bluuebunny/crossref_metadata_2025 huggingface dataset:
Self Propagating High Temperature Synthesis of Aluminium-Matrix-Composite Coatings by Means of Atmospheric Plasma Spraying
Authors: Bach Fr.-W. , Möhwald K. , Wenz T.
Published: August 2022

An important growth potential in thermal spraying industry consists of the development of new coating materials. Metal- or Ceramic-Matrix-Composites (MMC / CMC) are of special interest due to a variety of properties which can be influenced particularly by the ratio of matrix and reinforcing material. Thermal sprayed coating properties mainly depend on thermal and kinetic energy of the spray particles. An increase in thermal energy of sprayed particles can be obtained by Self Propagating High Temperature Synthesis (SHS) reaction between components of the spray material. Hence a higher adhesive strength, a lower porosity and an increased deposition efficiency can be expected. Aluminium-based spray materials, containing metal oxides, are suitable for the Self Propagating High Temperature Synthesis to produce MMC-coatings. For good contact between the reactants, powders of aluminium and chromium oxide for plasma spraying were prepared by mechanical alloying. Coatings characterization results on the base of optical microscopy, scanning electron microscopy (SEM), X-ray structure analysis (XRD) and measurements of velocity and temperature with a DPV2000 system. The plasma spraying process combined with SHS reaction of the spray material leads to raised enthalpy of spray particles combined with an increased ad-/cohesive strength and a lower porosity as well as an increased deposition efficiency.
The Influence of Spraying Parameters on In-Flight Characteristics of Tungsten Particles and the Resulting Splats Sprayed by Hybrid Water-Gas Stabilized Plasma Torch
Authors: Matejicek J. , Chumak O. , Konrad M. , Oberste-Berghaus J. , Lamontagne M.
Published: August 2022

Tungsten particles were sprayed by a novel plasma torch with hybrid water-gas stabilization (WSP®-H). Several spraying parameters were varied – arc current, argon flow rate, carrier gas flow rate and spraying distance. The temperature and velocity of the individual particles were monitored by the DPV 2000 optical sensor. Individual splats were collected on polished stainless steel substrates and analyzed by SEM to assess their melting, flattening and/or fragmentation. These features were correlated with the basic in-flight particle characteristics and conditions for production of dense coatings were sought for. Significant dependence of the splats morphology on spraying parameters was found, and important improvement of particle melting at WSP-H over conventional water stabilized plasma torch (WSP) was registered.
Aerodynamic Characteristics of High-Velocity Oxy-Fuel Thermal Spray Process
Authors: Katanoda H. , Matsuoka T. , Kuroda S. , Kawakita J. , Fukanuma H. , Matsuo K.
Published: August 2022

A special HVOF gun is used for aerodynamic research on internal flows of gas and particles in HVOF gun. The gun has rectangular cross-sectional area and has sidewalls of optical glass or transparent acrylic resin. Compressed air is used as process gas instead of combustion gas to visualize internal flow of the gun. The high-speed gas flows including shock waves in the gun are visualized by Schlieren technique. Particle trajectories in the gun are also visualized by high-speed digital video camera. The observation of erosion pattern created by particle collision on the barrel wall helps understand the particle trajectories throughout the barrel.
Real Time Control for Plasma Spray: Sensor Issues, Torch Nonlinearities, and Control of Coating Thickenss
Authors: Gevelber M. , Cui C. , Vattiat B. , Fieldman Z. , Wroblewski D. , Basu S.
Published: August 2022

Real-time control offers the potential to reduce plasma spray variations that affect yield and coating quality. Important factors for designing such controllers are discussed including dominant nonlinearities, cross-coupling interactions, and sensor issues. The performance of several alternative strategies to achieve better coating thickness control are evaluated.
On the Measurement of Substrate Temperature During Thermal Spraying
Authors: Moulla L. , Salhi Z. , Planche M.P. , Cherigui M. , Coddet C.
Published: August 2022

Substrate temperature is nowadays recognized as a key parameter to optimise the coating quality in the thermal spraying process. Generally parts being processed are in motion and therefore non contact temperature measurement devices are appropriate. In contrast to thermocouples, optical pyrometers have several advantages. First, they are easy to install and second they do not bring any disturbance to the measured system. Meanwhile, several problems may arise with those devices which are not always considered as they should be and in particular the variation of material emissivity temperature, the effect of the reflection of the external radiation or the attenuation of the optical signal due to the variable transmissivity of the optical path. The aim of this work was to develop algorithms for correcting optical pyrometer temperature measurements during thermal spraying by taking into account emissivity variations and radiation reflexion on the components. Emissivity of some materials with respect to the specific spectral band of the pyrometer and the influence of reflected radiations were measured. Results are discussed in order to point out the influence of each parameter on the temperature value.
Development of Highly Molten Chloride Corrosion Resistant Coatings Assisted by Mechano-Chemical Reaction
Authors: Ichikawa Y. , Ogawa K. , Shoji T. , Solonenko O.P.
Published: August 2022

