Optimization of Arc-Sprayed Ni-Cr-Ti Coatings for High Temperature Corrosion Applications

High Cr content Ni-Cr-Ti arc-spray coatings have proven successful in resisting the high temperature sulfidizing conditions found in black liquor recovery boilers in the pulp and paper industry. The corrosion resistance of the coatings is dependent upon the coating composition, to form chromium sulfides and oxides to seal the coating, and on the coating microstructure. Selection of the arc-spray parameters influences the size, temperature and velocity of the molten droplets generated during spraying, which in turn dictates the coating composition and formation of the critical coating microstructural features—splat size, porosity and oxide content. Hence it is critical to optimize the arc-spray parameters in order to maximize the corrosion resistance of the coating. In this work the effect of key spray parameters (current, voltage, spray distance and gas atomizing pressure) on the coating splat thickness, porosity content, oxide content, microhardness, thickness, and surface profile were investigated using a full factorial design of experiment. Based on these results a set of oxidized, porous and optimized coatings were prepared and characterized in detail for follow-up corrosion testing.     

Influence of Feedstock Materials and Spray Parameters on Thermal Conductivity of Wire-Arc-Sprayed Coatings

To manufacture a protective coating with high thermal conductivity on drying cylinders in paper production machines, a FeCrB-cored wire was developed, and the spraying parameters for wire-arc spraying were optimized in this study. The conventional engineering materials FeCrAl and FeCrMo coatings were produced as the reference coatings under the same experimental condition. It has been shown that the oxide content in coating influences the thermal conductivity of coating significantly. The FeCrB coating exhibits a relative higher thermal conductivity due to the lower oxide content in comparison with conventional FeCrAl and FeCrMo coatings. Moreover, the oxidation of in-flight particles can be reduced by decreasing the standoff distance contributing to the increase in the thermal conductivity of coating. Total energy consumption of a papermaking machine can be significantly reduced if the coatings applied to dryer section exhibit high thermal conductivity. Therefore, the FeCrB coating developed in this study is a highly promising coating system for drying cylinders regarding the improved thermal conductivity and low operation costs in paper production industry.     

喷涂距离对超音速火焰喷涂 CoCrAlYTa 涂层组织性能的影响

采用超音速火焰喷涂技术制备CoCrAlYTa涂层,研究了喷涂距离对涂层相组成、孔隙率以及硬度、弯曲强度、高温抗氧化性能的影响。结果表明:喷涂距离在200～300 mm范围内时,随着喷涂距离的减小,涂层的致密度增加,孔隙率下降,显微硬度和弯曲结合强度增加,但相组成基本不变,主要由CoAl,AlCo2Ta和CoTa3相组成;涂层致密度越高,在高温氧化过程中,表面越易尽早形成连续氧化膜并促进涂层中Al元素的选择氧化,因此随着喷涂距离的减小,涂层的高温抗氧化性能逐渐增强。     

Influence of Detonation Gun Spraying Conditions on the Quality of Fe-Al Intermetallic Protective Coatings in the Presence of NiAl and NiCr Interlayers

The paper presents results of detailed research of the application of detonation gun (D-gun) spraying process for deposition of Fe-Al intermetallic coatings in the presence of NiAl and NiCr interlayers. A number of D-gun experiments have been carried out with significant changes in spraying parameters which define the process energy levels (changes in volumes of the working and fuel gases, and the distance and frequency of spraying). These changes directly influenced the quality of the coatings. The initial results underlay the choice of the process parameters with the view to obtain the most advantageous of geometric and physical-mechanical properties of the coating material, interlayer and substrate. The metallurgical quality of the coatings was considered by taking into account grain morphology, the inhomogeneity of chemical content and phase structure, the cohesive porosity in the coating volume, and adhesive porosity in the substrate/interlayer/coating boundaries. The surface roughness level was also considered. It was found that the D-gun sprayed coatings are in all cases built with flat lamellar splats. The splats develop from powder particles which are D-gun transformed in their plasticity and geometry. A significant result of the optimization of D-gun spraying parameters is the lack of signs of melting of the material (even in microareas) while the geometry of the subsequently deposited grains is considerably changed and the adhesivity and cohesion of the layers proves to be high. This is considered as an undeniable proof of high plasticity of the D-gun formed Fe-Al intermetallic coating.     

