bluuebunny/crossref_metadata_2025 huggingface dataset:
Effective Parameters in Axial Injection Suspension Plasma Spray Process of Alumina Zirconia Ceramics
Authors: Tarasi F. , Medraj M. , Dolatabadi A. , Oberste Berghaus J. , Moreau C.
Published: September 2022

Suspension Plasma Spray (SPS) is a novel process for producing nano-structured coatings with metastable phases using extra small particles as compared to conventional thermal spraying. Suspension spraying involves, atomization, solvent evaporation and melts consolidation, which can cause substantial complexity in the system. Using feedstock mixtures for composite coatings, such as alumina and zirconia, intricacy of the system increases even more. There is consequently a need to better understand the relationship between plasma spray conditions and resulting coating microstructure and defects. In this study, an alumina/ 8 wt% yttria stabilized zirconia was deposited by axial injection SPS process. The effects of principal deposition parameters on the microstructural features are evaluated by using Taguchi design of experiment (DOE). The microstructural features include microcracks, porosities and deposition rate. To better understand the role of the spray parameters, in-flight particle characteristics, i.e. temperature and velocity were also measured. The role of the porosity in this multi-component structure is studied as well. The results indicate that thermal diffusivity of the coatings, an important property for potential thermal barrier applications, is barely affected by the changes in porosity.
Contamination Free Interface for Thermal Spray Deposition of MCrAlY Coatings through a New Surface Preparation Named Exclean
Authors: Russo D. , Scrivani A. , Rizzi G. , Lanzi A. , Giolli C.
Published: September 2022

The most commonly used structural materials for blades and other high temperature components of gas turbines are nickel base superalloys. A TBC protection coating system consists of a top coat of yttria partially stabilized zirconia and an underlying bond coat, usually MCrAlY (where M stands for Ni, Co or a combination of both). MCrAlY is normally deposited by the thermal spray processes: air plasma spray (APS), vacuum plasma spray (VPS/LPPS) or high velocity oxygen fuel (HVOF). The adhesion between the bond coat and the substrate, and therefore of the whole thermal barrier system, strongly depends upon the surface roughness. A high level of roughness generally denotes better adhesion, especially with the HVOF thermal spray process, where it is a necessity. Generally the roughness is reached by means of grit blasting with an abrasive media; this results in a certain level of surface contamination due to the entrapment of abrasive particles. The aim of this work was to set up a new surface preparation process in order to obtain a completely clean surface with a suitable roughness, which can be coated afterwards with HVOF or VPS/LPPS thermal spray technology. The tests carried out by this process on turbine blades, coated with a HVOF system, led to obtaining a coating/base material interface without any contamination caused by the surface preparation.
Comparation of Performance of Twea Sprayed Zinc and Zinc/Aluminium 85/15 Coatings for Ductile Iron Pipe Protection Against Corrosion
Authors: Gulec A. , Turk A. , Cevher O. , Ustel F. , Yilmaz F.
Published: September 2022

Ductile iron pipes (DIP) have been used worldwide since 1960s for water transmission and distribution mains. By 1979, ductile iron pipe largely replaced cast iron as the predominant material in water industry. Zn and Zn/Al 85/15 coatings applied by thermal spray technique are used for the protection of the ductile iron pipe against corrosion in heterogeneous soil conditions. In this study, heat treated and non-heat treated ductile iron pipe samples were coated with Zn and Zn/Al 85/15 in optimum spray parameters by twin wire electric arc (TWEA) spraying technique. The coatings were investigated by optical microscopy, scanning electron microscopy (SEM), and analyzed by energy dispersive spectrometer (EDS). Both Zn and Zn/Al 85/15 coatings showed fairly good lamellar structure with acceptable amount of internal porosities and oxides. Annealing oxides available on pipe surface helped the bonding of coatings. The protection performance of the coatings was compared with accelerated corrosion (salt spray) test according to the ASTM B 117 and corrosion products were analyzed by SEM and EDS technique. Salt spray test results showed that Zn/Al 85/15 coatings have better corrosion resistance than Zn coatings and annealing oxide on ductile iron pipe acts as a good corrosion resistant protective layer.
Corrosion Protection of Municipal Solid Waste Incinerator Superheaters by HVOF Thermal Spray Coatings
Authors: Guilemany J.M. , Torrell M. , Dosta S. , Miguel J.R.
Published: September 2022

Corrosion is a very important problem in the Municipal Solid Waste Incinerator (MSWI) superheaters. This problem causes the plant stops and tube replacements, promoting the loss of energy generation rate. The main corrosion agent is the chlorine deposits. HVOF coatings have been sprayed to improve corrosion resistance of the superheaters inside the MSWI boilers. Inconel 625 and Hastelloy C22 alloys have been sprayed as a powder feedstock material. The spray process has been analyzed by a Spray Watch system that allows carrying out the temperature and velocity measurements of the particles in flight in order to optimize the spraying process. The produced coatings have been characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) to evaluate the porosity and oxidation produced in the spray process. Laboratory oxidation test have revealed the formation of Cr2O3, NiO and Fe2O3 as corrosion products as well as Microanalysis by Energy dispersion Spectroscopy (EDS) composition profiles have been used to evaluate the penetration of the corrosion front inside the coating. The Nickel alloys show a good resistance in aggressive environment test and can be a good solution for the corrosion problems in the superheater tubes in MSWI.
Influence of Spray Parameters and Nozzle Geometry on Microstructure and Properties of HVOF Sprayed FeCr-VC Coatings
Authors: Wielage B. , Grund T. , Pokhmurska H. , Schuberth S.
Published: September 2022

