bluuebunny/crossref_metadata_2025 huggingface dataset:
The Characteristics of In-Flight Ti-6Al-4V Particles and the Coatings Formed by the Inner-Diameter High-Velocity Air-Fuel (ID-HVAF) Process
Authors: Khamsepour P. , Oberste-Berghaus J. , Aghasibeig M. , Moreau C. , Dolatabadi A.
Published: September 2022

High-velocity air-fuel (HVAF) is a combustion process that allows solid-state deposition of metallic particles with minimum oxidation and decomposition. Although HVAF and cold spray are similar in terms of solid-state particle deposition, slightly higher temperature of HVAF may allow further particle softening and in turn more particle deformation upon impact. The present study aims to produce dense Ti-6Al-4V coatings by utilizing an inner-diameter (ID) HVAF gun. The ID gun is considered a scaled-down version of the standard HVAF with a narrower jet, beneficial for near-net-shape manufacturing. To explore the potential of the ID gun in the solid-state deposition process, an investigation was made into the effect of spraying parameters (i.e., spraying distance, fuel pressure, and nozzle length) on the characteristics of in-flight particles and the attributes of the as-fabricated coating such as porosity, oxygen content, and hardness. Using online diagnostics to monitor temperature and velocity of in-flight Ti-6Al-4V particles is challenging due to exothermic oxidation reaction of fine particles, while larger particles are too cold to be detected from their thermal emission. However, DPV diagnostic system was successfully employed to differentiate the non-emitting solid particles from the burning ones. It was found that increasing air and fuel pressure of the ID-HVAF jet led to an increase of the velocity of the in-flight particles, and resulted in improved density and hardness of the as-sprayed samples. However, increasing the spraying distance had a negative effect on the density and hardness of the deposits. It was also observed that the phases of the Ti-6Al-4V deposits were altered by producing vanadium oxide due to the high temperature of the spray jet.
Comparison of Microstructure and Residual Stress of HVOF Double Carbides Coatings Deposited on Magnesium Substrate
Authors: Łatka L. , Jonda E. , Godzierz M. , Górnik M. , Tomiczek A.
Published: September 2022

Cermet double carbide coatings (WC-Cr3C2-Ni) were HVOF sprayed onto magnesium substrate. The variable parameter was spray distance (320, 360 and 400 mm). The microstructure of the coatings has been characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Additional, porosity and residual stress have been estimated. Phase composition of WC-Cr3C2-Ni cermet coatings consists of hexagonal WC carbide, as well as the Cr3C2 and Cr7C3 carbides. For the longest spray distance, minor presence of WC6O6 was detected, most likely as an effect of higher spraying distance, leading to partially oxidation of WC at powders particles boundaries. Comparing lattice parameters with model data it should be noted that no significant contribution of stress is present, due to minor changes in WC lattice parameters in comparison to ICDD data. It also should be noted that Cr7C3 carbide in WC-Cr3C2-Ni coating has different lattice parameters than ICDD data what shows its reactive nature. In obtained results it is clearly seen, that residual stress have the lowest values for coating sprayed from the shorter distance. This tendency is visible for both, linear and shear stress. The crystallite sizes are also the smallest for the shorter spray distance. Such fine structure shows a tendency to good redistribute of the thermal stress in the sprayed coating and also on the coating-substrate interface.
Improved Environmental Safety of Pipelines Using Highly Efficient Wire Arc Spraying
Authors: Hohnen T. , Lichtenthäler F. , Stark M.
Published: September 2022

