bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation of the Electrical Behavior of Thermally Sprayed Aluminum Oxide
Authors: Swindeman C.J. , Seals R.D. , Murray W.P. , Cooper M.H. , White R.L.
Published: May 2021

Electrical properties of plasma-sprayed aluminum oxide coatings were measured at temperatures up to 600 °C. High purity (>99.5 wt% pure Al2O3) alumina powders were plasma-sprayed on stainless steel substrates over a range of power levels, using two gun configurations designed to attain different spray velocities. Key electrical properties were measured to evaluate the resultant coatings as potential insulating materials for electrostatic chucks (ESCs) being developed for semiconductor manufacturing. Electrical resistivity of all coatings was measured under vacuum upon heating and cooling over a temperature range of 20 to 600 °C. Dielectric constants were also measured under the same test conditions. X-ray diffraction was performed to examine phase formation in the coatings. Results show the importance of powder composition and careful selection and control of spray conditions for optimizing electrical behavior in plasma-sprayed aluminum oxide, and point to the need for further studies to characterize the relationship between high temperature electrical properties, measured plasma-spray variables, and specific microstructural and compositional coating features.
Fatigue Strength of Ceramic-Coated Steel at Elevated Temperature
Authors: Sonoya K. , Tomisawa Y.
Published: May 2021

Low cycle fatigue tests were performed at room temperature (RT) and at 673 K for l%Cr-0.5%Mo steel comparing the specimens coated with chromium carbide by gas spraying and the ordinary uncoated specimens, and the mechanism of fatigue crack formation was investigated. Following observations and conclusions were made: (1) When sprayed with ceramic, the fatigue life suffers reduction at either temperature, but at 673 K, the degradation was so much smaller than that at RT that the fatigue life was actually, though slightly, longer than that at RT. (2) The cracks are initiated in the ceramic layer very early in the whole fatigue life, the crack initiation lifetime becoming the longer, the smaller the strain range. (3) The fatigue failure process can be viewed as comprising following steps: first, early initiation of fatigue crack at the surface of the ceramic coating, rapid propagation through it to the substrate metal, and initiation of crack in the metal, the initial rate of propagation of such a crack being a number of times (perhaps as much as one full order of magnitude) faster than that in uncoated steel.
Residual Stress in Net-Shape Plasma Sprayed Tubes: Measurement, Modeling and Modification
Authors: Bartlett A.H. , Castro R.G.
Published: May 2021

Residual stresses in net-shaped plasma sprayed tubes was measured by X-ray microdiffraction, as a function of radial position in the sample. A tensile to compressive hoop stress profile was measured, ranging 200 MPa in tension at the outer diameter, to ~125 MPa at the inner. A force balance model was used to explain the evolution of stresses when incrementally adding layers to the pre-existent material.
Effects of Powder Morphology, Microstructure, and Residual Stresses on Thermal Barrier Coating Thermal Shock Performance
Authors: Wigren J. , de Vries J.-F. , Greving D.
Published: May 2021

Thermal barrier coatings are used in the aerospace industry for thermal insulation in hot sections of gas turbines. Improved coating reliability is a common goal among jet engine designers. In-service failures, such as coating cracking and spallation, result in decreased engine performance and costly maintenance time. A research program was conducted to evaluate residual stresses, microstructure, and thermal shock life of thermal barrier coatings produced from different powder types and spray parameters. Sixteen coatings were ranked according to their performance relative to the other coatings in each evaluation category. Comparisons of residual stresses, powder morphology, and microstructure to thermal shock life indicate a strong correlation to thermal barrier coating performance. Results from these evaluations will aid in the selection of an optimum thermal barrier coating system for turbine engine applications.
Repair of Water Turbine Blades by Wire Electric Arc Spraying
Authors: Musil J. , Dolhof V. , Dvorácek E.
Published: May 2021

Water turbine parts damaged by cavitation erosion (CE) and/or slurry erosion (SE) may cause excessive operational costs for plants worldwide. The damages can be reduced by choosing more resistant materials and right technology in the first-production or at repair and overhaul. Thermal spray technologies have a great potential in the field of repairing works. Thick multilayered coatings deposited by wire electric arc spraying (WAS) has been developed and applied as CE and SE protection at the repair of stationary Francis turbine blades. Repair technology by WAS was performed on large eroded areas (1-3 m3) of preguide blades of Francis turbine: 1) local damaged depths 30-35 mm maximum were repaired by sprayed materials, 2) subsequently wire arc spraying of functional coating was applied. Three types of functional coatings with total thickness 10 mm a) duplex high - Cr stainless steel with NiAl bond coat, b) graded NiAl - Cr stainless steel coatings, and c) multilayered graded NiAl - Cr stainless steel coatings were compared by means of stress measurements and structural analysis. The coating structure influences very strongly the residual stress level and adhesive-cohesive strength. Multilayered graded NiAl - Cr stainless steel coatings showed the best results and were sprayed on water turbine blades in 4 Czech water power station during regular cut-off repair periods. After 30 - 36 months' continuous operation, Francis turbine blades repaired by WAS technology show better behaviour in comparison with original material from the point of wear resistance, reliability, cost-effect and life-time.
Modeling and Characterization of Residual Stresses and Microstructure in Thermal Barrier Coatings after Plasma Spraying
Authors: Persson C. , Bengtsson P. , Wigren J. , Greving D.
Published: May 2021

