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Proceedings Papers
ITSC2024, Thermal Spray 2024: Proceedings from the International Thermal Spray Conference, 40-48, April 29–May 1, 2024,
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The polymer cold spray (CS) process has been demonstrated as a promising coating and repair technique for fiber-reinforced polymer composites (FRPs). However, a noticeable variation in coating thickness (herein referred to as checkerboard pattern) often occurs in the initial (bond) layer of low-pressure CS deposition. The checkerboard pattern occurs due to essentially periodic variations in matrix thickness above the subsurface fiber weave pattern. When the bond layer exhibits the so-called checkerboard pattern, the CS deposition for subsequent layers may be negatively affected in terms of deposition efficiency, porosity, adhesion, surface roughness, and surface thickness consistency. The present work compares results of both numerical simulations and experimental studies performed to reveal the governing mechanisms for and elimination of checker-boarding. Numerical single particle impact simulations are conducted to observe various thermomechanical domains for CS impact on the FRP surface in different regions of the composite material. Complementary experimental CS studies of exemplar powders onto FRPs with various surface interlayer thicknesses are also presented. Experimental analyzes of deposits include microstructural observations to compare against the simulations while also providing practical strategies for the elimination of checkerboarding effects.
Proceedings Papers
ITSC2024, Thermal Spray 2024: Proceedings from the International Thermal Spray Conference, 49-58, April 29–May 1, 2024,
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Design, manufacturing, and utilization of efficient heating systems for pipelines and closed-pressure equipment are necessary for cold regions to compensate for heat loss and prevent damages that are caused by freezing of the enclosed liquid. Given large-scale financial losses that stem from failure and bursting of the pipes, the development of novel, efficient, and affordable heaters, which can lead to improved efficiency, cost savings, and environmental benefits across various industries and applications, is of crucial importance. Heating systems have already been produced via different high-temperature thermal spraying techniques to achieve higher efficiency compared to conventional heating cables. In this study, tin, as the heating element, was deposited by using the cold spray process onto alumina coating that was fabricated by flame spraying (FS) to provide electrical insulation. Techno-economic assessment of fabrication and utilization of the coating-based heaters was conducted. It was found that cold-sprayed heater coatings exhibit improved performance compared to other thermally sprayed heater coatings and conventional heater cables. Further, their fabrication and utilization were more economically feasible. The results suggest that the new generations of coating-based heating systems may be competitive with conventional heat tracers that are widely used in industry.
Proceedings Papers
ITSC2024, Thermal Spray 2024: Proceedings from the International Thermal Spray Conference, 59-66, April 29–May 1, 2024,
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In this work, thermally sprayed sustainable coatings with spray additives recycled from dry alkaline batteries and solid-oxide fuel cells are developed to allow the growth of drought-resistant plants like moss, microclover and chamomile. It is assumed that these plants anchor to the coating with their rhizoids and hence can be grown without the presence of soil. Preliminary tests of a thermally sprayed Yttrium Stabilized Zirconia (YSZ) ceramic coating on sheet metal confirms the growth of chamomile plant.
Proceedings Papers
ITSC2024, Thermal Spray 2024: Proceedings from the International Thermal Spray Conference, 67-73, April 29–May 1, 2024,
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In cold gas spraying, successful bonding occurs when particle impact velocities exceed the critical velocity. The critical velocity formula depends on material properties and temperature upon impact, relying mainly on tabulated data of bulk material. However, rapid solidification of powder particles during gas atomization can result in strengths up to twice that of bulk materials, causing an underestimation of the critical velocity. Thus, a re-adjustment of the semi-empirical calibration constants could supply a more accurate prediction of the requested spray conditions for bonding. Using copper and aluminum as examples, experimentally determined particle strengths for various particle sizes were 43% and 81% higher than those of the corresponding soft bulk materials. Cold gas spraying was performed over a wide range of parameter sets, achieving deposition efficiencies ranging from 2% to 98%. Deposition efficiencies were plotted as functions of particle impact velocities and temperatures, as calculated by a fluid dynamic approach. By using deposition efficiencies of 50%, the critical velocities of the different powders and the corresponding semi-empirical constants were determined. Based on particle strengths, the results reveal slight material-dependent differences in the mechanical pre-factor. This allows for a more precise description of individual influences by particle strengths on critical velocities and thus coating properties. Nevertheless, the general description of the critical velocity based on bulk data with generalized empirical constants still proves to be a good approximation for predicting required parameter sets or interpreting achieved coating properties.