Whenever large amounts of liquids or gases have to be transported over long distances, steel pipelines are used. They supply industry with raw materials, guarantee drinking water supplies to large cities, and convey energy sources around the globe. Despite the most stringent safety regulations, pipelines regularly suffer damage and leaks. Severe environmental pollution occurs when oil or gas pipelines, in particular, are damaged. In the case of both onshore and offshore pipelines, decontaminating the affected areas involves a great deal of time, effort, and cost. Moreover, in most cases the contamination cannot be eliminated completely. There are various reasons for damaged pipelines. Corrosion poses one of the greatest challenges here, and this can be influenced by the pipeline owners. There is a need for safe and reliable corrosion protection, and this is set to grow over the coming years. Based on current market data, between 13 and 18 million tons of line pipe were delivered in the years 2015 to 2020. This corresponds to a pipeline length of approx. 86,000 km per year. The objective of this paper is to illustrate why the corrosion protection currently used fails to work in some cases. It also aims to show how thermal coating can improve corrosion protection and what requirements its technical implementation must fulfil. To this end, line pipe is presented in the next chapter. Common standards and manufacturing processes are introduced. The third chapter outlines current corrosion protection measures. Moreover, weak points are analyzed by looking at damage that has already occurred. The requirements for thermal coating are determined based on this.
Influence of Process Parameters on Overall Costs of Surfaces Coated by Wire-Arc Spraying
Authors: Knoch M.A. , Wolf R.
Published: September 2022

Surface treatments and coatings are widely used to protect components from wear and corrosion. Of all available methods, thermal spraying is arguably the most versatile with regard to coating material and morphology. Surface roughness and porosity can be adjusted in a wide range depending on the requirements. However, as-sprayed coating surfaces inevitably exhibit a certain roughness necessitating post-treatment if a smooth surface is required. The surface roughness of thermal spray coatings is usually determined by the used powder fraction and the particles’ melting degree. Using wires as feedstock material allows for a certain influence on the particle size distribution by adjusting process parameters. In this study, the influence of nozzle geometry and atomizing gas pressure on coating quality, surface roughness and cost-efficient post-treatments of wire-arc sprayed Fe-based alloys with a wide hardness-range is investigated. To allow for easy transfer to real components, the sample geometry is based on real world examples of coatings for new components and repair of worn parts. Using adapted process parameters and air-flow, the surface roughness could be decreased to allow for a less time-consuming post-treatment by grinding. Especially in repair coatings for large area applications requiring a smooth surface finish, significant runtime and cost reductions are feasible.
Potentials of Thermal Spraying Processes in Silane-Doped Inert Gases
Authors: Rodriguez Diaz M. , Szafarska M. , Nicolaus M. , Möhwald K. , Maier H. J.
Published: September 2022

In addition to the proper functional properties, the adhesive strength represents one of the key criteria for industrial use of thermally sprayed coatings. Since conventional thermal spraying processes are almost carried out exclusively in air atmosphere, this leads to the oxidation of the particles and of interfaces within the coatings. As a result, conventional thermally sprayed metallic and metal-ceramic coatings are characterized by heterogeneous microstructures with interlamellar oxide fringes at the interfaces between individual splats and also between the coating and the substrate. This has a decisive influence on the bond strength and on the wear and corrosion protection properties of thermally sprayed coatings. The aim of this study is to present the potentials of thermal spraying processes carried out in a mixture of monosiliane and an inert gas at ambient pressure as an alternative to the known vacuum spraying process in order to prevent oxidation during the coating process. Using the example of arcsprayed coatings, it is demonstrated that the extremely low oxygen partial pressure in the silane-doped medium leads to coatings free of oxide seams with a reduced porosity and substantially enhanced properties.
Analysis and Comparison of In Situ Coating Thickness Measurements Using Two Different Sensing Techniques
Authors: Hudomalj U. , Fallahi Sichani E. , Weiss L. , Nabavi M. , Wegener K.
Published: September 2022

Coating thickness is considered to be one of the most important characteristics of thermally sprayed coatings. Therefore, it has long been the goal to be able to control it. This could be achieved by implementing an online, closed-loop control. A prerequisite for such a control mechanism is a feedback signal of the coating thickness with sufficiently small measurement uncertainty. Optical distance measurement techniques have been demonstrated in the past to produce promising results for such applications. This paper analyses the measurement uncertainty of an optical distance measurement technique based on confocal distance sensors used for in situ coating thickness evaluation. As an alternative, pneumatically actuated length gauges are also used for the in situ measurement. Both techniques are applied during atmospheric plasma spraying of samples in a carousel setup. The two sensing techniques are compared with a reference, destructive coating thickness measurement method. Pros and cons of using different in situ coating thickness measurement techniques for process control applications are discussed.
Optical Diagnostic Tools for Thermal Spray Processes
Authors: Zierhut J.
Published: September 2022

