bluuebunny/crossref_metadata_2025 huggingface dataset:
Material and Process Considerations for Developing and Qualifying Repair Coatings for Nickel / Chrome Replacement
Authors: Fitzgerald S. , Edwards C. , Randolph J.
Published: September 2022

High velocity oxygen fuel (HVOF) coatings have been in development for chrome replacement for aerospace applications and implemented for many applications over the past couple of decades. Now that these coatings have become common for newly manufactured parts, the need for repair and overhaul coating thicknesses beyond 0.254 mm (0.010 inch) for rework that traditionally would have thick chrome and nickel build-ups with chrome caps has started to develop. This requirement has been identified for high strength steel landing gear applications and will follow most likely in similar aircraft applications such as flap and slat tracks, actuators and other aircraft support structure. This paper will discuss the development and qualification requirements necessary, and related concerns in order to replace these thick repair coating applications with duplex coatings, or possibly with thick single coating applications that will meet the original design criteria for each part.
Thermal Spray Deposition of Fuel Cell Interconnect Material
Authors: Garcia E. , Coyle T.W.
Published: September 2022

In this work two different thermal spray techniques were used to deposit La0.9Sr0.1CrO3 interconnect material: high velocity oxy-fuel (HVOF) using a modified nozzle and atmospheric plasma spray (APS). Two different APS torches were employed: A commercial torch that uses Ar/H2 as plasma forming gases and a new torch design that uses CO2 gas mixtures. A substitute powder with similar physical properties to La0.9Sr0.1CrO3 was employed for the development and optimization of the process parameters to achieve the highest density before the deposition of the La0.9Sr0.1CrO3 on zirconium oxide substrates. The microstructures observed by scanning electron microscopy (SEM) and the phase composition of the coatings obtained from X-ray diffraction analysis are correlated to the spraying characteristics of the different techniques employed. The electrical resistivity of the as-sprayed coatings is discussed in terms of microstructure features and the phase composition. Post-deposition heat treatments were studied in order to reduce the electrical resistivity.
Comparison of Atmospheric Plasma Sprayed Anode Layers for SOFCs Using Different Feedstock
Authors: Hathiramani D. , Vaßen R. , Stöver D. , Damani R.J.
Published: September 2022

Atmospheric plasma spraying is a cost effective way to produce SOFC components. Doing so, sinter steps can be avoided, which is essential once a metallic support is used for the SOFC. Several properties are required regarding the micro structure of an optimized anode layer. Here gas permeability, electrochemistry, electronic conductivity, coefficient of thermal expansion as well as thermal shock resistance has to be considered. Different types of powder feedstock were investigated to develop an atmospheric plasma sprayed anode layer: (i) NiO or Ni together with YSZ as starting materials, (ii) agglomerates in which NiO and YSZ are already mixed on a sub-micrometer range, (iii) blended NiO/YSZ powder, (iv) separate injection of the individual NiO and YSZ powders, respectively into the plasma by two separate powder lines. The performance of APS anodes are measured in single fuel cell tests. Anode layers sprayed by a separate injection of the individual NiO and YSZ powders into the plasma show the best results.
The Recent Thermal Barrier Coating System in Gas Turbine
Authors: Kasumi S. , Takahashi T. , Kurimura T. , Mega M. , Torigoe T. , Narita J.
Published: September 2022

The thermal barrier coating (TBC) system is currently a standard technology of gas turbine hot gas path parts to achieve a highly reliable long life operation of engines for a power supply. Mitsubishi Heavy Industries, LTD. (MHI) has applied the TBC on the gas turbine blades, vanes and combustor parts. TBC system consists of MCrAlY as a bondcoat for oxidation protection at elevated temperature and YSZ (yttria stabilized zirconia) as a topcoat for efficient thermal barrier. The conditions where TBC has been in service are at the temperature up to 1500°C and with combustion gas environment. As far as the blades and the vanes are concerned, the MCrAlY bondcoat is coated by low pressure plasma spray (LPPS) or high velocity oxygen fuel (HVOF) system, and the YSZ topcoat is coated by atmospheric plasma spray (APS) system. In the case of the combustor parts, both the MCrAlY bondcoat and the YSZ topcoat are coated by APS. To increase the reliability and prolong the service life of the applied TBC in the gas turbine, it is very important to verify the coating properties, optimize the coating process parameters and control the coating process.
Effect of Substrate Temperature and Droplet Characteristics on Plasma Sprayed Zirconia Splats
Authors: Salimijazi H.R. , Pershin L. , Coyle T.W. , Mostaghimi J. , Rosenzweig L. , Moran E.
Published: September 2022

The current study has been focused on the final morphology of atmospheric plasma sprayed 8% yttria stabilized zirconia single splats. Single splats of two different sizes (-25 µm and +25/-45 µm) of ZrO2 8Y2O3 powder have been collected on polished stainless steel substrates at three different temperatures (Room, 300°C, and 600°C). The splat morphology and diameter, satellite particles, and splashing behavior were investigated using both scanning electron microscopy and image analysis software. The splat/substrate interface and splat curl up were studied from cross-sections prepared by focused ion beam milling. Results showed primarily pancake morphology and no evidence of delamination along the splat/substrate interface at 300oC substrate temperature and 100 mm spray distance. Overlapped splats showed evidence of melting (microwelding) at the splat boundaries. Splat thickness was measured to be less than 1 µm for all spray conditions. Roughness profiles of the surface of the deposited splats indicated microcracks had formed within the splats. Image analysis results exhibited a higher volume fraction of the splats relative to satellite particles at longer spray distance and higher substrate temperature. The average splat diameter increased as the substrate temperature increased.
Development Of Thin And Gastight Ceramic Coatings By Atmospheric Plasma-Spraying
Authors: Vaßen R. , Stöver D.
Published: September 2022