Thermal barrier coatings with a zirconia top coating and a NiCoCrAlY bond coating were plasma sprayed onto a nickelbase alloy. The pre-heating of the bond coated substrates and the cooling during the top coating spraying were varied to produce five different spray sets. A finite element model was developed to predict the heat transfer and the resulting thermal stresses during the spraying. A layer removal technique was used to measure the residual stresses in the as-sprayed samples. The measurements revealed low residual stresses in the top coatings and tensile stresses in the order of 150 MPa in the bond coating. A correlation between the measured top coating residual stresses and the substrate temperature in the end of the top coating spraying was found. In general, good agreement between modelled and measured residual stresses was found. The top coatings were found to contain vertical microcracks and the densities of the cracks were point-counted in the spray sets. A slight increase in microcrack densities was found as the spraying was performed onto a colder substrate. The densities of vertical microcracks were correlated to modelled in-elastic strain in the top coatings.
Nondestructive Characterization of Plasma Sprayed Coatings by Laser Ultrasonics
Authors: Viens M. , Drolet D. , Blouin A. , Monchalin J.-P. , Moreau C.
Published: May 2021

Nondestructive methods previously developed for the detection of flaws, such as delaminations, or for the evaluation of the elastic properties of materials, could be judiciously adapted in order to get a better assessment of plasma-sprayed coatings. Laser ultrasonics is a nondestructive evaluation method which relies on both optics and ultrasonics. A short-pulse laser generates an ultrasonic wave into the material to be inspected, and a long-pulse laser, coupled to an interferometer, detects the resulting ultrasonic displacement. Laser ultrasonics is a remote sensing method and therefore could be used for the monitoring of hot plasma-sprayed coatings during the deposition process. In this work, experiments were performed on samples composed of ZrO2 sprayed under different conditions onto thick copper substrates. The samples were first probed by conventional ultrasonic transducers and then by a non contact laser-ultrasonic scanning system. The two series of measurements agreed well. These experiments showed that, after calibration, the coating thickness could be measured during the deposition process, with a relatively good accuracy, by laser ultrasonics. The laser-ultrasonic scanning system also revealed non uniformity of more than 10% in the coating thickness of the tested samples. This thickness variation is possibly caused by a temperature gradient induced in the coatings during spraying.
Plasma Spraying of Self-Lubricating Cr2O3-CaF2 Coatings
Authors: Vos F. , Delaey L. , De Bonte M. , Froyen L.
Published: May 2021

Results are presented of a project analysing the relationship between the production parameters of plasma sprayed self-lubricating Cr2O3-CaF2 coatings and their structural, wear and lubricating properties. The production method consists of a preparation step where a powder blend of the matrix material (Cr203) and solid lubricant (CaF2) is agglomerated, followed by atmospheric plasma spraying (APS) of the agglomerates. Selection of the most appropriate agglomeration and plasma spray parameters as well as the microstructure of the coatings will be discussed.
Thermal Shock Resistance of Plasma Sprayed Tungsten Coatings
Authors: Urquiaga Valdes M. , Saint-Jacques R.G. , Moreau C.
Published: May 2021

Plasma sprayed tungsten coatings are considered as potential candidates for materials in contact with the plasma in future fusion reactors. In this work, the thermal shock resistance of these coatings is studied to determine which of five changed deposition parameters most influences the coating's performance. The thermal shocks were generated with a pulsed electron beam gun. The pulse duration was 0.2 and 0.5 s and the absorbed power density 60 MW/m2. Two series of samples were analyzed. One was plasma sprayed at atmospheric pressure (AP) and the other at low pressure (LP). The LP coatings were deposited on a molybdenum alloy (TZM). AP coatings were deposited on molybdenum and on water cooled copper coupons for fatigue tests. The porosity seems to be a positive factor for thermal shock resistance. The thickness of the coatings and the spraying atmosphere were found to strongly influence the thermal shock resistance. In the case of the fatigue test, some coatings withstood up to 1000 shocks of 0.5 s duration.
Technology Transfer
Authors: Naisbitt G. , Alderton T. , Bruce C.
Published: May 2021

High Velocity Oxy Fuel, (HVOF), is a high energy Thermal Spraying Combustion Process, producing high density coatings with hardness values in excess of 1200 VPN. Such coatings, using metal carbide spray material, are used extensively in the aerospace industry, in areas where high wear resistance is particularly important. The Linde Detonation Gun, CD-Gun'), has until recent times been the predominant system for applying these hard faced coatings. However, the advent of a number of new HVOF systems approximately 5 years ago, allowed Gas Turbine Repair and Overhaul bases the opportunity to offer a more competitive coating service, i.e. these "1st generation" HVOF systems allowed the development of comparable, if not superior coatings to these produced by the D-Gun. Having successfully developed and approved HVOF coatings for the use on Rolls-Royce Gas Turbine components for both Repair and New Manufacture, Rolls Wood Group addressed the problem of transferring HVOF technology from aerospace components to alternative markets, i.e. refurbishment of equipment used in Oil and Gas Production.
Performance of WC-Based, HVOF-Processed Coatings in Sliding Wear
Authors: Marple B.R. , Arsenault B. , Voyer J.
Published: May 2021

