bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Composite Coatings Composed of a Stainless Steel Matrix and Tungsten Carbide Nano-Inclusions by Plasma Spraying
Authors: Wittmann-Ténèze K. , Pereira J. M. , Brelivet P. , Bianchi L.
Published: November 2022

Tungsten-based cermets are well-known engineering materials finding applications in aerospace, nuclear equipment, and many other fields. Plasma spraying is an interesting industrial process to manufacture those refractory materials. Original plasma sprayed hard coatings for wear protection composed of a stainless steel matrix and inclusions of tungsten carbide (WC) nanoparticles were developed. To built-up the coatings, two precursors were injected separately in the plasma jet : a stainless steel micrometric powder was classically injected into the plasma jet using a carrier gas whereas WC nanoparticles were injected with a liquid carrier, like in the so-called process suspension plasma spraying. One of the challenges is to maintain the WC phase stoichiometry in the deposit, without decomposing the carbide into brittle W2C, W3C, and metallic tungsten, phenomenon usually occurring with thermal spraying techniques. Another issue is to succeed in including homogeneously the carbide nanoparticles in a sufficiently dense stainless steel matrix. Coatings with different WC contents were deposited on stainless steel substrates and investigated with respect to their microstructure by optical and scanning electron microscopy, porosity level using the Archimedean method, phase composition by X-ray diffraction and Vickers micro-hardness. Results have shown that coatings consisting of a stainless steel matrix containing inclusions of carbide nanoparticles can be produced by plasma spraying. The phase composition analysis indicated that nanoparticles are largely composed of the WC phase and contain a small amount of WC1-x phases. A slight increase of the porosity level was measured for coatings containing nanoparticles, compared to the pure matrix, probably due to the cooling effect of the WC carrier liquid on the in-flight characteristics of the stainless steel particles. Micro-hardness measurements gave similar values for with or without nano-sized particles, showing that the amount of WC included in the samples was insufficient to improve the hardness property.
Comparative Study of Thermal Sprayed Polymers for Wear Protection
Authors: Lima C. R. C. , Souza N. F. C. , Camargo F. M. , Camargo F.
Published: November 2022

Thermal spraying covers a range of spraying processes in which any metallic, ceramic or polymer-based material can be sprayed onto a substrate to be protected. This flexibility of thermal spraying makes the technology extremely successful in different engineering applications. Protection of the metallic components by hard oxide or ceramic-metallic coatings has proven to be an effective way to reduce wear and corrosion. Polymer coatings are increasing in importance as protection against corrosion and wear for several environmental conditions. Polymeric materials typically exhibit a low shear strength and low elastic modulus that make them viable for use under tribological conditions. Thermally sprayed polymers have the potential both to lower material costs and improve coating performance in drastic environments. In this work, a comparative study is carried out to evaluate the performance of some thermoplastic and hydrocarbon derived polymers deposited onto steel by thermal spray technology. Several tests were performed to evaluate the obtained coatings mainly related to tribological performance.
Comparative Study of the Melting and Atomization Properties of Iron-Based High-Carbide Alloys
Authors: Wielage B. , Schuberth S.
Published: November 2022

Thermally sprayed cermet powder coatings as well as bulk cermet materials sintered of carbide/metal powder blends are widely used in applications with severe abrasive wear conditions. A cost-saving alternative can be provided by using iron-based melt-atomised hard alloy powder feedstocks. Among them, commercial alloys containing high amounts of vanadium and carbon obtain outstanding wear resistance due to their high volume fraction of finely dispersed, hard vanadium carbides. However, their performance is still exceeded by cemented carbides. A further improvement of the wear properties of hard alloys basically can be attained by increasing their carbide content, concurrently considering the limitations of the melting and atomisation process regarding the melting temperature. A possible solution can be provided by alloying the basic system Fe-V-C with an additional strong carbide former like niobium. Subject of this work is the comparing investigation of the technologically important melting equilibria in the systems Fe-V-C and Fe-V-C-Nb.
Effect of Vacuum Heat Treatment on Tensile Strength and Fracture Performance of Cold-Sprayed Cu-4Cr-2Nb Coatings
Authors: Yu M. , Li W.-Y. , Zhang C. , Liao H. L.
Published: November 2022

A previous study indicated that dense thick Cu-4Cr-2Nb coatings could be formed by cold spraying, and the post-spray heat treatment could significantly influence the microstructure and microhardness of the as-sprayed Cu- 4Cr-2Nb coatings. In this study, the tensile strength and fracture performance of the Cu-4Cr-2Nb coatings after annealing were investigated. The vacuum heat treatment was conducted under 10-2 Pa at 850°C for 4 h. Results showed that the heat treatment had a great contribution to the healing-up of the incompleteness of the interfaces between the deposited particles. In addition, the coating microhardness decreased from 156.8±4.6 Hv0.2 for the as-sprayed coatings to 101.7±4.5 Hv0.2 for the annealed ones. The mean tensile strength of the annealed coatings was approximately 298.8±31.5 MPa compared to that of 45±10.5 MPa for the as-sprayed ones, which results from the partially metallurgically bonded zones between the deposited particles inducing by the heat treatment process.
Characterization of Mechanical Properties by Nanoindentation of Bimodal WC-VC-Co Coatings Processed by HVOF Thermal Spraying
Authors: Poblano-Salas C. A. , Cabral-Miramontes J. A. , Espinoza-Beltrán F. , Botello-De Jesús R.
Published: November 2022