Thermal spray is a widespread technology on the way to large scale production. Driven by industrial importance, companies of all sizes employ this technology, with research mainly driven to improve quality and reduce cost. In order to produce high-quality coatings, efforts have been made to provide on-line process control. To find out which parameters affect coating formation and thus which of these parameters should be monitored high level cost intensive diagnostic systems have to be used. This work introduces selected diagnostic systems for the on-line process control under the condition of serial production: shadow imaging for the particles (PSI), a system to measure particle velocities (PVI) and an integral working system using a qualitatively image algorithm (PFI).
Optimization of Segmented Thermal Barrier Coatings (s-TBC) for High-Temperature Applications
Authors: Yalcinyüz B. A. , Thomas G. , Hentschel Y. , Rupprecht C. , Kamutzki F. , Gurlo A.
Published: September 2022

Hot section components of stationary gas turbines such as turbine blades are coated with thermal barrier coatings (TBCs) to increase the high thermal strain tolerance thereby the improvement of the performance for the gas turbines. TBCs represent high-performance ceramics and are mostly composed of yttria-stabilized zirconia (YSZ) in order to fulfil the function of thermal insulation. The microstructure of conventional TBCs should be porous to decrease heat conduction. Besides porous TBCs, the recently developed vertically segmented thermal barrier coatings (s-TBCs) feature outstanding thermal durability. In this work, process parameter development for atmospheric plasma spraying (APS) of s-TBCs is presented. Within the experiments, relevant process parameters such as powder feed rate, surface speed and pathway strategy have been optimized. The aim of this work is to achieve a combination of low internal residual stress and high adhesive tensile strength for s-TBCs. For the formation of vertical cracks, the heat input into the powder feedstock material and the substrate must be controlled precisely.
Sublayer-Assisted Cold Spray Metallization of Carbon Fiber Reinforced Composites
Authors: Zhang T. , Padyyodi E. , Raoelison R.-N. , Sagot J.-C.
Published: September 2022

In order to investigate the potentials to improve the deposition efficiency and to functionalize the polymer-based substrates, six configurations of microparticles Sn, Zn, Al, Sn+Al2O3, Al+Al2O3, Cu+Al2O3 were cold sprayed on the substrate of Carbon Fiber Reinforced Polymer (CFRP) composites equipped with Cu-based sublayer or Al-based sublayer. The process conditions were kept unchanged. Microanalysis of sublayers and coatings was performed via a Scanning Electronic Microscope (SEM), the deposition mechanisms of different powders couplings on CFRP substrate were then discussed. The results indicated that although the deposition efficiencies were negative, the systems of Zn, Al and Al+Al2O3 perform better among all the configurations. It was found that the addition of alumina led to a lower deposition efficiency (DE), compared to the corresponding pure coatings. For single-component Sn, Zn and Al powders, they all showed an increasing trend of DE when changing the substrate from Cu-based systems to Al-based systems. The aim of this present work is to elaborate the intrinsic causes of erosion issues and to provide a reference value for picking spraying materials and preparing functionalized CFRP substrates. According to the SEM analysis, the insufficient deformation and escape behaviours of spherical copper powders explained for the difficulty of coating formation. It was noticeable that the surfaces of Al-based systems were more uniform than those of Cu-based ones, due to their desirable deformation abilities. Besides, the significant flattened particles, material mixing and melting phenomenon were observed in Al-involved systems, which would definitely contribute to the adhesive bonding between coating and substrate.
Novel Method of Predicting Deposition Efficiency in Cold Spray by Incorporating Sphericity into 1D Numerical Models
Authors: Ozdemir O. C. , Muftu S.
Published: September 2022

