MICROSTRUCTURE OF NiCoCrAlY COMPONENT IN PLASMA SPRAYED ZrO_2/NiCoCrAlY GRADED COATING

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Microstructure and corrosion resistance of Fe/Mo composite amorphous coatings prepared by air plasma spraying

Fe/Mo composite coatings were prepared by air plasma spraying （APS） using Fe-based and Mo-based amorphous and nanocrys- talline mixed powders. Microstructural studies show that the composite coatings present a layered structure with low porosity due to adding the self-bonded Mo-based alloy. Corrosion behaviors of the composite coatings, the Fe-based coatings and the Mo-based coatings were in- vestigated by electrochemical measurements and salt spray tests. Electrochemical results show that the composite coatings exhibit a lower polarization current density and higher corrosion potentials than the Fe-based coating when tested in 3.5wt% NaC1 solutions, indicating supe- rior corrosion resistance compared with the Fe-based coating. Also with the increase in addition of the Mo-based alloy, a raised corrosion re- sistance, inferred by an increase in corrosion potential and a decrease in polarization current density, can be found. The results of salt spray tests again show that the corrosion resistance is enhanced by adding the Mo-based alloy, which helps to reduce the porosity of the composite coatings and enhance the stability of the passive films.

Microstructure and Properties of Plasma Spraying Boron Carbide Coating

Microstructure of plasma spray boron carbide coating was studied by SEM and TEM. Its physical, mechanical and electrical properties were measured. The results showed that high microhardness, modulus and low porosity of B4C coating were manufactured by plasma spray. It was lamellar packing and dense. The B4C coating examined here contained two principal structures and two impurity phase besides major phase. The relatively small value of Young's modulus, comparing with that of the bulk materials, is explained by porosity . The Fe impurity phase could account for the relatively high electrical conductivity of boron carbide coating by comparing with the general boron carbide materials.

An Investigation on the Microstructure of Multi-phase Composite Coatings Synthesized by Plasma Spraying Self-reaction Composite Powders

Multi-phase self-reaction composite (denoted as MPc) coatings containing ceramic and metal multi-phases were fabricated by plasma spraying Fe2O3-Al composite powders. This technology successfully combines self-propagating high-temperature synthesis with plasma spraying. The morphology of the composite powders was examined by scanning electron microscope (SEM). The phase composition and microstructure of the composite coating are studied.

Preparation and characterization of nanostructured Al_2O_3-13wt.%TiO_2 ceramic coatings by plasma spraying

Nanostructured and conventional Al2O3-13wt.%TiO2 ceramic coatings were prepared by plasma spraying with nanostructured agglomerated and conventional powders, respectively. The microstructure and microhardness of the coatings were investigated using scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and microhardness measurement. Meanwhile, the friction and wear behaviors were analyzed and compared using a ball-on-disk tribometer. The results show that the conventional coating has lamellar stacking characteristic and has some pores. However, the nanostructured coating shows a bimodal microstructure, which is composed of both fully melted regions and partially melted regions. According to the microstructural difference, the partially melted regions can be divided into liquid-phase sintered regions （a three-dimensional net or skeleton-like structure： Al2O3-rich submicron particles embedded in the TiO2-rich matrix） and solid-phase sintered regions （remained nanoparticles）. The microstructural characteristics of the liquid-phase sintered region are formed due to the selective melting of TiO2 nanoparticles during plasma spraying. On the other hand, the TiO2 and Al2O3 nanoparticles of the solid-phase sintered regions are all unmelted during plasma spraying. Due to the existence of nanostructured microstructures, the nanostructured coating has a higher microhardness, a lower friction coefficient, and a better wear resistance than the conventional coating.

Microstructures and erosion resistance of plasma-sprayed WCp/NiCrBSi composite coatings

WCp/NiCrBSi composite coatings have been deposited by plasma spraying with the mixed powders of WC-12Ni and NiCrBSi. The coatings consist mainly of WC, γ-Ni, Ni3B, CrB, Cr2B, M7C3, M23C6 and W2C phases. The W2C content increases with increasing WC mass fraction in the powders. The porosity and microhardness of the coatings are related to the coating WC content. The excessive WC results in decreasing the microhardness due to increasing the porosity. The WCp/ NiCrBSi coating with 35 % WC mass fraction powder has more excellent erosion resistance. With an increase of impact angles from 15° to 90° the erosion rate of the coating increases, the erosion rate at 15° impact angle being approximately two times lower than that at 90° impact angle. Based on the wear morphology of the coatings at different impact angles, the wear mechanisms were discussed.

