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The WC particle size and its influence on the deposition of Co-based cermets are examined. Micron and nanostructured powders with similar Co content were employed. Varying the WC particle size influenced significantly the deposition... more
The WC particle size and its influence on the deposition of Co-based cermets are examined. Micron and nanostructured powders with similar Co content were employed. Varying the WC particle size influenced significantly the deposition efficiency of the coating process. Micrometer-structured WC–Co feedstocks did not permit coating build up when processed under comparable or elevated thermal spray parameters used for the
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ABSTRACT Hydroxyapatite (HA) and titanium composite coatings, which demonstrate good biocompatibility and load bearing capacity, are important in the topical area of prosthetics. In this study, hydroxyapatite and titanium composite... more
ABSTRACT Hydroxyapatite (HA) and titanium composite coatings, which demonstrate good biocompatibility and load bearing capacity, are important in the topical area of prosthetics. In this study, hydroxyapatite and titanium composite coatings were deposited on austenitic stainless steel (316L) substrates using the Direct Material Deposition (DMD) technique. The microstructures were characterized using optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Surface topography and roughness were assessed by SEM and profilometry, while Raman microscopy was employed to determine the nature of HA in the feedstock. The results indicate that average roughness increases with traverse speed and depends significantly on the power level. The crack orientation was found to be sensitive to traverse speed, while the number of cracks was related to the power level. Porosity decreased as the power level increased.
ABSTRACT Brookhaven National Laboratory (BNL) has developed thermally conductive composite liners for corrosion and scale protection in heat exchanger tubes exposed to geothermal brine. The liners cannot withstand roller expansion to... more
ABSTRACT Brookhaven National Laboratory (BNL) has developed thermally conductive composite liners for corrosion and scale protection in heat exchanger tubes exposed to geothermal brine. The liners cannot withstand roller expansion to connect the tubes to the tubesheet. It is not possible to line the ends of the tubes with the same material after roller expansion due to the nature of the current liner application process. It was requested that BNL evaluate plasma sprayed Ni-Al coatings for safe ending heat exchanger tubes exposed to geothermal brine. The tubes of interest had an internal diameter of 0.875 inches. It is not typical to thermal spray small diameter components or use such small standoff distances. In this project a nozzle extension was developed by Zatorski Coating Company to spray the tube ends as well as flat coupons for testing. Four different Ni-Al coatings were investigated. One of these was a ductilized Ni-AlB material developed at Oak Ridge National Laboratory. The coatings were examined by optical and scanning electron microscopy. In addition, the coatings were analyzed by X-ray diffraction and subjected to corrosion, tensile adhesion, microhardness and field tests in a volcanic pool in New Zealand.
ABSTRACT Titanium and titanium alloys have been extensively studied for many applications in the area of bone tissue engineering. However, dense titanium is prone to lead into aseptic loosening due to their high elastic modulus compared... more
ABSTRACT Titanium and titanium alloys have been extensively studied for many applications in the area of bone tissue engineering. However, dense titanium is prone to lead into aseptic loosening due to their high elastic modulus compared to natural bone. One way to lower the elastic modulus is to produce a porous structure of the metallic alloy by adjusting its porosity. Another concern is the bioinertness of titanium that have no direct chemical bonding with surrounding tissue. One approach to improve the healing process is the application of a calcium phosphate coating onto the surface of biomedical devices and implants. Biomimetic creation of surface using alkali heat treatment with silica addition was employed in this study. The porosity of the samples ranges from 60% to 70%. It was demonstrated that the biomimetic methods are suitable for inducing apatite on the titanium alloys surface.
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Ceramic-filled epoxy, ethylene methacrylic acid (EMAA) and ethylene tetrafluoroethylene (ETFE) coatings were evaluated for corrosion protection in a biochemical process to treat geothermal residues. The epoxy was brush applied whereas the... more
Ceramic-filled epoxy, ethylene methacrylic acid (EMAA) and ethylene tetrafluoroethylene (ETFE) coatings were evaluated for corrosion protection in a biochemical process to treat geothermal residues. The epoxy was brush applied whereas the other coatings were thermal sprayed. Atlas cell and peel strength tests were performed in aggressive environments including hypersaline brine and sulphur oxidizing bacteria (Thiobacillus ferrooxidans). It was found that the polymers were resistant to chemical attack and biodeterioration at the test temperature of 55°C. Corrosion of mild steel substrates coated with EMAA and ETFE occurred in Atlas cell tests that simulated an uninsulated lined reactor and this resulted in decreased adhesive strength. The ceramic-filled epoxy provided better substrate protection than the EMAA and EWE. Insulation of the reactors may improve coating performance since tlus would decrease the thermal gradient which affects permeation. The results of the research are also...