The present investigation shows the fabrication procedure of bimodal WC-VC-Co coatings processed by the HVOF thermal spray process. The effects of nanostructured phase contents on the microstructure and wear resistance of the coatings are included. Special attention is drawn to the mapping of elastic properties within the cobalt matrix, which were measured by nanoindentation. Finally, the influence of VC additions on the size, morphology and stability of the WC phase is also discussed.
Mechanical Property of Multi-Pass Cold Sprayed Aluminium Alloy Coatings for Repair Application
Authors: Rech S. , Trentin A. , Vezzù S. , Legoux J.-G. , Irissou E.
Published: November 2022

The cold spray, for its peculiarity, is becoming increasingly in the reconstruction or repair of damage aluminium alloy components, especially in the aviation industry. Both thin (<0.5mm) and thick (up to centimeters) coatings are necessary in order to achieve dimensional recovery of the components. Contrary to thin, thick coatings can be deposited in single-pass or in multi-pass giving different thermal and stress contribution to the components and coatings itself. The thermal input, the amount and the type of residual stresses (compressive or tensile) confer appreciable or depreciable characteristics to the coatings adhesion, the crack propagation and the coating mechanical property. In this study two sets, single and multi-pass aluminium alloy coatings of different thickness are deposited into Al6061 substrate. The metallographic analysis by electronic and optical microscopes, the four-point bending test and the Vickers microhardness are performed; also the multi-pass coatings were characterized by fractographic analysis. Finally the different coating adhesions to substrate and cohesions are compared by standard ASTM C633 adhesion and cohesion tests.
Milling and Cryo-Milling Affecting MCrAlY High Temperature Oxidation Mechanism
Authors: Giolli C. , Giorgetti A. , Scrivani A. , Bonferroni B. , Bolelli G. , Bozza F. , Lusvarghi L. , Fossati A. , DiFerdinando M. , Kim G. E.
Published: November 2022

This research aims to investigate the effects of employing cryo-milled and milled MCrAlY feedstock powders on the oxidation behaviour of low-pressure plasma sprayed (LPPS) and HVOF-sprayed coatings deposited onto a Ni-based superalloy substrate. Commercially-available powders with three different chemical compositions were selected and sprayed both in standard condition and after milling and cryo-milling processes. The LPPS and HVOF coatings, deposited onto an Inconel substrate, were diffusion-treated at 1080 °C (according to the industrial standard) and subjected to isothermal and cyclic oxidation tests. The outcomes of these tests show that transient oxidation is suppressed in the coatings obtained from milled MCrAlY systems, whose overall resistance to cyclic oxidation (number of cycles to failure) is approximately two times greater than that of standard coatings. This difference is not related to the nanostructural features induced on the powder particles by the milling process, because, after the diffusion treatment, all coatings exhibit identical γ-β two-phase microstructure, with no trace of the original nanostructure. The improvement is ascribed to the fine dispersion of nanometric Al2O3 grains within the milled powder particles: in the sprayed coatings, these nanometric oxides act as nuclei and favour the direct formation of an Al2O3 oxide scale.
Effect of Nitrogen Flow Rate on Mechanical Properties of Metallic Coatings by Warm Spray Deposition
Authors: Watanabe M. , Brauns C. , Komatsu M. , Kuroda S. , Katanoda H. , Gärtner F. , Klassen T.
Published: November 2022

In Warm Spraying (WS), the temperature of the combustion flame is reduced and controlled by injecting nitrogen gas into the combustion flame before the injection of spray powders. Thus, temperatures of spray particles are kept under their melting points with moderately heated and thermally softened states. As compared to HVOF-spraying, the oxidation of particles can be significantly suppressed due to lower deposition temperatures, whereas, as compared to cold spraying, the degree of particle deformation upon impact can be enhanced by attaining higher particle temperatures. In the present study, Ti, Cu, and Al coatings were fabricated by WS under various nitrogen flow rates. The mechanical properties of the coatings were evaluated by tubular coating tensile (TCT) and micro flat tensile (MFT) tests. For the lower impact temperature regime, the coatings became denser and the ultimate strengths of Ti or Cu coatings increased reaching a maximum by decreasing the nitrogen flow rates. A further decrease of nitrogen flow rates and reaching the upper temperature regime reduced the coating strength. These results clearly demonstrate how particle temperatures affect the microstructures and mechanical properties of WS coatings and that optimum spray conditions have to be balanced between softening and oxidation by adjusting particle temperatures.
Portable High Pressure Cold Sprayed Aluminum Alloy Coatings
Authors: Karthikeyan J. , Kay C. M. , Rininger M. W. , Brown E. C. , Steele M. S. , Porter J. , Eden T. J.
Published: November 2022