The thermal spray application of inert gas atomised iron based powders for combined wear and corrosion protection prospectively offers important economical advantages compared to the well-established cermet coatings due to their lower price. Recent studies revealed basic knowledge about the thermal spray processing of these materials. For protecting the substrate from corrosive media, coatings have to be dense and impermeable to fluids. Especially poor bonding, occurring between partially melted or unmelted spray particles, leads to open porosity. Hence a certain degree of melting of particles is required. The GTV K2 spray gun allows the use of different nozzles to vary process temperature and velocity in a wide range. This paper shows the influence of applicated nozzles and process conditions on coating characteristics. Powder and coating characterisation is carried out by means of optical microscopy, digital image analysis, SEM and XRD. Additionally, some results regarding microhardness and wear behaviour are given.
Thermally Sprayed Coatings with Stochastic Microstructures for Thermomechanically High Stressed Surfaces
Authors: Bach F.-W. , Möhwald K. , Drößler B.
Published: September 2022

New requirements for modern component part surfaces increasingly demand improvements over friction coefficients in the sense of a reduction of friction losses. A substantial control factor in terms of lower friction and wear is the use of coating solutions such as thermal spray coatings. In practice, the application of coatings by means of thermal spray is more and more often used for influencing tribological matching. However, surface microstructuring might represent an additional, further reaching solution for wear and friction behaviour improvements of tribologically high-stressed surfaces. The aim of the reported research project is the development of atmospheric plasma sprayed (APS) coatings with an inherent porous microstructure and surfaces with stochastically distributed nap volumes (from cut pores) regarding lubricant retention and -distribution in running surfaces of friction-type bearings. Subject of these investigations are in particular thermomechanically highly loaded hydrodynamic tribological matchings, amongst others by the example of a piston ring/cylinder system in engine blocks. The use of special fractioned Fe-base powders enables the production of a new type of coatings with an inherent porous microstructure, which offer advantages due to constantly regenerating their surface topology under wear, and maintain employment in tribological systems with increased loads due to optimized lubricant retention and distribution. Hence, this project has an emphasis on the design of optimal nap sizes in coating surface structure in dependence on the hydrodynamical load, as well as on investigations for the controllability of nap volumes by the design of suitable processes.
Tailor-Made Coatings for Turbine Applications using the Triplex Pro 200
Authors: Bobzin K. , Ernst F. , Richardt K. , Sporer D. , Fiala P.
Published: September 2022

In modern jet engines, the efficiency of the compressor stages is highly dependent on the clearance between blade tip and casing. In order to improve efficiency of gas turbines (i.e. areo engines as well as land based gas turbines), the gap between the rotating turbine blades and casing has to be minimized. Any increase in the gap results in power loss. Abradable coatings permit a minimization of the clearance and control of the over-tip leakage by allowing the blade tips to cut into the coating. Thermal sprayed abradable coatings aim at a well balanced profile of properties relevant for the application as abradable seals. Amongst others these include: abradability, ageing resistance, corrosion and oxidation resistance, surface finish and bond strength to substrate materials. In this work, abradable coatings consisting of a multiphase material, comprising a metal matrix in addition to a solid lubricant as well as a defined level of porosity, were developed using the Triplex Pro 200 (Sulzer Metco, Wohlen, Switzerland) in order to increase the reproducibility and deposition efficiency. Additionally the influence of the process parameters on coating characteristics such as porosity, hardness and, resulting from this, coating erosion properties and abradability was investigated.
Metal Foam Sandwich Structure as a High Temperature Heat Exchanger
Authors: Salimijazi H.R. , Pershin L. , Coyle T.W. , Mostaghimi J. , Chandra S.
Published: September 2022

Nickel-based superalloys can be used at temperatures up to 1050 °C in air. Superalloy open cell foam sheets with skin layers plasma sprayed on both sides can be used as high temperature heat exchangers provided that the two deposited skins are dense and well adhered to the open cell foam. In this study alloy 625 skins were deposited on each side of a sheet of metal foam by APS and HVOF to form a sandwich structure. Two densities of open cell foams, 20 and 10 pores per linear inch (ppi), were used in this study as the core. The initial Ni foam was converted to an alloy composition by plasma spraying aluminum and chromium on the foam’s struts with subsequent diffusion/solutionizing heat treatments before the alloy 625 skins were deposited. The microstructure of the coatings and the interface between the struts and skins was investigated. A layer of Ni-Al alloy was formed near the surface of the struts as a result of the heat treatment. The foam struts were imbedded more deeply into the coatings deposited by HVOF than the coatings deposited by APS.
FeNiW-Coatings for Casting Molds in the Aluminium Industry
Authors: Wilden J. , Jahn S. , Reich S. , Fischer G. , Drescher V.E.
Published: September 2022