In waste-to-energy power generation plants, increasing the combustion temperature improves plant efficiency. However, due to problems caused by molten chloride corrosion, the combustion temperature cannot be increased. Consequently, in order to increase the temperature, it is first necessary to protect components from molten chloride corrosion. In this study, CoNiCrAlY coating is proposed as a protective film against molten chloride corrosion. Three kinds of specimens were prepared. One was standard coating made from conventional CoNiCrAlY. The others included the addition of Mo to the CoNiCrAlY by two different techniques. One technique is mechanical alloying (MA), and the other is a gas-atomizing technique. The mechanic-chemical reaction that occurs during the mechanical alloying process can be expected to create new functionality for the material. The effect of Mo content was evaluated for corrosion resistance. These specimens were coated by low pressure plasma spraying (LPPS). The specimens were exposed to NaCl-KCl for the molten chloride corrosion test. The results of the corrosion tests show that corrosion resistance improved in only MA CoNiCrAlY coatings. These results reveal that mechanically alloyed CoNiCrAlY-Mo coating has excellent corrosion resistance, and its corrosion resistance behavior is different from that of gas-atomized CoNiCrAlY-Mo.
Experimental Investigation of Influence of Plasma Spraying Operational Parameters on Properties of Hydroxyapatite
Authors: Dyshlovenko S. , Pawlowski L. , Roussel P.
Published: August 2022

Excellent biocompatibility of hydroxyapatite (HA) is the main reason of application plasma-sprayed coatings onto orthopedic prostheses. A careful optimization of spray parameters is necessary to avoid thermal decomposition of HA onto less biocompatible products such as e.g. tricalcium phosphate, tetracalcium phosphate, calcium oxide and amorphous calcium phosphates. The spray parameters influence considerably the decomposition and the present study is devoted to understand this influence using on an experimental way. The design of experiments (DOE) was made using two-level 2N plan of experiments (N=5). In total, 32 experiments of spraying were carried out by varying following operational parameters: (i) composition of plasma working gases; (ii) electric power input; (iii) art of spraying (into water or onto substrate); (iv) carrier gas flow rate and; (v) art of injection (external and internal). Plasma-sprayed coatings and powders were analyzed by Fourier Transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The X-ray diagrams enabled to find the content of crystal phases. The content was a first response function described by a polynomial regression equation. The morphology of obtained deposits was also characterized using Scanning Electron Microscope (SEM). Their porosity was estimated using image analysis of coatings cross section images.
Oxidation Study of High Temperature Ti Compatible Abradable Seal
Authors: Fiala P. , Chilkowich A.P. , Hajmrle K. , Shiembob L.
Published: August 2022

The goal of this paper is to evaluate high temperature ageing properties of a new high temperature titanium blade compatible abradable material DurabradeTM 2614. Coatings were tested in as-sprayed condition and after ageing at 550°C and 655°C for up to 8,030 hours. Coating properties such as coating hardness, erosion resistance, and cohesive strength were evaluated at regular time intervals. Abradability was tested in as-sprayed condition and after ageing. The results show that coating hardness, GE erosion resistance, and cohesive strength of the new material change most in the first 200 hours and SMC90 erosion resistance, and oxidation weight gain change most in the first 1,000 hours and then they stabilize at values that guarantee good seal performance. The good performance of the new seal after 8,030 hours ageing has been demonstrated by abradability and erosion testing.
Plasma Sprayed Cast Iron Coatings Containing Solid Lubricant Graphite and H-BN Structure
Authors: Tsunekawa Y. , Ozdemir I. , Okumiya M.
Published: August 2022

Water atomized cast iron powder of Fe-2.17C-9.93Si-3.75Al (in wt%) were deposited onto an aluminum alloy substrate by atmospheric DC plasma spraying to improve its tribological properties. Pre-annealing of the cast iron powder allows to precipitate considerable amounts of graphite structure in the powder. However, significant reduction in graphitized carbon in cast iron coatings is inevitable after plasma spraying in air atmosphere due to the in-flight burning and the dissolution into molten iron droplets. Hexagonal boron nitride (h-BN) powders which have excellent lubricating properties like graphite were incorporated to the cast iron powder as solid lubricant by sintering process (1300 °C) to obtain protective coatings with low friction coefficient. The performance of each coating was evaluated using ring-on-disk type wear tester under paraffin base oil condition in air atmosphere. Conventional cast iron liner which has flaky graphite embedded in pearlitic matrix was also tested in similar conditions in order to make a comparison. Sections of worn surfaces and debris were characterized and wear behaviour of plasma sprayed coatings are discussed.
Microstructure and Properties of Nanostructured WC/Co Coating Deposited by Supersonic Plasma Spraying
Authors: Ma S. , Li C. , Ye X.
Published: August 2022

