Abstract In this paper, a diffusion kinetic model was applied to simulate the microstructure development in a MCrAlY-superalloy system at high temperatures. Both simulation and experimental results showed that γ+γ’ microstructure was obtained in the coatings due to Al depletion after oxidation. With the help of the modelling, the mechanism of the formation of the diffusion zones in the single crystal (SC) superalloy can be also analyzed. The results revealed that the inward diffusion of Al from coating affected the depth of secondary reaction zone (SRZ) with the precipitation of TCP phases while the depth of inter-diffusion zone (IDZ) was decided by the inward diffusion of Cr.

Abstract Thermally sprayed ceramic coatings can be used for wear protection as well as thermal and electrical insulation. When exposed to environments with high humidity, the water absorption of the ceramic coating has a tremendous impact on the electrical insulation. In thermally sprayed ceramic coatings, water can easily be absorbed by the porous microstructure of the coating. A general result of the water absorption is the reduction of the dc resistivity. However, in the high frequency regime of ac loads, contrary results were observed for sealed Al 2 O 3 coatings on steel substrates. Specimens exposed to high air humidity have shown an increased ac resistance compared to dry specimens if frequencies above 1 MHz are considered. To analyse this phenomenon, a novel measurement technique was developed to investigate the influence of the water absorption of detached ceramic coatings on the ac resistivity at high frequencies. Moreover, the water absorption of the ceramic is measured gravimetrically. To ensure the results are also applicable to ceramic coatings on substrates, the morphology of the coating was analysed using electron microscopy and compared to reference specimens deposited on steel substrates from [1].

Abstract The advantages of UV-curing polymers are well known and used in various coating and adhesive applications. Curing times of a few seconds and long application windows allowing an increased throughput in series production. The use of UV-curing polymers in sealers is beneficial, but so far insufficient due to only surface curing. With a newly developed dual-cure mechanism in sealers, it is now possible to combine deep penetration curing and surface curing. The hybrid sealers combine radical polymerization with subsequent polyaddition or polycondensation. The development of sealers for thermal sprayed (TS) coatings involves an extensive requirement profile. This includes properties such as corrosion protection, penetration depth and processing times. High penetration depths of the sealant into the coating system are important to ensure a protection over the full lifetime of the TS coatings. The depth of penetration of the developed sealers into various TS coatings was determined by measuring the gas permeability in a specially developed test procedure. The corrosion protection effect in combination with TS coatings was determined by measuring the cell voltage. In summary, two UV dual-cure sealers have been developed to seal TS coatings with deep penetration and corrosion protection.

Abstract Thermally sprayed coatings can be used in structural health monitoring devices where the coatings can reveal defects in the real-time integrity of the component through changes in mechanical, thermal or modal properties during service. In this emerging application, the mechanical properties of the coating are strongly affected by the interfacial bond between the coating and the substrate. This paper presents an analytical study of the interfacial stress distribution based on piezoresistive-stress constitutive relation of a coating layer. Both a single layer coating- and a bilayer coating-substrate system were considered. An analytical solution of the interfacial stress was developed by solving a Fredholm-Volterra singular integro-differential equation of a coating-substrate model using Chebyshev polynomials. Numerical simulation was conducted to analyze the effects of geometric and effective material properties of the coating-substrate system on the interfacial stress distribution. It was found that the susceptibility of the piezoresistive layer to delamination primarily relies on thicknesses of the coating layers and the stiffness of the intermediary insulating layer and substrate.

Abstract There are different concepts for TBC coating application that varies in the method of applying the coating layers. An analysis of the existing part portfolio sprayed with different coating concepts shows that there is a 75 % difference in spray performance depending on which concept is used. This could lead to major savings regarding costs and time. This paper shows the effective use of offline programming tools in combination with a detailed coating process analysis. Based on this a time optimized coating concept for vanes and blades was developed. The validation of this optimized coating concept shows an improvement of more than 7 5 % in spray performance leading to a coating time improvement of up to 40%.

