Preparation of Aluminum Coatings by Atmospheric Plasma Spraying and Dry-Ice Blasting and Their Corrosion Behavior

Aluminum coating, as an example of spray coating material with low hardness, was deposited by atmospheric plasma spraying while dry-ice blasting was applied during the deposition process. The deposited coatings were characterized in terms of microstructure, porosity, phase composition, and the valence states. The results show that the APS aluminum coatings with dry-ice blasting present a porosity of 0.35 ± 0.02%, which is comparable to the bulk material formed by the mechanical compaction. In addition, no evident oxide has been detected, except for the very thin and impervious oxide layer at the outermost layer. Compared to plasma-sprayed Al coatings without dry-ice blasting, the adhesion increased by 52% for Al substrate using dry-ice blasting, while 25% for steel substrate. Corrosion behavior of coated samples was evaluated in 3.5 wt.% NaCl aqueous using electrochemistry measurements. The electrochemical results indicated that APS Al coating with dry-ice blasting was more resistant to pitting corrosion than the conventional plasma-sprayed Al coating.     

Effect of Dry-Ice Blasting on Structure and Magnetic Properties of Plasma-Sprayed Fe-40Al Coating from Nanostructured Powders

Amorphous and nanocrystalline materials have attracted much interest in the field of new materials design because of their excellent mechanical and physical properties as well as their magnetic properties. In this work, Fe-40Al coatings were prepared from a nanostructured feedstock by atmospheric plasma spray combined with dry-ice blasting. The scanning electron microscopy, x-ray diffraction, tensile test, and magnetic measurements were used to investigate microstructure, phase structure, adhesion, and magnetic properties of the deposited coatings. The results showed that after using dry-ice blasting, the oxidation and porosity decreased and the atmospheric plasma-sprayed Fe-40Al coatings exhibited a soft ferromagnetic character with lower coercivity and higher saturation magnetization due to their lower degree of order. The plasma-sprayed Fe-40Al coating from the nanostructured feedstock has a very high adhesive strength.     

干冰微粒喷射工艺对等离子喷涂金属涂层结构和性能的影响

干冰微粒喷射法被应用到大气等离子喷涂中以改善涂层的性能。文中采用等离子喷涂和干冰微粒喷射工艺在不锈钢基体表面制备了钢涂层,并研究了涂层的微观结构、孔隙率、温度、氧化、表面粗糙度和结合强度等性能。结果表明,由于干冰微粒喷射具有较高的冷却效率,加之干冰微粒撞击所产生的机械作用,等离子喷涂制备的钢涂层呈现出更致密的结构特征。相比于空气冷却制备的涂层,干冰微粒冷却制备的涂层含有更少的氧化物。另外,干冰微粒喷射工艺对基体的预处理使得涂层的结合强度提高了将近14%,这是由于干冰微粒喷射工艺对基体上吸附的有机物质具有清洁作用,主要基于干冰颗粒的热、机械和膨胀的综合效应。     

大气等离子喷涂球磨Fe-Al合金制备FeAl涂层及其结构表征

FeAl金属间化合物具有良好的抗高温氧化和硫化、抗高温冲蚀性能与较高的高温强度,且密度小、成本低。将FeAl用作SOFC支撑体材料,不仅可提高SOFC的高温强度,而且可显著降低其制作成本。本研究采用机械合金化工艺制备了Fe–35Al粉末,通过大气等离子喷涂(APS)制备了FeAl涂层。利用XRD、SEM表征了球磨粉末及热处理前后涂层的微观结构。研究结果表明,通过大气等离子喷涂球磨粉末,可以制备出FeAl金属间化合物涂层,涂层经800℃热处理30h后,可提高FeAl相的有序度。     

FeAl and Mo–Si–B intermetallic coatings prepared by thermal spraying

FeAl and Mo–Si–B intermetallic coatings for elevated temperature environmental resistance were prepared using high-velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques. For both coating types, the effect of coating parameters (spray particle velocity and temperature) on the microstructure and physical properties of the coatings was assessed. Fe–24Al (wt%) coatings were prepared using HVOF thermal spraying at spray particle velocities varying from 540 to 700 m/s. Mo–13.4Si–2.6B coatings were prepared using APS at particle velocities of 180 and 350 m/s. Residual stresses in the HVOF FeAl coatings were compressive, while stresses in the APS Mo–Si–B coatings were tensile. In both cases, residual stresses became more compressive with increasing spray particle velocity due to increased peening imparted by the spray particles. The hardness and elastic moduli of FeAl coatings also increased with increasing particle velocity. For Mo–Si–B coatings, plasma spraying at 180 m/s resulted in significant oxidation of the spray particles and conversion of the T1 phase into amorphous silica and -Mo. The T1 phase was retained after spraying at 350 m/s.     