For applications in which two contacting surfaces are in constant motion relative to each other, materials that are both wear resistant and non-abrasive are often required. Such attributes become even more important when the moving contact occurs with no liquid lubricants present to facilitate sliding. In the present study several WC-based coatings deposited using the HVOF process and containing one or more metal constituents as the binder (or matrix) phase were evaluated to determine their performance under conditions cf sliding wear. Image analysis of the coatings indicated a level of porosity of less than 1%. Hardness measurements found that values for the Vickers microhardness number were in the range of 1100-1500. For the wear tests, the test couple consisted of a coated ring (thrust washer type design) rotating against a stationary carbon disk. For each test, the contact load, speed of rotation and duration were controlled. During the test, the temperature of the carbon disk and the torque were recorded using a data acquisition system. This data was used to determine the coefficient of friction for each couple which, together with the results of measurements of weight change, provided a measure of the comparative performance of the various coatings. The preliminary results indicated that the values for the coefficient of friction for the various couples ranged from 0.15 to 0.29. The three coating compositions consisting of lONi-WC, 12Co-WC and 17Co-WC were found to out-perform other WC-based materials in these sliding wear tests.
Cavitation Resistance of Thermal Spray Coatings
Authors: Kumar A. , Boy J. , Zatorski R. , March P.
Published: May 2021

Cavitation and erosion damage to hydroelectric turbines and pumps can be a major problem. The effectiveness of thermal sprayed cavitation-erosion resistant coatings for hydroelectric turbine and pumps was evaluated. The coatings evaluated were applied using High Velocity Oxyfuel (HVOF) and Plasma Spray systems. Hard facing cobalt based alloys were evaluated on coupons in the laboratory. Testing was performed using a cavitating jet erosion apparatus utilizing an operating pressure of 27.6 MPa. The results were compared to welded 308 stainless steel. Cavitation resistant austenitic stainless steel weld alloys were also evaluated. The results showed that the cavitation rate of the austenitic stainless steel weld alloys were as low as one third of the rate of the 308 stainless steel. The cavitation rate of the thermally sprayed hard facing coatings were more than three times higher than the rate of the 308 stainless steel. CERHAB glass enamel coatings containing 7 wt % wollastonite fibers were successful applied by using two combustion spray processes. The applied CERHAB coatings were successfully annealed using field portable heaters and may have application as a seal coat for thermal spray coatings applied in the field.
Effect of Metallic Matrix Composition on the Erosion-Corrosion Behavior of WC-Coatings
Authors: Rogne T. , Solem T. , Berget J.
Published: May 2021

In corrosive media the wear resistance of ceramic-metallic coatings is dependent on the corrosion resistance of the metal matrix. Other factors that will affect the coating deterioration are the corrosivity of the medium and any galvanic interaction from the surrounding material. This paper presents results from a study where different types of WC(Co/Cr/Mo/Ni) powders have been sprayed by HVOF, Diamond Jet 2600 Hybrid equipment. The properties of the sprayed coatings have been verified by metallographic studies and by erosion-corrosion testing both under corrosive and non-corrosive conditions. The results clearly demonstrate the importance of having a metal matrix at least as corrosion resistance as the surrounding materials. When wear exposed components in pipe systems, pumps or valves are coated with a WC type coating, the corrosion resistance of the metal matrix should be compatible to the material of the rest of the system. This is especially important when the surrounding materials are corrosion resistant alloys as stainless steels, where the coatings otherwise will act as an anode.
Tribological Behavior of Plasma-Sprayed Coating Layers in Cr2O3/TiO2
Authors: Park J.M. , Lee S.W. , Kim B.K.
Published: May 2021

Wear property of plasma spray coating in Cr2O3/TiO2 powder manufactured of spray dry method on the aluminum substrate was inspected for the application of piston-ring of automotive engine. The plasma spray coatings were varied with feed rate and particle size. Using the ball-on disc type tribometer, wear volume property and surface roughness were investigated. The delamination of the coating layers and wear track were observed with SEM. Also, the cross-section of wear track were investigated, using optical microscopy. As a result of experiment, wear mechanism was addressed.
Composite Fe/TiC Powders for Wear Resistance Coatings Using Plasma Spray Process
Authors: Vitiaz P. , Azarova T. , Talako T. , Ilyuschenko A. , Steinhauser S. , Wielage B. , Gieland U.
Published: May 2021

This work evaluates the potential of using new competitive powders of Fe/TiC system for plasma spraying of wear resistant coatings. To improve coating properties, Cr and Ni were added to the iron matrix. The results of complex investigations of plasma coatings from such materials are presented.
Characterization of Thermal-Sprayed Titanium Anodes for Cathodic Protection
Authors: Holcomb G.R. , Cramer S.D. , Bullard S.J. , Covino B.S. , Collins W.K. , Govier R.D. , McGill G.E.
Published: May 2021