Abstract Be it to save the environment or to save money, engineers everywhere attempt to use materials which can’t normally withstand the surface stress they will be exposed to on their own. This is one of the reasons for the constant interest in new and innovative coating technologies. One such innovation is the transplantation of thermal sprayed coatings. In the transplantation process the coating is integrated into a high-pressure die casting process. In contrast to the conventional process chain, the coating is not directly applied to the work piece, but to a mold insert. During the pressure casting the melt infiltrates the coating and thus creates a join. This way the coating is indirectly applied to the die-cast work piece after removal from the mold. Additionally, depending on the materials involved, a material bonding connection similar to brazing is possible and results in an increased adhesion of the coating. A potentially very interesting trait of the transplantation process is, turning an internal coating process into an external coating process. This allows the coating of inside diameters well below the usual limit of an internal spray gun. Due to the high geometric accuracy of the process this can be potentially done without any need for additional finishing steps.

Abstract Degradation of hot section components in the turbine section of gas turbines used in the power generation industry can cause significant problems including financial penalties associated with down time and a decrease in operating efficiency. Thermal barrier coatings (TBCs) have been used effectively for the past two decades to mitigate such losses. The advent of dense and vertically macro-cracked TBCs has seen increasing use, although there is little published data as to its efficacy in performance vis-à-vis standard TBCs. This paper will present some mechanical and high temperature test data of such coatings. Effects of spray process and powders will be examined and discussed. The purpose of this paper is to share some of the experiences of a service provider in discussing various coatings options available to the user of the gas turbine.

Abstract To obtain the desired functionality and provide sustainability for steel structures, costly maintain and repair is needed. For use in particularly critical environments thermally sprayed coatings based on zinc/ aluminum in combination with a sealing supply many advantages. The subject of the ongoing research project is to deepen the knowledge about the influence of the thermal spray process, the spraying parameters, the manufacturing and especially the sealing process on the durability of sealed ZnAl-corrosion protective coatings. Verification is provided by state of the art testing methods to evaluate the coatings quality. The overall objective of the study is to provide recommendations on approaches and boundary conditions for manufacturing and sealing of thermally sprayed coatings for corrosion protection.

Abstract The paper will describe a collaboration of the DoD Propulsion Environmental Working Group (PEWG), Oklahoma City Air Logistics Center (OC-ALC), Pratt & Whitney and Engelhard Corporation to qualify and transition High Velocity Oxy Fuel (HVOF) thermal spray of tungsten carbide coatings to replace electrolytic chrome plating for the repair of Pratt and Whitney (PWA) engines at the OC-ALC. This depot is the primary location for engine repair for the US Air Force. The paper details the engineering effort to qualify the HVOF tungsten carbide coating on PWA TF33 engine components as an precursor to qualifying the coatings for other military PWA engines. The paper also provides details of the transition of HVOF thermal spray technology into a new state-of-the-art production facility at the OC-ALC depot. The paper highlights a notably successful industry and government partnership to rapidly transition a world-class thermal spray capability into OC-ALC. The PEWG is a special management group that works with US military propulsion managers to educate/apprises government and industry collaborations of mature advanced pollutant free technologies and then facilitate the transition to full-scale production. Pratt and Whitney is the original equipment manufacturer of the TF33 engine and supplies other gas turbine engines to the Air Force and other military services. Engelhard Corporation is a surface and science company that develops technologies to improve customers’ products and processes. A Fortune 500 company, Engelhard is a world-leading provider of technologies for environmental, process, appearance, performance application and engineering solutions. Engelhard led the technology transition effort under contract to the PEWG. [This effort, as will be described in the paper, encompasses process engineering, coating qualification, spray parameter definition, tooling concepts, accelerated mission engine test support, inspection techniques, and production bed-down at the OCALC depot.]