In cold spray (CS) additive manufacturing process, micrometer scale particles accelerated through a supersonic nozzle are targeted on a surface with velocities in the rage of 300-1500 m/s in solid state. The impact energy of the particles leads them to deform plastically with high shear energy near the impact interface and adhere to the surface metallurgically, mechanically, and chemically. Using CS, deposition of metals, metal matrix composites, and polymers are achieved with high adhesive/cohesive strength and low porosity. Sensitivity of the CS additive manufacturing process to the variabilities in the process parameters are still being understood. Among the process parameters, particle morphology can have significant implications on drag forces, and therefore, on the particle impact velocity. This in turn affects the deposition efficiency (DE) and the quality of products. In this work, a new approach is introduced for computing DE by incorporating particle sphericity and its variation into one-dimensional numerical models. Size, sphericity, and the variability of size and sphericity of aluminum, copper, titanium, and tantalum particles are measured from static optical microscope images. The data is used for predicting impact velocity, temperature, and DE. The model results are then compared with particle velocity measurements.
As-Sprayed Highly Crystalline Yb2Si2O7 Environmental Barrier Coatings (EBCs) by Atmospheric Plasma Spray (APS)
Authors: Arhami F. , Moreau C.
Published: September 2022

High amorphous phase formation tendency, a desirable microstructure and phase composition and silicon evaporation are the challenges of spraying Yb2Si2O7 environmental barrier coatings (EBCs). This research addresses these issues by depositing as-sprayed high crystalline Yb2Si2O7 using atmospheric plasma spray (APS) without any auxiliary heat-treating during spraying, vacuum chamber, or subsequent furnace heat treatment, leading to considerable cost, time, and energy savings. Yb2Si2O7 powder was sprayed on SiC substrates with three different plasma powers of (90, 72 and 53 kW) and exceptional high crystallinity levels of up to ~91% and deposition efficiency of up to 85% were achieved. The silicon mass evaporation during spraying was controlled with a short stand-ff distance of 50 mm, and an optimum fraction of Yb2SiO5 secondary phases (<20 wt.%) was evenly distributed in the final deposits. The desirable microstructure, including a dense structure with uniform distribution of small porosities, was observed. The undesirable vertical crack formation and any interconnected discontinuities were prevented. Reducing the plasma power from 90 kW to 53 kW, while conducive for mitigating the silicon mass loss, was detrimental for microstructure by increasing the fraction of porosities and partially melted or unmelted fragments. The gradual decrease of the coating temperature after deposition alleviated microcracking but has an insignificant effect on the crystallinity level. Coatings annealed close to their operating temperature at 1300 °C for 24 hours demonstrated sintering and a crack healing effect, closing the tiny microcracks through the thickness. An improved coating composition was detected after annealing by the transformation of Yb2SiO5 to Yb2Si2O7 (up to ~10 wt.%).
High Velocity Flame Spraying (HVOF) of Ceramic – Polymer Composite Filaments
Authors: Sauter M. , Killinger A. , Grebhardt A. , Bonten C.
Published: September 2022

Thermal spraying of fine and ultrafine powders is realised by a novel method based on highly filled filaments as feedstock material for high velocity oxy fuel flame spraying (HVOF). Hereby, the desired coating material is supplied as finely dispersed powder within a polymer filament. Thus, the polymer works only as a transport medium and is fully decomposed when entering the combustion zone instantly releasing the solid dispersion, similar to the liquid dispersion medium in a suspension. It can work as an appropriate method to process fine and ultrafine powders. The solid nature of the dispersion medium poses several benefits compared to liquids, especially from the manufacturing point of view, since the process is geared to a wire flame spraying method. This work focusses on the challenges and benefits of this novel approach. First experimental results of spraying different filaments are presented.
Evaluation of Mechanical Properties of Dense HAD Al2O3 Coatings by Nanoindentation Method
Authors: Sanami K. , Shahien M. , Yumoto A. , Shinoda K. , Akedo J.
Published: September 2022

Hybrid aerosol deposition (HAD) is a new coating method to deposit homogeneous nano-structured ceramic coatings. An accurate evaluation of the fabricated coating properties is required. In this study, α-Al2O3 fine powder was sprayed by HAD. The obtained coatings were dense and uniform with a nanocrystalline structure. An X-ray diffraction measurement revealed that the fabricated HAD Al2O3 coatings mainly consisted of α-Al2O3 phase. The hardness and Young's modulus of the HAD Al2O3 coatings were evaluated by a micro-Vickers method and a nanoindentation method using the Weibull distribution. The hardness of HAD Al2O3 coatings measured by micro-Vickers was ~1400 HV (~15 GPa). The variation of mechanical properties of HAD coatings measured by the nanoindentation method was extremely small compared to those of plasma-sprayed coatings, which also indicates that HAD coatings contain less pores and cracks than plasma-sprayed coatings.
Development of Near Net Shaped Coatings for Reduced Postprocessing Costs in Valves
Authors: Bobzin K. , Wietheger W. , Burbaum E. , Schulz M.
Published: September 2022