Nanostructured and conventional WC/Co coatings were prepared by supersonic plasma spraying process respectively. The bonding strength, microhardness, tribological characteristics such as friction coefficient and wear resistance, microstructure and the phase ingredient were studied. The result of the XRD suggests that the coating contains low-carbon phase. TEM analysis reveals that WC phase with the dimension of about 100nm is dispersed in the nanostructured coating. Results of mechanical and tribological properties tests show that nanostructured coating has better performance in comparison with conventional one, with increase of about 40% in the bonding strength, 3% in the microhardness, 14% in the wear resistance, and a decrease of 0.06 in friction coefficient, respectively. After tribological properties tests, obvious plastic deformation was observed on the wear trace surface of the nanostructured coating, while microcrack existed on the surface of conventional coating. Superfine grain strengthening is the primary reason that enhances the performances of the coating.
Corrosion and Tribological Behaviour of Polyamide-Nitride Composite Coatings
Authors: Guilemany J.M. , Fernández D.
Published: August 2022

Over the last years, interest in thermally sprayed polymer coatings has increased. They have excellent corrosion and chemical resistance properties. Unfortunately, they have some limited properties like scratch and wear resistance. Fillers can be a good solution to improve these properties. In the Thermal Spray Centre of Barcelona, blends of polyamide powder with different contents of boron and silicon nitride have been flame-sprayed and studied. Microstructural characterisation of the composite coatings has been done using Optic and Scanning Electron Microscopies. Wear resistance has been evaluated by means of Ball on Disk (ASTM G99-90) and Rubber Wheel (ASTM G65-91) tests. Salt Spray Fog tests (ASTM B117-90) have been performed in order to evaluate their corrosion resistance.
Fractographic Approach to Wear Mechanisms of Selected Thermally Sprayed Coatings
Authors: Nohava J. , Enzl R. , Zahalka F. , Foucher C.
Published: August 2022

Coatings deposited by thermal spraying are widely used for applications where enhanced resistance to wear is a crucial factor. In this work we focused on HVOF and plasma sprayed WC-Co, NiCrSiB, Cr3C2-NiCr, AISI 316L and Cr2O3 coatings. The materials were examined by wet slurry abrasion tests, microhardness and roughness measurements. Systematic fractographic analysis in SEM was devoted to determine the main failure mechanisms of selected coatings. The WC-Co coating exhibited the lowest wear rate while 316L coating exhibited the highest wear rate. The plasma sprayed Cr2O3 coating exhibited wear rate higher than HVOF sprayed cermet coatings but lower than metal coating. In most cases it was found that the higher microhardness, the higher is the wear resistance of the coating. The most favorable microstructure was found to be a mixture of hard particles dispersed in tough metal matrix. Matrix-like structure and internal splat microstructure were the main factors controlling the wear resistance of the investigated HVOF and WSP coatings.
Computer Simulation of Heat Transfer and Phase State Under High–Energy Flux Impact on Solid Body Surface
Authors: Solonenko O.P. , Golovin A.A.
Published: August 2022

A numerical method and software were developed to predict non-stationary conjugated conductive heat transfer, melting and possible evaporation of materials under high energy fluxes impinging onto solid body surface (plasma jet, arc spot, laser or electron beam), and also subsequent cooling and solidification of the melted substrate layer. In the numerical procedure, the finite-element method was employed. The processes of interest can have different characteristic time and spatial scales, which in addition can suffer drastic changes at heat flux densities q ?[108 ;1014 ] W/m2. An advanced procedure was developed to enable dynamic adaptive triangulation of domains involved in the current numerical solution and characterizing the different phase states (liquid or solid) of the materials. This procedure, belonging to the class of the frontal algorithms, allows one to break a solution domain into triangles based only on the domain boundaries. The model applications of the developed simulation software are illustrated.
Impact Modeling of Thermally Sprayed Polymer Particles
Authors: Ivosevic M. , Cairncross R.A. , Knight R.
Published: August 2022

Thermal spray has traditionally been used for depositing metallic, carbide and ceramic coatings, however, it has recently been found that the high kinetic energy of the High Velocity Oxy-Fuel (HVOF) thermal spray process also enables the solventless processing of high melt viscosity polymers, eliminating the need for harmful, volatile organic solvents. A primarily goal of this work was to develop a knowledge base and improved qualitative understanding of the impact behavior of polymeric particles sprayed by the HVOF combustion spray process. Numerical models of particle acceleration, heating and impact deformation during HVOF spraying of polymer particles have been developed. A Volume-of-Fluid (VoF) computational fluid mechanics package, Flow3D®, was used to model the fluid mechanics and heat transfer during particle impacts with a steel substrate. The radial temperature profiles predicted using particle acceleration and heat transfer models were used as initial conditions in Flow3D® together with a temperature-dependent viscosity model to simulate polymer particles with a low temperature, high viscosity core and high temperature, lower viscosity surface. This approach predicted deformed particles exhibiting a large, nearly hemispherical, core within a thin disk, and was consistent with experimental observations of thermally sprayed splats made using an optical microscope.
Observation of Deformation and Microstructure at the Interface Between WC-Co HVOF Sprayed Coating and Carbon Steel Substrate
Authors: Owada A. , Watanabe M. , Kuroda S.
Published: August 2022

