涂层,调节不同喷涂工艺制备3种涂层.运用扫描电镜（SEM）、能谱分析（EDS）手段及LeiCa DMIMR图像分析系统对所制备涂层的组织形貌和成份进行表征与分析;并利用显微硬度仪对涂层的力学性能进行表征.结果表明：WC-CoCr涂层的孔隙率随着喷涂距离的增加而减小,进一步增加时涂层的孔隙率反而增大,涂层的显微硬度也随着喷涂距离的增加而减小,喷涂距离为370时其显微硬度达到最优,显微硬度值为1477.61HV0.3.通过以上工艺对比分析可知喷涂距离对涂层的性能影响较大.     

微纳米 涂层在 介质中的抗泥沙冲蚀性能研究

采用超音速火焰喷涂 (HVOF) 工艺制备了微纳米、 纳米和普通结构 WC-10Co4Cr 金属陶瓷涂层, 测量了涂层的显微硬度、 孔隙率和开裂韧性, 分析了三种 WC-10Co4Cr 涂层在 3.5wt% NaCl 溶液中的腐蚀电位和腐蚀电流密度, 研究了喷涂层在 NaCl 介质中的抗泥沙冲蚀性能, 并探讨了涂层在 NaCl 介质中的泥沙冲蚀机理。 结果表明： 微纳米 WC-10Co4Cr 涂层具有最优异的电化学性能; 相比于纳米、 微米涂层, 微纳米涂层的抗泥沙冲蚀磨损性能分别提高了 38% 和 78%。 微纳米 WC-10Co4Cr 涂层致密的组织结构、 高显微硬度 (1126HV0.3) 和高开裂韧性 (4.66MPa·m1/2) 有效减弱了泥沙冲蚀过程中的机械冲刷作用和电化学腐蚀作用。     

热喷涂WC-MoB-Co金属陶瓷涂层的耐腐蚀性能研究

本文采用团聚烧结法制备了WC-MoB-Co金属陶瓷喷涂粉末,使用超音速火焰喷涂技术在316L不锈钢基材上制备了WC-MoB-Co涂层;采用SEM、XRD表征了WC-MoB-Co粉末和腐蚀前后涂层的微观形貌及物相组成;测试了WC-MoB-Co涂层耐熔融锌铝腐蚀性能。研究结果表明,制备的WC-MoB-Co金属陶瓷复合粉末粒度集中、流动性好、松装密度高;WC-MoB-Co涂层结合强度高、孔隙率低;WC-MoB-Co涂层具有良好的耐腐蚀性能,随着腐蚀时间的延长,涂层中的WC颗粒逐渐参与反应。     

电弧喷涂Zn-Al-Mg-La-Ce涂层的耐腐蚀性能

采用电弧喷涂法制备Zn-Al-Mg-La-Ce涂层,通过盐雾试验对涂层进行腐蚀,利用能谱分析、X射线衍射分析、扫描电镜观察、极化曲线以及电化学阻抗谱等手段对腐蚀前后的Zn-Al-Mg-La-Ce涂层进行了研究.结果表明:实验制备的Zn-Al-Mg-La-Ce涂层具有较好的自封闭效果,组织致密,在腐蚀过程中表面的微观孔隙能够被自身的腐蚀产物有效堵塞,涂层表面形成的致密腐蚀产物层能够阻止腐蚀的进一步发生.因此,Zn-Al-Mg-La-Ce涂层具有优异的耐蚀性能.     

等离子喷涂制备铁基非晶合金涂层的结构及其耐腐蚀性能的研究

选用铁基非晶合金粉末(含有Cr,Mo,Ni,P,B,Si)采用等离子喷涂方法在Q235低碳钢和不锈钢基体上制备合金涂层,通过金相显微镜、X射线衍射和扫描电子显微镜研究分析了涂层的相组成和显微结构。研究结果表明:该涂层与基体结合紧密,涂层均匀致密度高,涂层主要由非晶组成;涂层由变形成条带状的粒子相互搭接而成,其中含有少量未熔粒子和氧化物。所制备的铁基非晶涂层气孔率约2.5%,硬度为750～850 HV0.1。通过在H_2SO_4、HCl和NaOH溶液中进行浸泡腐蚀和三电极电化学分析,表明该涂层具有优异的耐腐蚀能力。     

热喷涂制备高熵合金涂层的研究现状与展望

首先介绍了高熵合金的理论基础。然后从不同的热喷涂工艺出发,综述了等离子喷涂、超音速火焰喷涂、高速电弧喷涂、冷喷涂四种技术在制备高熵合金涂层上的研究发展现状,重点从原料选用、制备工艺优化、性能研究、后处理工艺等方面对以上四种热喷涂技术制备高熵合金涂层的研究进行系统地归纳与总结。最后提出现有制备高熵合金涂层的热喷涂技术较少、热喷涂材料受限、高熵合金设计盲目这三个问题,针对性地提出了在优化已有技术的基础上开发新技术;开发高熵陶瓷、高熵非晶合金、高熵复合材料等新型热喷涂材料;沿用材料基因组理念建立高熵合金数据库这三点热喷涂制备高熵合金涂层在未来的发展趋势。      

Ceramic coatings for a corrosion-resistant nuclear waste container evaluated in simulated ground water at 90 °C

Ceramic materials provide an innovative opportunity for corrosion-resistant coatings for nuclear waste containers. Their suitability can be derived from the fully oxidized state for selected metal oxides. Ceramic coatings applied to plain carbon steel substrates by several thermal spray techniques have been exposed to 90 °C simulated ground water (at 10 times typical concentration) for nearly 6 years. Thermal spray processes examined in this work included plasma spray, high-velocity oxy fuel (HVOF), and detonation gun. Some thermal spray coatings have demonstrated superior corrosion protection for the plain carbon steel substrate. In particular, the HVOF and detonation gun thermal spray processes produced coatings with low connected porosity, which limited the growth rate of corrosion products. It was also demonstrated that these coatings resisted spallation of the coating even when an intentional flaw (which allowed for corrosion of the carbon steel substrate underneath the ceramic coating) was placed in the coating. An approach for a theoretical basis for prediction of the corrosion protection provided by ceramic coatings is also presented. The theoretical development includes the effect of the morphology and amount of the porosity within the thermal spray coating and provides a prediction of the exposure time needed to produce a crack in the ceramic coating. This article is based on a presentation made in the symposium “Effect of Processing on Materials Properties for Nuclear Waste Disposition,” November 10–11, 2003, at the TMS Fall meeting in Chicago, Illinois, under the joint auspices of the TMS Corrosion and Environmental Effects and Nuclear Materials Committees.     

Ni-20Al 丝材制备及涂层微结构特征研究

开发了三种不同结构的 Ni-20Al 丝材, 对其火焰喷涂工艺性和涂层微结构特征等进行分析, 并与商用 Metco 405NS 丝材及所制备的涂层进行了对比。 结果表明, 丝材结构影响了火焰加热时热量由丝材表面向芯部的 传导, 导致丝材熔化状态产生显著差异, 进而决定了喷涂焰流的稳定性以及相关涂层组织的均匀性。 其中, 采用 轧制拉拔包丝技术制备的 Ni-20Al 丝材, 呈现出优异的喷涂工艺稳定性, 所制备的涂层组织均匀, 平均显微硬度 和结合强度分别可达 348.3 HV0.05、 62 MPa, 与 405NS 丝材制备涂层性能基本一致, 具备了较好的应用潜力。