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ABSTRACT Thermal spray consists of a group of coating processes that are used to apply metal or non-metallic coatings to protect a functional surface or to improve its performance. There are some 40 processing parameters that define the... more
ABSTRACT Thermal spray consists of a group of coating processes that are used to apply metal or non-metallic coatings to protect a functional surface or to improve its performance. There are some 40 processing parameters that define the overall coating quality and these must be selected in an optimized fashion to manufacture a coating that exhibits desirable properties. The proper combination of processing variables is critical since these influence the cost as well as the coating characteristics.Because of this high number of processing parameters, a major challenge is to have full control over the system and to understand parameter interdependencies, correlations and their individual effects on the in-flight particle characteristics, which have significant influence on the in service coating properties. This paper proposes an approach, based on the Artificial Neural Network (ANN) method, to play this role and illustrates the model's design, network optimization procedures, the database handling and expansion steps, and analysis of the predicted values, with respect to the experimental ones, in order to evaluate the network's performance.Research highlights► Artificial Neural Network (ANN) successfully predicted particle characteristics. ► Predicted values in overall show minimum scatter with the experimental values. ► Expansion of database improved trained ANN's performance. ► Results show possibility of ANN to set up a control system for the spray process.
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ABSTRACT Fabrication of components that require magnetic parts such as in micro motors and micro generators demands an alternative to micro machining processes that are costly and time consuming. In this study, Nd–Fe–B coatings with an... more
ABSTRACT Fabrication of components that require magnetic parts such as in micro motors and micro generators demands an alternative to micro machining processes that are costly and time consuming. In this study, Nd–Fe–B coatings with an average thickness of 200 μm were deposited onto stainless steel substrates by an atmospheric plasma spray technique using amorphous feedstock powder of spherical morphology. The microstructure of the coatings shifted from lamellar to spherical in nature as standoff distance (SOD) increased. The total porosity of the coatings exhibited a minima with respect to SOD and ranged from 1.8 to 8.2%. Two distinct phases; i.e., the Nd-rich and Fe-rich phases, were observed and imply phase separation during the plasma spray process. Occurrence of phase separation was argued to arise due to metastable phase formation and non-equilibrium solidification. The Fe-rich phase increased with increasing SOD due to longer in-flight time allowing non-equilibrium solidification to occur. The presence of two phases results in a bimodal Weibull distribution for Vickers hardness data. However, Weibull plots for Knoop hardness and elastic modulus show monomodal behaviour. The correlation between the degree of data scattering, as reflected by the Weibull modulus, with porosity and phase percentage was determined.
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... All rights reserved 09659773 97 17.00 + .00 NANOMATERIAL POWDERS AND DEPOSITS PREPARED BY FLAME SPRAY PROCESSING OF LIQUID PRECURSORS J. Karthikeyan, CC Berndt, J. Tikkanen*, JY Wang, AH King and H. Herman The Thermal Spray Laboratory... more
... All rights reserved 09659773 97 17.00 + .00 NANOMATERIAL POWDERS AND DEPOSITS PREPARED BY FLAME SPRAY PROCESSING OF LIQUID PRECURSORS J. Karthikeyan, CC Berndt, J. Tikkanen*, JY Wang, AH King and H. Herman The Thermal Spray Laboratory ...
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... All rights reserved 0965-9773/97 $17.00 + .00 PH S0965-9773(97)00037-8 PREPARATION OF NANOPHASE MATERIALS BY THERMAL SPRAY PROCESSING OF LIQUII) PRECURSORS J. Karthikeyan, CC Berndt, J. Tikkanen, JY Wang, AH King and H. Herman... more
... All rights reserved 0965-9773/97 $17.00 + .00 PH S0965-9773(97)00037-8 PREPARATION OF NANOPHASE MATERIALS BY THERMAL SPRAY PROCESSING OF LIQUII) PRECURSORS J. Karthikeyan, CC Berndt, J. Tikkanen, JY Wang, AH King and H. Herman Department ...
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SUMMARY A fracture mechanics approach is applied to measuring the adhesion of plasma and flame sprayed coatings of mild steel, nickel-aluminium composite and alumina applied to a mild steel substrate. The experimental method essentially... more
SUMMARY A fracture mechanics approach is applied to measuring the adhesion of plasma and flame sprayed coatings of mild steel, nickel-aluminium composite and alumina applied to a mild steel substrate. The experimental method essentially involves incorporating t he c oating into either a double torsion or double cantilever beam geometry. The results show that the coating adhesion can be quantitatively determined and several trends are discerned and related to the fracture morphology. The metal coatings exhibit a high a dhesion when compared to the ceramic coating and this may be related to p lastic deformation of the individual l amellae, of which the coating is made up, during failure. In particular it has been found that the significantly greater adhesion of ceramic coatings applied over Ni - A1 bond coatings on steel, compared with the ceramic coated directly onto steel, may be attributed to the deformation of the metallic coating in the region of the bond coating-ceramic interfac...