The mechanical deformation and microstructure formation at the interface of a high velocity oxygen fuel (HVOF) sprayed WC-Co splat on a carbon steel (0.45%C) have been studied by the focused ion beam (FIB) cross-sectioning and examined by scanning electron microscopy (SEM). Several types of WC-12wt.%Co powders with different WC particle sizes, 0.2 ~ 7.0µm were used for spraying to investigate the size effect of these WC particles onto the splat morphology and microstructure around the interface. The interface fracture toughness of the coatings made of these powders was evaluated by the pre-notched four-point bending test and the correlation between the splat microstructure and the toughness variation was investigated. The interface fracture toughness of these WC-12%Co coating / carbon steel was evaluated as about 600~1700J/m2. It was revealed that the WC particle size in the original powders has large effects onto the interface adhesion.
Experiences in Education/Training and Qaulification of Thermal Spraying Personnel According International Guidelines and Standards
Authors: Böhme D. , Huber R. , Ohliger-Volmer A.
Published: August 2022

In the field of thermal spraying a lot of things have been and still are happening concerning education and training of personnel. The education and training of thermal sprayers according EWF-Guideline is required frequently in combination of the international standard DIN EN ISO 14918 “Approval Testing of Thermal Sprayers” - especially in the German-language countries. Meanwhile about 13 ETS courses were held at the German Welding Institute. Also interested in the education and training of thermal sprayers are countries like Poland and China. In France thermal spray personnel was educated and trained in a company internal course. Sweden and Norway run ETS courses in cooperation. The EWF education and training course of the ETSS European Thermal Spraying Specialist will be offered by the German Welding Institute in Munich - SLV München - for the nineth time in October 2005. Since about 1993 European Committees of EWF (European Federation of Welding, Joining and Cutting) and CEN (European Committee or Standardization) worked out education and training guidelines and qualification standards of thermal spray supervising personnel and sprayers and established them step by step. The meanwhile created and internationally accepted EWF-education and training guidelines of supervising personnel and thermal spray workers involve also the new ISO standards of the Thermal Spraying Co-ordinator and the Approval Testing of Thermal Sprayers. The ISO personnel qualification and quality management standards result together with the EWF education and training guidelines in a sound QM-system, which meets the increased demands of trade and industry of high quality sprayed coating. Experiences in applying these guidelines and standards are introduced.
Shear Force on Wire Tips in Wire Arc Spraying System
Authors: Pourmousa A. , Montazeri H. , Mostaghimi J.
Published: August 2022

In order to find the size and shape of particle detachments in the wire-arc spraying system, it is required to find the shear force on the electrodes (wire-tips). To solve the gas flow problem, the system was divided into two regions: (1) upstream and (2) downstream of the nozzle exit. In region 1, the axisymmetric turbulent gas flow is numerically solved and compared to its approximate analytical solution. In the second numerical region, which includes the tips of the two wires, shear force on the electrode surfaces is evaluated from the gas flow velocity profile adjacent to the electrodes. The gas flow in these regions is solved using the FLUENT software. Abstract only; no full-text paper available.
Development of a Technique for Hard Coating of Component Parts by Synthesis of Silicon Carbide in Thermal Spray Processes
Authors: Bach Fr.-W. , Möhwald K. , Drößler B.
Published: August 2022

The Goal of this research project is the development of a thermal spray technique for production of layers with high SiC content. Due to its physicochemical characteristics, silicon carbide (SiC) is a material which is particularly well suited as a component of wear-protection layers [1]. In thermal spray, however, silicon carbide can not be processed easily, since it disintegrates and sublimates into the gaseous phase at the prevailing high process temperatures under atmospheric conditions. In this project, SiC-phases of the spray layers are to be in-situ synthesized from silicon and carbon-containing substances during the spray process. Silicon containing solids are to be brought into reaction with carbon-containing solids, liquids and gases. For economic reasons, this technique is aimed at using low-priced basic materials to be processed by flame- and plasma spraying techniques with only slight modifications to existing atmospheric spraying equipment; thus the said SiC coatings might become an alternative to assigned hard material coatings. In this first step the technologic-mechanical potential and thus the feasibility and usability of a yet to develop coating system by different synthesis routes should be evaluated.
Influence of WC-Co Type Thermal Spray Powder Characteristics on HVOF Coating Properties
Authors: Song X. , Liu W. , Cui Y. , Wu C. , He M.
Published: August 2022

With the incoming of HVOF, the coating properties and application extent of WC-Co type have been greatly improved, in the recent years, we found that the characteristics of WC-Co powder has some influence on its coating properties prepared by HVOF. In this paper, study has been prepared on powders made from aboard and Beijing General Research Institute of Mining & Metallurgy properties such as fluidity, aspect, profile of coating SEM and carbon content, also phase structure and properties analysis of HVOF coating has been made. Finally, influence of powder preparing technology and HVOF technology parameters of different powders for coating properties have been described.
Thermal Properties of Continuously Graded Thermal Barrier Coatings Deposited by Supersonic Plasma Spray
Authors: Shikui Z.
Published: August 2022