Effect of some parameters on microstructure and hardness of alumina coatings prepared by the air plasma spraying process

The spraying distance, substrate temperature, coating thickness and surface roughness of substrate during deposition play an important role on the plasma spray coating process and effect the final properties of the coatings. Al₂O₃ coatings on AISI 304 L stainless steel substrate were prepared to investigate the effects on the coating of these parameters. The results indicated that the parameters such as the spraying distance, substrate temperature, coating thickness and substrate roughness were fairly effected the hardness, porosity and surface roughness of Al₂O₃ coatings. The lowest surface roughness and the lowest porosity and the highest hardness values of Al₂O₃ coating were obtained for the spraying distance of 12 cm and the surface roughness of 3.28 μm and the substrate temperature of 500 °C. It also found that the increases of coating thickness were lowered the hardness and enhanced the porosity and the coating roughness.     

等离子喷涂ZrO2热障涂层工艺参数优化设计

为了深入研究等离子喷涂ZrO2粒子的飞行特征与涂层性能之间的关系，采用三水平四因素正交试验法对主气、辅气、电流及喷涂距离等4个主要参数进行了优化设计，并采用DPV2000热喷涂在线监测仪测定了ZrO2粒子的飞行特征参数，通过IA32定量金相分析软件对涂层的孔隙率进行了测试。结果表明，影响ZrO2粒子温度的主要因素为主气和辅气，影响ZrO2粒子飞行速度的主要因素为喷涂距离和辅气。     

Oxidation control in atmospheric plasma spraying coating

Thermal spray coatings are formed by successive impingements and interbonding materials among the splats, solidified individual molten particles. Depending on the processing conditions employed during the spray process, deposits are produced with an assortment of microstructures and properties. This study highlights how the coating oxidation differences are influenced by the mechanisms involved during the spray process. The commercial steel powder referenced Amdry XPT 512 is chosen for a systematic study of comparison across different spraying techniques. Steel particles were sprayed with a F4 plasma torch and with a shrouded plasma spray process used in order to protect particles against atmospheric oxidation. The plasma jet was successively shielding by an inert gas shroud and by an oxidizing gas shroud. In-flight oxidation and post impact oxidation present in coatings are discussed in detail and the effects of these mechanisms on coating properties are addressed. The comparison was made on in-flight particle characteristics and on coating properties in terms of oxide content and porosity level. Using shrouded gas, in-flight characteristics are quite similarly independent of the nature of the shrouded gas. This way, the comparison of oxide contents present in the coatings corresponds to in-flight oxidation and is completely dependent on the nature of the shrouded gas. Comparing these results to those obtained by APS, a decrease in both velocity and temperature of in-flight particles was observed leading also to a significant decrease in oxide contents and to a slight increase in porosity level compared to coatings sprayed with air shrouding.     

Optimization of Atmospheric Plasma Spray Process Parameters using a Design of Experiment for Alloy 625 coatings

Alloy 625 is a Ni-based superalloy which is often a good solution to surface engineering problems involving high temperature corrosion, wear, and thermal degradation. Coatings of alloy 625 can be efficiently deposited by thermal spray methods such as Air Plasma Spraying. As in all thermal spray processes, the final properties of the coatings are determined by the spraying parameters. In the present study, a D-optimal experimental design was used to characterize the effects of the APS process parameters on in-flight particle temperature and velocity, and on the oxide content and porosity in the coatings. These results were used to create an empirical model to predict the optimum deposition conditions. A second set of coatings was then deposited to test the model predictions. The optimum spraying conditions produced a coating with less than 4% oxide and less than 2.5% porosity. The process parameters which exhibited the most important effects directly on the oxide content in the coating were particle size, spray distance, and Ar flow rate. The parameters with the largest effects directly on porosity were spray distance, particle size, and current. The particle size, current, and Ar flow rate have an influence on particle velocity and temperature but spray distance did not have a significant effect on either of those characteristics. Thus, knowledge of the in-flight particle characteristics alone was not sufficient to control the final microstructure. The oxidation index and the melting index incorporate all the parameters that were found to be significant in the statistical analyses and correlate well with the measured oxide content and porosity in the coatings.