The manufacture of thin (< 100 µm) and different, dense ceramic layers by atmospheric plasma spraying can be achieved by using appropriate coating conditions. Major process parameters are certainly particle temperature and velocity and also substrate temperature. Hence, the particle properties have been controlled and optimized by the use of particle diagnostic tools, the substrate temperature was controlled by the use of pyrometers. Another important parameter is the choice of an appropriate powder to avoid cracks and pores in the coating. In the paper the influence of the mentioned parameters will be discussed and several examples of dense coatings given. Applications in the field of solid oxide fuel cells, environmental barrier coatings, and membranes will be described.
Improved Mechanical Properties by Nanoreinforced HVOF-Sprayed Ceramic Composite Coatings
Authors: Neufuss E. , Dyshlovenko Turunen , Varis T. , Keskinen J. , Fäll T. , Hannula S-P.
Published: September 2022

HVOF thermal spraying has been developed to deposit dense ceramic coatings with improved protective properties for various applications. Even though HVOF coatings are much denser as compared to ordinary plasma sprayed coatings, the coating properties are inferior as compared to bulk ceramics because of pores and microcracks, which influence adversely the coating properties, i.e. toughness, hardness and wear resistance. One strategy to improve the properties of the coatings is to decrease the grain size of the ceramic phase and to add toughening elements to the microstructure. Nanocrystalline coatings have been found to offer better thermal shock resistance, lower thermal conductivity and better wear resistance than their conventional counterparts. In this paper we describe the development of nanocrystalline ceramic composite coatings, where the grain size of ceramic has been decreased and a few percents of alloying element has been added in order to toughen the coating. Dense nanostructured alumina coatings alloyed with Ni and ZrO2 nanosized particles were manufactured by HVOF spraying by using HV2000 spray gun. Mechanical properties, especially elastic modulus and relative fracture toughness were studied. Used techniques were instrumented nanoindentation and KIC evaluation. As a result coatings with nearly 100% improvements in relative fracture toughness were produced for nanoreinforced alumina composite coating. Results are compared with the microstructure, hardness and abrasive wear resistance of the coatings.
Microstructure and Mechanical Properties of Yttria Partially Stabilized Zirconia Coatings Deposited by Laser-Assisted Air Plasma Spraying
Authors: Dubourg L. , Moreau C.
Published: September 2022

In laser-assisted air plasma spraying (LAAPS), a laser beam interacts simultaneously with the coating surface during plasma spraying in order to increase the coating surface temperature and possibly remelt the coating surface. As a result, the microstructure is partially densified and macrocracks can be inhibited. In this paper, LAAPS was performed to improve the mechanical properties of ZrO2 – 8 wt.% Y2O3 coatings. The coating microstructure was characterized by optical microscopy, SEM and X-ray diffraction. The mechanical characterization was done by hardness measurements, thermal shock resistance and erosive wear tests. Results showed that laser assistance may induce: (1) a decrease of the amount of microcracks and interlamellar pores, (2) a columnar dendritic structure in the coating splats and (3) an improvement of the thermal shock resistance. LAAPS did not affect the hardness or the erosive wear resistance of yttria partially stabilized zirconia coatings.
Photocatalytic Function of FeTiO3 in Composite TiO2-FeTiO3 Coatings Prepared by Plasma Spray
Authors: Ye F.-X. , Ohmori A. , Tsumura T. , Nakata K. , Li C.-J.
Published: September 2022

The compositions and photocatalytic activity of plasma sprayed TiO2, TiO2-30%FeTiO3, TiO2-50%FeTiO3 and FeTiO3 coatings were investigated. The influence of FeTiO3 compound on the photocatalytic activity of TiO2 coating was clarified. The TiO2-30%FeTiO3 coating sprayed under the arc current of 400 A had good photocatalytic activity because the coating did not contain the unfavorable Fe2TiO5 phase. The relative deposition speed of TiO2-30%FeTiO3 powder under the arc current of 400 A was approximate to 4 µm/pass. Although pure FeTiO3 compound nearly did not show photocatalytic performance, the existence of FeTiO3 could improve the photocatalytic activity of anatase TiO2 if FeTiO3 contacts coherently with it, which was explained using two-steps electron transfer model.
Hot Salt Corrosion Behavior of High Velocity Arc Sprayed Fe-Al Based Composite Coatings
Authors: Zhang W. , Xu W. , Xu B.
Published: September 2022