Casting molds in the aluminium industry show a short lifespan due to the high corrosiveness of aluminium melts and alternating thermal and mechanical loads. By using new materials, in example pseudoalloys containing tungsten, the lifetime of casting molds can be elongated up to hundredfold. Today, casting molds made of steel are state of the art. In spite of the advantages of pseudoalloys, high manufacturing cost and the increasing commodity price of tungsten prohibit the use of molds consisting of these progressive materials. By coating the standard steel molds with a FeNiW-layer, the excellent thermal and corrosive resistance of the pseudoalloy surface can be combined with minimal manufacturing costs. For present work steel substrates had been coated with FeNiW-pseudoalloys. Therefore, arc spraying and different deposit-welding methods (Laser, Plasma, TIG) had been compared. By modifying the machine parameter set, a smooth transition between substrate and coating was realized. Thermal and chemical resistance of the samples will be tested. In this paper first results are presented.
Friction and Wear Properties of Plasma Sprayed Nanostructured Chromium Oxide Coatings
Authors: Li Q. , Li S. , Yang W.
Published: September 2022

Nanostructured chromium oxide coatings were deposited on stainless steel with an axial powder feeding plasma spray system. Friction and wear properties of the coatings were investigated in view of friction coefficient and volumetric wear loss of the coatings with a SRV oscillating friction and wear tester in a ball-on-disc configuration. The morphology and microstructure of the coatings were evaluated by light microscopy, field emission scanning electron microscopy and X-ray diffraction. The results showed that the nanostructured chromium oxide coatings were harder and had a lower friction coefficient and much better wear resistance than the conventional chromium oxide coatings.
Fabrication of Bulk Nanocrystalline Ceramic Materials
Authors: Chraska T. , Neufuss K. , Dubsky J. , Ctibor P. , Klementova M.
Published: September 2022

An alternative method to produce bulk nanocrystalline materials and avoid the powder compaction step is to produce amorphous material by rapid solidification followed by controlled heat treatment to introduce nanocrystalline structure. The extremely high cooling rates in plasma sprayed particles give rise to formation of nonequilibrium phases, which may become amorphous for certain materials. Five different materials studied in this work are based on near-eutectic mixtures of alumina, zirconia and silica. The powder feedstock materials have been plasma sprayed using water stabilized plasma torch (WSP) and subsequently heat-treated to prepare nanocomposite materials with varying nanocrystallite size. The as-sprayed materials have very low open porosity and are mostly amorphous. The as-sprayed amorphous materials crystallize at temperatures around 950°C with an associated volume shrinkage of 1-2%. The resulting structure is best described as nanocomposite with very small crystallites (12 nm on average) embedded in inter-crystallite network. Role of the silica compound on phase composition, microstructure, and mechanical properties of the as-sprayed and annealed materials is discussed. Elastic properties were measured for the nanocrystalline materials. The as-sprayed amorphous materials exhibit high hardness and high abrasion resistance. Both properties are significantly improved in the heat treated nanocrystalline samples.
Self Healing Mechanism in Thermal Barrier Coatings
Authors: Kochubey V. , Sloof W.G.
Published: September 2022

During service damage in terms of small cracks develops in thermal barrier coatings (TBC), composed of partially yttria stabilized zirconia (PYSZ), and applied to gas turbine components made of Ni-base superalloys coated with an aluminide diffusion or MCrAlY overlay coating. Growth and coalescence of these microcracks results in cracks that run parallel to the interface with the substrate leading to failure by delamination of the TBC. A mechanism is proposed to heal the micro-cracks in a TBC by introducing MoSi2 particles. Upon high temperature expose in air, in the range of 1200 °C, MoSi2 forms amorphous SiO2 that can fill micro-cracks, thereby restoring the integrity of the TBC.
Failure Mechanism for Thermal Fatigue of Thermal Barrier Coating Systems
Authors: Giolli C. , Scrivani A. , Rizzi G. , Borgioli F. , Bolelli G. , Lusvarghi L.
Published: September 2022

High temperature thermal fatigue causes the failure of Thermal Barrier Coating (TBC) systems. Due to the difference in thickness and microstructure between thick TBCs and traditional thin TBCs, they cannot be assumed a-priori to possess the same failure mechanisms. Thick TBCs, consisting of a CoNiCrAlY bond coat and Yttria Partially Stabilised Zirconia top coat with different values of porosity, were produced by Air Plasma Spray. Thermal fatigue resistance limit of TBCs was tested by Furnace Cycling Tests (FCT) according to the specifications of an Original Equipment Manufacturer (OEM). TBC systems were analyzed before and after FCT. The morphological and chemical evolution of CoNiCrAlY/TGO microstructure was studied. Sintering effect, residual stress, phase transformation and fracture toughness were evaluated in the ceramic Top Coat. All the tested samples passed FCT according to the specification of an important OEM. Thermal fatigue resistance increases with the amount of porosity in the top coat. The compressive in-plane stresses increase in the TBC systems after thermal cycling, nevertheless the increasing rate has a trend contrary to the porosity level of top coat. The data suggest that the spallation happens at the TGO/Top Coat interface. The failure mechanism of thick TBCs subjected to thermal fatigue was eventually found to be similar to the failure mechanism of thin TBC systems made by APS.
Comparison of Coating Stresses Produced by High Velocity Liquid/Gas Fuel and Triplex Pro 200 Plasma Processes using In-Situ Coating Stress Measurement
Authors: Molz R. , Valarezo A. , Sampath S.
Published: September 2022