Proceedings Papers
ITSC 2017, Thermal Spray 2017: Proceedings from the International Thermal Spray Conference, 190-192, June 7–9, 2017,
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Wire arc is an effective and affordable type of coating process. Detailed understanding of it helps improving design and optimization of currently available guns. In wire arc process, an arc forming between two charged wires generates enough heat to melt the metallic wires. Blow of air at high velocity over this bath of molten metal leads to atomization. The formed droplets are then accelerated towards the substrate where they impact and solidify during the coating process. The current work is a follow up to our earlier numerical study where numerical simulation of wire arc spraying using ANSYS FLUENT revealed flow circulations inside the gun can affect flow pattern and contribute to energy dissipation. In this study, an attempt has been made to validate and measure this matter using experimental procedures and to seek potential ways of improvement.
Proceedings Papers
ITSC 2017, Thermal Spray 2017: Proceedings from the International Thermal Spray Conference, 193-199, June 7–9, 2017,
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NiCr-Mo composite coating was prepared by plasma spraying of shell-core-structured NiCr-Mo powders. The morphologies of the NiCr-Mo powders and microstructure of the corresponding NiCr-Mo coating were characterized by SEM. Furthermore, the erosion behavior of the NiCr-Mo coating at impact angles of both 30° and 90° was investigated, and was further compared with that of the Ni20Cr coating and the In-738 alloy bulk. Results showed that fully-dense and homogenous NiCr-Mo coating with excellent interface bonding and no pure Mo inclusions was obtained. Furthermore, the erosion test results showed that the erosion rate of the optimized NiCr-Mo coating is lower than that of NiCr coating at both impact angles. Moreover, the NiCr-Mo coating presented excellent erosion resistance which was comparable as that of In-738 alloy bulk, attributing to the fully-dense microstructure and metallurgical interface bonding within coating.
Proceedings Papers
ITSC 2017, Thermal Spray 2017: Proceedings from the International Thermal Spray Conference, 200-204, June 7–9, 2017,
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The alloying concept of High-Entropy Alloys (HEA) has attracted much scientific interest due to an interesting combination of properties. Previous investigations have shown that high hardness and strength, comparable to bulk metallic glasses, can be achieved. Furthermore, HEAs show distinct ductility and good high-temperature resistance. First investigations on tribological properties are indicating high wear resistance. Previous investigations of the alloy system AlCoCrFeNiTi in bulk state have shown promising properties. Therefore, the alloy AlCoCrFeNiTi with equimolar composition was selected for transferring bulk properties to thermally sprayed coatings. The focus of this contribution is on studying tribological properties of thermally sprayed HEA coatings to enlarge the field of possible applications. Feedstock material production was carried out by high-energy ball milling (HEM) and inert gas atomization. Subsequently, coatings were deposited by Atmospheric Plasma Spray (APS). Tribological properties of the coatings under different wear regimes were investigated in ball-on-disk wear tests, oscillating wear tests and scratch tests. The tribological properties are compared with a conventional hard chrome plating and correlated with microstructure.
Proceedings Papers
ITSC 2017, Thermal Spray 2017: Proceedings from the International Thermal Spray Conference, 205-207, June 7–9, 2017,
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Metallic coatings can be produced easily with thermal spray and cold gas spray processes. However, when coating thicknesses below 50 μm are required for economical or technological reasons, the use of these well-established processes becomes more challenging. The company OBZ Innovation GmbH has developed spray processes that can produce metallic coatings with thicknesses of less than 20 μm. Such coatings are of interest for applications such as cold gas sprayed silver coatings with high purity and good electrical conductivity. Thinner sprayed coatings of such valuable materials have economic advantages, and the process may be competitive with commonly used thin film coating methods.
Proceedings Papers
ITSC 2017, Thermal Spray 2017: Proceedings from the International Thermal Spray Conference, 208-213, June 7–9, 2017,
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In current process techniques to manufacture sliding bearings, bronze components are soldered to the respective parts, which is cost and energy intensive. Apart from that, so far most bearing materials still contain lead, which in new applications is omitted by EU law to avoid associated health risks. The present study aims to offer solutions for both by using cold gas spraying as additive manufacturing technique for processing bearings directly onto steel parts and by applying that to new lead-free bronze alloys. A lead-free bronze alloy was processed as powders by gas atomization and classified to optimum sizes for cold spraying. During cold spraying, the process gas pressures and temperatures as well as the substrate temperature were varied with the aim to study influences by impact conditions and effective surface temperature on particle deformation and bonding. Respective coatings show low porosity, high hardness and high electrical conductivities. With properties similar to that of bulk cast material respectively manufactured parts should meet the requirements for new bearing applications.