Fe-Al based composite coatings were deposited on Grade 20 steel substrates by High Velocity Arc Spraying (HVAS) technology. Hot salt corrosion properties of the coatings were studied at the temperatures of 450 °C,650 °C and 800 °C . Results showed that the corrosion resistance of the Fe- Al/Cr3C2 composite coatings changed little with the increase of temperature, contrasted to the substrate and Fe-Al coatings. The excellent corrosion resistance of the Fe-Al/Cr3C2 composite coatings was attributed to the oxidation of the iron, aluminum and chromium to form protective scales. In hot salt, there are mainly iron oxides at the outer corrosion surface; aluminum and chromium oxides are found at the inner corrosion surface, which can effectively protect the Fe- Al/Cr3C2 composite coatings from corrosion.
Roughness Enhancement of HVOF Sprayed MCrAlY Bond Coatings for Adhesion Improvement of Ceramic Top Layers
Authors: Bach Fr.-W. , Mohwald K. , Engl L. , Duda T.
Published: September 2022

High velocity oxyfuel flame spraying (HVOF) has a great potential for replacing the low pressure plasma spraying (LPPS) process in most applications for hot corrosion protective MCrAlY coatings for turbine hot gas path parts. Compared to LPPS coatings, state-of-the-art HVOF sprayed MCrAlY coating systems feature competitive hot corrosion protective properties. Low HVOF facilities investment costs and a stable, easy process controlling are major advantages in terms of application. Besides hot corrosion protective single layers, MCrAlY coating systems are used as bond coats for ceramic thermal barrier coatings (TBC). But HVOF sprayed MCrAlY coatings show a comparatively low surface roughness which leads to a poor adhesion of the ceramic top layer, restricting the application area of HVOF. This paper deals with a development project which aims on roughness enhancement of HVOF sprayed MCrAlY coatings in order to improve the bonding properties of the TBC. In the project’s framework, several HVOF systems and different powders were investigated. Parameter sets were developed considering both a high surface roughness and a low level of defects in the coating.
Characterisations and Corrosion Resistance of HVOF Cr3C2-NiCr on Ni-Base Superalloys at 900°C in Molten Salt Environment
Authors: Sidhu T.S. , Prakash S. , Agrawal R.D.
Published: September 2022

In this study, high velocity-oxy fuel (HVOF) technique was used to deposit Cr3C2-NiCr coating on the Ni-base superalloys for their hot corrosion applications. The coatings were characterised with regard to coating thickness, porosity, microhardness and microstructure. The hot corrosion behaviours of the bare and Cr3C2-NiCr coated superalloys were studied after exposure to molten salt (Na2SO4-60%V2O5) at 900°C under cyclic conditions. Optical microscopy, XRD, SEM/EDAX and EPMA techniques were used to characterise the coatings. The thermogravimetric technique was used to establish kinetics of corrosion. The structure of the as sprayed Cr3C2-NiCr coating mainly consisted of γ-nickel solid solution with very low intensity peaks of Cr7C3 and Cr2O3 phases. Some porosity (less than 1.5%), inclusions, unmelted and semi-melted powder particles were observed in the structure of the coatings. Coating microhardness values were found to be in the range of 850-900 Hv (Vickers hardness). The Cr3C2- NiCr coating was resistant to hot corrosion in the given molten salt environment at 900°C. The hot corrosion resistance imparted by Cr3C2-NiCr coatings may be attributed to the formation of oxides of nickel, chromium, and spinels of nickel and chromium.
A Novel Nano-Composite Wire Material: The Low Cost and Enhanced Properties Coating Design
Authors: Georgieva P. , Thorpe R. , Yanski A. , Seal S.
Published: September 2022

Due to their enhanced mechanical properties and high range applications in severe environments use, there is ongoing research in the area of amorphous metallic glasses and nanostructured materials. The science and mechanisms leading to these exceptional properties are discussed herein. The arc sprayed coatings produced for study in this paper show remarkable performance and are analyzed in-depth using advanced characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Additional analysis of the mechanical properties of the coatings show enhanced strength and hardness, good wear and corrosion properties, along with high temperature corrosion and oxidation resistance.
Mechanical Properties of Plasma Sprayed Alumina-Zirconia Nano-composite Film
Authors: Sodeoka S. , Suzuki M. , Inoue T.
Published: September 2022

Alumina-zirconia nano-composite coating were fabricated by plasma spraying using agglomerated feedstock from alumina and yttria partially stabilized zirconia fine powders of about 100 nm in diameter. The coating was very dense and showed the striped contrast in the splats. XRD analysis and TEM observation revealed that the splats contained gamma-alumina and tetragonal-zirconia crystals, which sizes were under 10 nm. The striped contrast in the splats corresponded to the inhomogeneous distributions of these crystals. To investigate the mechanical properties of this nano-composite coating, micro-hardness and fracture toughness were measured. The critical strain energy release rate of nano-composite coating was 106.4 J/m2, which was two times larger than YSZ coating.
Nanostructured Abradable Coatings for High Temperature Applications
Authors: Lima R.S. , Marple B.R. , Dadouche A. , Dmochowski W. , Liko B.
Published: September 2022