Continuously graded yttria stabilized ZrO2 /NiCoCrAlY coatings were prepared using a high efficiency supersonic plasma-spray system and the thermal shock properties of the coatings were studied. The specimens were so prepared that the two kinds of powders with different melting point were fed to the different regions of the plasma jet by using two powder feeders. The two powders melted perfectly at the same power, and the overheating of the powder with lower melting point was avoided. In this way, a continuously graded transition layer was obtained. The Results show that the continuous change of the coefficients of thermal expansion and thermal conductivity in the transition layer leads to a excellent thermal shock resistance of the totally 0.9mm thick TBCs. The thermal shock cycles of the specimens which underwent heating by oxygen-acetylene to 1200 C and then quenching into water reached moer than 200.The coatings’ surface was still perfect without any visible cracks. The analysis shows that the dense structure and the sufficient plastic deformation of the particles depressed the formation of TGOs, which, together with the continuously graded thermal expansion coefficient and thermal conduction coefficient, contributes to the long thermal shock resistance of the coatings. Abstract only; no full-text paper available.
High Temperature Characteristics Research of CoCrAlYTa Coating
Authors: Song X.J.
Published: August 2022

High temperature alloy powder CoCrAlYTa made by vacuum-atomized technology has satisfied properties such as spherical degree, fluidity and low oxygen quantity etc. Compact and steady high temperature properties coating was prepared when CoCrAlYTa was blast sprayed onto stainless steel. In this paper, several high temperature working performance like hot shocking, high temperature oxidation and high temperature corrosion of CoCrAlYTa coating got was studied, the micro-structure of coating was analyzed with metallographical analysis, SEM and XRD. Experiments results indicated that, with the added of Y and Ta, the structure and toughness of chromium and aluminum oxidation membrane in the coating was improved, overall, blast spraying coating has excellent high temperature characteristics. Abstract only; no full-text paper available.
Alumina-Titania Coatings Deposited by Laser-Assisted Air Plasma Spraying: Microstructure and Mechanical Characterization
Authors: Dubourg L. , Lima R.S. , Moreau C.
Published: August 2022

Alumina-titania coatings deposited by air plasma spraying (APS) are widely used to protect components against wear at low temperatures. It is known that microstructures formed by the post-laser remelting of as-sprayed coatings exhibit a densification but also numerous macrocracks due to the rapid cooling and thermal stresses. By using the laser-assisted air plasma spraying (LAAPS), the laser beam interacts simultaneously with the plasma torch in order to increase coating surface temperature and possibly superficially remelt the coating. As a result, the microstructure is partially densified and macrocracks, which are generally produced in the post-laser irradiation treatment, can be inhibited. In addition, this hybrid spraying can be done without the post-treatment of coating. In this paper, LAAPS was performed to improve the mechanical properties of Al2O3-13%TiO2 coatings. The coating microstructure was characterized by SEM and X-ray diffraction. The mechanical characterization was done by hardness measurements, erosive wear tests and abrasion wear tests. Results showed that laser assistance may induce: (1) the disappearance of vertical and horizontal macrocracks due the laser irradiation in the coatings for a laser irradiation density lower than 34 W.mm-2, (2) an important decrease of the amount of microcracks in the deposited splats, (3) the partial transformation of the metastable γ-Al2O3 phase in the equilibrium α-Al2O3 phase, (4) a hardness increase of 11%, (5) an improvement of the erosive wear resistance by 12% and (6) an improvement of the abrasive wear resistance by 38%.
Research on the Coating Performance Produced by Arc Spraying using High Velocity High Energy Combustion Gas
Authors: Huang X. , Wang R. , Zhang T. , Xu L.
Published: August 2022

In this paper describes the design of the arc spray gun with secondary atomization, which using the mixture of propane and air as the main gas and the compressed air as the gas for secondary atomization. The test shows that in the high velocity airflow produced by the combustion of propane – air mixture, the atomized particle size is less than 20 micron. In the second- combustion thermal airflow, the high temperature area of the arc beam is obviously lengthened at the same time the combustion gas environment restrains the oxidation of the spraying materials. Because the speeds of particles are improved greatly, the coatings obtained are denser. Through practical application it shows that this system can obtain stable deposition efficiency, high bond strength, and low roughness and greatly reduce the cost of machining. Abstract only; no full-text paper available.
Correlation of Plasma Process Conditions, Phase Content, and Photocatalytic Performance of Induction Plasma-Sprayed Titania Coatings
Authors: Burlacov I. , Heimann R.B. , Müller M.
Published: August 2022

Systematic variation of the induction plasma spray (IPS) conditions, i.e. (i) plasma power, (ii) carrier gas flow rate, and (iii) powder feed rate was performed to deposit TiO2 coatings using statistical design of experiments (SDE) methodology. The microstructure, surface morphology, and anatase-rutile ratio of the coatings were studied by grazing-incidence X-ray diffraction (GIXD) and surface mapping with micro-probe Raman spectroscopy to determine the spatial phase distribution of anatase and rutile. The photocatalytic activity of the TiO2 coatings was tested by decomposition of 4-chlorophenol in aqueous solution in the dark and under UV irradiation. The rates of pH changes measured were compared with those of standard Degussa P-25 coatings. The photocatalytic activity of the samples shows a reasonable correlation with the phase content and the plasma processing conditions prevailing during coating deposition.
Development of Gas-Tight Zirconia Electrolyte Layers by Atmospheric Plasma-Spraying
Authors: Vaßen R. , Hathiramani D. , Stöver D.
Published: August 2022