铝基非晶纳米晶复合涂层的喷涂工艺

为了研究喷涂参数对涂层性能的影响规律,采用高速电弧喷涂技术制备铝基非晶纳米晶复合涂层,利用正交试验法系统研究喷涂电流、喷涂电压、喷涂距离、喷枪移动速度和雾化空气压力对涂层性能的影响规律。优化后的工艺参数为喷涂电流160 A,喷涂电压36 V,喷涂距离200 mm,喷枪移动速度300 mm/s,雾化空气压力0.7 MPa,喷涂参数对涂层性能影响的主次顺序为：雾化空气压力、喷涂电压、喷枪移动速度、喷涂电流和喷涂距离。采用扫描电子显微镜(SEM)、能谱仪（EDS）、X射线衍射仪（XRD）和透射电镜（TEM）对工艺优化后的涂层进行分析,同时对涂层的显微硬度和孔隙率进行了测试。结果表明,采用优化参数制备的涂层组织结构致密,孔隙率为1.13%,硬度可达392 HV0.1,涂层具有明显的非晶纳米晶相,非晶含量约为24.2%。     

Study on Reactive Atmospheric Plasma-Sprayed In situ Titanium Compound Composite Coating

A titanium composite coating containing in situ synthesized oxides or nitrides was deposited on mild steel by reactive atmospheric plasma spraying. The relationships between the porosity, hardness, the phase composition of the sprayed coatings, and the spraying parameters were investigated. Titanium powders were used as starting powder materials. XRD analysis and microhardness test revealed that titanium oxides and nitrides were synthesized during the spraying process. The longer the spraying distance, the more the Ti nitrides’ content in the coating. It is shown that the Ti nitrides’ content has a significant influence on coating hardness. An in situ titanium composite coating with a hardness value of 1534HV_0.1 and an adhesive strength of 55.4 MPa was made with appropriate spraying parameters.     

等离子喷涂氧化铝基复合涂层研究进展

随着等离子喷涂技术的发展,等离子喷涂氧化铝基复合涂层在防腐蚀、耐磨损和航天航空等领域得到了广泛应用。首先简要介绍了新型等离子喷涂技术(激光等离子喷涂、悬浮液等离子喷涂和超音速等离子等)和主要喷涂工艺参数(喷涂功率、送粉方式和喷涂距离等),然后从改善涂层耐腐蚀性能的角度出发,阐述了第二相、喷涂工艺参数和后处理工艺对涂层气孔率的影响及与涂层耐腐蚀性能的关系。重点分析了硬度、喂料特征和激光熔覆技术对氧化铝基复合涂层耐磨损性能的影响,详述了影响硬度的因素,以及喷涂粉末特征和激光熔覆处理对复合涂层微观结构的影响。在电磁波吸收性能研究方面,论述了吸收剂含量、涂层厚度和多种电磁波吸收剂匹配以及喷涂参数的调整对等离子喷涂氧化铝基复合涂层吸波性能的影响。最后对以等离子喷涂技术制备性能更加优异的氧化铝基复合涂层提出了展望。     

Densification of plasma-sprayed titanium and tantalum coatings

Thermal spraying of corrosion- resistant coatings of titanium and tantalum is difficult; dense coatings are not produced, and oxidation of these metals increases coating porosity. In this study, oxidation during plasma spraying was reduced with a shrouding system. Porosity and oxide content also were minimized by optimizing the spraying parameters. After optimization, the coatings still had open porosity and thus were incapable of protecting the substrate material against corrosion in water solutions containing 3 % NaCl. Therefore, posttreatments for improvement of corrosion resistance were studied. Electron beam fusion produced corrosion resistance equal to or better than that of bulk commercial samples of titanium and tantalum.     