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ABSTRACT A robust single hidden layer feed forward neural network (SLFN) is used in this study to model the in-flight particle characteristics of the atmospheric plasma spray (APS) process with regard to the input processing parameters.... more
ABSTRACT A robust single hidden layer feed forward neural network (SLFN) is used in this study to model the in-flight particle characteristics of the atmospheric plasma spray (APS) process with regard to the input processing parameters. The in-flight particle characteristics influence the structure and properties of the APS coating and, thus, are considered important parameters to comprehend the manufacturing process. The training times of traditional back propagation algorithms, mostly used to model such processes, are far slower than desired for implementation of an on-line control system. Use of slow gradient based learning methods and iterative tuning of all network parameters during the learning process are the two major causes for such slower learning speed. An extreme learning machine (ELM) algorithm, which randomly selects the input weights and biases and analytically determines the output weights, is used in this work to train the SLFNs. Performance comparisons of the networks trained with ELM algorithm and standard error back propagation algorithms are presented. It is found that networks trained with ELM have good generalization performance, much shorter training times and stable performance with regard to the changes in number of hidden layer neurons. The trends represent robustness of the trained networks and enhance reliability of the application of the artificial neural network in modelling APS processes.
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ABSTRACT Porosity is one of the most important microstructural features in thermal spray coatings and has been actively studied and measured by many methods. Image analysis techniques have become popular techniques in determining porosity... more
ABSTRACT Porosity is one of the most important microstructural features in thermal spray coatings and has been actively studied and measured by many methods. Image analysis techniques have become popular techniques in determining porosity in coatings because of simplicity, accessibility, and an ability to measure both open and closed porosities as well as pore characteristics such as size, shape, orientation, and spatial distribution. In the current study, an image analysis technique has been complemented by several stereology procedures to determine the porosity level and characteristics of pores within coatings. Stereology protocols such as Delesse, DeHoff, and Cruz-Orive analyses were used to derive the porosity level, pore size, and shape distributions, and the effectiveness of each stereology protocol was compared. Standoff distance (SOD) and annealing process did not alter the distribution trend of number of pores but influenced the distribution of pore volume fractions significantly. The bivariate size–shape distribution of the pores was used to predict the dominant pore type and fractions of pores that arose from different formation mechanisms. It was found that nearly spherical pores that originated from gas bubbles and entrapped gas pockets dominate at shorter SOD, while the different types of pores become more evenly distributed when the SOD was increased.
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ABSTRACT Polymeric composites, with either metallic or ceramic fillers, have been manufactured by thermal spray, and their mechanical properties have been measured. The advantage of this technology is that it allows on-site manufacture... more
ABSTRACT Polymeric composites, with either metallic or ceramic fillers, have been manufactured by thermal spray, and their mechanical properties have been measured. The advantage of this technology is that it allows on-site manufacture and is a repairable composite system, with virtually no cure time and no release of volatile organic compounds. Fracture mechanisms have been studied to examine mechanical modeling of the composite system.
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ABSTRACT This paper presents the application of the artificial neural network into an atmospheric plasma spray process for predicting the in-flight particle characteristics, which have significant influence on the in-service coating... more
ABSTRACT This paper presents the application of the artificial neural network into an atmospheric plasma spray process for predicting the in-flight particle characteristics, which have significant influence on the in-service coating properties. One of the major problems for such function-approximating neural network is over-fitting, which reduces the generalization capability of a trained network and its ability to work with sufficient accuracy under a new environment. Two methods are used to analyze the improvement in the network’s generalization ability: (i) cross-validation and early stopping, and (ii) Bayesian regularization. Simulations are performed both on the original and expanded database with different training conditions to obtain the variations in performance of the trained networks under various environments. The study further illustrates the design and optimization procedures and analyzes the predicted values, with respect to the experimental ones, to evaluate the performance and generalization ability of the network. The simulation results show that the performance of the trained networks with regularization is improved over that with cross-validation and early stopping and, furthermore, the generalization capability of the networks is improved; thus preventing any phenomenon associated with over-fitting.
