Review Nano and macro-structured component fabrication by electron beam-physical vapor deposition (EB-PVD)

The objective of this paper is to demonstrate the versatility of electron beam-physical vapor deposition (EB-PVD) technology in engineering new materials with controlled microstructure and microchemistry in the form of coatings. EB-PVD technology is being explored in forming net-shaped components for many applications including space, turbine, optical, biomedical and auto industry. Coatings are often applied on components to extend their performance and life under severe environmental conditions including thermal, corrosion, wear, and oxidation. In addition, coatings have been used in designing and developing sensors. Performance and properties of the coatings depend upon its composition, microstructure and deposition condition. This paper presents recent results of various materials including ceramic, metallic, and functionally graded coatings produced by EB-PVD. Simultaneous co-evaporation of multiple ingots of different compositions in the high energy EB-PVD chamber has brought considerable interest in the architecture of functional graded coatings, nano-laminated coatings and designing of new structural materials that could not be produced economically by conventional methods. In addition, high evaporation and condensate rate allowed fabricating precision net-shaped components with nanograined microstructure for various applications. This paper will also present the results of various metallic and ceramic coatings including chromium, titanium carbide (TiC), hafnium carbide (HfC), tantalum carbide (TaC), hafnium nitride (HfN), titanium-boron-carbonitride (TiBCN), and partially yttria stabilized zirconia (YSZ), and HfO₂-based TBC coatings deposited by EB-PVD for various applications.     

Thermal conductivity investigation of zirconia co-doped with yttria and niobia EB-PVD TBCs

A technique used to improve the life cycle and/or the working temperature of the turbine blades uses ceramic coatings over metallic material applied by electron beam-physical vapor deposition (EB-PVD). The most usual material for this application is yttria doped zirconia. Addition of niobia, as a co-dopant in the Y₂O₃–ZrO₂ system, can reduce thermal conductivity. The purpose of this work is to evaluate the influence of the addition of niobia on the microstructure and thermal properties of the ceramic coatings. This new formulation will, in the future, be able to become an alternative to the composition currently used by the aerospace field in EB-PVD thermal barrier coatings (TBC). A significant reduction of the thermal conductivity, measured by laser flash technique, in the zirconia ceramic coatings co-doped with yttria and niobia when compared with zirconia–yttria coatings was observed.     

Functionally gradient ceramic/metallic coatings for gas turbine components by high-energy beams for high-temperature applications

Failure of turbine blades generally results from high-temperature oxidation, corrosion, erosion, or combinations of these procedures at the tip, and the leading and trailing edges of a turbine blade. To overcome these limitations, functionally gradient ceramic/metallic coatings have been produced by high-energy beams for high-temperature applications in the aerospace and turbine industries to increase the life of turbine components. Thermal spray processes have long been used to apply high-temperature thermal barrier coatings to improve the life of turbine components. However, these processes have not met the increased demand by the aerospace and turbine industries to obtain higher engine temperatures and increased life enhancement as a result of the inhomogeneous microstructure, unmelted particles, voids, and poor bonding with the substrate. High-energy beams, i.e. electron beam-physical vapour deposition (EB-PVD), laser glazing, laser surface alloying, and laser surface cladding, have been explored to enhance the life of turbine components and overcome the limitations of the thermal spray processes. EB-PVD has overcome some of the disadvantages of the thermal spray processes and has increased the life of turbine components by a factor of two as a result of the columnar microstructure in the thermal barrier coating (TBC). Laser glazing has been used to produce metastable phases, amorphous material, and a fine-grained microstructure, resulting in improved surface properties such as fatigue, wear, and corrosion resistance at elevated temperatures without changing the composition of the surface material. Laser surface alloying and laser surface cladding have shown promising results in improving the chemical, physical, and mechanical properties of the substrate's surface. Metal-matrix composite coatings have also been produced by a laser technique which resulted in increased wear and oxidation-resistant properties. The advantages and disadvantages of thermal spray processes, EB-PVD, laser glazing, laser surface alloying, and laser surface cladding will be discussed. Microstructural evolution of thermal barrier coatings, recent advancements in functionally gradient coatings, laser grooving, and multilayered textured coatings will also be discussed.     

Substrate Effects on the High-Temperature Oxidation Behavior of Thermal Barrier Coatings

The high-temperature oxidation behaviors of the NiCrAlYSi/P-YSZ thermal barrier coatings (TBCs) produced by electron beam-physical vapor deposition (EB-PVD) on directionally solidified (DS) and single crystalline (SC) Ni-based superalloy substrates were investigated. The cross-sectional microstructure investigation, isothermal and cyclic oxidation tests were conducted for the comparison of oxidation behaviors of TBCs on different substrates. Although TBC on DS substrate has a relatively higher oxidation rat...     