Thermally sprayed WC/CoCr coatings are established in the valve industry for wear protection. However, conventional coatings have to be cost-intensively postprocessed. Therefore, the aim of this study is to develop near net shaped (nns) WC/CoCr-coatings with a high wear resistance in order to avoid the expensive grinding postprocess. For the development of the nns coatings a parameter study is used to investigate the influence of the stand-off distance and hydrogen volume flow rate in the HVAF process. The parameter study indicates the influence of the hydrogen volume flow and the stand-off distance on the porosity, microhardness and wear resistance of the coatings. The developed coatings exhibit a low porosity and high wear resistance. Through the correlation of the coating properties with the process parameters, promising parameter ranges for a further development of HVAF-sprayed nns coatings of WC/CoCr can be identified. With these results, first benchmarks for HVAF process parameters, hydrogen flow rate and stand-off distance, could be delivered, advancing the overall goal of reducing manufacturing costs of valves.
Cold Spray of Hydroxyapatite Coatings: Interest of PEEK as an Intermediate Layer
Authors: Chatelain D. , Denoirjean A. , Guipont V. , Rossignol F. , Tessier-Doyen N.
Published: September 2022

In the last 15 years, the cold spray process has demonstrated a great efficiency for the deposition of metallic powders. In this case, the consolidation of coatings is achieved thanks to the high kinetic energy of unmelted particles exhibiting a ductile behaviour. Dealing with ceramics, cold spray is also of great interest because one can expect properties not reachable with classical thermal spray technologies thanks to lower involved temperatures. However, cold spray of ceramics still remains challenging because of the ceramics intrinsic brittleness. Here, in the specific case of hydroxyapatite and to overcome this brittleness issue, we investigate the role of an intermediate PEEK layer between the substrate and the deposit. We highlight how this sublayer previously deposited by FS or air APS spraying can help improving the consolidation of the coating and its growth.
Production of Titanium Dioxide with Optimum Heterojunctions and Coating Production via Cold Spray
Authors: Hawkins A. , Guo D. , Steeves A. , Variola F. , Jodoin B.
Published: September 2022

Titanium dioxide (TiO2) coatings possess high appeal due to self-cleaning properties that can accelerate decomposition of organic pollutants. The global objective is to develop a cold sprayable feedstock powder with an outer titanium dioxide shell that maximises anatase-rutile heterojunctions for enhanced photocatalytic activity under ultraviolet light and the development of cold spray process parameters for successful deposition of this powder into thin photocatalytic coatings. The objective of this reported first step of our global research effort to produce superior photocatalytic TiO2 coatings by cold spray is to successfully engineer anatase and rutile nanostructure heterojunction shells on pure titanium (CP-Ti) powder known to be easily sprayable by cold spray and then verify its photocatalytic properties through exposure to an organic pollutant, methylene blue (MB). Anatase and rutile heterojunctions are desired due to high activity, stability and broadened bandwidth as opposed to each singular nanostructure. The resulting powder coming out of this first step was characterized using Raman spectroscopy to verify the presence of the desired heterojunctions. The photocatalytic reactivity was tested and evaluated through the degradation of methylene blue upon contact with the TiO2 powder. Results of this first step showed growth of desired heterojunctions and high reactivity of the produced powder.
Investigation of Novel Nano-Carbide WC/CoCr Coatings Applied by HVAF
Authors: Bobzin K. , Wietheger W. , Burbaum E. , Johann L. M. , Rempe L. J. , Matikainen V. , Kanerva U. , Karhu M. , Lagerbom J. , Kaunisto K. , Lartigue J.-F.
Published: September 2022