Abstract The author carried out in 2003 a multiclient survey and research covering thermal spraying industry in China. This work mainly focus on the productive level and scale of thermal spraying equipment and materials, application and coating job shop, R&D in universities and institutes as well as the develop trends of thermal spraying industry in China. This presentation intends to provide general pictures on thermal spraying industry in China, by offering data and analysis, forecasts the future of thermal spraying in China.

Abstract In this paper the point of view for the industrial coating manufacturing is presented. The perspective for industrial manufacturing of thermal spray coatings and facts that effect on the processibility of coatings in real life is often requested but seldom published. The perspective is from Pikoteknik Oy, which has a wide and long-term experience in the improvement and repair of machine parts in-situ, containing measurements, machining, coating and balancing of rolls and cylinders. Pikoteknik Oy is able to perform maintenance of paper cylinders on-site including pretreatments, thermal spraying and balancing quickly and skillfully. Due to their versatile state-of-the-art equipment, they are able to work flexibly on-site. To be able to operate on-site there are special demands for equipment, personnel and scheduling. The quality of the final product is in the hands of operator. Destructive testing is not possible to carry out and large amount of variables, such as moisture and positioning of equipment's exist. Grinding and grit blasting must carry out without dust formation due to the surrounding bearings and sensors. Large amount of experience and special knowledge is needed to be able to produce high quality coatings over paper cylinders.

Abstract To address drawbacks with conventional destructive adhesion tests, two advanced nondestructive methods were developed to characterize the acoustic response of coating-substrate bonding. These new tests, immersion ultrasonic testing and laser shock adhesion testing, are discussed in this contribution. The paper describes the test process and results as compared to traditional destructive testing. The advantages and drawbacks of the techniques are addressed.

Abstract A typical feature of plasma sprayed zirconia-based coatings is that their depostion efficiencies are low. Thus, from the economic view of reducing cost, how to improve the depostion efficiency of plasma sprayed zirconia-based coatings is very important for practical application. In this paper, spray-dried nanostructured powders and conventional powders were used as feedstocks to deposit nanostructured and conventional zirconia coatings by atmospheric plasma spraying(APS). Deposition efficiencies for both nanostructured and conventional zirconia coatings deposited under different spraying parameters were comparatively measured. The obtained results revealed that the spray-dried nanostructured powders possessed higher deposition efficiency than that of conventional powders. In addition, it was found that spraying parameters had strongly influence on microstructure and microhardness of zirconia coatings. Therefore, in order to obtain high quality zirconia coating, proper spraying parameters must be considered.

Abstract Instrumented indentation is well-suited as a technique for probing mechanical behaviour of coatings; it requires minimal specimen preparation, can be performed multiple times on a single specimen, and can measure behaviour over various length scales, by recourse to appropriate indenter tip selection. However, the complex nature of the deformation fields under the tip, coupled with complex (e.g. anisotropy, nonlinearity) coating properties necessitates robust means of interpretation in order to extract stress-strain behaviour. Here we present a simple method, based on empirical work by Tabor, for converting coating indentation force-depth data to stress-strain curves. Using this method, results of indentation can thus be used to quantify mechanical behaviour of coatings deposited by different processes, and subjected to post-processing treatments, providing a powerful supplement to microstructural characterization. In addition, we show how anisotropic elasticity of coatings, measured via indentation, can qualitatively identify the existence of different microstructual features. Finally, we explore subsurface strain mapping as a technique to quantitatively compare elastoplastic behaviour of coatings to bulk, isotropic materials.

Abstract The Hitachi MaxJet II is a unique multi-purpose combustion gun. It can be used for spraying wire but it also has the capability to spray multiple materials via-powder and powder cord form. The equipment operates using commonly available gases: compressed air, Oxygen and Propane or Mapp gas. It requires no major facility cost since it uses only a 35 cfm air compressor and 115 volt power supply. Safety is assured with a safety purge system, separation of electrical and gases systems and flash back arresters. The small compact system weighs less than two hundred pounds, which makes it easily movable for on site work. It’s low capital investment and high quality coatings with low porosity and excellent bond strengths. The electronic pusher type wire feed provides consistent feed rates for a large variety of wires and wire sizes (1/16”, 1/8”, and 3/16”). The spray gun weighs only three pounds and can be mounted on a robot or used for hand spray applications. It functions well in a shop environment or onsite spraying of bridge components.