Superior characteristics of the cold sprayed coating have led to many high-tech applications. Until recently, all these applications were carried out using ‘stationary’ systems only, while some applications such as in-situ repair of aircraft body/engine parts require a portable system. Recently a ‘Portable High Pressure Cold Spray System’ called KINETIKS 2000-2 has been developed. This system is capable of 400 C/20 bars nitrogen/helium jet, and produces dense coatings with clean interfaces of many materials. In order to establish the suitability of this process for producing aluminum alloy coatings for aerospace and other high tech industries, various aluminum alloys (CP-Al, HP-Al, 6061 Al, 7005 Al) coatings were produced over many substrate materials (2024 Al, 7005 Al, 4041 Steel, ZE41A Mg). Coatings were characterized using microstructure, bond strength, bend test, corrosion studies, etc. Microstructural study showed that dense coatings with about 2-4% porosity values were produced with clean and well bonded interfaces. Bond strength of these coatings varied between 20 to 35 MPa, Bend test results showed that the coatings have adequate strengths and could withstand severe strain conditions. Salt fog corrosion studies (ASTM B 117) showed that the coatings impart corrosion resistance to the substrates.
Structural and Mechanical Properties Analysis of Si/Mullite/BSAS Environmental Barrier Coatings Exposed to Thermal Cycling in Water Vapour Environment
Authors: Cojocaru C. V. , Levesque D. , Moreau C. , Lima R. S.
Published: November 2022

The ongoing development of environmental barrier coatings (EBCs) offers the prospect to implement the full potential of silicon-based ceramics for high temperature structural applications. The current state-of-the-art EBC system comprises a Si bond coat, a mullite (3Al2O3·2SiO2) interlayer and a (1-x)BaO·xSrO·Al2O3·2SiO2, 0 ≤ x ≤ 1 (BSAS) crack-resistant and water vapour attack resistant top coat. In this study, the influence of water vapour corrosion on the structural and mechanical properties of plasma-sprayed Si/Mullite/BSAS architectures was assessed by furnace thermal cycle testing (e.g., 100 cycles, 2h/cycle at 1300°C). Commercially available mullite and BSAS powders were used to produce crystalline coatings by air plasma spraying. Fully crystalline mullite and celsian BSAS coatings were engineered under controlled conditions on silicon coated, sintered α-SiC Hexoloy substrates. The overall performance at high-temperature of these functionally graded EBCs is discussed and correlated to their microstructural characteristics.
Nano Modified NiCrAlY Coatings for Bond Coat for Gas Turbine Blades
Authors: Sahu S. , Khanna A. S.
Published: November 2022

Oxidation behavior of NiCrAlY powder, blended with nano and micro sized Al2O3 and Y2O3 was studied to understand the effect of nano/micro oxide powder dispersion. The blended powders were applied on the IN 718 substrates by HVOF technique. The present work compares the oxidation behavior of IN 718 superalloy, coated with NiCrAlY powders, dispersed with nano and micro Y2O3, Al2O3 oxide. Coated samples were characterized by XRD, SEM/EDAX in terms of surface composition, scale cross section and the identification of different phases. The oxidation tests were carried out at 1223K, 1323K, 1423K in air. Oxidation kinetics infer that at 1223 K and 1323 K, nano yittria addition, in fact, resulted in higher oxidation rate, while nano alumina addition resulted in lower oxidation rate. The effect was more pronounced at 1423 K, where the nano and micro size alumina, yttria addition, resulted in bringing down the oxidation rate considerably.
Deposition Behavior and Adhesion Strength of Cold-Sprayed TiO2 Particles
Authors: Yamada M. , Dickinson M. E. , Shima K. , Tjitra Salim N. , Nakano H. , Fukumoto M.
Published: November 2022

Cold-spraying has been developed as a high-quality metallic coating process. Recently, it became possible to fabricate a brittle ceramic coating using a particular nano-structured powder. In order to improve and control the process, the bonding mechanism should be understood. In this study, the bonding mechanism between cold-sprayed TiO2 particle and stainless steel substrate was investigated by cross-section observation and quantitative adhesion strength measurement for the individual particles. The adhesion strength was measured by the combination using of scanning probe microscope (SPM) imaging and nano scratch test. The result clearly revealed a correlation in adhesion strength with splat diameter. The smaller splat diameter exhibited higher adhesion strength, though it is generally difficult to penetrate the cold-sprayed small particles through a shock wave formed in front of the substrate. The cross-section microstructure of the splats prepared by focused ion beam (FIB) showed the particular deposition behavior of the TiO2 particle. The collided particle didn’t deform the substrate surface and deformed the particle itself. The bottom center of the splat is densified by the deformation and the other parts maintain the porous structure or broke up. Hence the higher adhesion strength of smaller splat was caused by this typical TiO2 deposition behavior.
Abnormal Intermetallic Compound Formation of Cold Sprayed Cu-Sn Coatings
Authors: Ko K. H. , Choi J. O. , Lee H.
Published: November 2022