Thermal-sprayed titanium coatings were investigated as anodes for impressed current cathodic protection systems for steel reinforced concrete structures. The coatings were applied by twin-wire thermal-spraying using air and nitrogen as atomizing gases. The coatings were non-homogeneous due to oxidation and nitridation of the molten titanium with the atmospheric gases oxygen and nitrogen. The primary coating constituents were α-Ti (containing interstitial nitrogen and oxygen), γ-TiO and TiN. Nitrogen atomization produced coatings with less cracking, more uniform chemistry, and lower resistivity than air atomization.
An Assessment of Galvanic Effects in Thermal Sprayed Coating Systems
Authors: Hodgkiess T. , Neville A.
Published: May 2021

This paper focuses on the influence and role of galvanic interactions in the corrosion behaviour of thermally-sprayed coated components. Coatings, of different chemistry and applied by various processes (including HVOF) to substrates of carbon steel or stainless steel, have been utilised to facilitate study of galvanic corrosion phenomena both between coating and substrate and also within the coating itself. The experiments have involved the measurement of galvanic currents between separate specimens and also the microscopical examination of galvanic interactions on single specimens. Galvanic corrosion effects, on both a macroscale or microscale, have been observed and the implications of these for coating and coating/substrate integrity are discussed.
Effect of Thermal Spray Parameters on the Adhesion of Polymer-Based Coatings on Steel
Authors: Bao Y. , Gawne D.T. , Zhang T.
Published: May 2021

The adhesion of plasma sprayed polyamide and PMMA coatings to steel depends markedly on the plasma arc power, the spraying distance and the substrate temperature. Each of these process parameters shows an optimum value with respect to adhesion. The underlying reason for this behaviour is the pronounced sensitivity of polymers to temperature. Heat transfer analysis and electron microscopy indicate that a critical amount of heat is required to be transferred from the flame to the feedstock particles in order to provide sufficient splat flow but avoid coating thermal degradation. Inadequate flow leads to interfacial voidage while degradation gives inferior bonding and porosity.
On the Change in Stress State Associated with Bond Coat Oxidation during Heat Treatment of a Thermal Barrier Coating System
Authors: Tsui Y.C. , Clyne T.W. , Reed R.C.
Published: May 2021

Thermal barrier coating systems have been heat treated in order to study the oxidation kinetics of the bond coat. All the surfaces of Ni superalloy substrates were sprayed with ~100 μm of a NiCrAlY bond coat, with or without ~250 μm of a ZrO2 top coat. Thermogravimetric analysis (TGA) was used to monitor continuously the mass change as a result of oxidation of the bond coat during heating at 1000°C for 100 hours in flowing air. In addition, some specimens were heated to 1000°C in static air, cooled to room temperature, weighed and re-heated cyclically. The total exposure time was 1000 hours. Rates of weight gain were found to be higher for the cycled specimens, despite the absence of air flow. This is attributed to damage to the oxide film, which was predominantly α-Al2O3, as a consequence of differential thermal contraction stresses. The changing residual stress state during heat treatment was predicted using a previously-developed numerical model. A thin (1 mm) substrate with ~100 μm bond coat and ~250 μm ZrO2 top coat was used in these simulations, which incorporated creep of the bond coat and the lateral strain associated with oxidation. It is concluded from these computations that, while high stresses develop in the oxide layer, the associated driving forces for interfacial debonding remain relatively low, as do specimen curvature changes. It seems likely that coating spallation after extensive oxide layer formation arises because the interface is strongly embrittled as the layer thickens.
Properties of ZrO2-7wt%Y2O3 Thermal Barrier Coatings in Relation to Plasma Spraying Conditions
Authors: Funke C. , Siebert B. , Stöver D. , Vaßen R.
Published: May 2021

Superalloy samples were coated with thermal barrier coatings (TBC). This TBC-system consisted of two layers. The first layer was a vacuum-plasma sprayed, corrosion resistant layer (MCrAlY) which also acted as a bond coat. The ceramic top layer was atmospheric-plasma sprayed Y2O3-stabilized ZrO2. In order to produce different microstructures, the plasma-spraying parameters for the production of the ceramic coatings were varied. The different ceramic coatings were characterized in terms of porosity and mean elastic modulus. The porosity distribution was also investigated due to its influence on the measured elastic modulus. To record the changes of the plasma sprayed Zirconia due to sintering, the mean elastic modulus of selected coatings was measured as a function of annealing time. One series of TBC-coated specimens was cyclically oxidized at a maximum temperature of 1100°C. After 500 h of thermal cycling, creep within the MCrAlY-bond coat led to a coating failure at both the internal beveled edge and free edge around the specimen. A finite element analysis study of the cyclic oxidation experiment was performed to gain insight into the stress redistributions within the bond coat as a function of time. During the initial temperature increase, critical tensile normal stresses developed above the MCrAlY-Zirconia interface at the free edge. However, these normal stresses became compressive for all following cooling cycles. On the other hand, large tensile normal stresses developed above the MCrAlY-Zirconia interface at the beveled edge during all the cooling cycles. Therefore, high normal stresses responsible for debonding were present within the ceramic coating during all cooling cycles with the most critical stresses occurring at the free edge during the first cooling cycle and near the beveled edge for all the following cooling cycles.
Assessment of Thermal Barrier Coatings by Plasma Deposition
Authors: Ravichandran K.S. , An K. , Taylor R.
Published: May 2021