The coating stresses induced by thermal spray using a High Velocity Gas Fuel (HVOF) and Liquid Fuel (HVLF) gun and a High Velocity Plasma (HVP) gun with the high velocity nozzle are compared using a curvature based in-situ coating stress analysis approach that measures the deflection of a beam while a coating is applied to it. This novel diagnostic tool provides new insights into the internal stresses generated in a coating system during the actual application of the coating. Coatings were sprayed with three process guns and the same material feed stock that result in similar coating structures and properties. HVOF, HVLF and HVP processes induce similar particle energy states at high velocity regimes as measured with particle diagnostic tools during spraying but due to the differences in particle history are expected to result in different coating stresses. In some cases the actual measured stress conditions using the in-situ coating stress method were dramatically different. Analysis is presented to explain the reason for these surprising results. The understanding of these differences will lead to an improved methodology for mapping coating processes from one another along with a more in depth understanding of coating stresses buildup.
Molten Zinc Corrosion of WC-Co Coatings in Al-Added Zinc Bath
Authors: Huang T.-S.
Published: September 2022

To increase the service life of a sink roll in a continuous galvanizing line has been an important issue in steel industry. It was shown that sink rolls are vulnerable to molten zinc corrosion and can be improved by thermal spraying with WC-Co coatings. Four WC-12Co thermal sprayed coatings were investigated in this study. Samples were immersed in Al-added zinc bath (460°C) for testing. The results show that the conventional coatings are more resistant to molten zinc corrosion than the nanostructured ones. It was also found that coatings containing η- phase have longer life in the zinc bath. Accumulation of Al on the coating surface was also observed.
Electrically Conductive Flame Sprayed Aluminium Coatings on Textile Substrates
Authors: Voyer J. , Schulz P. , Schreiber M.
Published: September 2022

Electrically conductive and flexible Aluminium coatings using powder and wire flame spraying were successfully deposited onto diverse textiles. The influence of different process parameters as well as the fabric materials on the electrical conductivity and microstructure of the metal-fabric composites were studied. Preliminary results show that in order to obtain excellent coating surface conductivity values, a specific coating quantity higher than 20 mg/cm2 is necessary. After further optimization of the spraying parameters, a very good specific surface conductivity (~500 Si) could be obtained even with reduced coating quantities. This corroborates that by performing an adequate parameter optimization a reduction of the specific coating quantity could be done while still keeping high conductivity values. Furthermore, when the coating quantity is reduced, the flexibility of the fabric substrates is better conserved. This study illustrates that optimized electrically conductive composites with flexible fabric substrates can be produced, without any preliminary thermal or chemical fabric specifications.
Optimization of Solution Precursor Plasma Spray Process by Statistical Design of Experiment
Authors: Wang Y. , Coyle T.W.
Published: September 2022

The solution precursor plasma spray (SPPS) process, in which a solution precursor of the desired resultant material is fed into a plasma jet by atomizing gas or high pressure, was developed in the 1990’s and has been studied extensively since then. Recently, it has been shown that the SPPS process is suitable for deposition of porous electrodes for solid oxide fuel cells (SOFC). High efficiency SOFC requires electrodes with 30%-40% porosity. Because of the complexity of the SPPS process and the large number of processing parameters, it is difficult to investigate the effect of each parameter on the two important properties, i.e. coating porosity and deposition efficiency, separately. Design of experiments can use a small number of experimental runs to analyze the effect of each processing parameter on the properties of the fabricated product, after which the processing parameter combinations for fabricating a target product can be found. In this project, a small central composite design, a second order statistical model, was used to analyze and optimize the SPPS process for Ni-YSZ anode deposition. The processing parameters investigated include: 1) Hydrogen flow rate, which determines arc voltage, 2) Current , 3) Solute flow rate, 4) Solution concentration, 5) Distance between nozzle and gun, and 6) Stand off distance. The effects of the selected processing parameters were analyzed, and the resultant model used to select a combination of processing parameters which produced a coating with the desired characteristics.
A Comparative Microstructural Investigation of Nanostructured and Conventional AI2O3 Coatings Deposited by Plasma Spraying
Authors: Zois D. , Vardavoulias M. , Lekatou A. , Panagiotopoulos I. , Vazdirvanidis A.
Published: September 2022