Cu-Sn composites coatings by cold spray with wide ranges of particle size and shape (round to flake) were investigated regarding their intermetallic compound (IMC) formation. It was found when certain size and shape combination of Cu-Sn composite raw materials were employed, the embedded Cu-Sn IMCs such as Cu6Sn5 and Cu3Sn were observed even in as-sprayed states without additional heat treatments. These results implied that the impact energy of colliding particles of the cold spraying could be enough to activate IMC compounding process. It seems that this can be also true in several composite systems that have relatively low activation energy of IMC compounding. After post annealing, the Cu6Sn5 formed in as-coated state were transformed into the Cu3Sn phase and the residue of unreacted Sn particles were fully changed into the Cu3Sn phase (Cu6Sn5 →Cu3Sn). These conversion processes also depended strongly on the choices of the shape and size combinations of Cu and Sn particles.
B4C-Ni Composite Coatings Prepared by Cold Spray of Blended or CVD-Coated Powders
Authors: Feng C. , Guipont V. , Jeandin M. , Amsellem O. , Pauchet F. , Saenger R. , Bucher S. , Iacob C.
Published: November 2022

In the oil industry, logging systems involving geological sensors are designed to operate under increasing severe service conditions of deep and horizontal boreholes. Under these conditions, metal matrix composites (MMCs) with ceramic reinforcement are applied on components to achieve wear and corrosion resistant systems. The ‘cold spray’ could be described as a cold and inert process to form coating layers through severe plastic deformation of a ductile metal. Ceramic/metal MMC coating could be achieved by co-deposition of a ceramic with a ductile material. In this work, it was it was investigated the use of MMC B4C-Ni coating from both mechanically milled blends or B4CNi CVD coated batches. Powder blends involving Ni powder with fine or coarse B4C powders were prepared by mechanical milling. Three CVD coated B4C-Ni powder batches were synthesized with 30, 40 and 50 Ni wt% respectively. Cold spray coatings were achieved with 1 pass and 5 passes to investigate the building-up mechanisms and interfaces with AISI316L. Powders and cold sprayed coatings microstructures were observed by optical and scanning electron microscopies and further quantitative image analysis were carried out to determine the content of B4C embedded in the Ni matrix of B4C-Ni cold spray coatings. The highest B4C vol.%, up to 45%, could be reached in the case of B4C-Ni coated powder. Micro-hardness values of such MMC coatings were also determined through Vickers micro-indentation. The beneficial role of the Ni surrounding layer on coating formation is discussed in relation to the unique features of the microstructures obtained by cold spray of B4C-Ni coated powders.
What are the Benefits of an Association Such as GTS for a Thermal Spray Company?
Authors: Krömmer W. , Heinrich P.
Published: November 2022

GTS is now almost 20 years old and has nearly 200 members from all thermal spray sectors. In this time, a great deal has been accomplished and GTS members are already using those tools GTS has made available to them and which are important for them. Here, the original idea of enhancing the quality of our technology and maintaining it at a high level continues to be an essential building block. In addition, many areas have been accessed in which an association can make more effective progress than each company on its own. With respect to issues such as further education and training, safety, environment, REACH and the compilation of guidelines, to name but a few, this idea has been successfully applied. The work of many in our organization has yielded many fruits and continues to make a difference. However, the benefits for each of us only become visible if we all actively work together. What is central to all the advantages which GTS offers is the candid discussion among its members and the opportunity for each member to quickly find his place in the group and to put these benefits to good use. The fundamental idea which GTS represents has therefore not changed in all this time: a high quality standard, cooperation, education and training, public relations all combined within the association’s guidelines and many working papers which are available to its members.
Ultra-Small Angle X-Ray Scattering (USAXS) in-situ Quantification of Void Network Evolution During Annealing of Nanometer-Sized YSZ Plasma-Sprayed Coatings
Authors: Montavon G. , Ilavsky J. , Denoirjean A. , Fauchais P. , Bacciochini A. , Wittmann-Teneze K.
Published: November 2022

Suspension plasma spraying (SPS) is able to process a stabilized suspension of nanometer-sized feedstock particles to form thin (from 20 to 100 µm) coatings with unique microstructures. The void network architecture of these ceramic coatings is a challenge to be characterized and quantified using commonly used techniques due to small sizes involved. Nevertheless, the discrimination of these pore architectures in terms of size and shape distribution, anisotropy, specific surface area, etc., is critical for the understanding of processing, microstructure, and properties relationships. USAXS (Ultra-Small Angle X-Rays Scattering) appeared as a suitable measurement technique allowing discriminating the void size distribution over a large range (up to four orders of magnitude). Results indicate that as-sprayed SPS coatings exhibit unusual porous architecture: 1) average void size is about the same than the feedstock one; i.e., nanometer sizes with multimodal void size distribution; 2) about 80% of the voids exhibit characteristic dimensions smaller than 30 nm; 3) the total void content varies between 13 to 20% depending upon considered operating parameters. In-situ annealing measurements were performed as they proved to deliver more relevant results compared to ex-situ measurements: even at temperatures as low as 800°C, the microstructure transforms - while the total void content does not change significantly. Indeed, it has been demonstrated that the smallest voids (equivalent diameters smaller than 50 nm) coalescence was the predominant mechanism and that it was more sensitive to temperature than time.
Localized Zinc Coatings on Automotive Steel Sheets by Cold Spray Technology
Authors: Ducos M. , Gay B. , Verbiest P. , Verschave Ch. , Hoel H. , Vanden Eynde X.
Published: November 2022