Proceedings Papers
ITSC 2017, Thermal Spray 2017: Proceedings from the International Thermal Spray Conference, 214-220, June 7–9, 2017,
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The advantages of the solid state deposition process Cold Spray (CS) over conventional spray technologies go hand in hand with the requirement of high and well-predictable particle velocities. The acceleration of particles primarily takes place within the CS-nozzle while measurements of their velocity are conducted downstream of its exit. Despite their essential value, these observations are limited, in that only the result of the acceleration can be evaluated, not the actual driving mechanisms themselves. Previous work has indicated that there is no conclusive understanding of these mechanisms, especially in cases of increasing particle loading. This study therefore presents a transparent rectangular CS-nozzle design (made out of quartz) for a low stagnation pressure regime. A novelty to the field of thermal spray is the first report of particle in-flight measurements within the CS-nozzle using Particle Tracking Velocimetry (PTV) at varying particle loadings and pressure levels. It is found that particle velocities in the jet decrease with increasing particulate loading as the momentum exchange of the gas is enhanced, while in the subsonic flow region, the average velocity level increases due to particle-particle interactions with shallower axial velocity profiles. This effect is aggravated for higher working pressures, as energetic collisions cause increasing losses, depending on the number density of particles. This study forms the basis for a comprehensive nozzle-internal analysis.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 140-143, May 10–12, 2016,
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During suspension plasma spraying, the evaporation of liquid from the solution precursor alters the composition of the working gases thereby changing their thermal transport properties. This aim of this work is to better understand how aqueous calcium-phosphate, used in the synthesis of hydroxyapatite, affects thermal transport in Ar-H 2 plasma gas mixtures. Transport properties of the working gases were determined before and after injection of the precursor solution using T&TWinner, a free computational tool for thermochemistry. The results show that a significant increase occurs in the thermal conductivity of the Ar-H 2 gas mixture after the injection of the calcium-phosphate solution, but there is little change in momentum transfer between the working gases and solution droplets based on viscosity calculations. Although the software predicts an increase in the heating ability of the Ar-H 2 plasma jet, the absence of fully melted splats in the coatings suggests that it is not enough to melt HA particles.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 144-150, May 10–12, 2016,
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Bronze materials such as Ni-Al-bronze show exceptional performance against corrosion, erosive wear, and cavitation erosion due to their high fatigue strength and resistance to plastic deformation, and are thus used for ship propellers and in turbines, pumps, and other equipment where alternating stresses occur. Usually, the respective parts are cast, but in this study, a number of opportunities are evaluated to apply bronze as a coating to critical part surfaces. Initial experiments with cold gas spraying were promising enough to assess the use of warm spraying, a nitrogen-cooled HVOF process that provides similar particle impact velocities but higher particle temperatures, while still minimizing the effects of oxidation. The formation and performance of warm sprayed Ni-Al-bronze coatings was systematically investigated for different combustion pressures and nitrogen flow rates. Substrate preheating was also used to improve coating adhesion. The coatings obtained show low porosities, high strengths, and in some cases, cavitation resistance similar to that of the bulk material.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 151-155, May 10–12, 2016,
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High-Sn bearing alloys have been used for more than a century in many areas of industry. They are typically applied by casting, although thermal spraying is gaining in use, particularly for component repairs. This study evaluates the effects of HVOF spray parameters on the velocity, temperature, size, and trajectory of Babbitt particles and correlates the in-flight characteristics with coating porosity and intermetallic phase distribution. In the experiments, Babbitt layers up to 370 μm thick were deposited on carbon steel substrates while measuring particle properties and deposition efficiency. Coating samples were analyzed by means of optical and electronic microscopy and some were chemically etched to reveal the size and distribution of intermetallic phases. Test results show a significant refinement in intermetallic phase distribution when compared with commercial flame and arc-sprayed coatings.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 156-160, May 10–12, 2016,