溶胶浸渗处理对EB-PVD 制备的YSZ电解质涂层的影响

为探索溶胶浸渗处理对电子束物理气相沉积(EB-PVD)制备8%摩尔比的氧化钇稳定氧化锆(8YSZ)涂层微观结构及性能的影响,采用EB-PVD工艺在沉积速率1μm/min的条件下制备了8YSZ电解质涂层.制备态涂层的断面表现为疏松的柱状晶结构,导致涂层的气密性差,因此对涂层进行了溶胶浸渗处理,即首先在负压下将涂层浸渗在钇锆的溶胶内,再进行550℃保温2 h的热处理.SEM分析表明,溶胶分解产物可以堵塞柱状晶间的孔隙,其渗入涂层的深度可达3μm.浸渗处理后,涂层的气体扩散系数由未处理态的6.78×10-5cm4/(N.s)降低至8次浸渗处理后的6.54×10-6cm4/(N.s).8次溶胶浸渗处理后涂层的电导率相比处理前提高不超过10%.     

Tailored microstructure of zirconia and hafnia-based thermal barrier coatings with low thermal conductivity and high hemispherical reflectance by EB-PVD

Zirconia and hafnia based thermal barrier coating materials were produced by industrial prototype electron beam-physical vapor deposition (EB-PVD). Columnar microstructure of the thermal barrier coatings were modified with controlled microporosity and diffuse sub-interfaces resulting in lower thermal conductivity (20–30% depending up on microporosity volume fraction), higher thermal reflectance (15–20%) and more strain tolerance as compared with standard thermal barrier coatings (TBC). The novel processed coating systems were examined by various techniques including scanning electron microscopy (SEM), X-ray diffraction, thermal conductivity by laser technique, and hemispherical reflectance.     

Nano-grained Net-Shaped Fabrication of Re Components by EB-PVD

Cost-effective net-shaped forming components have brought considerable interest into the Department of Defense, the National Aeronautics & Space Administration, and the Department of Energy. Electron beam-physical vapor deposition (EB-PVD) offers flexibility in forming net-shaped components with tailored microstructure and chemistry. High-purity rhenium components, including rhenium-coated graphite balls and rhenium plates and tubes, have been successfully manufactured by EB-PVD. EB-PVD rhenium components exhibited submicron and nano-size microstructure with high hardness and strength as compared with chemical vapor deposition (CVD). It is estimated that the cost of rhenium components manufactured by EB-PVD would be less than the current CVD and powder-high-temperature isostatic pressure technologies.     

Numerical study on modification of ceramic coatings by high-intensity pulsed ion beam

ZrO₂ ceramic coatings, which often call thermal barrier coatings (TBCs), fabricated by electron beam physical vapor deposition (EB-PVD), are widely used in high-temperature environment of aircraft and industry gas-turbine engines, because of the excellent strain tolerance imparted by the columnar structure. However, channels separating the columnar grains in EB-PVD TBCs provide paths for oxygen or other aggressive species from ambient atmosphere into the bond coat, resulting in the premature spallation-failure during high-temperature service. In our previous study, high-intensity pulsed ion beam (HIPIB) technique has been proposed to modify the EB-PVD TBCs, where a melted, densified top layer can be produced as a result of extremely thermal effect induced by the HIPIB irradiation. In this paper, HIPIB melting process is investigated numerically using a physical model based on experimental data, taking into account the surface morphology of HIPIB-melted TBCs to explore the mechanism of interaction between HIPIB and the coatings. Deposition process of the beam energy in TBCs was simulated by Monte Carlo method, and the non-linear equations describing the thermal conducting process were solved numerically based on the deposited energy to obtain the evolution of the temperature field of TBCs. The calculated melting depth of irradiated EB-PVD TBCs is consistent with results obtained in the HIPIB irradiation experiments.     

Microstructural evolution during friction surfacing of tool steel H13

Coatings of AISI H13 tool steel were made on low carbon steel by friction surfacing. Detailed microstructural studies and microhardness tests were carried out on the coatings. Studies revealed defect-free coatings and sound metallurgical bonding between the coating and the substrate. In addition, mechanical interlocking on a very fine scale was observed to occur between the coating and the substrate. Coatings exhibited martensitic microstructure with fine grain size and with no carbide particles. Coatings in as-deposited condition showed very high hardness (58 HRC) compared to the mechtrode material in annealed condition (20 HRC). Based on these findings, microstructural evolution during friction surfacing of H13 tool steel is discussed. The current work shows that friction surfaced tool steel coatings are suitable for use in as-deposited condition. Further improvements in coating microstructure and properties are possible with appropriate post-surfacing heat treatment.     