Atmospheric plasma-spraying (APS) is an attractive process for the production of solid oxide fuel cell layers. However, especially the manufacture of gas-tight electrolyte layers is a major challenge as typical APS ceramic coatings contain microcracks and pores which allow an easy penetration of gases. To overcome this problem a detailed understanding of the formation of microcracks and pores in the coating was developed. These ideas and the conclusions made will be described in detail. Major influencing factors were identified to be substrate temperature, particles temperature and velocity, particle size, and the way the plasma gun is moved. According to the outcome of these considerations spraying experiments have been performed with different yttria stabilized zirconia (YSZ) powders including spray dried and fused and crushed types. Porous, tape-casted metallic plates were used as substrates. Employed measures for the coating optimization lead to a significant reduction of both length and opening of the microcracks. These results were in accordance with the outcome of leakage tests. It was possible to improve the leakage rates by several orders of magnitude and to achieve sufficiently low values for an application as solid oxide fuel cell electrolyte without any subsequent thermal treatment.
Effective Laser-Cladding through the Application of Magnetic Induced Forces
Authors: Wilden J. , Bergmann J.P. , Dolles M.
Published: August 2022

In the last years laser beam cladding was recognised as a high quality coating process. Low thermal influence, high cooling rates, metallic bonding, minimal surface roughness are only some of the positive aspects. On the other hand the process efficiency is very low and the running costs in comparison to PTA or Thermal Spraying are high. Attempts to improve the productivity aim to enhance the efficiency of the beam source itself or to optimize the energy management. This is for example possible through a higher coating speed or through hybrid setups, which allow the use of an additional preheat source (e. g. plasma-assisted laser cladding). Regarding flexibility, defined as the capability of a process to answer in a short time to application requests, the effectiveness of laser cladding can be widely increased through free forming (shaping) of coatings without additional clamping devices. The geometric shape of the coating seam is mainly defined by gravity and surface tension of the melt. An additional force, as for example Lorentz force, can optimize the geometry and improve the process conditions. Wide seams allow for example a low number of overlapping layers when coating large areas and rise the specific area deposition rate. Slim coatings on the contrary are advantageous when generating 3-dimensional structures. The induced force depends from the applied magnetic field and the flow of an electric current. The presented investigations clarify the physical background, the interaction of the magnetic force and the geometric shape of the coating and the possibility to apply them for technical coatings. The application of an external force made it possible to increase the efficiency of the laser cladding process and to gain more interest of the industry.
Improved Process Controls of Combustion Sprayed Clearance Control Coatings Through Sensor Diagnostic Technology
Authors: Fiala P. , Hajmrle K. , Dorfman M.R. , Dambra C. , Mallon J.
Published: August 2022

Sensor technology is becoming more of a production tool to help improve production quality, reliability and reduce manufacturing costs. Combustion sprayed abradable seal products are a family of materials where this technology will be helpful to the applicator and end user. Although these materials have been used for over forty years with wide success in the aerospace and industrial gas turbine industries they can be sensitive to spray process variables. Changes in spray processing conditions during spraying will change the desired microstructure and coating properties. This paper looks at a commercially available combustion powder and how process parameters such as gas flows and powder feed rates affect output process variables such as particle velocity and temperature. This paper will also discuss the importance of understanding the influences that particle temperature and velocity have on coating properties such as hardness, erosion and coating strength. Deposit efficiency of these combustion powders is also measured as a function of particle temperature and velocity. Based on particle temperature and velocity, sensor diagnostic tools can provide warnings about process changes resulting in fast corrective action. The benefits of this sensor technology are the potential for less inspection requirements, improved microstructure control, reduced in-service failures, and less time and labour required for stripping coated components that may not meet specification standards.
Influence of Reflected Radiations on in Flight Particle Temperature Measurements
Authors: Klein D. , Salhi Z. , Coddet C.
Published: August 2022

Characteristics of in flight particles before they impact on the substrate influence strongly the quality of coating obtained by plasma spraying. Various optical techniques can be used to measure the in-flight particle characteristics; some of these techniques require the use of high- speed two-color pyrometers to collect the light emitted by the particle during the in-flight period when they pass through the measurement volume. However, the intense radiation coming from the plasma can affect the particle thermal radiation and lead to erroneous measurements. This work was dedicated to the study of reflected light coming from the plasma and scattered by the injected particles. To achieve this goal, sprayed particles were analyzed by optical emission spectrometry. The light scattered by the particles was found to influence significantly the measured temperature. This work allows thus the estimation of the accuracy of temperature measurements on particle surface for the thermal spraying process. Abstract only; no full-text paper available.
Transient Thermal Analysis and Coating Formation Simulation of Arc Spray Process
Authors: Zhu Y. , Liao H. , Coddet C.
Published: August 2022