Formation of Iron-aluminide Coating through Annealing of Shrouded Plasma-sprayed Iron/Aluminum Composite

The formation of iron aluminide coating was attempted through annealing of plasma-sprayed iron/aluminum composite deposit.Shrouded plasma spraying with nitrogen as protective gas was employed to prepare iron/aluminum composite coating using mechanically blended iron and aluminum powders with Fe/Al atomic ratio of 65:35.Annealing of the as-sprayed coating was carried out in argon atmosphere at 450,500,550,and 600 o C for different durations.The microstructure of the coatings was characterized by scanning electron microscopy and X-ray diffraction.The effect of annealing on the microstructure and phase evolution in the coatings was examined.The results show that iron/aluminum composite coating with low oxide inclusions and porosity is deposited by shrouded plasma spraying.It is found that Fe2Al5 intermetallics forms as an intermediate phase in the composite coating during annealing.As the annealing duration and temperature increase,iron aluminide intermetallic phases in the coatings increase and the microstructure becomes more homogeneous.After annealing at 600 o C for 336 h,FeAl and Fe3Al intermetallic phases will present in the coating as the main phases.     

等离子喷涂FeCoCrNiMo高熵合金涂层高温氧化行为的研究

目的 基于海工装备与船舶动力装置对高温环境抗氧化涂层的需求,研究Fe CoCrNiMo高熵合金（High Entropy Alloy,HEA）涂层制备工艺、微观组织结构与抗高温氧化行为之间的关系,探索其在船舶主机、海洋钻井平台温管等高温部件应用的可行性。方法 使用大气等离子喷涂（Atmospheric Plasma Spraying,APS）工艺制备Fe CoCrNiMo涂层,设计正交试验来选取不同孔隙率的涂层试样。通过XRD、SEM和EDS分析涂层的物相组成、微观结构和元素组成。对涂层进行氧化试验,分析其氧化行为。结果 通过正交试验优化Fe CoCrNiMo涂层制备工艺后,涂层孔隙率为2.85%～7.52%。对具有代表性的7.52%孔隙率涂层（记为H1）和2.85%孔隙率涂层（记为H2）进行分析,发现涂层物相结构为简单FCC结构,微观组织为典型的层状结构,氧化物和HEA相在涂层内部分布明显。FeCoCrNiMo涂层的氧化行为遵循抛物线定理,在氧化过程中,化学性质活泼的Cr最易析出并生成氧化物。具有较低孔隙率的H2涂层更快生成致密氧化层,氧化质量增速较低,经15 h氧化后,H1和H2涂...     

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.     

粉末中C抑制FeAl熔滴氧化机制及其对等离子喷涂层组织与性能的影响*

大气等离子喷涂（APS）金属时,熔滴不可避免地发生氧化是难以获得粒子间结合充分的致密涂层的主要原因。以FeAl金属间化合物为例,提出一种在粉末中添加亚微米金刚石颗粒引入碳源,以期利用碳在高温下优先氧化的特性抑制等离子喷涂飞行粒子中Fe、Al元素的氧化,获得无氧化物的高温熔滴从而制备低氧含量（质量分数）、粒子间充分结合的FeAl金属间化合物涂层的新方法。采用APS制备Fe Al涂层,研究金刚石的添加对涂层氧含量、碳含量、涂层内粒子间结合质量与硬度的影响规律,探讨FeAl熔滴飞行中的氧化行为。采用商用热喷涂粒子诊断系统测量APS喷涂中的粒子温度,通过SEM与XRD表征了涂层的组织结构,并表征涂层的结合强度与硬度。结果表明,在等离子射流的加热和Fe、Al元素放热反应的联合作用下,飞行中FeAl熔滴的表面温度可达2 000℃以上,满足C原位脱氧的热力学条件。与不含碳的传统Fe Al涂层中的氧含量随喷涂距离的增加而显著增加的规律完全不同,用Fe/Al/2.5C粉末喷涂时涂层中的氧含量随距离的增加而减小,表明飞行中熔滴的氧化得到抑制,实现了C原位脱氧抑制金属元素氧化的自清洁氧化物的效应。FeAl/...     