HVOF sprayed WC–Co coatings: Microstructure,mechanical properties and friction moment prediction

This study aims at gaining a better understanding of the microstructural features that control the mechanical and the tribological performances of WC–12 wt.% Co coatings under High Velocity Oxygen Fuel (HVOF) spraying conditions. This paper looks at the influences of the HVOF process parameters for WC–12Co material on the microstructural and the tribological behaviours of the coatings. The correlation between the coating microstructure and the wear behaviour is investigated by observing and analysing the microstructure and by studying the friction moment using enhanced statistical tool based on neural computations. According to the experimental and the numerical results, it has been shown that the spray parameters affect the phase composition, hardness and porosity of HVOF sprayed WC–12Co coatings and the correlations with HVOF process parameters are fully predictable in the steady-state regime.     

Erosion of thermal barrier coatings

Abstract

Thermal barrier coatings have been used within gas turbines for over 30 years to extend the life of hot section components. Thermally sprayed ceramics were the first to be introduced and are widely used to coat combustor cans, ductwork, platforms and more recently turbine aerofoils of large industrial engines. The alternative technology, electron beam physical vapour deposition,(EB-PVD) has a more strain-tolerant columnar microstructure and is the only process that can offer satisfactory levels of spall resistance, erosion resistance and surface finish retention for aero-derivative engines.

Whatever technology is used, the thermal barrier must remain intact throughout the turbine life. Erosion may lead to progressive loss of TBC thickness during operation, raising the metal surface temperatures and thus shortening component life. Ballistic damage can lead to total TBC removal.

This paper reviews the erosion behaviour of both thermally sprayed and EB-PVD TBCs relating the observed behaviour to the coating microstructure. A model for the erosion of EB-PVD ceramics is presented that permits the prediction of erosion rates. The model has been validated using a high velocity erosion gas gun rig, both on test coupons and samples removed from coated components. The implications of erosion on component life are discussed in the light of experimental results and the model predictions.     

Microstructural evolution of titanium nitride (TiN) coatings produced by reactive ion beam-assisted, electron beam physical vapor deposition (RIBA, EB-PVD)

Titanium nitride (TiN) coatings have been successfully deposited on 304 stainless steel substrates by reactive ion beam-assisted, electron beam-physical vapor deposition (RIBA, EB-PVD). The hardness values of the TiN coatings varied from 800 to 2500 VHN depending on the processing condition. The lattice parameter and hardness variation were correlated with processing parameters such as: deposition rate, bias, ion source energies, process gas, substrate temperature, and coating composition. The hardness of the TiN coatings increased with increasing ion energy. The ion energies combined with the deposition rate were the limiting factors controlling the degree of surface texturing. Surface texturing was only observed for those coatings deposited >8 Å/s.     

Measurements of the thermal gradient over EB-PVD thermal barrier coatings

Conventional two-layered structure thermal barrier coatings (TBCs), graded thermal barrier coatings (GTBCs) and graded thermal barrier coatings with micropores were prepared onto superalloy DZ22 tube by electron beam physical vapor deposition (EB-PVD). Thermal gradient of the TBCs was evaluated by embedding two thermal couples in the surfaces of the tube and the top coat at different surrounding temperatures with and without cooling gas flowing through the tube. The results showed that higher thermal gradient could be achieved for the GTBCs with micropores compared to the two-layered structure TBCs and GTBCs. However, after the samples were heated at 1050°C, the thermal gradient for the GTBCs with or without micropores decreased with the increase of heating time. On the other hand, the thermal gradient for the TBCs increased with the increase of heating time. Cross-section observations by scanning electron microscopy showed that the change in microstructure was the main reason for the change of the thermal gradient.     