Thermal conductivity is an important design parameter for thermal barrier coatings. Accurate thermal conductivity data is therefore required to ensure proper design and reliability of gas turbine blades. In the present research, thermal conductivities of Al2O3 and 8wt.% Y2O3 stabilized ZrO2 (8YSZ) coatings, made by air plasma spray, were determined from the measurements of thermal diffusivity and specific heat as a function of temperature. Thermal diffusivity was determined by the laser flash technique. Specific heat was determined by a Differential Scanning Calorimeter (DSC). Detailed analyses of the results indicate that the thermal conductivity is sensitive to coating density (porosity), interfaces between splats as well as the interface between the coating and the substrate. Additionally, thermal conductivity evaluations of these coatings were also influenced by the accuracy and relevance of the data on bulk monolithic materials. Further, analyses of sensitivity of the laser flash technique to variations in the coating and the substrate parameters, for the coatings evaluated in this study, were also performed. The results are discussed in the context of coating characteristics, reference conductivity data for dense materials and the sensitivity of the measurement method to coating parameters.
Process Combination Thermal Spraying/Nitriding—Wear, Corrosion Resistance, and Coating Structure
Authors: Nestler M.C. , Spies H.-J. , Herrmann K.
Published: May 2021

At the present, components which require both nitriding and locally a thermal sprayed coating or nitrided components which should l)e reworked are usually nitrided before spraying and the area to be coated is masked during nitriding or is prepared before spraying by locally removing the nitrided layer by grinding. Seen technically, advantages are to be expected if the nitriding process can be carried out after spraying. Moreover a post-nitriding of thermal sprayed coatings is of interest for improving coating characteristics, mainly wear resistance. Understanding the behaviour of sprayed coatings during nitriding in comparison to bulk materials will help to understand generally the behaviour of such coatings in gas atmospheres at increased temperatures. The objectives of the project are the investigation of the interaction between thermal spraying and nitriding, and the optimisation of both processes to achieve improved bonding, wear and corrosion characteristics respectively to get nitriding of the substrate through the coating without spalling or cracking. Furthermore the behaviour and structural changes of different coatings at increased temperatures are determined. The metallographic, X-ray, wear and corrosion results of the resulting compound coatings and parts are presented. Possible new applications are discussed. The project is funded by the German Research Ministry.
Phase Composition Changes in Annealed Plasma-Sprayed Zircon-Alumina Coatings
Authors: Dubsky J. , Neufuss K. , Kolman B.
Published: May 2021

Phase transformations and/or decomposition of deposited compounds have an indisputable influence on materials properties of plasma sprayed deposits. Using water stabilized plasma, free-standing parts were manufactured from a mechanical mixture of zircon and alumina powders and annealed. The phase composition was determined by X-ray diffraction and the chemical composition was checked by x-ray microanalysis. ZrSiO4 during plasma spraying decomposes into ZrO2 and SiO2. In the as-sprayed condition, after a relatively fast quenching, the following phases can be found: a very fine eutectic mixture of tetragonal and monoclinic ZrO2, amorphous SiO2 and a spinel phase of Al2O3. On annealing for 2 hours at 1300 and 1500 °C the spinel Al2O3 transformed to corundum. At the same time, amorphous silica crystallized. Tetragonal ZrO2 transformed to the monoclinic modification and together with SiO2 formed again ZrSiO4. At the highest annealing temperature Al2O3 and SiO2 partialy reacted to form a small amount of mullite (3Al2O3.2SiO2).
The Gas Permeability of Plasma Sprayed Ceramic Coatings
Authors: Fox A.C. , Clyne T.W.
Published: May 2021

A simple test procedure, based on steady state flow through a membrane, has been developed for measurement of the gas permeability of specimens over a range of temperature. The reliability of this equipment has been verified by testing solid disks containing single perforations and comparing the measured flow rates with those expected on the basis of laminar flow. Coatings of yttria-stabilised zirconia have been produced by plasma spraying in vacuum and in air. The specific permeability of these coatings has been measured at temperatures ranging up to 600°C, using hydrogen gas. It has been found that permeability is increased for coatings produced with longer stand-off distances and at higher pressures. Porosity levels have been measured using densitometry and microstructural features have been examined using SEM. A model has been developed for prediction of the permeability from such microstructural features, based on percolation theory. Agreement between predicted and measured permeabilities is good, although it is clear that more comprehensive data are needed in order to validate the model systematically.
Increase in the Reliability of Thermal Sprayed Coatings
Authors: Steinhäuser S. , Wielage B. , Hofmann U. , Zimmermann G.
Published: May 2021

The characterisation of the effectiveness of sealing was studied by metallographical investigations as well as comparing the investigations with respect to the corrosion- and wear behaviour of the used thermal sprayed coatings and last but not least by measuring of the insulation resistance of the coating system. The obtained results show that there are differences between the used sealants and it is possible through a mechanical treatment of sealed coatings to remove the sealants from the coatings. In the corrosion test the sealants show their efficiency. The sealants insulate the open porosity and prevent the corrosion attack owing to the interconnected pores.
High Performance Super-Austenitic Surface Alloy Using Plasma Coating and Laser Treatment
Authors: Khanna A.S. , Sridhar K. , Deshmukh M.B.
Published: May 2021