Zn coatings have been applied on steel substrates used by Renault for the manufacturing of car bodies. We had the task to make these on-line thin coatings on smooth and non de-oiled surfaces with a translation speed of 1 m/s. Furthermore, in certain cases, these coatings were situated on a visible surface of the car body and on a precise position. The coating process must be adapted to the clean conditions of the current automotive industry. The development of this application has been focused mainly on the study of a new zinc powder grade as well as on the projection procedure which had to adapt to the constraints and to the productivity of an automotive manufacturing line. Cold Spray addresses all these requirements. Positive results obtained on the mechanical examinations, the accelerated corrosion tests and chippings tests demonstrate that such new coatings meet the specifications of the customer for this kind of processes.
Sliding Wear Behavior of HVOF Sprayed Metal Matrix Carbides
Authors: Altuncu E. , Ustel F. , Turk A. , Uzun A.
Published: November 2022

WC-CoCr coatings are deposited by HVOF process for improving surface resistance of low alloyed steels. In this study we examined the wear characteristics of WC-CoCr coatings on low alloyed steel substrate under different test conditions, using a sliding wear test unit with abrasive ball. In experimental studies discussed the effects of test load, temperature, work medium and sliding distance on the wear characteristics of coatings. Weight loss, wear track depth and width were observed . It was found that the weight loss of coatings increased in dry medium conditions. Wear weight loss was significantly reduced in lubricated condition due to decreasing friction. The wear track surface profile changed with lubrication and increasing temperature in test conditions. Under the base oil lubricated conditions the WC-CoCr coating performed well.
Analysis of Ni-Al Coatings In-situ Processed by Plasma Transferred Arc
Authors: Brunetti C. , Mendes F. H. , Pintaude G. , D’Oliveira A. S. C. M.
Published: November 2022

Ni-Al intermetallic alloys are known for exhibiting superior high temperature properties. Processes such as thermal spray, combustion synthesis, physical vapor deposition and laser have been used to produce these coatings. However, the deposition of these alloys by means of plasma transferred arc (PTA) has not been widely studied. This study evaluated Ni-Al coatings processed in-situ by PTA. Coatings were processed with Ni and Al elemental powders (65%atNi-35%atAl) onto an AISI 1020 steel substrate. Different current intensities were used (70 to 120 A) to produce different dilution levels and thus different Fe contents in the coatings. The stand torch off was 10.0 mm. The plasma gas, shield gas and powder carrier gas flows were 2.0, 15.0 and 1.0 l.min-1, respectively. The powder feed rate was 5.8 g.min-1 and a travel speed of 100 mm. min-1 was used. The coatings were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, optical microscopy and instrument indentation tests. The development of Ni aluminides was confirmed by X-ray diffraction for all current intensities. It was verified that the microstructure, hardness and the elastic modulus were influenced by current intensity and by the Fe content in the coatings.
Thermal Barrier Coatings on Surfaces with Micro-Machined Roughness Profiles
Authors: Seiler P. , Bäker M. , Rösler J. , Schweda M. , Beck T.
Published: November 2022

Thermal barrier coating systems are used to enhance the temperature resistance of hot section components in gas turbines. The coatings protect the underlying nickel based components and consist of the bond coat (BC) the thermal barrier coating (TBC) and a thermally grown oxide (TGO) between the BC and TBC. The coating systems fail in service at or near the TBC/TGO interface. To study the failure mechanisms a simplified coating system is introduced which consists of a MCrAlY bond-coat material as the substrate, a TGO, and a yttria-stabilised zirconia TBC as a topcoat. The TBC is applied by atmospheric plasma spraying on top of specimens with defined roughness profiles, manufactured by a micromachining process. The main advantage of micro-machining is a defined interfacial roughness between the TBC and the BC in contrast to sandblasted specimens. Furthermore, a FEM simulation of the coating system was developed which approximates the interface by sinusoidal functions. This simplified model system and additional FEM calculations show the influence of varying the interfacial roughness between the BC and the TBC.
Effect of Hardness in Blasted Substrate Surface on Adhesive Strength of Sprayed Coatings
Authors: Maruyama T. , Kishita T. , Kobayashi T.
Published: November 2022

The effect of the hardness in the substrate surface blasted by a grit blasting process on the adhesive strength of Zn-Al sprayed coatings is investigated to find the adhesive strength is improved by work hardening of the substrate surface. The adhesive strength between a substrate of a carbon steel and sprayed coatings of Zn-Al alloy sprayed by a wire flame spraying process is measured. The substrate is roughened by the grit blasting process with white alumina girt in various blasting angles and blasting time. The hardness is measured in around 20 micro-meter depth from the substrate surface. The adhesive strength increases with increasing the hardness even if the surface roughness is almost same. There is the definite correlation between the adhesive strength and the hardness rather than the surface roughness.
Net Energy Return (EROEI) of Thermal Barrier Coatings in Turbine Engines
Authors: Bardi U. , Borri C. , Giolli C. , Giorgetti A. , Meneghetti S. , Nocivelli J. , Scrivani A.
Published: November 2022