基于熔融因子的纳米结构涂层制备工艺优化EI北大核心CSCD

在热喷涂制备微米/纳米双结构涂层的工艺优化研究中缺乏对颗粒状态与喷涂工艺和涂层结构性能之间关系的综合分析。针对大气等离子喷涂制备双模态微观结构的热障涂层过程开展工艺参数优化研究。首先基于试验测量和数值仿真模拟所获得的颗粒状态以及射流信息,计算可表征飞行粒子受热状态的熔融因子分布,同时开展试验研究获得给定喷涂工况下涂层微观结构和沉积效率。最后以熔融因子为中间参数,研究并建立喷涂工艺-飞行粒子状态-涂层结构特性相关关系。结果表明,数值仿真模拟得到的纳米团聚颗粒状态与试验测量结果基本一致。纳米结构涂层微观结构主要缺陷为未熔纳米团聚粒子及微裂纹。在纳米结构涂层制备过程中,随着喷涂距离增加,飞行粒子的熔融因子先增大后减小,涂层沉积效率先增加后降低,孔隙率和未熔粒子数则先减小后增大。主气流量的增加则会导致熔融因子减小。在喷涂功率相近情况下,采用低电流高电压的组合会使得飞行粒子熔融因子分布取值较大,进而使得涂层沉积效率增加、孔隙率降低。使用熔融因子分析喷涂工艺参数对纳米团聚粉末颗状态和涂层结构特性的影响关系,可用于指导纳米双结构涂层制备过程工艺控制。     

Cold-Sprayed Nanostructured Pure Cobalt Coatings

Cold-sprayed pure cobalt coatings were deposited on carbon-steel substrate. Submicrometer particles for spraying were produced via cryomilling. Deposits were produced using different processing conditions (gas temperature and pressure, nozzle-to-substrate distance) to evaluate the resulting variations in grain size dimension, microhardness, adhesion strength, and porosity. The coating mechanical properties improved greatly with higher temperature and carrying-gas pressure. The coating microstructure was analyzed as a function of spraying condition by transmission electron microscopy (TEM) observations, revealing many different microstructural features for coatings experiencing low or high strain rates during deposition.     

丝电爆喷涂过程工艺参数对涂层性质的影响

采用气体放电式丝电爆装置进行丝电爆喷涂试验,利用扫描电镜分析涂层性质特点,认识喷涂距离和能量密度对涂层性质的影响。结果表明,在不同工艺参数下,可获得四类性质的涂层,其中液相喷涂层和气相沉积涂层与基体结合强度较高;沉积在金属丝上能量密度和喷涂距离直接影响涂层性质。     

Effect of HVOF Processing Parameters on the Properties of NiCoCrAlY Coatings by Design of Experiments

The effect of three principal, independent, high-velocity oxygen fuel (HVOF)-processing parameters on the properties of NiCoCrAlY coatings deposited using commercial powders is reported here. The design of experiments (DoE) technique at a two-level factorial and a central composite rotatable design was used to analyze and optimize the HVOF spraying process. The deposition parameters investigated were (1) fuel flow, (2) oxygen flow, and (3) stand-off distance. The effect of these processing variables was evaluated using selected responses, including porosity and oxide content, residual stresses, and deposition efficiency. Coatings with low porosity as well as with low residual stress were obtained using high fuel-rich conditions at a stand-off distance between 250 and 300 mm. At shorter and longer stand-off distances, respectively, either excessive flattening of splats or un-molten condition occurred, resulting in high levels of porosity and residual stress. The response surface, the empirical relationships among the variables, and the response parameters allowed the selection of optimum deposition parameters and the improvement of coating properties.     