Nanostructured and conventional Al2O3 powders have been plasma sprayed, under the same parameters, to produce coatings on 304 stainless steel. The nanopowder was fabricated by mechanical attrition techniques and composed of agglomerates of nanoparticles, whereas the conventional powder consisted of solid granules. In order to maintain the beneficial effect of the nanostructure in the final coating, a fraction of the powder’s nanostructure should be retained in the coating after spraying. Dissimilarities were observed between the two types of coating, regarding porosity, roughness, deposition efficiency and α-Al2O3 to γ-Al2O3 proportions, which are related with the different percentages of semimolten particles in the coatings. The nanocoatings retained a higher percentage of semimolten particles than the conventional coatings, owing to the higher porosity of the nanoparticle agglomerates, as compared to the conventional solid granules. The molten part of both conventional and nanostructured coatings consisted of γ-Al2O3 of columnar morphology. In order to investigate the mechanism of the melting front advance into the particle interior during their presence in the plasma stream, the particles were sprayed directly into distilled water. The nanoparticles mainly formed hollow spheres, whereas the conventional particles mainly formed compact spheres. The internal porosity of the solidified nanoparticle agglomerates, which affected the overall coating porosity, was linked to the hollow sphere phenomenon.
Influencing Parameters on the Turning Process of Fe-Based Thermal Sprayed Coatings
Authors: Wilden J. , Jahn S. , Fischer G. , Wang S.
Published: September 2022

Thermal Spray processes are widely used to fabricate corrosion and wear resistant coatings respectively. However, these coatings have to be finished generally in subsequent steps, for example by turning, milling or grinding, to adjust the the required properties, e.g., surface roughness and accuracy. Up to now grinding is the most common post processing for wire arc sprayed coatings, but in recent years the hard turning technology gained high interest for coating treatment due to high machining efficiency. The aim of the present work is to enhance the machinability of different thermal sprayed coatings. DoE-based experiments regarding surface roughness, cutting forces and temperatures in the cutting zone had been carried out. Within the investigations a significant increase of hardness due to the hard turning process at Fe-Mn coatings had been verified. This effect, the force induced martensitic transformation, could improve the mechanical properties of the coating considerably. Based on the investigations presented in this paper, a deeper understanding of post processing of thermal sprayed coatings is given.
Three-Dimensional Analysis of Cold-Sprayed Coatings using Microtomography
Authors: Rolland G. , Borit F. , Guipont V. , Jeandin M. , Bara L. , Bourda C.
Published: September 2022

In this work, the microstructure of silver coatings obtained by cold spraying with a fine and a rather coarse powder were investigated. Cold-sprayed microstructures strongly depend on the deposition process parameters. These parameters have an influence on porosity, plastic strain, particle-to-particle bonding mechanisms. The originality of this study rests on the use of X-ray microtomography, which is shown to be a very powerful technique to investigate into cold-sprayed coatings. Several samples were machined from coatings by electro-discharge machining (EDM) then scanned using microtomography. Porosity fraction was determined by three-dimensional image analysis and compared to classical two-dimensional analysis of micrographs. A difference between the two methods was exhibited, which showed sample preparation effects. Consequently, X-ray microtomography seems to be well adapted to study cold-sprayed coatings thoroughly. Another result from this work was the characterization of the morphology of pores and deformed particles. Bonding mechanisms in cold spray could therefore be discussed. In addition, the knowledge on deformed particles allowed to simulate cold-sprayed coatings with build-up models. This will be done in a further work
HVOF Sprayed Nylon-11/Nanodiamond Composite Coatings: Production & Characterization
Authors: Stravato A. , Mochalin V. , Picardi S.C. , Knight R.
Published: September 2022

High velocity oxy-fuel (HVOF) combustion spraying has previously been shown to be a viable method for depositing polymer and polymer/ceramic composite coatings. The addition of hard particulate reinforcing phases to soft polymeric matrices should improve their durability and wear performance. Nano-sized diamond is an ideal reinforcing phase, owing to its high hardness and desirable thermal properties. Composite coatings comprising a Nylon-11 matrix reinforced with nanodiamonds have been successfully produced by HVOF. An important challenge is preserving the structure of the nanoparticles after thermal spray deposition and achieving a uniform dispersion of them within the polymeric matrix. Raman spectroscopy and X-ray diffraction confirmed the presence and retention of nanodiamonds after HVOF deposition. Understanding of the role of variables including the % loading of reinforcing phase in the matrix and powder preparation route are necessary. The coatings exhibited improved sliding wear resistance in macromechanical tests. Nanoindentation studies demonstrated an improvement in deformation behavior and recovery of the HVOF nanodiamond Nylon-11/nanodiamond composites subjected to deformation.
Numerical Modeling of Warm Spray (Two-Stage HVOF) Process
Authors: Katanoda H. , Kawakita J. , Kuroda S.
Published: September 2022

The warm spray gun was developed to make a coating of temperature-sensitive material, such as titanium, on a substrate. The gun has a combustion chamber followed by a mixing chamber, in which the combustion gas is mixed with the nitrogen gas at room temperature. The temperature in the gun can be controlled in the range of about 1500 - 2500 K by adjusting the mass flow rate of nitrogen gas. The mixed gas is accelerated to supersonic speed through a converging-diverging nozzle followed by a straight passage. In this paper, the performance of the warm spray gun is investigated by the simulation program in order to deeply understand the performance of the warm spray gun. The gas flow as well as the velocity and temperature of titanium particle inside and outside the gun are predicted by the numerical simulation.
HVOF Sprayed Coatings by Customized Cermet Materials for Specific Applications
Authors: Kitamura J. , Mizuno H. , Tawada S. , Aoki I.
Published: September 2022