Thermal barrier coatings (TBC) are normally based on yttria partially stabilised zirconia (YPSZ) coatings and are commonly used coatings in the high temperature, combustion region of gas turbines. TBC permit to increase the temperature of combustion, increasing the thermodynamic efficiency of the engine. Therefore, an engine equipped with TBC can produce a larger amount of energy over its lifetime. This increase in produced energy can be compared with the energy needed for the manufacturing and installation of TBC. The comparison can be performed in terms of the “energy return” (or “energy returned for energy invested”, EROI or EROEI). The qualitative analysis performed in the present study indicates that this return is large in comparison to that of other energy producing systems.
Impact of Particle Size Distribution on the TBC Coating Deposition and Performance
Authors: Li L. , Belov V.
Published: November 2022

Thermal barrier coatings (TBCs) functioning in the aviation and power generation industries have heavily relied on plasma sprayed yttria stabilized zirconia (YSZ) on MCrAlY bond coated engine components. Among those factors which may impact the repeatability and reliability of a TBC coating, powder feedstock is one of the most important while being the challenging to control constituents as it is difficult to keep the powder chemistry, morphology and size distribution exact the same from lot to lot, year after year. In this study the authors systematically vary the size distribution of one type of commercial YSZ powder to explore the effect of the size distribution on the TBC deposition and the coating performance. Deposition rate and efficiency are quantitatively compared for those experimental powders. The coating microstructures and performances for different sizing are also evaluated analytically. Understanding the impact of the powder variation on the coating deposition and performance is essential to determine the quality control standards.
Phase Stability and Thermal Conductivity of Plasma Sprayed Scandia, Yttria-Stabilized Zirconia TBCs
Authors: Li Q. , Gong S. , Liu H. , Yang W. , Li S.
Published: November 2022

Zirconia stabilized with a combination of scandia and yttria (ScYSZ) powder for plasma spraying was synthesized by chemical coprecipitation process in the experiment, and the ScYSZ powder contains 7.0mol% scandia and 1.5mol% yttria. The microstructure, phase stability and thermal conductivity of plasma sprayed ScYSZ thermal barrier coatings (TBCs) were investigated. The results revealed that the ScYSZ TBCs had excellent stability to retain single metastable tetragonal t′phase even after high temperature (1500 °C) exposure for 300 hours and did not undergo a tetragonal-to-monoclinic phase transition upon cooling. Furthermore, the ScYSZ TBCs had lower thermal conductivity than 3.5-4.5mol% yttria-stabilized zirconia TBCs currently used in gas turbine engine industry. ScYSZ TBCs could be developed as a novel TBCs for advanced gas turbine engines.
Plasma Sprayed Zirconium Thermal Diffusion Behavior
Authors: Hollis K. J.
Published: November 2022

Zirconium (Zr) metal is of interest for chemical corrosion protection and nuclear reactor core applications. Inert chamber plasma spraying has been used to produce thin Zr coatings on stainless steel (SS) substrates. The coatings were deposited while using transferred arc (TA) cleaning/heating at 5 different current levels. In order to better understand thermal diffusion governed processes, the coating porosity, grain size and interdiffusion with the substrate were measured as a function of TA current. Low porosity (3.5% to < 0.5%), recrystallization with fine equiaxed grain size (3-8 µm diameter) and varying elemental diffusion distance (0-50 µm) from the coating substrate interface were observed. In addition, the coatings were low in oxygen content compared to the wrought SS substrates. The Zr coatings sprayed under these conditions look promising for highly demanding applications.
Deposition of Surface-Melted YSZ Particles by Flame Spraying
Authors: Li C.-J. , Wang X.-M. , Li C.-X. , Yang G.-J.
Published: November 2022

It is usually difficult to deposit effectively spray particles with a much limited melting in thermal spraying. In the present study, flame spraying was employed to produce yttria-stabilized zirconia (YSZ) particles at a limited melting. The melting degree of YSZ particles was controlled by flame combustion intensity and flying distance of spray particles within gas flame. The velocity of spray particles was quantitatively measured. The effects of spray distance and acetylene flow rate on the particle velocity, and deposition behavior were examined. The surface morphology of deposited particles was characterized by scanning electron microscopy. The bonding between deposited YSZ particles and YSZ substrate was examined from cross section. The spray particles in different melting states were obtained by changing flame spray parameters. The deposition experiment revealed that the YSZ particles at different melting states from only surface layer melted state, semi-melted state to substantially melted state can be successfully deposited on YSZ substrate by controlling substrate temperature. As a result, YSZ surfaces with different morphologies of particles from a near spherical shape, hat-on-frustum shape and hat-shape with different neck sizes, to a pancake shape and well spread disk shape have been created.
Influence of HVOF Spraying Parameters on the Wear Resistance of Al-SiC Composites Coatings Deposited on ZE41A Magnesium Alloy
Authors: López A. J. , Rams J. , Torres B. , Rodrigo P. , Campo M.
Published: November 2022