Microstructure studies of air-plasma-spray-deposited CoNiCrAlY coatings before and after thermal cyclic loading for high-temperature application

In the present study, bond-coats for thermal barrier coatings were deposited via air plasma spraying（APS） techniques onto Inconel 800 and Hastelloy C-276 alloy substrates. Scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, X-ray diffraction（XRD）, and atomic force microscopy（AFM） were used to investigate the phases and microstructure of the as-sprayed, APS-deposited Co Ni Cr Al Y bond-coatings. The aim of this work was to study the suitability of the bond-coat materials for high temperature applications. Confirmation of nanoscale grains of the γ/γ′-phase was obtained by TEM, high-resolution TEM, and AFM. We concluded that these changes result from the plastic deformation of the bond-coat during the deposition, resulting in Co Ni Cr Al Y bond-coatings with excellent thermal cyclic resistance suitable for use in high-temperature applications. Cyclic oxidative stability was observed to also depend on the underlying metallic alloy substrate.

Characterization of functionally graded ZrO_2 thermal barrier coatings sprayed by supersonic plasma spray with dual powder feed ports

The functionally graded thermal barrier coatings （FG-TBCs） with 80%ZrO2-13%CeO2-7%Y2O3 （C-YSZ）/NiCoCrAlY were prepared using a recently developed supersonic plasma spraying（S-PS） with dual powder feed ports system. The thermal shock experiment of FG-TBCs specimens was carried out by means of the automatic thermal cycle device, in which the samples were heated to 1200℃ by oxygen-acetylene flame jet then water-quenched to ambient temperature. The temperature—time curves of specimens and photographs can be watched on-line and recorded by a computer during the test. The results show that the totally 1mm-thick FG-TBCs have excellent thermal shock resistance due to the fact that the coatings have no any peeling-off after 200 thermal cycles. The microstructures and morphologies of FG-TBCs were characterized and analyzed by SEM.

Microstructure characteristics of coating with amorphous phases prepared from Fe-based alloy powders by plasma spray

In this paper, alloy powders mixed with a molar ratio of Fe ： P ： C of 80 ： 13 ： 7 were sprayed on Q235 steel by plasma spray method to prepare coating with amorphous phases. The phase composition of the mixed alloy powders and prepared coating were characterized by X-ray diffraction （ XRD ）. The morphology and the composition cf the coating were analyzed by scanning eleetron microscopy （SEM） nnd energy dispersive apectroscopy （ EDS ）. In addition, the thermal stability ef the coating with amorphous phases was characterized by differential thermal analyzer （ DTA ）. Tile results showed that, usirtg mixed alloy powders with a molar ratio of Fe： P： C of 80：13：7, the coating containing certain amount of amorphous alloys was suceessathlly prepared through atmospheric plasma spray technique. In the coating, the main phases were determined to be Fe, FeP aad Fe2P. The crystallization of the coating started from about 461°. Tile coating was mechanically adhered to the substrate.

FORMATION OF GRADIENT COATING OF Fe-BASED ALLOY WITH RARE EARTHS BY PLASMA SURFACING

A gradient coating of Fe-based alloy was manufactured with rare earths (RE) by plasma surfacing on Q235 steel substrate. The coatings were studied by using X-ray diffraction(XRD), scanning electron microscope(SEM), differential thermal analyzer(DTA), and electron probe micro-analyzer (EPMA). The results show that the phases of the two kinds of coatings(with and without RE) both include α-Fe, Fe7C3, Fe3C, Cr2B, Fe2B and FeB. The microstructure of F314 coating is mainly hypereutectic, the pro-phases Cr7C3 and Cr2B are loose, crassi, spiculate and contain microcracks. The brittleness of the coating is high, and the average hardness is 787 HV. When 0.8wt% RE was added into the F314 alloy, the microstructure varied from hypoeutectic to hypereutectic continuously, The hardness appears as gradient distribution with the highest value of 773 HV, meanwhile, the brittleness decreases significantly. The formation of gradient structure depends on the fallowing factors: (i) the conversion of RE. The addition of RE lowers the elements point and Fe-C eutectic temperature, thus the base metal melting acutely. (ii) the heating of plasma arc. Graded temperature results in directional solidification, thus the gradient structure forms easily. The main reasons for the hardness decrease with RE addition in the alloy are the ratio of hard phase lowering and the hardness of the hard phase decreasing.

Parameter optimization for plasma-sprayed Al2O3p/Al composite coatings on AZ31 magnesium alloy

Al2O3p/Al composite coatings were prepared on the surface of AZ31 magnesium alloy by plasma spraying technology with mixed powders of Al and Al2O3. An orthogonal test containing six factors and five levels was carried out to acquire the optimum technical parameters. Mierostruetures and properties of the composite coatings were studied. The results show that the coatings consist of Al2O3 particulates distributed uniformly and Al matrix, and the interface between the particulate and matrix is continuous, compact and clean. With increasing the mass fraction of Al2O3 in the mixed powders, the volume fraction of Al2O3 in the coatings iacreases. The Al2O3p/Al composite coating with 14% Al2O3 volume fraction has more compact microstrueture and more satisfactory properties.