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 Dispersed TiC Content on the Microstructure and Thermal Expansion Behavior of Shrouded-Plasma-Sprayed FeAl/TiC Composite Coatings

FeAl intermetallic matrix composites reinforced by ceramic particles such as titanium carbide have attracted much attention in recent years. In this study, shrouded plasma spraying with nitrogen as a protective gas was employed to deposit FeAl/TiC composite coatings. Fe-35Al powder and Fe-35Al/TiC composite powders containing 35 and 45?vol.% TiC prepared by mechanical alloying were used as feedstock powders. The microstructures of the ball-milled powders and the as-sprayed coatings were characterized by scanning electron microscopy and x-ray diffraction. The mean coefficients of thermal expansion (CTEs) of FeAl and FeAl/TiC were measured. The results showed that dense FeAl and FeAl/TiC coatings with low oxide inclusions were deposited by shrouded plasma spraying. The mean CTEs measured in the present study were reasonably consistent with those calculated based on the formula. As a result, the mean CTE of FeAl-based composite coating can be properly controlled by adjusting TiC content in the composite coating to match with those of different substrate materials.     

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。     

大气等离子喷涂制备Fe基非晶涂层及微观结构表征

选用Fe-10W-4Cr-3Ni-2Mo-4B-4Si-1C(质量比)合金粉末作为喷涂原料,采用大气等离子喷涂工艺在1Cr18Ni9Ti不锈钢基底上制备了Fe基涂层。利用扫描电镜、透射电镜和X射线衍射仪表征了粉末和涂层的相组成和微观形貌;用Olycia m3分析软件对涂层的孔隙率进行测定;用热分析系统对喷涂粉末和涂层从室温到1 173K范围的DSC曲线进行记录;同时,测定了涂层的显微硬度和结合强度。结果表明:大气等离子喷涂制备的Fe基涂层与基底的结合良好,涂层较为致密并且存在灰色氧化带组织,表现出典型的层状组织结构;涂层不但具有低的表面粗糙度和孔隙率,而且具有高的显微硬度和结合强度;所制备涂层中的非晶含量约为89.2%(质量分数),涂层中形成的晶相组织为纳米晶结构。     

Technical note: Plasma-sprayed ceramic thermal barrier coatings for smooth intermetallic alloys

A durable ceramic thermal barrier coating is applied directly to a smooth, highly oxidation resistant intermetallic alloy in two layers. The first layer of ceramic is applied by low pressure plasma spraying and the second layer is applied by conventional atmospheric pressure plasma spraying. This approach would allow the use of plasma sprayed ceramic coatings in applications where a metallic bond coat is not desirable.     

Formation and structure of composite coating of HDA and micro-plasma oxidation on A3 steel

Composite coatings were obtained on A3 steel by hot dipping aluminum(HDA) at 720 ℃ for 6 min and micro-plasma oxidation(MPO) in alkali electrolyte. The surface morphology, element distribution and interface structure of composite coatings were studied by means of XRD, SEM and EDS. The results show that the composite coatings obtained through HDA/MPO on A3 steel consist of four layers. From the surface to the substrate, the layer is loose Al2O3 ceramic, compact Al2O3 ceramic, Al and FeAl intermetallic compound layer in turn. The adhesions among all the layers are strengthened because the ceramic layer formed at the Al surface originally, FeAl intermetallic compound layer and substrate are combined in metallurgical form through mutual diffusion during HDA process.Initial experiment results disclose that the anti-corrosion performance and wear resistance of composite coating are obviously improved through HDA/MPO treatment.     

TiAlNb intermetallic compound coating prepared by high velocity oxy-fuel spraying

Ti_28.35Al_63.4Nb_8.25 (at.%) intermetallic compound coatings were sprayed onto 316 L stainless steel substrates by HVOF processes using various parameters. By varying the grit blasting pressure between 0.11 and 0.55 MPa, the effects of substrate roughness on the adhesion of TiAlNb thermal sprayed coatings were investigated. The microstructure, porosity and microhardness of the coatings were characterized by SEM, XRD, Image Analysis and Vickers hardness analysis. The tensile adhesion test (TAT) specified by ASTM C 633-79 was used to measure the tensile bonding strength of the coating. The results show that the coatings with substrate roughness of 8.33 μm displayed the best combined strength. TiAlNb coatings had a lamellar microstructure with different spraying parameters. The porosity, bonding strength, microhardness of coatings were assessed in relation to the spraying processes. The thickness of bond coat on the bond strength of coatings was also discussed.     