Nanostructured yttria stabilized zirconia abradable coatings were produced via air plasma spray (APS) and compared to conventional abradable coatings based on the composite CoNiCrAlY+BN+polyester also sprayed via APS. The microstructures of the coatings were analyzed using SEM and the hardness determined via Rockwell Y measurements. It was possible to engineer nanostructured abradables with a high degree of plasticity by controlling the amount, morphology and distribution of the nanostructured phase embedded in the coating microstructure. Room temperature rub-rig tests were performed for both types of coatings under different blade tip speeds and seal incursion rates simulating operating conditions of gas turbines. The nanostructured abradables exhibited good performance indicating that abradable coatings engineered in this fashion have potential for industrial application at elevated temperatures.
Nanophased WC-12Co Thermal Spray Coatings for Wear Resistant Applications
Authors: Petsas N. , Papapanos G. , Vardavoulias M. , Moutsatsou A. , Celis J.P. , Matteazzi P.
Published: September 2022

The purpose of the present study is to investigate the influence of critical HVOF spray parameters on mechanical properties of WC–12Co coatings obtained from nanophased powder used as feedstock material. A Taguchi design of experiments approach was used for the selection and optimization of process parameters and coating properties. An L9 table was used for the evaluation of the effect of spray distance, oxygen/fuel ratio, gun traverse speed and feed rate on coating microhardness, adhesion strength, porosity and deposition efficiency – thickness. Results show clearly that each parameter affects in a different way and percentage each property. Furthermore, the comparison of XRD data with a conventional WC–12Co coating indicates that the nanostructure of the initial powder is maintained in the coating, whereas in the conventional one the formation of W2C phase is evident. Finally, fretting tests show similar behavior in terms of friction coefficient, but a significant improvement regarding wear resistance in the case of the nanophased coating.
Impact of Partially Molten Plasma-Sprayed Zirconia Particles on Glass Surfaces
Authors: McDonald A. , Chandra S. , Moreau C.
Published: September 2022

Plasma-sprayed yttria-stabilized zirconia particles (~40 µm diameter) were photographed during impact (velocity ~200 m/s) on a glass surface that was maintained at either room temperature or 400°C. A droplet that approached the surface was sensed using a photodetector and after a known delay, a light source was triggered to illuminate the particle in order to photograph it with a charge-coupled device (CCD) camera. A rapid two-color pyrometer was used to collect the thermal radiation from the particles to follow the evolution of their temperature and size, in-flight and after impact. The fully molten particles spread into a thin liquid splat after impacting the surfaces. The partially molten particles disintegrated into small satellite fragments immediately upon impact. The surface area, as indicated by the pyrometric signals, of the partially molten particles during spreading were almost an order of magnitude smaller than that of the fully molten particles. The pyrometric signals, characteristic of the impact of partially molten zirconia, provide a novel method of identifying partially molten ceramic particles after impact on a flat surface.
Mapping Deposition Parameters and Microstructures of Plasma Sprayed Spinel
Authors: Samadi H. , Coyle T.W.
Published: September 2022

Magnesia-alumina spinel (MgAl2O4) is an oxide ceramic with broad applications as a high temperature and corrosion resistant material. Its moderate coefficient of thermal expansion (7-8 x 10-6 K-1) may allow it to be used as a plasma spray coating on metallic substrates with coefficients of thermal expansion of ~12x10-6 K-1. Two important factors affecting the microstructure and properties of plasma sprayed coatings are the particle temperature (Tp) and particle velocity (Vp) in the plasma jet. The particle temperature and velocity are influenced by a substantial number of operating parameters. Using a statistical design of experiments approach, deposition parameters, microstructure, and physical properties of air plasma sprayed spinel coatings are linked through mapping versus in-flight particle temperature and velocity. The Tp-Vp maps provide a basis for depositing coatings with controlled structures.
Shrouded Plasma Processing of Solution Precursors
Authors: Sadangi R.K. , Shukla V. , Kear B.H.
Published: September 2022

A shrouded-plasma spray process is described for the production of a metastable powder, deposit or preform. A high enthalpy atmospheric DC arc-plasma torch is used as heat source and a solution precursor as feed material. An aerosol-or liquid-jet of solution precursor is delivered to a steady-state reaction zone within the shrouded-plasma flame, where rapid and controlled precursor decomposition occurs. Depending on the operating conditions, the precursor material is pyrolyzed, melted or vaporized, prior to quenching to form a metastable nano-sized powder. This method is capable of processing a host of metastable materials, including the difficult-to-process refractory metals, oxide and non-oxide ceramics, as well as their composites. In this paper, we will discuss our results on multi-component oxide systems.
HVOF Sprayed Multi-Scale Polymer/Ceramic Composite Coatings
Authors: Gupta V. , Niezgoda S. , Knight R. , Twardowski T.E. , Cairncross R.A.
Published: September 2022

The High Velocity Oxy-Fuel (HVOF) combustion spray process has been used successfully for spraying polymers and polymer-matrix composite coatings. Spraying of polymer ceramic composite powders produced by ball-milling nominal 60 ..m Nylon-11 with different size scale (7 nm to 15 µm) ceramic reinforcements is an effective method of producing semi-crystalline micron and nano-scale reinforced composite coatings. Polymer matrix composite coatings with nominal 10 vol. % of different size scale silica and alumina reinforcements have been produced. The levels of filler loading in both the feedstock powders and HVOF-sprayed coatings were determined by thermo-gravimetric analysis (TGA) and compared using ashing. Particle size analysis, microstructural characterization and the elemental compositions of the feedstock powders and as-sprayed coatings were determined by optical and scanning electron microscopy and energy dispersive spectroscopy. The influence of dispersion, distribution and size of the reinforcing phase was studied and correlated to coating microstructure and process parameter variations. The scratch resistance of the coatings was measured as a function of reinforcement size and compared with those of the pure HVOF-sprayed Nylon-11 coatings.
Effect of Reinforcement Size on the Scratch Resistance and Crystallinity of HVOF Sprayed Nylon-11/Ceramic Composite Coatings
Authors: Niezgoda S. , Gupta V. , Knight R. , Cairncross R.A. , Twardowski T.E.
Published: September 2022