Wear leads to high material and energy losses in various industries. The manufacturing of novel nano-carbide WC/Co powder feedstock materials promises a further increase in the performance of thermally sprayed wear protection coatings. A novel experimental powder and a commercial ultra-fine carbide WC/CoCr reference are thermally sprayed onto a 1.0038 substrate by High Velocity Air Fuel (HVAF) spraying. The specimens are metallographically prepared and analyzed by means of light microscopy (LM) and scanning electron microscopy (SEM). Vickers Hardness testing is conducted by microindentation and the porosities are determined by optical image analysis. X-ray diffractometry (XRD) analysis are used to investigate the phase retention. Fine nanocrystalline WC-structures are preserved in the dense coatings. A significant effect of powder type on the porosity of the coating was found. No systematic relationships could be identified between the coating structure and the parameter settings. It was possible to influence decarburization via both the powder type and the selected parameters. The resulting experimental coatings exhibit high hardness values in the range of the commercial ultrafine carbide WC reference. The novel nano-structured coating can contribute to reduced wear and therefore improve the efficient utilization of critical raw materials like tungsten.
Wear Resistant Nano-Carbide WC-CoCr Coating by Novel Powder Manufacturing Method
Authors: Matikainen V. , Lagerbom J. , Kaunisto K. , Heino V. , Bobzin K. , Wietheger W. , Burbaum E. , Johann L. M. , Lartigue J.-F. , Kanerva U. , Karhu M.
Published: September 2022

Surface quality lifetime and wear resistance of protective coatings can be improved by decreasing carbide grain size from submicron to nanoscale. In this study, experimental WC-CoCr powders were manufactured via novel powder manufacturing approach using water-soluble raw materials. Produced powders were sprayed with the High-Velocity Air-Fuel (HVAF) spray process to control the particle temperature and to avoid in-flight decomposition of the nanocarbides. As a result, dense and wear resistant coatings with nanosized carbides were produced. Reference coatings were sprayed using commercial sub-micron WC-CoCr powder to compare the properties of the experimental coatings to the current state-of-the-art. Phase composition and microstructural characterization of the coatings were carried out with X-ray diffraction and electron microscopy, respectively. Mechanical properties were studied by using microhardness tester, as well as rubber wheel abrasion and cavitation erosion wear tests. The wear surfaces were characterized after the abrasion and cavitation erosion tests to understand the effect of nano-carbides on degradation mechanisms. Coatings with the nanosized carbides in the structure showed excellent mechanical properties in wear testing, and even outperformed reference coatings in cavitation erosion test. Based on the obtained results, these novel nano-carbide coatings are promising alternatives for demanding applications in which better surface quality lifetime is vital.
Suspension Sprayed Thin Metallic Coatings for Electric Panel Heaters
Authors: Kummer H. , Winkelmann M. , Wüst F. , Hartmann S. , Trenkle F. , Krieg P. , Killinger A.
Published: September 2022

The use of suspensions in the thermal spraying process, makes it possible to apply sufficiently thin (<30 μm), metallic coatings made of nickel-chromium alloy 2.4869 (NiCr8020). High velocity oxy-fuel suspension flame spraying (HVSFS) is used to manufacture these thin metallic coatings in order to be able to effectively use them as electric panel heaters. Area heating capacities of 25 W cm-2 are possible with them and heating rates of 15 K s-1 even outperform many ceramic heating elements. In addition, it provides a flexible way to apply the heating coatings directly to the components to be heated. The use of fine powders in the micron and sub-micron ranges allows a more precise adjustment of the coating thickness, compared to conventional thermal spraying techniques, even in the thickness range below 10 μm. Therefore, an adaption to customer needs is possible regarding the electric panel heater characteristics, like electric resistance, applied voltages and current range and heating rates.
Refurbishment of Damaged Railway Material by Cold Spray
Authors: Delloro F. , Tebib M. , Lesage T.
Published: September 2022

The health of railway material is of paramount importance for the safety of rail transportation. Railways are subject to heavy mechanical loading and to harsh environments, causing corrosion and damage that can bring to failure. The cold spray process has a great potential as an efficient and portable refurbishment technology, with the advantage of avoiding thermal effects on the substrate. In this study, a proof of concept for the cold spraying of railway steel onto a similar material is presented. This represents a first step towards the development of a cold spray solution for railway repair. First, the as-atomized steel powder revealed to be hardly sprayable. A heat treatment was then optimized and applied to the powder to induce microstructural evolution and to improve deposition efficiency and material quality. Therefore, the refurbishment of damaged railway samples by cold spray was proven to be viable. Finally, mechanical testing assessed the restoration of the structural properties needed for the application.
Metal Knitting: A Method to Control Morphology and Properties in Cold Spray Additive Manufacturing
Authors: Váz R. F. , Canales H. , Sanchez J. , Ocaña U. , Albaladejo V. , Garcia Cano I.
Published: September 2022