等离子喷涂AlSi-ployester封严涂层工艺优化研究

采用AlSi-ployester粉末和PARXAIR-3710等离子喷涂系统制备封严涂层.为使AlSi-ployester等离子喷涂涂层获得优良的涂层性能,选择涂层结合强度为判据,通过正交试验对AlSi-ployester等离子喷涂工艺进行了优化.利用扫描电镜,Axio lmager.A lm金相图像分析系统等手段对涂层形貌和孔隙率进行分析,同时对涂层的硬度、抗热震性能进行了测试.确定优化后的工艺参数为:电弧电流790A.主气流量62.7 L/min,辅气流量5 L/min,喷涂距离100mm.结果表明,电弧电流、主气流量、辅气流量、喷涂距离对AlSi-ployester涂层结合强度具有不同的影响,在优化的喷涂工艺参数条件下,AlSi-ployester涂层结合强度可达6.9MPa,具有较好的硬度和热震性能,可为今后等离子喷涂系统工艺参数的选定提供参考.     

高速火焰喷涂高质量NiCoCrAlTaReSiY抗氧化涂层

研究了用高速火焰喷涂(HVOF)替代低压等离子喷涂(LPPS)沉积高质量的MCrAlY涂层。试验用粉料为NiCoCrAlTaReSiY,采用以煤油为燃料的K2型HVOF系统沉积涂层,研究喷嘴长度、喷涂工艺参数对粉末沉积工艺过程以及涂层性能的影响;测量涂层的孔隙率及氧含量,观察涂层经真空热处理以及高温空气氧化后的显微结构,测量了Al、O等元素在氧化涂层中的分布。结果表明,所沉积的NiCoCrAlTaReSiY涂层具有优越的抗氧化性。     

Microstructural Studies of Cold Sprayed Copper,Nickel, and Nickel-30% Copper Coatings

Cold spraying enables to produce metallic coatings with low porosity level and low oxygen content. Several material properties such as electrical conductivity and corrosion resistance rely on these properties. Aim of this study was to characterize microstructural properties of cold sprayed copper, nickel, and nickel-30%copper coatings. Microstructures, denseness, and deformation of particles were investigated. SEM analysis and corrosion tests were done to get information of through-porosity. Open porosity has an important role on protectiveness of anodically protective coatings, such coating materials like copper and nickel. In this study, cold-sprayed Cu coating was fully dense. However, cold-sprayed Ni and Ni-30%Cu coatings seemed to be microstructurally dense but some porosity in some areas of the coatings especially in some parts of particle boundaries was noticed after corrosion tests. Furthermore, effect of annealing to microstructure and corrosion test behavior was studied. Cold sprayed Ni coating became denser during heat treatment.     

前驱体溶液等离子喷涂参数对涂层形貌的影响及沉积行为机理研究

目的对不同喷涂工艺参数下涂层的相结构、显微形貌进行研究,确定优化的喷涂工艺参数,讨论分析涂层的沉积行为机理。方法采用前驱体溶液等离子喷涂(SPPS)的方法制备纳米Yb_2O_3稳定的ZrO_2(YbSZ)涂层。在传统等离子喷涂的基础上,增加液料雾化装置,雾化喷嘴将溶液雾化后直接注入到等离子弧中,通过控制喷涂距离及喷涂功率,研究了涂层相结构、结晶度、晶粒尺寸以及显微形貌的变化趋势,并且结合显微形貌讨论了沉积机理。结果涂层呈现团聚大颗粒、纳米级粒子、大小均匀的孔隙三种显微形貌,大颗粒之间呈堆积形态。当喷涂功率为30 kW时,涂层呈现m-ZrO_2,平均晶粒尺寸达669 nm。随着喷涂距离、喷涂功率的增加,样品中检测到单一的t-ZrO_2相,而且纳米尺寸颗粒的数量大大增加,孔径变小。随着喷涂距离由60 mm增加到100 mm,平均晶粒尺寸先由429 nm减小到177 nm,随后又增加到319 nm。结论喷涂参数影响晶粒的结晶度、晶粒尺寸以及涂层的显微形貌,低功率下得到的涂层存在糊状未结晶组织。增大喷涂功率,可以有效增大结晶度和晶粒尺寸;随着喷涂距离的增大,晶粒尺寸先减小后增大。雾化液滴在等离子火焰中一般要经历浓缩、饱和、固化、析晶形核长大、粒子重熔扁平化的历程,喷涂功率越高,经历温区越高,液滴演变就越充分,通过优化工艺参数可以得到不同结构性能的功能涂层。