The high velocity oxy-fuel (HVOF) combustion spraying of ball-milled Nylon-11/ceramic composite powders is an effective, economical and environmentally sound method for producing semi-crystalline nano- and micron-scale reinforced polymer composite coatings. Polymer matrix composite coatings reinforced with multiple scales of ceramic particulate materials are expected to exhibit improved load transfer between the reinforcing phase and the matrix due to interactions between large and small ceramic particles. An important step in developing multi-scale polymer matrix composite coatings and associated load transfer theory is determining the effect of reinforcement size on the distribution of the reinforcement and the properties of the composite coating. Composite feedstock powders were produced by dry ball milling Nylon-11 with fumed silica particles of 7, 20 and 40 nm, with fumed alumina particles of 50 and 150 nm, and with white calcined alumina 350 nm, 1, 2, 5, 10, 20, 25 and 50 µm at 10 % by volume overall ceramic phase loadings. The effectiveness of the ball-milling process as a function of reinforcement size was evaluated by SEM, EDS microanalysis and by characterizing the behavior of the powders during HVOF spraying. The microstructures of the as-sprayed coatings were characterized by optical microscopy, SEM, EDS and XRD. The reinforcement particles were found to be concentrated at the splat boundaries within the coatings, forming a series of interconnected lamellar sheets with good 3-dimensional distribution. The scratch resistance of the coatings improved consistently and logarithmically as a function of decreasing reinforcement size and compared to those of HVOF sprayed pure Nylon-11.
Implementation of Neural Networks into Modern Process Control Equipment
Authors: Schmitt R. , Doeren J. , Bobzin F. , Lugscheider E. , Ernst F.
Published: September 2022

Previous investigations of thermal spraying processes have shown that the relations between process parameters and the objective measurements are very complex. An approved approach to control complex processes is the application of Neural Networks (NN). Thus, Neural Networks have been designed to control the process of APS and HVOF spraying. Feed forward Neural Networks (Multi Layer Perceptron, MLP) are used. They are able to control a process. The way to train the Neural Network is to conduct as many experiments as possible, this is the major difficulty for the industrial use of Neural Networks. To save time and money DoE (Design of Experiments) is used to create an optimal experimental plan for the training. For testing the implementation of Neural Networks coatings are sprayed with APS, using DoE. The Neural Networks are combined with the particle flux imaging (PFI) tool. In future this combination will be able to provide an open loop control for thermal spray processes. The Neural Networks will be integrated with the software of the PFI-unit in order to create an easy to handle and affordable process control device. First experiments have been done with the APS process by spraying ZrO2 onto steel substrates. Afterwards the porosity of the coating was correlated to the recorded images and to the process parameters.
Influence and Significance of Noise Factors in Plasma Sprayed Surface Coatings
Authors: Bobzin K. , Lugscheider E. , Ernst F. , Zwick J. , Richardt K. , Landes K. , Forster G.
Published: September 2022

The number of parameters influencing the plasma spraying process is very high. Only a part of these parameters can be controlled online; some of them such as gas flows, current, voltage and spraying distance can be controlled easily, others such as particle temperature and velocity can only be controlled with substantially higher effort. As differences from parameter values preinstalled or given at the start of the process, the noise factors affect the coating properties in different ways and show big effects on the coating quality. Nevertheless there is only little knowledge about the significance of several noise factors and about the influence of small process parameter fluctuations on the coating properties. Because some of these noise factors such as plasma torch degradation cannot be avoided, the aim of this work is to determine the sets of coating parameters, where the influence of noise factors is minimized. This should be achieved by using online diagnostic tools, that afford the observation of fast and easy controllable process characteristics. On the other hand process errors shall be identified in an early process stage using appropriate diagnostic methods.
A New Approach to Online Thickness Measurement of Thermal Spray Coatings
Authors: Nadeau A. , Pouliot L. , Nadeau F. , Blain J. , Berube S.A. , Moreau C. , Lamontagne M.
Published: September 2022

In the past ten years, significant progress has been made in the field of advanced sensors for particle and spray plume characterization. However, there are very few commercially available technologies for online characterization of the as-deposited coatings. In particular, coating thickness is one of the most important parameter to monitor and control. Current methods such as destructive tests or direct mechanical measurements can cause significant production downtime. This paper presents a novel approach that enables online, real-time and non-contact measurement of individual spray pass thickness during deposition. Micron-level resolution was achieved on various coatings and substrate materials. The precision has been shown to be independent from surface roughness or thermal expansion. Results obtained on typical HVOF and plasma sprayed coatings are presented. Finally, current fields of application, technical limitations and future developments are discussed.
Effect of Substrate Surface Topography and Temperature, on Millimeter and Micrometer Sized Splat Formation and on Thermal Contact Resistance
Authors: Cedelle J. , Vardelle M. , Fauchais P. , Tanaka Y.
Published: September 2022

