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Proceedings Papers
ITSC2023, Thermal Spray 2023: Proceedings from the International Thermal Spray Conference, 458-465, May 22–25, 2023,
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Thermal spray processes benefit from workpiece cooling to prevent overheating of the substrate and to retain metallurgical properties (e.g., temper). Cold-gas “plume quenching” is a plume-targeting cooling technique, where an argon curtain is directed laterally above the substrate surface to re-direct high temperature gases without impacting particle motion. However, there has been little investigation of its effect on the molten particles and the resulting coating properties. This study examined high- and medium- density tantalum and nickel coatings, fabricated by Controlled Atmosphere Plasma Spray with and without plume quenching on aluminum and titanium substrates. To compare the effect of plume quenching, the deposition efficiency was calculated through coating mass gain, and the coating density, stiffness, and adhesion were measured. The tantalum and nickel coatings were largely unaffected by plume quenching with respect to deposition efficiencies, coating density, adhesion, and stiffness. These results indicate that a plume quench could be used without affecting the coating properties for high- and medium-density metals while providing the benefit of substrate cooling that increases with higher plume quench gas flow rates.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 282-287, June 2–4, 2008,
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Due to the nature of the HVOF and other thermal spray processes, residual stress build up in thick deposits is a significant and limiting problem. The residual stress-state that evolves in a deposit is largely dependent on the thermal conditions to which the system has been subjected, and is a combination of quenching stresses, which arise during deposition, and cooling stresses, post-deposition. It follows that precise control of these phenomena is essential, if a thick deposit or one with low levels of residual stress are to be thermally sprayed. This paper applies looks at analytical and finite element techniques used to predict quenching and cooling stresses within tungsten carbide-cobalt thermally sprayed deposits. The analysis investigates and predicts the quenching and cooling stresses using improved analytical and FEA techniques by validating the models with experimental results such as X-Ray Diffraction and the Hole Drilling Method. The result of this paper is a thermo-mechanical equation for quenching stress which includes the effects of misfit strain, the Poisson’s effect, variation of coating and substrate thicknesses, thermal expansion and process temperature effects.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 778-784, June 2–4, 2008,
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Residual stress build up in thick thermal spray coatings is a property of concern. The adhesion of these coatings to the substrate is strongly influenced by the residual stress generation during the coating deposition process. In the HVOF spray process, due to lower processing temperature and higher particle velocity as compared to plasma spraying, significant peening stresses are generated during the impact of semi molten particles on the substrate. The combination of these peening stresses together with quenching and cooling stresses that arise after deposition can be of significant importance. In this paper both a numerical finite element analysis (FEA) method, to calculate peening, quenching and cooling residual stresses, and experimental methods, as Modified Layer Removal Method (MLRM) and Neutron Diffraction analysis, are applied. The investigation is performed for thick Inconel 718 coatings on Inconel 718 substrates. Combined, these numerical and experimental techniques yield a deeper understanding of residual stress formation and a tool for process optimisation. The relationship between the stress state and deposit/substrate thickness ratio is given particular interest.
Proceedings Papers
ITSC 2007, Thermal Spray 2007: Proceedings from the International Thermal Spray Conference, 1105-1108, May 14–16, 2007,
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Producing nanostructured materials through metastable phases is an interesting novel route in the field of ceramic materials. Due to their small grain size and uniform structure, these nanostructured bulk materials exhibit very interesting properties. Metastable coatings can be produced starting from microstructured powders through atmospheric plasma spray (APS) technique, followed by a quenching route. The initial powders are melted during the spraying and deposited over a substrate that is quenched with liquid nitrogen (LIN) feeders, producing metastable coatings. The thermal sprayed coatings have been characterized using XRD, SEM, FESEM and EDS in the Thermal Spray Centre (CPT) of the University of Barcelona. The properties of such coatings have been also studied obtaining promising results.