Abstract This research delivers an integrated performance of generic coating-substrate systems under impact loading, and comprehends the understanding of underpinning failure mechanisms. This investigation thus benchmarks the coating design process for high impact stress applications. Repeated severe impacts to the coatings often result in poor performance by cracking and delamination from the coating-substrate interface. The durability and delamination resistance of coatings depend on the choice of coating and substrate materials, coating deposition process and service conditions. The design of overlay thermal spray coatings thus requires an optimization of these parameters. A thorough understanding of the underpinning failure mechanisms is thus critical for future coating developments. This investigation thus provides an insight to the role coating and substrate properties on the impact resistance of coated materials, and maps the relationship between the impact resistance of WC-Co and WC-CrC-Ni coatings on a variety of substrates. Results indicate that coating’s delamination resistance during impact loading not only depends upon the hardness and roughness of the substrate material, but more importantly, substrates with higher work-hardening coefficient indicate a higher delamination resistance during impact loading.

Abstract The shielding controlled plasma spraying process is investigated to improve corrosion resistance of the metal surface. In this process, a shielding nozzle that covers just the spraying area is attached in front of the tip of a commercial plasma spray gun nozzle, and the environment surrounding the plasma jet is controlled by nitrogen flow. As the oxygen concentration in the shielding nozzle is maintained as low as 0.5%, the metal oxide contents in volume of CoNiCrAlY coating and the porosity of the coating reduced to 0.2% and 0.3% respectively under optimal spray particle size. The corrosion potential of CoNiCrAlY coating sprayed by this process in an acid solution including chloride ions is staying about -150 mV for 1000 hours, and no rust is observed during this test. On the other hand, that of the coating sprayed by atmospheric plasma spraying process changes from about -300 mV to about -500mV for 1000 hours, and the rust comes to the surface of the coating after 10 hours. Therefore the developed shielding controlled plasma spraying process is concluded to improve the corrosion of the metal.

Abstract The phase transformation and reaction of ZrO 2 -CaO- ZrSiO 4 and ZrO 2 -Y 2 O 3 -ZrSiO 4 coatings with manganese oxide at 1273 K were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). SiO 2 phase formed in the coatings, which was from the ZrSiO 4 decomposed and easy react with manganese oxide or CaO. SiO 2 has precedence over react with CaO than manganese oxides for ZrO 2 -CaO-ZrSiO 4 coatings, and which result in to promote t-m phase transformation. On the contrary, the reaction between SiO 2 and MnO is primary for the ZrO 2 -Y 2 O 3 -ZrSiO 4 coatings and result in the damage or exfoliation on the surface of the coatings.

Abstract Thermally sprayed coatings are often anisotropic due to their manufacturing processes. However, identification of anisotropic properties is very difficult not only because of such material systems but also their small scales. The present work present a new procedure based on nano-indentation technique and inverse analysis to characterize transversely isotropic elastic-plastic coatings. In particular, it uses Kalman filter, which processes the indentation measurements to extract unknown material parameters. This procedure employs load-penetration records of two indenters, spherical and Berkovich. An advantage of this method is that it requires minimum specimen preparations and the measurement procedure is straightforward. APS NiAl coating is indented and their records are used to estimate its anisotropic factors. The results support the effectiveness of the new procedure.

Abstract The short description of traditional methods of thermal sprayed coatings (TSC) structure characterization is given. The main parameters of structure and physico-mechanical properties of TSC, which influenced on their wear resistance are considered. The system approach for analyses of structure of TSC and the scheme of TSC properties prediction is proposed. The classification of structure levels of wear resistant coatings, obtained by thermal spraying, and models of their elements are proposed. The advisability of use of methods of structure-simulation modeling of TSC is shown.