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In this investigation, an air plasma sprayed TBC system consisting of a CoNiCrAlY bond coat (BC) and a YSZ topcoat (TC) is produced with a PVD AlOx interlayer in order to study its effect on thermally grown oxides. For comparative purposes, a reference TBC without the AlOx interlayer was also prepared and studied. A cyclic thermal load was applied to both systems and the coatings were examined after 6, 12, 24, 40, and 80 cycles. Crack lengths were measured in the YSZ layer and TGO thicknesses were assessed at the BC-TC interface. An examination of coating microstructures revealed the expected mixed-mode failure in both TBCs. In comparison to the reference TBC, the system with the AlOx interlayer showed reduced crack formation in the TC and slowed TGO formation at the BC-TC interface both during and after thermal treatment.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 161-167, May 10–12, 2016,
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In this work, a mechanically clad NiCr powder feedstock was deposited on alumina substrates by atmospheric plasma arc spraying. The resultant splats were analyzed for features such as interfacial bonding, splat classification and, critically, Cr distribution. Using a slice-and-view sectioning technique in a dual-beam FIB-SEM system, a representative splat exhibiting discrete Ni and Cr regions was physically deconstructed then reconstructed with visualization software to analyze individual layers with the splat. Although the powder feedstock contained Ni particles clad with clusters of Cr, the splats solidified into distinct layers of Ni and Cr with no signs of interaction between them. A model formulated based on this observation shows that the distribution of Cr cladding on the Ni particulates influences the amount and location of Cr around the solidified Ni splats.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 168-172, May 10–12, 2016,
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This study investigates arc behavior associated with twin-wire arc spraying and the effect of pulsed current power on arc formation and coating properties. It is shown through false color images and by calculations that arc length is directly related to voltage and that a “natural” frequency can be obtained from voltage fluctuations. By applying current pulses at this frequency, arc movement along the wire tips is effectively controlled because the arc reignites with each current pulse. This results in coatings with lower oxide content and a microstructure nearly free of the lamellae typically found in dc arc spray deposits. Further improvements are likely to be achieved by optimizing the configuration of the wire guides relative to the gas nozzle.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 173-178, May 10–12, 2016,
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In this work, gas-atomized FeCr powders were deposited on aluminum substrates by HVOF spraying, forming dispersion strengthened coatings with a dense layered structure and low porosity. SEM, TEM, and XRD analyses show that the coatings primarily consist of amorphous matrix (40%) with precipitated nanocrystals and hard boride phases. A number of coating properties, including microhardness, bonding strength, and thermal conductivity, were measured and are correlated with spraying conditions.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 179-183, May 10–12, 2016,
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In this investigation, different atomizing gases, arc wire spray guns, and wire sizes were used to deposit ZnAl coatings on high-strength steel substrates. Sample sets corresponding to different gas mixtures and pressures as well as other parameters were produced and the coatings obtained were evaluated based on morphology, porosity, composition, phase distribution, and oxide content. The results are presented and discussed, particularly with regard to corrosion lifetime and performance.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 184-189, May 10–12, 2016,
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In this work, a design-of-experiments approach is used to map the main parameters of a high-velocity airfuel (HVAF) spraying process. Chromium carbide based material with a NiFeCrSi matrix was sprayed with varying gas flows and nozzle designs while monitoring their effect on particle temperature, velocity, and coating build-up. It was found that sufficient heating is critical to abrasive wear resistance and that particle temperatures are primarily controlled by fuel flow rates. Nozzle geometry, on the other hand, had the biggest effect on particle velocity, which was found to increase nearly 100 m/s by switching from a cylindrical to a convergent-divergent design.
Proceedings Papers
ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 190-195, May 10–12, 2016,
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A numerical model of a supersonic compressible plasma flow has been developed with the aid of CFD software to describe the thermodynamic and transport properties of a plasma jet in order to investigate the PS-PVD process and how to optimize it for thermal barrier coatings and, in particular, the formation of columnar microstructures. The required properties of the plasma gas mixtures were obtained as a function of temperature and pressure from thermodynamic calculations in chemical equilibrium with the effect of ionization. Two-dimensional Monte Carlo simulations were conducted to provide insight on the evolution of columnar microstructure, accounting for self-shadowing and vapor incidence angle but ignoring the effect of diffusion. Simulated structures and predicted values are presented and compared with actual images and measurements.
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