Many properties (thermal, electrical, mechanical) of thermal sprayed coatings are strongly linked to the real contacts between the “piled-up” splats. The quality of this contact depends on droplet parameters at impact (size, temperature, velocity) and substrate parameters (temperature, topography). Two different techniques have been developed in order to study the plasma sprayed particle behaviour at impact. The first one allows direct observation under direct current (dc) plasma spray conditions, while the latter one, based on the millimetre sized free falling drop, enables the visualization of flattening phenomena, but at larger scale. These two techniques bring complementary approaches and results. The latter show that flattening time and cooling rate of the lamellae (metallic and ceramic) are improved with the stainless steel substrate surface modification at the nanoscale when corresponding to a positive skewness parameter obtained by preheating it over the transition temperature. Experiments of wettability show that the presence of nanopeaks increases the contact angle of the liquid on the substrates and reduces thermal contact resistance at interface. It has also been shown that, when adsorbates and condensates are not eliminated from the surface, even with a positive skewness, the thermal contact resistance is increased.
Effect of Torch Hardware and Operating Parameters on Oxy-Acetylene Powder Flame Spray Heat Flux
Authors: Cates J.W. , Urrea D.A. , Hall A.C. , Neiser R.A. , Smith M.F. , Beatty D.E. , Mayer A.J. , Roemer T.J. , Hirschfeld D.A. , Cook D.J.
Published: September 2022

The effect of torch hardware, operating parameters, and powder type on substrate surface heat flux was quantitatively investigated using calorimeters. The Sulzer-Metco 6P oxyacetylene torch with two nozzles and two air caps and the Alamo PG-550 torch were studied using designed experiments to show the effects of total combustible gas flow, oxy-fuel ratio, air flow, and standoff distance on surface heat flux. Air caps which directed cooling air toward the flame produced lower heat flux than air caps providing gun cooling. For the 6P torch, nozzle geometry did not have a significant effect on heat flux. With low air flow rates, both torches exhibited similar heat fluxes. At high air flows, the surface heat flux of the PG-550 was larger than that of the 6P.
High Speed Visualization and Plume Characterization of Hybrid Spray Process
Authors: Stanisic J. , Kosikowski D. , Mohanty P.S.
Published: September 2022

The hybrid spray process that combines arc-spray with HVOF/plasma jet, has recently demonstrated its effectiveness in the deposition of functionally gradient coatings. This approach aims at exploiting the attributes of both the arc-spray technique combined with those of the HVOF/APS technique. This paper presents high speed visualization and plume characterization of an Arc/HVOF hybrid spray gun as well as a twin-wire arc spray gun. The physics of atomization in hybrid spray process is examined using high-speed camera. A DPV-2000 particle diagnostics sensor is used to measure particle velocity, temperature, size and distribution. The influence of feed material, arc-spray parameters, and the jet parameters on the particle characteristics is presented. The differences in the in-flight characteristics between the hybrid and the twin wire arc process have been discussed aided by the observed atomization phenomena with the high speed camera.
Prospect for Plasma Spray Process On-Line Control Via Artificial Intelligence (Neural Networks and Fuzzy Logic)
Authors: Kanta A.F. , Montavon G. , Planche M.P. , Coddet C.
Published: September 2022

Parametric drifts and fluctuations occur during plasma spraying. These drifts and fluctuations originate especially from the electrode wear and intrinsic plasma jet instabilities: the plasma net power varies in this case modifying significantly its thermodynamic properties and transport coefficients hence modifying the momentum and heat transfers to the particles. It is possible to control the in-flight particle characteristics by adjusting continuously the operating parameters, in particular the power parameters. Due to the large amplitudes of these drifts and fluctuations, the strategy to adopt will depend on the required corrections to apply to the particle characteristics. Developing a reliable controller requires: (i) implementation of reliable sensors to accurately diagnose in-flight particle characteristics but also some other parameters, such as surface temperature during spraying; (ii) development of a robust command, to insure the stability of the control system. Fuzzy logic permits to define parametric correction rules and the command can be based on these algorithms; (iii) linking of the robust command to a predictive model. Artificial neural networks, among other artificial intelligence protocols such as genetic algorithms, proved to be able to predict in-flight particle and coating characteristics; (iv) validation of the corrections with an extensive database used as a reference. Coupling neural protocols to fuzzy logic should permit the development of such an independent controller which could adjust in real time the operating parameters as a function of the measured in-flight particles to manufacture a coating with identical conditions among its entire thickness. This paper aims at presenting the methodology and the controller and at simulating the spray operation.
Evaluation of Adhesion Strength and Residual Stress of HVOF Sprayed Metallic Coatings
Authors: Yokoyama K. , Watanabe M. , Kuroda S. , Gotoh Y.
Published: September 2022