Stainless Steels are required for many applications for ship building as well as for offshore structures such as oil exploration. AISI type 304 stainless steel is not very suitable for such applications as it has a strong tendency for pitting and crevice corrosion. Even type 316 and 317 stainless steels which have respectively 2.5 and 3.5% Mo are not very effective in these environments. Commercially available stainless steels, viz., Avesta 254 SMO is being employed for such applications because of its strong resistance to pitting and crevice corrosion. This is mainly because of high Mo concentration (6.5%). Such steels are not only costly but are prone to form deleterious phases such as delta ferrite and sigma during welding or other heat treatment operations. Hence, an alternative technique to restrict Mo at the surface is needed. In the present work, surface alloys consisting of an austenitic stainless steel with Mo content as high as 10-12% have been formed on stainless steel type 304 substrates. These steels show enhanced passivity and strong resistance to pitting corrosion.
The Effects of Post Heating an HVOF Sprayed Fusible Coating
Authors: Moskowitz L.
Published: May 2021

Fusible coatings of Nickel-Chromium alloys with various amounts of Boron and Silicon commonly used for severe load applications. The coating is normally sprayed, then fused by heating to the point of liquation. The fusing process causes powder coalescence and increases density. At the same time, the high fusing temperatures creates a “brazed” bond which gives these coatings extremely high adhesive bond strengths. The improved bond strength is the result of the metallurgical bond as compared to the majority of thermal spray coatings which rely only on mechanical bonding mechanisms. The fusing operation is very sensitive, especially when a hand torch fuse is required. To circumvent these problems, a study was conducted to see if high density HVOF sprayed coatings might achieve fused quality by furnace heating to temperatures well below the liquation point. Various times and temperatures were surveyed. Bond strength tests of coatings sprayed to heavy thicknesses, hardness and impact tests, and metallography were used for evaluation. It was determined that heating as low as 1500° F for three hours could improve the properties of an as-sprayed HVOF coating to where it developed characteristics very similar to that of a fused coating.
Inflight Behavior of Dissimilar Co-Injected Particles in the Spraying of Metal-Ceramic Functionally Graded Materials
Authors: Fincke J.R. , Swank W.D. , Haggard D.C.
Published: May 2021

In the spraying of functionally graded coatings the particle ensemble delivered to the substrate can vary from a relatively low melting point metallic particle to a significantly higher melting point ceramic particle. At various stages in the spray process the particle ensemble can be either predominantly metallic, ceramic, or an intermediate combination. For co-injected particles the mixtures do not behave as a simple linear superposition of the spray patterns of the individual particle types. The particle temperature, velocity, size distributions, and pattern characteristics of the resulting spray fields is examined for all ceramic particle sprays (ZrO2), all metallic particle sprays (NiCrAlY), and for a 1:1 mixture. The major particle-particle interaction occurs in the injector itself and results in a modified spray pattern which is different from that of either material sprayed alone. The particle velocity distributions generally exhibit a bimodal nature which is dependent on the size and density of the injected particles.
Computational Analysis of a Three-Dimensional Plasma Spray Jet
Authors: Dussoubs B. , Fauchais P. , Vardelle A. , Vardelle M. , Themelis N.J.
Published: May 2021

An analysis of a d.c. plasma jet is presented using a three-dimensional commercial fluid dynamics code, ESTET. This code solves the coupled conservation equations of mass, species, momentum and thermal energy equations for a compressible and turbulent fluid in control volume and finite difference formulation. Computations take into account fluid turbulence using a standard k-s model with the Launder and Sharma correction for the laminar zones, e.g. the plasma core. Two series of spraying conditions differing in the total gas flow rate (30 and 60 slm) and the arc current (300 and 600 A, respectively) are computed. The process parameters are independently varied about the nominal operating conditions. The effect of the variation of primary and secondary gas flow rate, effective power and powder carrier gas flow rate on flow fields characteristics, is discussed.
In-Situ Measurement of Particle Concentration and Velocity Using a Non-lntensified CCD Camera
Authors: Knuuttila J. , Saarenrinne P. , Hernberg R. , Lehtinen T. , Mäntylä T.
Published: May 2021

The deposition efficiency (DE) of a particular powder for a particular thermal spray process is very important factor when coating economics is being considered. There are many coating applications, however, where it is also important to know how the deposition efficiency changes during a longer coating process. Normally the DE is determined as mass ratio of powder fed into the process and corresponding weight gain of the sample. In this work the deposition efficiency has been determined for aluminum oxide powder in atmospheric plasma spraying using different spray parameters and electrode wear states. The coating process and in-flight particles were monitored using a fast non-intensified CCD-camera. Using digital image analysis the relative hot particle concentrations and velocity distributions were calculated from images. The possibility to use a CCD camera based monitoring system for in-situ measurement of DE is discussed. Additional laser illumination and PTV measurements were performed to verify the cold particle flux unseen by the plain CCD camera.
Influence of the Spray Parameters on the Transient Pressure within a Molten Particle Impacting onto a Flat Substrate
Authors: Montavon G. , Feng Z.G. , Coddet C. , Feng Z.Q. , Domaszewski M.
Published: May 2021