A finite difference model for the thermal analysis of the dynamic stochastic multiple particle deposition process of thermal spray was developed in this paper. Contrary to the traditional layer by layer deposition model, the thermal contribution of individual particles randomly distributed around the spray jet center was taken into account so as to simulate coating formation process. New material was dynamically added onto coating/substrate surface with prescribed gun movement. Latent heat effect was introduced by defining the enthalpy of the material as a function of temperature in order to take into account solidification induced phase change. Real thermal spray process can be simulated with adjustable particle size, spray deposition rate, velocity of gun movement, etc.
Residual Grit on the Substrate Surface in Roughening Treatment: Quantitative Evaluation and a Reduction Technique
Authors: Maruyama T. , Kobayashi T. , Tsujimoto K. , Tani K. , Tanaka K.
Published: August 2022

Generally, the surface of a substrate is roughened by blasting in pretreatment thermal spraying. Since some of the grit remains on the substrate surface, sprayed coating and the adhesion property characteristics are degraded. However, it seems that there is almost no research on this problem. In this study, residual grit is quantitatively evaluated, and a technique for reducing grit is proposed. For residual grit reduction, a solid lubricant was used, and applied to the surface of a substrate or grit; reduction of residual grit was confirmed. After blasting with solid lubricant, it remained on the substrate surface, which could be removed by heating the substrate.
Splat Formation Under YSZ Hollow Droplet Impact Onto Substrate
Authors: Solonenko O.P. , Mikhalchenko A.A. , Kartaev E.V.
Published: August 2022

Formation of splats from hollow YSZ droplets deserves a special attention for thermal spraying. In this case, immediately prior to particle – substrate collision, we have a drop that consists of a liquid shell enclosing a gas cavity heated to a temperature close to the melt temperature. As the drop impinges onto the substrate, it suffers considerable deformation resulting in a rise of the gas pressure and in a decrease of gas temperature. The paper presented includes the results of the model experiments carried out under full control of the key physical parameters (KPPs) - temperature, velocity and size of droplet, and temperature of polished substrate, in which the starting powder was a specially prepared powder consisting exclusively of the hollow spherical YSZ particles. The main goal of the paper is to discuss and study the possible splat formation scenarios under above-mentioned conditions.
Sliding Wear of Plasma Sprayed ZrO2 Coatings using Nanostructured Powder
Authors: Ding C. , Liang B. , Chen H.
Published: August 2022

Plasma sprayed yttria-stabilized zirconia coatings were deposited using nanostructured and conventional powders with optimized process parameters. The sliding wear of both coatings against stainless steel were examined with a block-on-ring test under dry friction condition. It was found that the friction coefficients and wear rates of coatings deposited using the nanostructured powder were lower than that of coatings deposited using the conventional powder. The high wear resistance of the plasma sprayed ZrO2 coating using the nanostructured powder is attributed to its enhanced cohesion, improved microhardness and homogeneous microstructure.
Nanostructured NiTi Coatings Produced by Low Pressure Plasma Spraying
Authors: Ajdelsztajn L. , Sickinger A. , Schoenung J.M.
Published: August 2022

This work describes the synthesis and characterization of nanostructured coatings produced by low pressure plasma spraying (LPPS) of cryomilled NiTi powder. Ni and Ti powders (60 and 40 wt %, respectively) were cryomilled together and LPPS sprayed onto stainless steel substrates. The elemental powders reacted and alloyed during cryomilling forming a nanocrystalline grain structure with nanodispersed oxide and nitride phases. These nanodispersoids are formed due to contamination by the milling media (liquid nitrogen). After spray deposition, the coatings presented a nanostructured microstructure with enhanced mechanical properties when compared with conventional NiTi coatings sprayed under the same conditions. High hardness and toughness values together with intrinsic corrosion resistance of the NiTi alloy lead to the formation of an attractive coating material for applications where corrosion and wear resistance are required. The ability to synthesize the NiTi from elemental Ni and Ti powders and the refinement of the microstructure achieved during milling makes the cryomilling process together with thermal spray of the nanostructured NiTi coatings a unique process and coating to be used in engineering applications. Abstract only; no full-text paper available.
The Delamination Wear Mechanism of Thermally Sprayed Coating
Authors: Zhu Z. , Xu B.-S. , Liu Y. , Chen Y.-X. , Ma S. , Li Z.-X.
Published: August 2022

The delamination wear mechanism of the thermally sprayed coatings was studied by analyzing coatings structural feature and stress distribution on the warm surface, and the influencing factors on the delamination wear were discussed. And the delamination wear mode of coating was developed. The results show that, the thermally sprayed coatings have typical aspect of lamellar structure. There are oxide layers between splats, and there also exist porosity and micro-crack in the coatings. The coating surface was subjected to alternately tensile stress and compression stress caused by normal load and friction force during sliding. In a certain depth below the surface, there exists maximum shear stress. Therefore fatigue damage will take place at subsurface of the coating under alternate stress. The adhesion strength between splats of coating prepared by HVAS is by far lower than casting material because of lamellar structure. And the adhesion strength between splats is further weakened due to the defects (such as porosity and micro-crack) appearing mostly on the boundaries between thin oxide sheets and splats. When the fatigue damage accumulates to a certain value, micro-cracks initiate at the defects between splats. Then these micro-cracks grow, connect, and propagate along the defects between splats. Finally, these cracks shear to the coating surface leading to spallation of the splats, and thus wear debris is generated. By repeating the above process delamination of the coatings will occur. Reducing friction coefficient, increasing coatings hardness and adhesion strength between inter-splats are the basic methods to improve the wear resistance of thermally sprayed coatings. Abstract only; no full-text paper available.
Investigations on Corrosion Protective Layers in Waste Incineration Plants
Authors: Crimmann P. , Bendix D. , Faulstich M.
Published: August 2022