Microstructural features and properties of plasma sprayed YPSZ/NiCrAlY thermal barrier coating (TBC)

The plasma sprayed thermal barrier coating (TBC) consists of NiCrAlY bond coating and yttria partially stabilized zirconia (YPSZ) top coating. NiCrAlY coating mainly contains Ni solid solution with face centered cubic lattice, Al_2O_3 oxides and pores. The most obvious feature of YPSZ coating with tetragonal zirconia is a lot of vertical microcracks in this coating. The thermal insulation capability of the TBC increased with an increase in YPSZ coating thickness, the temperature drop across the TBC increasing from 60℃ to 92℃ with increasing YPSZ coating thickness from 100 μm to 500 μm. The thermal shock resistance of the TBC decreased with increasing YPSZ coating thickness and cracks initiated mainly in original vertical microcrack tips of the YPSZ coating and propagated not only along YPSZ coating/ NiCrAlY coating interface but also through NiCrAlY coating. The oxidation process of the TBC at 1 200℃ can be divided into two stages: transient oxidation stage with rapid oxidation rate and steady oxidation stage with slow oxidation. Their transition time was about 10 hours. The weight gain for 100 hours was 3.222 mg/mm2. It is favorable to increase YPSZ coating toughness and to decrease the pores and oxides of the TBC system for improving thermal shock resistance and oxidation resistance of the TBC.

Laser Surface Annealing of Plasma Sprayed Coatings

Laser surface annealing provides a rapid and efficient means for surface alloying and modification of ceramic materials. In this study, Alumina-13% Titania coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by Excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. The surface structure of the treated coating was examined by field emission scanning electron microscope and X-ray diffraction (XRD). A detailed analysis of the effects of various laser parameters including laser energy density (fluence), pulse repetition rate (PRR), and number of pulses on the morphology and the microstructure of the coatings are presented.

等离子喷涂ZrO_2-NiCoCrAlY梯度涂层的成分分布与力学性能

在 Zr O2 - Ni Co Cr Al Y梯度涂层中 ,由基体到涂层表面 ,Zr O2 的含量逐渐增多 ,Ni Co Cr Al Y的含量逐渐减少 ,形成一种无宏观结合界面的成分连续变化的组织结构。随 Zr O2 组元含量的升高 ,Zr O2 - Ni Co Cr Al Y复合涂层的密度基本呈线性降低 ;涂层硬度则先降低后升高 ,含 6 0 vol% Zr O2 的复合涂层具有最低的硬度值 ;富含 Ni Co Cr Al Y组元的复合涂层的孔隙率略低。与双层涂层相比 ,成分梯度化的分布使梯度涂层的内聚强度和涂层与基体的结合强度都得到了明显地提高 ;涂层与基体的结合界面是梯度涂层

等离子喷涂NiCoCrAlY/Al_2O_3涂层的制备及摩擦性能研究

目的：制备等离子喷涂NiCoCrAlY/Al2 O3高温固体润滑耐磨涂层,并研究该涂层的摩擦性能和磨损机理。方法采用喷雾造粒、化工冶金包覆和固相合金化技术制备NiCoCrAlY/Al2 O3复合粉体,用等离子喷涂技术在45#钢表面制备NiCoCrAlY/Al2 O3复合涂层。用SEM和XRD等手段分析粉体和涂层的显微结构和物相组成,研究涂层从室温到800℃的摩擦磨损性能,探讨NiCoCrAlY/Al2 O3复合涂层在室温和高温下的磨损机理。结果 Al2 O3颗粒表面均匀包覆着一层致密的NiCoCrAlY合金,包覆层厚度大约为3~5μm；等离子喷涂NiCoCrAlY/Al2 O3复合涂层呈典型的层状结构,涂层各层间结合良好,涂层中孔隙率约为2.84%,主晶相为NiCrAl合金相和Al2 O3相。涂层的摩擦系数随温度的升高逐渐降低,在室温下约为0.64,800℃时在0.4以下。高温下,金属氧化物的形成是摩擦系数降低的主要原因。涂层的磨损率随温度的升高先升高后降低。涂层在低温下为脆性断裂和磨粒磨损,高温下为氧化磨损、磨粒磨损、塑性变形和金属氧化物的转移。结论等离子喷涂NiCoCrAlY/Al2 O3复合涂层是一种性能优良的高温固体润滑耐磨涂层。