High velocity oxy-fuel (HVOF) sprayed cermet coatings are required in various industrial fields due to their excellent properties, such as combination of wear resistance, corrosion resistance, high hardness, high bonding strength and stability under high temperature. In order to utilize them in the fields, optimization of composition and structure of the coatings are essentially important meaning that both spray powders and spray conditions are key process parameters. In this paper, developed spray powders of cermet materials are introduced for the specific applications, where 1. cavitation erosion, 2. mechanical impact, 3. corrosion by molten alloy and 4. general abrasive wear are major factors that damage the coatings. In order to solve these factors, HVOF coatings of 1. WC/Co/Cr with large WC particle, 2. WC/Cr3C2/Ni with addition of metal or alloy, 3. MoB/CoCr composed of double boride and 4. WC particle size in WC based cermet, are proposed and these merits are described.
Copper Particle Impact Onto Aluminium by Cold Spray
Authors: King P. , Zahiri S. , Jahedi M.
Published: September 2022

Copper particles with median diameter 15.2 micrometres were cold sprayed onto a polished aluminium 1139 substrate. Under the spray conditions used, deep embedment of the copper particles occurred. The as-sprayed copper particles were dissected using a focussed ion beam (FIB), and their microstructure investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At the crater wall an intense shear zone developed due to sliding of copper past aluminium. Evidence of melting is presented.
PTA Processing of Ceramic Coatings
Authors: Drozda F.O. , Takano H. , Oliveira A.
Published: September 2022

Welding of dissimilar materials in particular ceramics to metals is a technical challenge with attractive economical consequences. In this study a ceramic coating was processed by plasma transferred arc (PTA). ZrO2–7wt.%Y2O3 powders were deposited on low carbon steel plates and on Ni based alloys layers previously welded on a steel plate. Coatings were evaluated regarding the soundness and features of the metal/ceramic bond. Results showed that the pair ZrO2–7wt.%Y2O3 /metallic alloy played a major role on the quality of the processed surfaces determining the effectiveness of the bonding. The presence of Al in the Ni based intermediate layer was detrimental to the adhesion of the ceramic coating. Deposition of ZrO2–7wt.%Y2O3 on NiCrFe intermediate layers allowed for a metal/ceramic bond resulting on 3,0mm thickness coatings. Ceramic deposits exhibited cracks, whose features were altered after a stress relief treatment of the substrate (AISI 1020+NiCrFe layer) prior to the deposition of ZrO2–7wt.%Y2O3. Transverse section analysis revealed the presence of second phase particles in the ceramic coating and the diffusion of elements from the intermediate Ni based layer into the ceramic deposit.
Numerical Investigation of the Heat Insulation Behavior of Thermal Spray Coatings by a Unit Cell Model Approach
Authors: Liu F.R. , Zeng K.L. , Wang H. , Zhao X.D. , Ren X.J. , Yu Y.G.
Published: September 2022

In the recent decade, considerable numerical models have been built up to simulate the thermal spray process. However, much less work has focused on the prediction of thermo-physical properties of the thermal spray coating, in particular the heat insulation properties. In this paper, a microstructure integrated finite element model is developed to investigate the heat insulation behavior of the thermal spray coating. A two-layer model is used to calculate thermal conductivity of the coating, where one layer stands for the coating by a unit cell, while another one for a standard material with known thermal conductivity. In the proposed unit cell model, pores and unmelted particles are assumed spherical and randomly distributed, and the interface between the coating and the unmelted particles is perfectly debonding. Based on the predictions, the effect of the pores, unmelted particles, cracks and their respective distributions on the heat insulation behavior of the coating has been further discussed in the paper.
Innovative High-Speed Camera System Diagnostics of Plasma Torch Fluctuations
Authors: Schein J. , Forster G.
Published: September 2022

Instabilities in plasma torches can result in poor particle heating and thus a production of low quality coatings. In order to investigate these fluctuations numerous experiments have been performed using high speed cameras taking pictures at a rate of 1000 images/s to create sequences with duration of few seconds total. Individual exposure times are usually in the range of few microseconds. In order to improve upon these parameters a new high speed camera system (HOBAS) was developed, which has been demonstrated to acquire short film sequences at a rate of 106 images/s using exposure times of down to 1ns/image. The camera system is based on a regular CCD camera mated with an MCP, where the MCP is triggered rapidly while the image is moved across the CCD-chip, thus enabling it to record multiple images during the CCD integration interval. Results of investigations will be presented using this instrument to detect plasma jet fluctuations in single electrode and multi electrode plasma torches.
Study on the Detection of Melting Temperatures and Sources of Errors using Two-Color Pyrometry for In-Flight Measurements of Plasma Sprayed Particles
Authors: Mauer G. , Vaßen R. , Stöver D.
Published: September 2022