Proceedings Papers
ITSC 2005, Thermal Spray 2005: Proceedings from the International Thermal Spray Conference, 1444-1448, May 2–4, 2005,
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A particle-sampling probe has been designed and constructed for the continuous collection of nano-powders produced by the plasma spray synthesis (PSS) process. The probe comprises a powder sampling line (inner tube), a quench gas line (outer tube) and a water-cooling jacket surrounding the outer tube. A sample holder is disposed at the exit of the inner tube to hold a standard 3.08 mm diameter TEM copper grid which is used to collect the powders by means of the pumping pressure differential. Quenching gas is introduced to the probe, via the outer tube to quench and entrain the as-synthesized clusters. After each sample collection event, the inner tube can be cleaned in-situ by means of a water injection, and then dried using a compressed gas flow. The results obtained to date indicate that the sampling probe location in the plasma reactor and the quenching gas flow rate employed are the most important parameters involved in the satisfactory operation of the sampling probe.
Proceedings Papers
ITSC 2004, Thermal Spray 2004: Proceedings from the International Thermal Spray Conference, 679-682, May 10–12, 2004,
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Several compositions of agglomerated ZrO 2 (Y 2 O 3 ), Al 2 O 3 and MgAl 2 O 4 powders were plasma sprayed through an axial injection torch into a water quenching chamber in order to obtain a fully melted and homogenized, metastable particle nanostructure. This metastable extended solid solution morphology allows the powder to be subsequently heat treated and superplastically formed into ceramic parts with potentially excellent optical and mechanical properties. Light microscopy, SEM and XRD analyses were used to evaluate the melt-quenched powder properties, and some comparison was made to previous work performed with traditional radial injection plasma torches. Thick build-ups were also sprayed from the melt-quenched powders to test their ability to superplastically flow. Results showed that during a single processing through the torch the axial injection equipment produced powders with a significantly higher fraction of fully homogenized powders than previously attainable. Homogenization of powders comprised of a larger particle size range was also achieved.
Proceedings Papers
ITSC 2003, Thermal Spray 2003: Proceedings from the International Thermal Spray Conference, 1041-1046, May 5–8, 2003,
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Molybdenum powder has been plasma sprayed on stainless steel, brass and aluminum substrates. The substrate melting phenomenon is observed and investigated by means of scanning electron microscopy (SEM) and scanning white light interferometery (SWLI). It is found that the flower-shape splat morphology is typical for molybdenum on all three substrate materials when the substrate is at room temperature. Notable substrate melting is manifested through the energy dispersion analysis of X-ray (EDAX) map and Robinson back-scattered image of cross-sections of splats. It has been shown that the substrate material plays an important role in substrate melting phenomenon. The lift angle of the petals of splats and the maximum crater depth have been characterized and compared. Both of these increase in the sequence, from stainless steel, brass to aluminum. A ‘volume of fluid’ (VOF) based model coupled with rapid solidification has been used to simulate splat deformation, solidification, substrate melting and resolidification. The numerical & analytical results agree quite well with the experimental data. A substrate melting mechanism is proposed based on the time scales of the droplet solidification and substrate melting to explain the formation of flower like splat morphologies.
Proceedings Papers
ITSC1999, Thermal Spray 1999: Proceedings from the United Thermal Spray Conference, 318-320, March 17–19, 1999,
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Thermal spraying is a widespread coating process with various applications in many industry branches. To be able to spray successfully on the sensitive materials an in-situ temperature control is most beneficial. The objective of this paper is to find out the correlation between the mechanical properties of some coating-substrate variations and temperature history of the coating made by HVOF. The paper describes the processes involved in implementation of the thermographic measurement systems into the HVOF spray system to measure the temperature of the coating on aluminum and steel during spraying. It was observed that when spraying on aluminum, the temperature of the coating has a marked influence on the adhesion. Tests with a steel substrate show how the hardness of the WC-CoCr depends on the quenching speed of the coating during spraying. Paper includes a German-language abstract.