High velocity oxygen fuel has been used as fabrication technique for manufacturing aluminium coatings reinforced with different weight percents of silicon carbide particles on Mg-Zn alloys used as substrates. The aim of the investigation is to improve the tribological performance of the ZE41A magnesium alloy. The parameters of the thermal projection system have been optimized in order to maximize the SiC particles incorporation in the aluminium matrix of the coating. Pin-on-disc tests were developed to characterize the tribological behavior of the different specimens. Minor degradation of the magnesium alloy was achieved after . Composite coatings with thicknesses of about 120 µm, reinforced with about 10 wt.% and with high adhesion to the substrate were achieved. After the coating parameters were optimized, the wear rate of the magnesium with the composite coatings decreased by two orders of magnitude in comparison to that of the uncoated magnesium alloy.
Investigation of In-Flight Particle Characteristics of HVOF Sprayed MCrAlY Coatings
Authors: Saechua W. , Zhang D. , Voisey K. T. , McCartney D. G.
Published: November 2022

The MCrAlY type coatings provide oxidation protection and good adhesion between the ceramic topcoat and the substrate. The high velocity oxy fuel (HVOF) process is currently being introduced to make the bond coats instead of conventional low pressure plasma spraying due to lower cost. In this research, the METJET-III HVOF liquid fuel system was used to produce MCrAlY coatings and the Tecnar DPV2000 was used to investigate in-flight particle temperature, velocity and diameter. To examine the coating-build, the wipe test was used to reveal the particle deformation on the substrate with different spraying parameters and correlated impact behaviour with particle properties. It was found that increasing of total fuel plus oxygen flow rate, percent stoichiometry and stand-off distances did not dramatically change the particle temperature. Increasing of percent stoichiometry and stand off distance led to reduction in particle velocity while increasing of the total fuel plus oxygen flow rate led to increase in the particle velocity. The average particle velocity below 640 m/s seems to make less splat formation than the average particle velocity above 750 m/s. Compiling results of the coating microstructure, the splat formation and the in-flight particle measurements revealed the effect of spraying parameters on the coating characteristics.
Effect of Substrate Roughness on Splat Formation of a Thermally Sprayed Polymer Coating
Authors: Alamara K. , Saber-Samandari S. , Berndt C. C.
Published: November 2022

Polypropylene (PP) was flame sprayed onto rough mild steel substrates at room temperature (RT) that was preheated at 70 °C, 120 °C, and 170 °C. Single solidified droplets (splats) were collected and analysed to understand how processing variables influenced the thermal spray coating characteristics. The splat morphology was characterized in detail using optical and scanning electron microscopy (SEM). The splats exhibited a disk-like shape with a large central viscous core and a fully melted wide rim with a thin edge. The splat size increased with increasing substrate temperature. A unique flat microstructure was observed on the surface of the splat deposited onto the RT substrate, whereas a flowing pattern appeared on the splat surfaces deposited onto the preheated substrates and the pattern increased by increasing the substrate temperature. The results of this study revealed improved splat-substrate adhesion by heating the substrate from RT to 170 °C. On the basis of the result, the influence of substrate parameters on splat morphologies was employed to establish a relationship between the microstructural characteristics and processing variables of flame sprayed polymeric coatings.
The Influence of CMAS Attack on the Lifetime of Thermal Barrier Coatings
Authors: Steinke T. , Jarligo M. O. , Mack D. E. , Vaßen R. , Stöver D.
Published: November 2022

Oxide compounds basically composed of calcium, magnesium, aluminum and silicon cations also known as CMAS, can be deposited on the surface of thermal barrier coatings (TBC) of gas turbine blades. Under certain operation conditions these compounds have been found to aggressively degrade the TBC, hence affecting the thermo-mechanical properties of the underlying component. Detailed investigation on the interaction of CMAS and the atmospheric plasma sprayed (APS) yttria-stabilized zirconia (YSZ) TBC was performed in a burner rig test facility under thermal gradient cycling conditions and at the same time CMAS deposition. This novel and unique test approach promises a coating screening and characterization test under service conditions. Variable exposure times at approximately 1250°C/1050°C surface/substrate temperatures were applied. The lifetime of the TBC was indicated by the number of thermal cycles until significant spallation occurred. X-ray spectroscopy and microstructural analyses were conducted on the cycled samples to determine the effect of thermo-chemical interactions. It was found that with extended heating period of 10 times the standard cycle, the number of sustainable load alternations heating/cooling was reduced. Interaction of CMAS and YSZ induces formation of glassy soda-silicate phase. Thermal cycling of thermo-physically mismatched TBC and glass melt causes crack formation and coating failure.
Microstructural Investigation of Thermally Sprayed Ceramic Coatings by Laser Acoustic Surface Waves
Authors: Barbosa M. , Schneider D. , Puschmann R. , Toma F.-L. , Berger L.-M.
Published: November 2022