Architecture of thermal barrier coatings produced by electron beam-physical vapor deposition (EB-PVD)

Extremely high temperatures and severe atmospheric conditions in the hot section of aircraft engines during operation result in degradation and structural failures of turbine components. Replacing these components is very expensive. Thermal barrier coatings (TBC) composed of ZrO₂-8wt%Y₂O₃(8YSZ) applied by Electron Beam-Physical Vapor Deposition (EB-PVD) to turbine components offer excellent properties for thermal protection and resistance against oxidation - induced erosion and corrosion. However, the life of turbine components is still limited due to premature failure of the TBC. It is hypothesized that the life of the coated components can be extended by lowering the thermal conductivity of the TBC by creating multiple non-distinct or distinct interfaces and alloy additions such as Nb-oxide which will result in a reduction in the thermal conductivity and oxygen transport through the coating. This paper presents the microstructural results of standard 8YSZ, layered 8YSZ, Nb-oxide alloyed 8YSZ and functionally graded 8YSZ with Nb-oxide deposited by EB-PVD. TBC samples were examined by various methods including scanning electron microscopy (SEM), high-resolution optical microscopy (OM), X-ray diffraction (XRD), and thermal cycling tests. The preliminary results strongly suggest that multiple interfaced TBC exhibits better oxidation resistant properties as compared to standard and alloyed TBC.     

Structural characterization of nanocrystalline lanthanum oxyfluoride films obtained by chemical vapor deposition

This study is devoted to a thorough structural and microstructural characterization of nanophasic LaOF-based thin films. The coatings were synthesized by Chemical Vapor Deposition (CVD) onto Si(100) substrates at growth temperatures between 250 and 500 degrees C, using La(hfa)3.diglyme (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = bis(2-methoxyethyl)ether) as both La and F molecular source under nitrogen + wet oxygen atmospheres. The system structure and microstructure were investigated by Glancing Incidence X-ray Diffraction (GIXRD) and X-ray microdiffraction. The most relevant sample features, with particular attention to the phase composition as a function of the synthesis conditions, are critically discussed.     

Microstructure and texture of EB-PVD TBCs grown under different rotation modes

The role of vapor incidence pattern (VIP) on the microstructure and texture of thermal barrier coatings (TBCs) produced by electron-beam physical vapor deposition (EB-PVD) is examined. Two distinct VIPs are induced by proper design of the substrate rotation mode. One is the sunrise–sunset pattern typical of conventional deposition on the curved face of a rotating cylinder (mode A), and the other is a conical pattern resulting when deposition is done on the cylinder base at an offset distance from the plume axis (mode P). These geometries afford fundamental insight on the processes of microstructure and texture evolution and also have practical implications to the variability of properties that may be expected between the body and platform regions of a turbine airfoil. Comparable deposition rates and thickness uniformity can be achieved by proper selection of the experimental geometry. Both coatings exhibit the typical 100 texture normal to the substrate, but mode A also yields a preferred in-plane orientation which is absent in mode P. The ensuing differences in column packing and tip shadowing yield lower densities and larger pipe-like inter-columnar voids in mode P. The absence of an in-plane evolutionary selection mechanism in the latter also leads to narrower columns than in mode A.     

EB-PVD工艺制备SiC/ZrO_2涂层的微观组织结构研究

本文利用EB-PVD工艺在高温合金表面制备SiC/ZrO2防热涂层,对制备态和不同温度晶化处理后的涂层进行了微观组织结构分析。结果表明,随退火温度升高,SiC结晶程度提高,Ramam光谱出现了SiC的TO带和LO带;SiC层中分散的sp2杂化碳团簇产生了急剧的聚集,形成了大的团簇结构。退火处理后SiC表层发生钝性氧化,涂层表面C元素含量大幅度减少,而O元素含量迅速增加;XPSC1s和Si2p谱峰的中心向高结合能方向发生了偏移;表层中C-C键的含量减少,Si-O键的含量逐渐增加。     

高温防护涂层研究进展

高温防护涂层在防止航空涡轮发动机抗高温腐蚀以及延长发动机寿命方面起着越来越重要的作用。电子束物理气相沉积和等离子喷涂是目前制备高温涂层的两种最重要方法。本文综述了高温涂层国内外研究的进展,介绍了几种新型高温防护涂层,讨论了涂层使用的局限性及其发展前景。     

Optical and structural study of EB-PVD ZrO2 thin films

The behaviour of the crystalline properties of ZrO₂ films prepared by electron beam physical vapour deposition (EB-PVD) is investigated as a function of their deposition rates. In this paper, the conditions for the preparation of tetragonal zirconia from yttria stabilized zirconia and from monoclinic powder as starting materials are reported. The variation of the crystallite size as a function of the deposition rate is studied and, additionally, the optical characterization that permits to determine the refractive index is presented. The obtained values are in agreement with the bulk ones showing that EB-PVD prepared samples have good performance for optical and protective coatings.     

热障陶瓷涂层的最新发展

综述了现代航空发动机用热障陶瓷涂层的最新发展，着重介绍了双陶瓷层，电子束物理气相沉积（EB－PVD）和溶液等离子喷涂（SPS）纳米热障陶瓷涂层的性能和特点。