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ABSTRACT Aluminum oxide is widely used for plasma spraying. Alumina deposits consist of a number of metastable crystallographic modifications, which at elevated temperatures, transform to the stable α phase. It was shown that additions of... more
ABSTRACT Aluminum oxide is widely used for plasma spraying. Alumina deposits consist of a number of metastable crystallographic modifications, which at elevated temperatures, transform to the stable α phase. It was shown that additions of various oxides changed the phase composition and shift phase transformation temperatures. This paper addresses the variation of phase compositions and temperatures of the phase changes for plasma-sprayed alumina deposits manufactured with alumina-base materials containing O2O3 and TiO2. This study combines the results obtained from energy dispersive analyzer of X-rays (EDAX) and scanning electron microscopy (SEM) chemical analysis, differential thermal analysis (DTA), and X-ray powder diffrac-tion (XRD) quantitative phase analysis of as-sprayed and annealed samples of alumina deposits and shows how the two additives change the phase composition and the α-phase formation temperature. This transformation temperature varied by nearly 200 °C. The metastable alumina sequences were also influenced by the chemical composition; for example, the content of 6 alumina varied between 0 and 55 wt %.
Research Interests: Materials Engineering, Mechanical Engineering, Scanning Electron Microscopy, X Rays, Plasma spray coatings, and 11 morePhase Stability, Chemical Analysis, Phase Change, Thermal Spray Technology, Phase Transformation, Differential Thermal Analysis, Aluminum oxide, Chemical Composition, Elevated Temperature, Phase Analysis, and Plasma Spraying
ABSTRACT Formation of voids is inevitable in plasma sprayed coatings and the role of voids on coating properties has long been established. In fact, the void content within coatings is adjusted by optimizing the process parameters to... more
ABSTRACT Formation of voids is inevitable in plasma sprayed coatings and the role of voids on coating properties has long been established. In fact, the void content within coatings is adjusted by optimizing the process parameters to obtain coatings with desirable performance. Quantification of voids via image analysis allows determination of not only the void content within a coating, but also the spatial distribution of the voids. Void content in plasma sprayed neodymium iron boron (Nd-Fe-B) coatings was adjusted by changing the standoff distance, and was found to vary from 1.8 to 8.2%. Spatial distribution parameters, which include nearest neighbor distance (d min), mean near neighbor distance (d mean), and nearest neighbor angle (θn), were determined via the Dirichlet tessellation method. Coefficient of variation (COV) values of d min and d mean allow determination of inhomogeneity and degree of clustering of the voids within a coating. The θn values reveal the anisotropic behavior of voids within plasma sprayed coatings. The influence of void content and its spatial distribution within the coatings on the microhardness and elastic modulus of coatings was determined.
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ABSTRACT Thermal spray coatings are composed of millions of heated particles driven at high velocities onto a substrate, thereby building up and forming a consolidated coating. Thus, investigating single solidified droplets contributes to... more
ABSTRACT Thermal spray coatings are composed of millions of heated particles driven at high velocities onto a substrate, thereby building up and forming a consolidated coating. Thus, investigating single solidified droplets contributes to the fundamental understanding of the evolution of a surface coating and its properties. In this study, the single splat morphology and thermal characteristics of flame-sprayed ethylene methacrylic acid (EMAA) splats, deposited at various stand-off distances onto glass and mild steel substrates, are investigated using scanning electron microscopy, differential scanning calorimetry, and thermal gravimetric analysis. This study indicates that the microstructure of EMAA coatings can be controlled by judicially selecting the thermal spray parameters rather than by using the trial and error methods that are often used at present.
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ABSTRACT Thermal spray fabrication of rare-earth permanent magnetic coatings (PMCs) presents potential manufacturing routes for micro-magnetic devices. Despite this potential, thermal spray of PMCs is still not widely explored due to... more
ABSTRACT Thermal spray fabrication of rare-earth permanent magnetic coatings (PMCs) presents potential manufacturing routes for micro-magnetic devices. Despite this potential, thermal spray of PMCs is still not widely explored due to oxidation concerns. It was established that oxidation leads to the loss of ferromagnetic phases in these materials and results in deterioration of magnetic performance. Although this review focuses on a specific class of material, i.e., magnetic materials, there is significant technical crossover to all classes of feedstocks that are employed in thermal spray processing. The oxidation mechanisms and the associated influencing factors are explored in this work to implement effective processing techniques during the deposition process. This paper reviews the various stages and mechanisms of oxidation in thermal spray processes. The factors that influence the extent of oxidation depend on the type of oxidation that is dominant and rely on the type of spray system, powder injection position, and the particle size of feedstock. Among the aspects that are reviewed include the oxygen-fuel ratio for high velocity oxygen-fuel (HVOF), current intensity, gas flow rate, particle size, spray distance, and substrate temperature. Protection strategies to minimize oxidation in thermal spray processes, such as gas shrouding and shielding, are presented. © 2013 ASM International.