Young’s modulus is not only one of the important mechanical properties of thermally sprayed coatings but also a sensitive indicator of the coating’s microstructural defects. The ceramic coatings studied in this work were based on Al2O3, TiO2 and Cr2O3 and prepared by APS (Atmospheric Plasma Spraying), HVOF (High Velocity Oxy Fuel spraying) and suspension-HVOF spraying. The Young’s modulus was systematically studied by laser acoustic surface waves, which is a non-destructive, fast and reliable technique, using two different devices: a tabletop tester for samples and small components (LAwave) and a hand-held portable device. For oxide coatings, it was observed that the results distinctly vary depending on the spray technology. A comparison with the values derived from the instrumented indentation test shows that for most investigated ceramic coatings lower values were measured by laser acoustics. This is due to the influence of the pores and defects in the coatings. The LAwave results are expected to be close to the effective modulus of the material, due to the larger material volume evaluated during the test, which takes the coating defects into consideration.
Modeling Properties of HVOF Thermally Sprayed WC-Co Coatings Based on Particle-in-Flight Characteristics
Authors: Tillmann W. , Hussong B. , Kuhnt S. , Rudak N. , Weinert H.
Published: November 2022

Numerous factors, such as the spray parameters and non-predictable conditions, during the spraying process influence the properties of thermally sprayed coatings. However, the condition of the particles at the moment of impact on the substrate is the most crucial factor for the morphology and the mechanical properties of a coating. Thus, nowadays particle analyzing systems are employed in order to explain the relation between the process parameters and the properties of a layer. Yet, modeling of thermal spray processes is conducted disregarding particle parameters and only correlating process parameters with layer properties. This article presents a new approach on process modeling, for relating spray parameters to particle-inflight conditions. The modeling of the particle properties in relation to the process parameters shall allow conducting targeted adjustments during the running process, to optimize particle properties. This method will enable to influence coating properties during the spraying process, eliminating the influence of unpredictable environmental or process-related disturbances. In a series of experiments, spray beam properties were measured in an HVOF thermal spray process with agglomerated and sintered WC-Co powder. Spray parameters were correlated to the particle-in-flight conditions, which were measured by utilizing two particle analyzing systems.
Injection Optimization of Composite Powders using Laser Based Particle Visualization
Authors: Crawford D. , Gansert R. , Wright D.
Published: November 2022

Laser Based Particle Visualization instruments such as SprayCam provide a unique picture into the radial injection of powders in APS processes. Traditional injection optimization methods utilizing these instruments involve optimization of particle temperature and velocity while measuring the particle plume position in the plasma. The goal of these optimization techniques is to ensure maximum energy transfer to materials with a high melting point and a low thermal conductivity, such as is typical for materials applied as thermal barrier coatings. Conversely, optimizing energy transfer of composite powders with a low melting point and a high thermal conductivity, such as Al-8Si-20BN, has very little effect, thus it is difficult to optimize the injection process of this material in the traditional fashion. In addition, these materials have a tendency to bounce off the plasma rather than penetrate it due to their low inertia, resulting in low deposition efficiencies. A new method of injection optimization of these powders is proposed utilizing Laser Based Particle Visualization Techniques to view the injection from above in order to maximize powder injection into the plasma. A real-time examination of particle plume width inside the plasma will be conducted, varying an array of torch conditions while deposition efficiency is monitored.
WC-Co/Metal Multi-Layer Coatings by Warm Spray Deposition
Authors: Watanabe M. , Komatsu M. , Kuroda S.
Published: November 2022

WC-Co/copper coatings with 8 layers were fabricated by warm spray deposition in order to investigate the effect of ductile layer inclusion on their fracture behavior. Bending strength, work of fracture, and surface hardness of freestanding coatings were examined by three point bending tests after removal of the substrates. The multilayered samples showed nonlinear stress-strain curves due to cracks in the WC-Co layers and plastic elongation of the copper layers. The multilayered samples with lower volume fraction of copper showed even lower bending strength than the monolithic samples of WC-Co and copper and no beneficial feature in mechanical performance was found. On the other hand, the samples containing higher volume fraction of copper exhibited more than twice higher work of fracture and moderately better bending strength than the monolithic WC-Co coatings, while the surface hardness was almost identical among all samples instead of the monolithic copper. The ductility of copper layers and the plastic constraint by the intact WC-Co layers attributed to enhance their mechanical properties. It has been concluded that cermet/metal laminate coatings can be one alternative approach to further improvement of the mechanical properties of thermal sprayed cermet coatings.
Tribological Properties of HVOF Sprayed Nanostructured Composite Coatings
Authors: Żórawski W. , Burakowski T. , Skrzypek S.
Published: November 2022

Nanostructured materials are of particular scientific interest because of their physical and mechanical properties, which are superior to those of conventional materials. They are more widely used in various industrial applications mainly due to decreasing production costs. The work is concerned with a study of the tribological properties of a HVOF sprayed composite of nanostructured WC12Co mixed with nanostructured Fe3O4, having the properties of solid lubricant. The coatings were sprayed by means of a Hybrid Diamond Jet system. A T-01 ball on disc tribological tester was used to study their resistance to wear and determine the coefficient of friction on the basis of friction force obtained in the course of continuous measurement at a set load. Result of investigations were compared with properties of coatings sprayed with standard WC12Co/ Fe3O4. The microstructures and compositions of the nanostructured powders and coatings were analyzed by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray analysis. Their phase composition was studied using a Bruker D8 Advance diffractometer.