In-flight particle temperature measurements during atmospheric plasma spraying (APS) of Tungsten, Molybdenum, and Yttria stabilized Zirconia by two-color pyrometry are analyzed statistically. The particle temperature distributions allow assessing the melting status of the particles. Particularly the melting temperature and the particle fractions being still molten or already solidifying can be identified. Furthermore, the relevant systematic and material dependant sources for measurement errors using two-color pyrometry are investigated. Their influence is estimated and corrected best possible. As far as there is reliable data available on the emissivity of the powder material there is good agreement between the corrected measured melting temperatures and reference data.
Evidence of the 2-Stage Build-Up Process in Cold Spray from the Study of Influence of Powder Characteristics on Ti-6Al-4V Coating
Authors: Christoulis D.K. , Borit F. , Guipont V. , Jeandin M.
Published: September 2022

During the deposition of metallic cold sprayed coatings, it could be observed that only a thin layer is formed on the substrate and further building-up of a thick coating is not enabled. As for other thermal spray techniques, the formation of cold sprayed coatings can be divided to two stages: the creation of the first layer onto the substrate and the building-up of the coating itself onto as-sprayed layers. This two-stage build-up process was evidenced according the study of two Ti-6Al-4V powders exhibiting different characteristics (particle size, morphology, oxygen content, hardness, etc) which were sprayed by cold gas dynamic spraying onto substrates of different nature with various hardnesses (Ti-6Al-4V, AISI 304L, Al-alloy 2017). The phenomenology of the two-stage process is investigated in the present study. Cold spray conditions with pure nitrogen or pure helium as processes gas were applied to achieve a significant difference for particle velocities. The first stage of the process was completed by both powders with the formation of a first coating layer onto the various substrates. However, very different features for particle-substrate interactions (penetration depth and comparative deformation) were observed. For the particle-particle interaction (the second stage of the process), despite similar spraying conditions for both powders, the results were completely different since the formation of thick coating was achieved only with one of the powders. It was found that the intrinsic ductility of the material powder is the main parameter to promote the successful completion of both stages in order to achieve thick coatings.
New Generation Perovskite Thermal Barrier Coating Materials
Authors: Ma W. , Jarligo M.O. , Mack D.E. , Pitzer D. , Malzbender J. , Vaßen R. , Stöver D.
Published: September 2022

Advanced ceramic materials of perovskite structure have been developed for potential application in thermal barrier coating systems, in an effort to improve the properties of the pre-existing ones like yttria stabilized zirconia. Yb2O3 and Gd2O3 doped strontium zirconate (SrZrO3) and barium magnesium tantalate (Ba(Mg1/3Ta2/3)O3) of the ABO3 and complex A(B’1/3B”2/3)O3 systems respectively, have been synthesized using ball milling prior to solid state sintering. Thermal and mechanical investigations show desirable properties for high temperature coating applications. On atmospheric plasma spraying, the newly developed TBCs reveal promising thermal cycle lifetime above 1300°C.
Role of High-Temperature Creep Stress in Thermally Grown Oxide Growth of Thermal Barrier Coatings
Authors: Ogawa K. , Nakao Y. , Seo D. , Miura H. , Shoji T.
Published: September 2022

Thermally grown oxide (TGO) grows at the top / bond coating interface of the thermal barrier coating (TBC) in service. It is supposed that the failures of the TBC occur due to thermal stress and the decrease of adhesive strength caused by the TGO growth. Recently, large local stress has been found to change both the diffusion constant of oxygen through an existing oxide and the rate of chemical reaction at the oxide / oxidized material interface. Since high thermal stress occurs in the TBC, the volume expansion of the newly grown oxide, and centrifugal force, the growth rate of the TGO may change depending on not only temperature but also the stress. The aim of this study is to make clear the influence of stress on the growth rate of the TGO quantitatively. As a result, the thickness of the TGO clearly increases with increase of the amplitude of the applied stress and temperature. The increase rate of the TGO thickness is approximately 23% when the applied stress is increased from 0 to 205 MPa at 900 °C, and approximately 29 % when the stress is increased from 0 to 150 MPa at 950 °C.
Characterization of Mesoporous Nanocrystalline TiO2 Deposited by Vacuum Cold Spray using Ceramic-Polymer Composite Powder
Authors: Yang G. , Fan S. , Gao J. , Li C. , Xi Y. , Li C.
Published: September 2022

Vacuum cold spray is a promising method to deposit nanocrystalline ceramic coating. The effective control of porous structure within nanostructured coating is essentially important to enhance the performance of the mesoporous nanocrystalline coatings for applications to catalyst and photo-electrode. In this study, the ceramic-polymer composite powders were employed as spray feedstocks for vacuum cold spray to control the pore structure in the deposits. The ceramic-polymer composite powders were made from nano-sized TiO2 (25nm), ZrO2 (30nm) and Al2O3 (30nm) and polyethylene glycol (PEG). The surface morphologies and the cross-sectional microstructures of the coatings were characterized using scanning electron microscope (SEM). The pore size distribution was measured using a nitrogen adsorption approach. The results showed that the deposition during spraying was implemented through the composite particles in a size ranging from submicrometers to several micrometers. Through post-spray heat treatment of the deposit, the PEG can be completely removed to increase the porosity in the deposit. The pores exhibited a bimodal distribution. The small pores present the size from several nanometers to tens of nanometers. Moreover, the size of large pores is in micrometer scale. The porosity and pore size distribution can be controlled by the composition of the composite powder.
Influence of the HVOF Gas Composition on the Thermal Spraying of WC-Co Submicron Powders (- 8 + 1 μm) to Produce Superfine Structured Hard Material Coatings
Authors: Tillmann W. , Vogli E. , Baumann I. , Matthaeus G. , Ostrowski T.
Published: September 2022