The purposes of the present study are firstly to establish a reliable experimental method to evaluate the adhesion strength and secondly to reveal the relationship between the adhesion strength and the residual stress in the coatings. SUS304 stainless steel coatings were deposited on low carbon steel substrates by HVOF spraying. Two types of samples were fabricated. One is a cylindrical shape for the adhesion test and the other has a rectangular dimension for residual stress evaluation. The tensile adhesion tests were carried out by modifying the conventional test method. Circumferential interface cracks were introduced by putting carbon thin layer on the substrate before spraying, and the edge of the substrate was masked to prevent undesirable deformation during spraying. The interface fracture toughness was estimated from the load at failure and the width of carbon area in radial direction (corresponding to the crack length) by finite element analysis. The residual stress was evaluated by measuring the relaxed strain at the substrate surface for reduction of the coating thickness. Thinning of the coatings was performed by polishing. It was possible to evaluate the adhesion strength of SUS304 steel coatings with good reproducibility for the samples deposited under various spray conditions. The correlations between adhesion strength and residual stress will be discussed.
MoB/CoCr Spray Coating with Higher Durability in Molten Al and Al-Zn Alloys
Authors: Mizuno H. , Aoki I. , Tawada S. , Kitamura J.
Published: September 2022

MoB/CoCr, a novel thermal spray material, with high durability in molten Al and/or Al-Zn alloys has been developed to utilize for die casting parts of Al alloy, and for hot continuous dipping roll in Zn and Al-Zn plating lines. The durability of the MoB/CoCr coatings prepared by high velocity oxy-fuel (HVOF) spraying has been investigated using a molten metal immersion tester. The immersion tests revealed that the MoB/CoCr coating has much higher durability without dissolution in the Al alloys than conventional spray coatings, such as WC/12%Co and WC/10%Co/4%Cr, as well as various other surface modification methods. The MoB/CoCr coating also has showed higher durability in the molten Al-Zn alloy when the coefficient of thermal expansion (CTE) of the substrate is similar to that of the MoB/CoCr. The lifetime of the coating on stainless 316L substrate, widely used as the hot continuous dipping roll, was insufficient because of the generation of cracks due to a large difference in the CTE between the MoB/CoCr coating and substrate. Basic anneal examinations have revealed that optimization of coating structure by changing undercoat material and its thickness is effective to improve the lifetime.
Plasma Transferred Arc Deposition of Beryllium
Authors: Hollis K. , Bartram B. , Withers J. , Storm R. , Massarello J.
Published: September 2022

The exceptional properties of beryllium (Be) including low density and high elastic modulus, make it the material of choice in many defense and aerospace applications. However, health hazards associated with Be material handling limit the applications that are suited for its use. Innovative solutions that enable continued use of Be in critical applications while addressing worker health concerns are highly desirable. Plasma Transferred Arc solid freeform fabrication is being evaluated as a Be fabrication technique for civilian and military space based components. Initial experiments producing beryllium deposits are reported here. Deposit shape, microstructure and mechanical properties are reported.
Plasma Spray Formed Yttrium Oxide Crucibles
Authors: Hollis K. , Bartram B.
Published: September 2022

Plasma spray forming ceramic components on a mandrel provides a way of net shape forming of difficult to machine materials. In addition, the structure of plasma sprayed ceramics contains fine porosity that improves strain accommodation as compared to sintered ceramics. However, plasma spray forming causes complex stress states in materials that may lead to cracking during spraying or during separation from the mandrel. Monitoring surface temperatures by infrared videography and controlling deposit surface temperature by directed cooling can be used to minimize thermal gradients and minimize part cracking. Control of thermal stresses is also necessary for proper separation of the sprayed part from the mandrel. Details of the plasma spray forming of yttrium oxide crucibles show how temperature monitoring, directed cooling, and robot manipulation are used to produce a crack free crucible.
Novel Nickel-Cermet Hardcoatings
Authors: Sherman A. , Garrett W. , Conklin M.
Published: September 2022

Current thermal spray chrome replacement and hardfacing materials primarily use WC or Cr3C2 as hardphase materials and contain chrome. A series of cermet alternatives based on lower weight and cost ceramic particles including alumina, silicon carbide, boron carbide and titanium nitride were applied via HVOF and tested for wear and frictional properties under various loading conditions. Furthermore, based upon highly promising initial results, thermal spray particle designs were modified for lower cost and improved performance.
Wear Behaviour of APS and HVOF Sprayed Ceramic Coatings
Authors: Bolelli G. , Cannillo V. , Lusvarghi L. , Turunen E. , Varis T. , Fält T. , Hannula S.-P.
Published: September 2022

Plasma sprayed oxides are effective coatings against wear and corrosion. Low particle velocity in the plasma jet causes a limited interlamellar cohesion. HVOF-sprayed ceramic coatings emerged as an improved alternative. In this paper, microstructural characteristics and tribological performances of HVOF sprayed Al2O3, nanostructured Al2O3 and Cr2O3 coatings are compared to reference plasma-sprayed Al2O3 and Cr2O3. The microstructure is analysed by SEM, EDS and XRD. Hardness and fracture toughness are investigated by instrumented indentation and elastic modulus by 3-point bending. Steel wheel and rubber wheel tests have been used to assess dry particle abrasion resistance. Sliding wear resistance is tested by pin-on-disk at room temperature and at 400°C, against SiC and 100Cr6 steel balls. HVOF-sprayed coatings are denser and have better interlamellar cohesion thanks to increased particle velocity. They are harder, tougher, possess a higher elastic modulus and lower porosity. Dry particles abrasion resistance is definitely superior to plasma-sprayed ceramics due to higher toughness; sliding wear resistance is higher, particularly at 400°C.
Correlation between Process Maps of HVOF-Sprayed WC-Co Coatings and Wear Resistance
Authors: Valarezo A. , Choi W.B. , Gouldstone A. , Sampath S.
Published: September 2022