Cold Spraying (CS) is a thermal spray process capable of producing dense and thick coatings by the spraying of powders under high velocity and relatively low temperature. The high deposition efficiency and the thickness of each pass make possible the use of CS to produce freestanding parts, as an additive manufacturing process (CSAM). Traditionally, CS is performed spraying perpendicularly to the substrate, which ensures maximum deposition efficiency among other benefits. This, however, presents two main disadvantages for CSAM. First, by keeping the spraying angle constant, there is not much control on the final geometry of the part being built, and, second, the resultant part’s properties show anisotropy depending on whether this property is measured along the spraying axe or not. In this work, we present a method (Metal Knitting) that aims to help reduce both disadvantages. Metal Knitting is based on the performance of certain spraying movements that build near squared shapes step-by-step like in a knitting process. The principle of the method and examples are presented in this work, as well as some results on the anisotropy of 316L stainless steel freeform parts obtained by CSAM, measuring the tensile stress, hardness, and evaluating the microstructure in different directions of the material. The effect of annealing on the material properties is also investigated.
Assessment of Agglomerated Ceramic Powders Under Impact by Cold Spraying
Authors: Celeste G. , Guipont V. , Missoum-Benziane D. , Kermouche G. , Sao-Joao S. , Girard-Insardi S. , Chatelain D.
Published: September 2022

Most of ductile metals can be deposited by cold spray (CS). For brittle ceramic, such solid-state deposition process is still questionable, but some recent work on Ti02 or hydroxyapatite powders have shown that micrometric ceramic powder could be deposited by CS. In this work, it is claimed that the nature and the porous architecture of a ceramic powder with agglomerated ultra-fine grains play an important role on the impact behaviour. The aim of this work is to investigate the deformation behaviour of ceramic agglomerated powders under high velocity impact. Two different powders, respectively 3YSZ and Y2O3, were selected in order to study their architectures (particle size, porosity, density, crystallite size, etc.). Cold spray “splats” experiments, with various spraying distances to vary the particles velocities upon impact, were carried out to observe the deformation and fragmentation. In case of Y2O3, cold spray with dynamic vacuum surrounding atmosphere up to 3kPa were also prepared to evaluate the role of the atmosphere on the resulting impact. In parallel, in situ SEM micro-compression tests at 10−2 s−1 on cross-sectioned 3YSZ particles involving flat-punch nano-indentation and micropillar compression were performed. By modelling the compression tests, the aim is to identify a Drücker-Prager behaviour law suitable for an agglomerated ceramic powder under quasi-static compression. Such deformation behaviour could help to better understand the compaction behaviour of agglomerated powders.
Particle Acceleration Through Coaxial Co-Flow Nozzles for Cold Spray Applications
Authors: Sharma A. K. , Vashishtha A. , Callaghan D. , Nolan C. , Bakshi S. , Kamaraj M. , Raghavendra R.
Published: September 2022

The present study numerically investigates the effectiveness of co-flowing nozzles for cold spray applications. A convergent-divergent axi-symmetric nozzle system was simulated with high-pressure nitrogen flow. The particle acceleration is modelled by a two-way Lagrangian approach and validated with reference to experimental values reported in the literature. An annular co-flowing nozzle with circular central nozzle was simulated for nitrogen gas flow. The momentum preservation for central nozzle flow was observed, which results in higher particle speed for longer axial distance after nozzle exit. It is envisioned from the outcome that utilization of co-flow can lead to reduction in the divergent section length of cold spray central nozzles, which may ultimately help to address clogging issues for continuous operation. Co-flow operating at 3 MPa, same as with a central nozzle, can increase supersonic core length up to 23.8%.
Systematic Study of the Effects of Powder Preconditioning on Flowability and Deposition in Polymer Cold Spray
Authors: Brennan D. A. , Bacha T. W. , Tiitma Ü. , Haas F. M. , Stanzione J. F.
Published: September 2022