This paper is devoted to the investigation of the transient pressure occurring at the impact of a molten particle onto a flat substrate surface under different thermal spray conditions. In this paper, the mathematical model developed is based on the following assumptions: laminar, viscous and incompressible fluid; the mixed velocity-pressure model is employed to construct the finite element model. The choice of pressure penalty coefficient, which depends on the Reynolds number, is crucial for the results. This is discussed in this paper. The numerical results show that the pressure at the particle-substrate interface is strongly affected by the processing parameters, especially by the particle density and the impact velocity. The influence of spray parameters and material properties are also discussed.
Measurement of the Crystallinity of Hydroxyapatite Deposited by Plasma Spray
Authors: Rustichelli F. , Yang B. , Antolotti N. , Bertini S. , Girardin E.
Published: May 2021

As part of a characterization and mechanical research about hydroxyapatite (HA) plasma deposits for hip prosthesis, we addressed the problem of determining their crystallinity. A traditional normalization method employed by several laboratories is based on X-ray diffraction by a powder mixture of the investigated HA sample with a standard of crystalline powder, namely Al2O3. This method is quite unsatisfactory, as very often delivers unreasonable results. In order to overcome these difficulties we investigated some new methods for determining the crystallinity of HA sample, which are based on X-ray diffraction. All these methods provide reasonable results.
Nanoindentation Study of Thermal Spray Deposits
Authors: Leigh S.H. , Berndt C.C. , Ferber M.K. , Riester L.
Published: May 2021

The nanoindentation technique has been applied to thermal-sprayed metal, cermet and ceramic deposits. The hardness and elastic modulus were determined from the load-displacement curves. Each test was implemented by varying the penetration depth (100, 200, 300 and 400 nm) in the same test location and at least 20 tests were performed. The results were compared to those from microindentation tests. The nanoindentation test, essentially, measured the submicrometer scale properties of thermal spray deposits, which can be considered as "near-intrinsic" properties of the coatings. Thus, these measurements exclude most of the microstructural factors that influence the "macroscale" properties. The nanoindentation test exhibits significantly greater hardness and elastic modulus values than the microindentation test.
Fracture Behavior and Tensile Adhesive Properties of HA Coatings
Authors: Khor K.A. , Cheang P.
Published: May 2021

The attractive bioactive properties of HA are significantly reduced upon plasma spraying because of the phase transformation that accompanied the deposition process. One major factor that influence the extent to which the transformation occur appears to be the morphology and physical states of the HA raw powders. This paper reports the study on the influence of powder morphology and property on the fracture behaviour and tensile adhesive strength of plasma sprayed HA coatings. Three types of powders were used in the study; calcined HA (CHA), spray dried HA (SDHA) and flame spheroidised HA (SHA). The particle size range of 53 - 75 μm was employed for all 3 types of powders to effect an accurate comparison of the powders. Results show that the cohesive bond strength of the SHA coating was the highest because of the denser microstructure created by well-formed lamella splats. A correspondingly lower bond strength was recorded with less coherent coatings generated by agglomerated CHA and SDHA powders.
Study of Oxide Layers Obtained onto 304L Substrate Heated by a DC Plasma Jet
Authors: Pech J. , Hannoyer B. , Bianchi L. , Fauchais P. , Denoirjean A.
Published: May 2021

The preheating of metallic substrates before powder deposition in air plasma spraying improves the adhesion of oxide coatings, provided heating is performed with an optimal procedure to avoid a too high oxidation state of the surface. It means that the temperature level and heating time have to be monitored carefully. In these conditions a thin layer (<100 nm) of oxides is formed on the substrate surface, the resulting contact of the molten droplets impinging the hot substrate is excellent (Rth<10-7 m2.K/W) and the adhesion properties of coatings are enhanced. This paper is devoted to the study of the metallic surface. The substrate heating and thus oxidation are obtained with a d.c. Ar-H2 plasma jet flowing in air of which the stand off distance is maintained at 100 mm. The parameters investigated are macroscopic surface temperature and heating time. The characterization of the oxide layers is achieved by Mossbauer spectroscopy, near grazing X-ray diffraction, near UV-Visible-near IR spectroscopy and specular reflection infrared spectroscopy. At the end of this paper an attempt will be made to correlate these characterizations to the splats microstructure and coatings adhesion.
Residual Stress Analysis of Plasma Sprayed Thermal Barrier Coatings
Authors: Teixeira V. , Andritschky M. , Fischer W. , Stöver D. , Buchkremer H.P.
Published: May 2021