The general method of process maps to understand and control thermal spray processes has been applied to monitor the deposition of WC-Co by high velocity oxygen fuel (HVOF). A selected number of particle state conditions (velocity and temperature) has been performed to produce a variety of coatings. Microstructure, mechanical properties, and wear resistance were evaluated and compared. A second order process map for sliding wear, impacting particle erosion and abrasive wear control can be constructed from the process map to provide the limits within which the particle state can be changed to achieve a predefined coating specification. The mechanisms behind the wear resistance are discussed within the framework of wear maps –third order process map-in the context of analysis of inter splat de-bonding, mechanical properties of the coating, and delamination failure.
Effect of Torch Hardware on Oxy-Acetylene Powder Flame Spray Performance
Authors: Urrea D.A. , Cates J.W. , Hall A.C. , Neiser R.A. , Smith M.F. , Hirschfeld D.A. , Mayer A.J. , Beatty D.E. , Roemer T.J.
Published: September 2022

The effect of hardware on operating parameters and the resultant coating are qualitatively known; however, the quantitative effects have not been well defined. This study quantitatively characterizes particle temperature and velocity for the Sulzer-Metco 6P oxy-acetylene torch with 3 different nozzles and 3 air caps and also, the Alamo PG-550 then relates those data to particle diagnostics, deposition efficiency and coating microstructure. Both torches were evaluated using statistically designed experiments where the process inputs of oxy-fuel ratio, total combustible gas flow, and standoff distance were varied. Both torches can access similar regions of particle temperature - particle velocity space. Increasing total combustible gas flow increased particle velocity with little effect on particle temperature. Increasing oxy-fuel ratio decreased particle temperature with little effect on particle velocity. Higher particle velocity and particle temperature conditions yielded denser, less porous coatings. Flame cooling air caps increase the particle speed while decreasing particle temperature. Nozzles which inject powder directly into the flame jets significantly increase particle temperature as compared to nozzles which do not. Deposition efficiency is shown to not only be affected by particle temperature and particle velocity where hotter and faster usually increase efficiency, but is also dependent on the distribution of particles within the plume.
Properties of SiC-Reinforced Aluminum Alloy Coatings Produced by the Cold Spray Deposition Process
Authors: Sansoucy E. , Ajdelsztajn L. , Jodoin B. , Marcoux P.
Published: September 2022

SiC-reinforced Al-12Si alloy coatings were produced using the Cold Gas Dynamic Spraying deposition process. Feedstock powder mixtures containing 20% and 30% vol. of particulate SiC were used. The composite coatings’ bond strengths and microstructures were evaluated, as well as the porosity and the SiC content. It was found that approximately 45% of the SiC particulate blended with the aluminum alloy was embedded in the coatings. The SiC was homogeneously distributed inside the Al-12Si matrix. Particle velocity measurements revealed that the addition of up to 30% vol. of SiC did not change the Al-12Si particle velocities.
Densification of Ti Coatings by Bi-modal Size Distribution of Feedstock Powder During Warm Spraying
Authors: Kawakita J. , Watanabe M. , Kuroda S. , Katanoda H.
Published: September 2022

Warm Spray has demonstrated that it could fabricate comparatively dense metal coatings keeping with high purity during the atmospheric process. Its key technology is the control of the temperature of the supersonic combustion jet prior to supplying feedstock. So far, even titanium (Ti), known as one of materials difficult for the atmospheric process, could be deposited with less oxidation and higher density of the resulting coatings. For instance, the porosity and oxygen content of two coatings obtained were 2.3 vol% and 0.28mass%, and 1.1vol% and 0.92mass%, respectively. Further densification of Ti coatings was achieved by bi-modal size distribution of feedstock powder upon Warm Spraying in this study. When bigger Ti particles were mixed with the usual feedstock powder under 45 µm, the coating porosity was decreased to 0.8vol% simultaneously with the low oxygen content of 0.26mass%, which was comparable to the level of feedstock powder. This densification is caused by the balance of the enhancement of the peening effect by big particles and of optimization of the filling rate of the big and small particles.
A Three-Dimensional Analysis of the Cold Spray Process: Effect of Substrate Location and Shape
Authors: Samareh B. , Dolatabadi A.
Published: September 2022

A three dimensional model of a Cold Gas Dynamic Spray system with a peripheral non-axisymmetric powder feeder is studied in this work. It is found that the stagnation pressure alternates for different substrate stand-off distances due to the nature of the supersonic flow interaction with the substrate. One can find the optimum substrate location for any given operating condition which results in minimum pressure buildup on the substrate. The three-dimensional analysis shed more light on the complex gas and particle flow fields generated due to the three-dimensional particle injection process. Additionally, the three-dimensional model allows us to further investigate the effect of practical substrate shapes (such as convex and concave) on the flow field and consequently to determine the optimum conditions to deposit coating particles.