空气等离子喷涂板式SOFC连接体保护涂层的性能

在中温平板型固体氧化物燃料电池（ITSOFC）设计中,可以采用金属作为连接材料.Fe-16Cr合金是较为理想的金属连接材料,它存在的主要问题是连接体阴极侧表面的高温氧化和腐蚀,会导致电池性能的迅速降低.本研究采用空气等离子喷涂的方法喷涂了La0.8Sr0.2MnO3-σ（LSM）钙钛矿型保护涂层在金属连接板的表面,并讨论了主要过程参数及其作用效果.研究发现,喷涂后热处理是降低涂层孔隙率的有效方法,经喷涂-热处理后,涂层的孔隙率可降至1%以下.等离子喷涂LSM保护涂层后,Fe-16Cr合金的耐高温氧化性能明显提高,氧化速率降低了76%.     

抗菌元素对纳米TiO2涂层结构和性能的影响

目的为克服纳米氧化钛在黑暗条件下不具有抗菌效果这一缺点,使用抗菌金属元素Cu、Zn和Ag掺杂以提高其抗菌性能。方法利用大气等离子喷涂技术在钛合金表面制备Cu、Zn和Ag掺杂的TiO_2复合涂层。利用X射线衍射仪(XRD)、拉曼光谱仪(Raman)和场发射扫描电子显微镜(FE-SEM),对涂层的物相组成和表面形貌进行表征。利用接触角测量仪、三位轮廓仪、电化学工作站和电感耦合等离子体原子发射光谱,对涂层的亲水性、表面粗糙度、耐腐蚀性能和抗菌离子释放情况进行表征。利用细菌和涂层共培养实验来评价涂层的抗菌效果。结果抗菌金属元素掺杂没有改变TiO_2涂层的主要相结构,涂层主要由金红石相组成。涂层具有微米级的表面粗糙度,表面由粒径小于50 nm的粒子组成。掺杂使TiO_2涂层的亲水性略有降低。Cu掺杂的涂层的耐腐蚀性能大幅提升,抗菌金属离子在各涂层中都可以释放,且Cu掺杂涂层中的释放量最高。与细菌共培养24 h之后,TiO_2涂层没有显示出抗菌效果,掺杂后涂层表现出优异的抗菌性能。在有水存在的条件下进行紫外光预辐照,可以显著提高TiO_2涂层的抗菌性能,且掺杂后的涂层在经过预辐照后抗菌性能的提升大于TiO_2涂层。结论抗菌金属元素掺杂不改变涂层结构,同时大幅提高了等离子喷涂TiO_2涂层在黑暗条件下的抗菌性能,紫外预辐照处理能够使没有抗菌性能的TiO_2涂层具备抗菌效果,也能进一步提升掺杂涂层的抗菌效果。     

Comparison of ZrB<Subscript>2</Subscript>-MoSi<Subscript>2</Subscript> Composite Coatings Fabricated by Atmospheric and Vacuum Plasma Spray Processes

In this work, ZrB₂-20 vol.% MoSi₂ (denoted as ZM) composite coatings were fabricated by atmospheric plasma spray (APS) and vacuum plasma spray (VPS) techniques, respectively. Phase composition and microstructure of the composite coatings were characterized. Their oxidation behaviors and microstructure changes at 1500 °C were comparatively investigated. The results showed that VPS-ZM coating was composed of hexagonal ZrB₂, tetragonal and hexagonal MoSi₂, while certain amount of ZrO₂ existed in APS-ZM coating. The oxide content, surface roughness and porosity of VPS-ZM coating were apparently lower than those of APS-ZM coating. The mass gain of APS-ZM coating was maximum at the beginning (1500 °C, 0 h) and then decreased with the oxidation time extending, while the mass of VPS-ZM coating gradually increased with increasing the oxidation time. The possible reasons for the different oxidation behaviors of the two kinds of coatings were analyzed.     

Hydroxyapatite coatings for biomedical applications deposited by different thermal spray techniques

Thermally sprayed hydroxyapatite (HAp) coatings are widely used for various biomedical applications due to the fact that HAp is a bioactive, osteoconductive material capable of forming a direct and firm biological fixation with surrounding bone tissue.Bioceramic coatings based on nanoscale HAp suspension and microscale HAp powder were thermally sprayed on Ti plates by high-velocity suspension flame spraying (HVSFS) technique and atmospheric plasma spraying (APS) as well as high velocity oxy fuel spraying (HVOF) technique. HVSFS is a novel thermal spray process developed at IMTCCC, for direct processing of submicron and nano-sized particles dispersed in a liquid feedstock.The deposited coatings were mechanically characterized including surface roughness, micro hardness and coating porosity. The bond strength of the layer composites were analyzed by the pull-off method and compared for the different spray techniques. Phase content and crystallinity of the coatings were evaluated using X-ray diffraction (XRD). The coating composite specimen and initial feedstock were further analysed by scanning electron microscope (SEM) and rheology analysis.