冷喷涂NiCoCrAlY涂层的微观性能研究

运用冷喷涂技术制备了NiCoCrAlY合金涂层,通过扫描电镜和能谱仪对涂层表面以及横截面的微观结构、喷涂粒子之间的结合变形情况进行了观察和成分分析,运用显微硬度计对制备的NiCoCrAlY合金涂层内部的显微硬度进行了测量。结果表明,只有使用氦气作为载气时才能运用冷喷涂技术制备出NiCoCrAlY合金涂层,使用空气和氮气作为载气时无法制备;在不同粉体成分下,NiCoCrAlY合金粉体的沉积特性不同,所制备的涂层微观性能也不同。

等离子喷涂NiCoCrAlY/Al_2O_3高温固体润滑耐磨涂层的抗氧化性能研究

目的研究等离子喷涂NiCoCrAlY/Al2O3高温固体润滑耐磨涂层在850℃时的高温抗氧化性能和抗氧化机理。方法采用喷雾造粒、化工冶金包覆技术制备NiCoCrAlY/Al2O3复合粉体,并采用等离子喷涂技术在45#钢表面制备NiCoCrAlY/Al2O3复合涂层。采用SEM和XRD研究粉体和涂层的显微结构和物相组成,并采用马弗炉研究复合涂层在850℃的恒温氧化动力学曲线,通过研究氧化96 h以后涂层表面的组织形貌,探讨NiCoCrAlY/Al2O3复合涂层的抗氧化机理。结果 NiCoCrAlY合金层均匀致密地包覆在Al2O3颗粒的表面,包覆层厚度约为3-5μm。复合粉体的主要组成为Al2O3相和NiCoCrAlY合金相,没有其他杂质相的存在。等离子喷涂NiCoCrAlY/Al2O3复合涂层氧化动力学曲线分为大斜率直线、抛物线和系数几乎为0的抛物线等3个阶段。氧化96 h以后,涂层的氧化质量增量为4.9 mg/cm2左右,表面形成了一层连续的氧化物保护膜,经EDX分析,氧化膜层主要由Al,O,Cr和Ni组成。结论等离子喷涂NiCoCrAlY/Al2O3复合涂层具有良好的高温抗氧化性能,涂层中Ni,Cr,Al的氧化以及硬质相Al2O3的加入是涂层抗氧化的主要原因。

等离子喷涂ZrO_2/NiCoCrAlY梯度涂层中ZrO_2组元的显微结构特征

ＺｒＯ２／ＮｉＣｏＣｒＡｌＹ梯度涂层中的８％Ｙ２Ｏ３（按质量计）部分稳定ＺｒＯ２组元在等离子喷涂后的快速凝固和冷却过程中，发生了ｃ→ｔ′非扩散型相变和ｃ→ｔ扩散型相变，以及少量的ｔ→ｍ相变。涂层中ＺｒＯ２主要由未转变的ｃ相及转变产物ｔ相和ｔ′相组成，并存在少量的ｍ相。ｃ相晶粒尺寸较大；ｔ′相为类似板条马氏体的孪晶组织；ｔ相为均匀细小的等轴晶，平均尺寸为０．２μｍ左右；ｍ相具有孪晶结构。

NiCoCrAlY涂层的抗中性盐雾腐蚀性能

通过中性盐雾腐蚀试验研究了低膨胀高温合金GH907基体上采用低压等离子喷涂制备的NiCoCrAlY涂层和NiCr涂层的抗腐蚀性能,并对其腐蚀形貌与产物进行了分析。结果表明:盐雾腐蚀500 h后,NiCoCrAlY涂层表面出现了失光变色,在表面出现了几个无破坏性的腐蚀坑,涂层表面大部分仍保持较好的完整性,其腐蚀等级仅下降到9级;而NiCr涂层的表面出现了较多的腐蚀斑点,涂层的完整性已经被破坏,涂层表面产生了腐蚀裂纹,其腐蚀等级下降到4级;腐蚀产物主要为镍、铁、钴等的氧化物,NiCoCrAlY涂层表现出较强的抗中性盐雾腐蚀性能。

低压等离子喷涂NiCoCrAlYTa涂层微观结构及抗氧化性能

采用低压等离子喷涂技术在镍基单晶高温合金上制备了NiCoCrAlYTa涂层,利用OM、SEM和EDS研究了涂层的微观结构和涂层中各元素的分布,用XRD对涂层物相进行分析,测定了涂层的显微硬度和断裂韧性,并比较了涂层和合金的抗高温氧化性能。结果表明,涂层中Al、Cr、Co和Ni元素分布均匀,主要由γ-Ni、β-NiAl、γ'-Ni3Al和少量CrCoTa相组成,涂层/合金界面处形成Al、Cr、Co和Ni元素浓度台阶。涂层的显微硬度和断裂韧性分别为350.8 HV0.3和2.73 MPa.m1/2。涂层比镍基单晶高温合金的高温抗氧化性能好。