Deep-drawing is a widely used sheet metal forming process in the aircraft and automotive industry. The manufacturing of modern parts with complicated shapes and curvatures requires forming tools with highest shape accuracy even at complex surface geometries. However, the application of novel, high-strength sheet metals combined with a continuous increase in productivity impose high tribological demands on forming tools and finally lead to increasing wear. In order to minimize the high costs for the repair and maintenance of such tools it is crucial to enhance their service life by an appropriate surface modification, which is able to preserve the high shape accuracy. Conventional coatings obtained by thermal spraying of coarse grained feedstock materials are not suitable to achieve this aim. In this collaborative study, the feeding and HVOF spraying of WC-Co submicron powders (- 8 + 1 µm) have been investigated to manufacture superfine structured, wear resistant near-net-shape coatings with improved macroscopic properties and smooth surfaces. Special equipment for the powder feeding and a novel HVOF flame spraying system designed by Thermico (optimized for the processing of fine-scaled powder fractions) have been employed. Correlations related to the process dynamics at varying HVOF gas compositions, the thermokinetic particle behavior in-flight and corresponding coating properties have been analyzed.
Effects of Silver Addition on Mechanical Properties of Plasma Sprayed SOFC Interconnect Layer
Authors: Park S.D. , Kumar S. , Lee S.C. , Lee C.
Published: September 2022

In this study, interconnect layer of solid oxide fuel cell (SOFC) was built up from spray-dried La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and blended LSCF-Ag through atmospheric plasma spraying (APS). Microstructure and phase of each coating was analyzed through scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Furthermore, bond strength, micro-hardness, thermal cycle test and oxidation test were performed and compared. The coatings prepared from spray-dried LSCF have higher porosity and cracks at inter-particle boundaries. However, the coatings with silver addition presented reduced cracks and porosity due to relatively high ductility of silver, resulting in higher mechanical properties.
Mechanical Modelling of Highly Heterogeneous Thermally Sprayed Abradable Coatings
Authors: Seichepine J. , Coddet C. , Sporer D. , Lourtie D.
Published: September 2022

Abradable coatings are widely used in aerospace turbine engines to improve seal performance between rotating and stationary parts and thus the engine efficiency. As they are elaborated by thermal spraying of composite powders, these materials are highly heterogeneous. Their behaviour in working conditions is quite complex and not fully understood. This study contributes to a better knowledge of the mechanical behaviour of a range of abradable coatings. Finite Element calculations were derived from the analysis of micrographs and allowed to estimate the coefficients of an anisotropic elastic law of behaviour. Several models were investigated in the case of an AlSi-PE (Polyester) coating. As the PE % appeared to be a determinant factor, its influence was quantified ranging from 0% to 100%, using virtual micrographs deduced from the original ones. The computed Young's moduli Ex (in coating longitudinal direction) were quite consistent, considering the hypotheses made. An empirical relationship giving the variation law of Ex versus the PE % was suggested and applied to predict the modulus Ex of a real coating, which was close to the measured value.
Modeling of Plasma-Sprayed Thermal Barrier Coatings for Prediction of Residual Stress
Authors: Arai M.
Published: September 2022

The surfaces of gas turbine components are coated by thermal barrier coatings (TBCs) with a plasma spraying technique. Spallation damage is an essential problem, as well known, in usage of TBC. A lot of efforts for TBC interfacial strength examination had been done, however studies examined how residual stress are formed after the process and also the coating stress changes with temperature were limited. In this report, the residual stress prediction model is proposed based on the splat deposition process. Simplified model including the plasma sprayed process is developed based on shear-lag theory. The simplification is given in continuous particle deposition process. That is, continuous particle deposited coating is modeled as a single layer, which is called by "deposition layer" in this study. This deposition layer is assumed to impact directly onto the substrate. The binding layer is also introduced to express multiple cracks caused by quenching stress in splats and sliding deformation at splat boundary. It is shown that the numerical analysis has good agreement with the associated experiments.
Development of Nanostructured Lanthanum Zirconate Coating and Its Thermal Stability Properties
Authors: Zhao X. , Zeng K. , Xie J. , Ren X. , Yu Y.
Published: September 2022

In this paper, nanostructure Lanthanum zirconate thermal barrier coatings (MCrAlY+ La2Zr2O7) were prepared by atmospheric plasma sprayed (APS). The microstructures and thermal stability properties were systematically studied by Scanning Electric Microscopy (SEM), transmission electron microscope (TEM) and X-Ray diffraction(XRD). The results showed that the nanostructured lanthanum zirconate coatings were typical lamellar structure which was composed of columnar grains about 90nm in diameter. A large quantity of micro-cracks and homogeneous distributed fine pores formed in the nanostructured zirconia coating. After ablation at 1300 °C for 24 h, no apparent phase transformation was observed in lanthanum zirconate coating. The growth mechanism of the grains was subsequently discussed.