ZrO27Y2O3 plasma sprayed coatings were applied on high temperature Ni-based alloys precoated with a thin, dense, stabilized zirconia coating produced by Physical Vapour Deposition. This contribution concerns with the experimental and numerical analysis of residual stresses in PVD/Plasma Sprayed TBC's systems after coating deposition and after high temperature testing, such as cyclic oxidation and rapid thermal cycling. The thermal residual stress developed in the plasma sprayed top coating during spraying was simulated by using an heat transfer FEM program and an elasto-plastic biaxial stress model which calculate the stress gradients in coating/substrate system. The residual stress distributions within the TBC undergoing thermal cycling is then calculated by a biaxial stress model, taking into account the residual stress due to the deposition technique of the PVD and plasma sprayed top coating and the presence of the growing oxide interlayer. The residual stress within the upper layers of the top coating was verified experimentally by X-ray Diffraction for the as-deposited and thermal cycled samples, and the stresses within PVD bond coating and oxide interlayer were measured by microRaman spectroscopy technique in cross-sectioned samples. The measurements are in good agreement with residual stress modelled results.
HVOF- and VPS-Coatings Using Nanostructured Iron-Based Alloys
Authors: Brandt O.C. , Siegmann S. , Isch H.-P.
Published: May 2021

In thermal spraying, Fe-based alloys are often applied for relatively thick and inexpensive coatings. The main advantage of the Fe-based alloy coatings is their high ductility as compared to ceramic and hardmetal coatings. Other advantages such as high toughness, easy machineability and satisfactory corrosion resistance are characteristic of Fe-based alloys. The wear resistance is not outstanding, but nevertheless acceptable for a large number of applications. A further improvement of the wear resistance can be achieved by reinforcing the Fe-based alloy coatings, e.g. by addition of nitrogen to the spraying powder.
Thermal Spray Forming Using the HVOF Technique
Authors: Guilemany J.M. , Miguel J.R. , Dougan M.J. , de Paco J.M. , Dong Z. , Libre J.
Published: May 2021

The feasibility of using the HVOF process for the thermal spray-forming of free-standing components has been investigated. HVOF spray forming offers a number of potential advantages compared to the established procedure of plasma forming, including increases in component density, and reduction in material decomposition during spraying. Using blends of carbide and superalloy powders in various proportions, HVOF spraying has been successfully used to form free-standing cylinders and cones of various lengths and thicknesses. Microstructural examination of the spray-formed material has shown a homogeneous distribution of carbides in the superalloy matrix, with very low levels of porosity. Refinement of the procedure has allowed reduction of the matrix content, and the forming of fragile materials.
COMPORTAMENTO DIFERENCIAL DE LINHAGENS DE ALGODÃO A Cercospora gossypina
Authors: Dalbelo Puia Jacqueline , Ricini Martins Bruna , Borsato Leandro Camargo , Vigo Sandra Cristina
Published: May 2021

A mancha foliar causada pelo fungo Cercospora sp. tem se tornado uma doença de grande importância para o algodoeiro, destacando-se pela sua alta severidade e grandes perdas econômicas. Uma maneira de potencializar o manejo da doença, encontra-se no uso de cultivares resistentes. Nesse sentido, o presente trabalho teve como objetivo avaliar o comportamento de vinte e cinco genótipos de algodão a Cercospora gossypina. O experimento foi realizado em casa de vegetação, com delineamento em blocos casualizados com quatro repetições por genótipos. Plantas de algodão com 25 dias de idade foram inoculadas com a suspensão fúngica do patógeno. Foram realizadas quatro avaliações de severidade da doença, com início aos sete dias após a inoculação, utilizando-se uma chave descritiva. Foram calculadas, a área sob a curva de progresso da doença para cada genótipo avaliado. Os genótipos FM 906, FM 975, CNPA 2015 126 B2 RFRL2, CNPA 2015 82 B2RFRL2, BRS 432 B2RF, TMG 44, CNPA 2015 231 B2RF, CNPA 2015 530 B2RF, TMG 81 WS, FM 954, CNPA 2014 155 B2RF, FM 975 GLT, DP 1536 B2RF, CNPA 2015 512 B2RF e FM 983 apresentaram os menores índices de severidade da doença. Estudos que caracterizem os níveis de suscetibilidade de genótipos de algodão em relação a doença são fundamentais, a fim de selecionar os mais adequados ao manejo da doença.
Palavras-chave: suscetibilidade; Gossypium L.; mancha de cercospora.
 
Differential behavior of cotton lines Cercospora gossypina
 
ABSTRACT: Leaf spot caused by the fungus Cercospora sp. has become a disease of great importance for cotton, standing out for its high severity and great economic losses. One way to improve the management of the disease is the use of resistant cultivars. In this sense, the objective of the present work was to evaluate the behavior of twenty-five cotton lines against Cercospora gossypina. The experiment was conducted in a greenhouse, with randomized block design and four repetitions per line. Cotton plants with 25 days of age were inoculated with fungal suspension of the pathogen. Four evaluations of disease severity were performed, starting at seven days after inoculation, using a descriptive key. The area under the disease progress curve was calculated for each genotype evaluated. The strains FM 906, FM 975, CNPA 2015 126 B2 RFRL2, CNPA 2015 82 B2RFRL2, BRS 432 B2RF, TMG 44, CNPA 2015 231 B2RF, CNPA 2015 530 B2RF, TMG 81 WS, FM 954, CNPA 2014 155 B2RF, FM 975 GLT, DP 1536 B2RF, CNPA 2015 512 B2RF and FM 983 showed the lowest disease severity rates. Studies that characterize the susceptibility levels of cotton strains in relation to the disease are fundamental in order to select the most suitable for disease management.
Keywords: susceptibility; Gossypium L; cercospora spot.