Corrosion in the hot gas area of waste incineration plants is a severe problem that often causes premature damage of components. In general, these components are made of base materials, which are not stable in corrosive conditions (boiler steel). Thermal spraying is an alternative to the most usual process cladding, which has the potential to create cost-efficient protective coatings. Until now, there are still not enough experiences about quality assurance (porosity, oxides) and long run behaviour inside the incineration plants with sprayed coatings. Since many years, ATZ Entwicklungs zentrum is involved in the development and/or advancement of materials, technologies, and applications of thermal spraying for corrosion protection. Currently, pipes, coated with different materials and different technologies are tested by different strategies (corrosion tests under laboratory scale and/or directly in incineration plants).
Charges Generation and Separation in Plasma Sprayed TiO2-Fe3O4 Coatings
Authors: Ye F.-X. , Ohmori A. , Li C.-J.
Published: August 2022

TiO2 based coatings are promising photocatalyst as they are chemically stable and nontoxic. To develop more effective photocatalyst with cost effective plasma spraying technique, TiO2 and TiO2-Fe3O4 coatings were prepared using agglomerated anatase TiO2 and composite TiO2-Fe3O4 powders, respectively. The photocatalytic activity and photoelectrochemical characteristics of sprayed coatings were examined. The photo-response of the sprayed TiO2 electrode was comparable to that of single crystal TiO2, but the breakdown voltage approximated to 0.5V (vs. SCE). The short-circuit current of TiO2 was 1.05mA/cm2, which was 15 times comparing with that of TiO2-Fe3O4 electrode under 30mW/cm2 xenon light illumination. N-type TiO2 semiconductor particle reacted with Fe3O4 or Fe2O3 particle and concurrently produced p-type FeTiO3 in plasma spraying processes. FeTiO3 compound obviously improved the photocatalytic activity of the TiO2 coating for the formation of p-n junction between p-type FeTiO3 and n-type TiO2, which may spatially separate the photo-generated electrons and holes. As a result, plasma-sprayed TiO2-Fe3O4 coatings are promising candidates for the applications to photocatalyst.
Direct Observation of Deformation and Solidification Process of Metallic Molten Droplet on to Substrate by using High Speed Video Camera System
Authors: Oki S.
Published: August 2022

Deformation and solidification process of molten metal droplets was directly observed by high speed video camera system. These processes depend on the droplet property, and affect the microstructure of splats. Relationship between formation process and microstructure of splats was discussed. Abstract only; no full-text paper available.
Resin/Diamond Surfaces Enhance Microstructural Analysis of Thermally Sprayed Coatings
Authors: Blann G.A. , Lucas G.
Published: August 2022

Microstructural analysis has played, and continues to play, a key role in the development of thermally sprayed coatings. The advances in equipment and consumable technology for evaluating coatings have enabled laboratory personnel to accurately observe the coating characteristics in a cost effective manner and with great confidence. Microstructural analysis has been important in the development of new thermally sprayed coatings used for aerospace, automotive, electronic, bio-technology, petroleum and other high and low tech applications. The coatings that are being developed consist of a combination of materials that vary in hardness and general microstructural characteristics. Accurate microstructural analysis is more important than ever because these new, complex coatings cannot be produced successfully without control of the microstructure. Established metallographic techniques have not always been able to produce accurate results. A resin bonded diamond surface was developed which reduces the damage created during the grinding and lapping of a variety of coating types while maintaining the flatness and integrity of the overall coating microstructure.
The Indentation Tests for Evaluation of HVOF Coatings’ Mechanical Properties
Authors: Houdkova S. , Enzl R. , Zahalka F. , Blahova O.
Published: August 2022

Indentation tests were provided with various applied loads and indentors’ profiles to determine the mechanical properties of selected HVOF coatings. The four well-known wear resistant coatings, WC-17%Co, Cr3C2-25%NiCr, NiCrSiB and AISI 316L, sprayed by TAFA JP-5000, were tested. Besides the common indentation tests (e.g. coatings surface hardness and microhardness), the indentation fracture toughness (IFT) and Young modulus of elasticity (E) were measured using Vickers and Knoops indentors profiles, resp. From the Vickers indentation results, the IFT was evaluated in terms of 18 models for KIc determination. The big differences between results of used models were found. For evaluation of E, the Knoop indentation in three different orientations was used. The measurement results show the anisotropic behavior of sprayed coatings. Based on the measured data, the relation between coatings properties with respect to the coating unique microstructure was proved.