The cold spray process is sensitive to variations in feedstock and requires consistent powder properties, particularly flowability, to produce uniform structures. Poor powder flow causes a cascade of effects arising from erratic feeding including deposits with void spaces and inconsistent geometries. These issues result in deposits which are not suitable for testing and prevent sample replication, hindering experimental evaluation of deposits. Powder flowability is largely affected by the material preconditioning and storage conditions; with flowability directly affecting the deposit properties of deposition efficiency (DE), porosity, and surface finish. In this study, the flowability and deposit quality of a fluoropolymer-based powder was evaluated with changing pretreatment conditions. Powder flowability was analyzed by mass flowrate (g/s), the Carr angle of repose, and the Hausner ratio. Flowability was evaluated for powders as received, after sieving (45-100 μm), with drying at elevated temperature (80 °C), with inert gas vacuum purging, and after 72 hrs. of exposure to high relative humidity (95% RH). Powders exposed to humid conditions were also dried under inert gas vacuum purging to determine the effectiveness of the process as a reconditioning method. Preconditioned powders with the highest flowability according to these tests were sealed in metal containers, stored under 95% RH for one week, and reevaluated to determine the ability of this preconditioning and storage method to protect materials from exposure to undesirable conditions. Next, the effect of preconditioning on cold spray deposit quality was evaluated for the fluoropolymer-based powder with the best and worst flowability. The choice of spray conditions was informed by simulation of particle velocity and temperature distribution at impact using one-dimensional compressible flow modeling, couple with thermal analysis of the powder. The DE was determined gravimetrically, surface roughness was evaluated using a profilometer, and microstructure was evaluated using a scanning electron microscope (SEM). The ability to manipulate powder flowability through simple preconditioning methods and quickly evaluate the properties of the feedstock before use in the manufacturing process, coupled with straightforward and rapid evaluation the resultant deposit; will save time and money, and accelerate research efforts, compared to evaluating powder suitability by trial and error.
Ultrasonic Atomization as an Alternative Route for Metal Powder Production
Authors: Sokołowski P. , Kustroń P. , Korzeniowski M. , Sajbura A. , Piwowaczyk T. , Szostak-Staropiętka R. , Kiełbasiśnki R.
Published: September 2022

The use of metal powders is dynamically increasing in many different fields of research and industry. The development of additive manufacturing technology or innovative thermal spray processes still enhance the range of possible applications. This means that there is a big demand for high quality metal powder materials. Currently, the atomization methods, like water or gas atomization, seem to be most established technologies for metal powder production. This work concerns the development of an innovative technology of metal powder manufacturing, namely ultrasonic atomization. First, the general idea of ultrasonic atomization is discussed. The designing of sonotrode, in order to generate appropriate ultrasonic field responsible for metal stream atomization, is discussed. Then, the ultrasonic set-up was verified by using non-contact fiber optic displacement sensor. Finally, the developed system was preliminary tested under water loading and confirmed positively in terms of ultrasonic atomization capabilities.
Investigation of the Effect of Low-Temperature Annealing and Impact Angle on the Erosion Performance of Nickel-Tungsten Carbide Cold Spray Coating Using Design of Experiments
Authors: Kazasidis M. , Verna E. , Yin S. , Lupoi R.
Published: September 2022

This study investigates the solid particle erosion performance of cold sprayed tungsten carbide-nickel coatings using alumina particles as erodent material. After coating fabrication, specimens were annealed in an electric furnace at a temperature of 600 °C for 1 hour. The coatings were examined in terms of microhardness and microstructure in the as-sprayed (AS) and annealed (AN) conditions. Subsequently, the erosion tests were carried out using a General Full Factorial Design with two control factors and two replicates for each experimental run. The effect of the annealing on the erosion behavior of the coating was investigated at the two levels (AS and AN conditions), along with the impact angle of the erodents at three levels (30°, 60°, 90°). Finally, two regression models that relate the impact angle to the mass loss were separately obtained for the two cold spray coatings.
A Decade of Development, Optimization and Scale Up of a Thin Barrier Layer for Metal-Supported Solid Oxide Fuel Cells
Authors: Leblanc L. , Hinckley R. , Alinger M. , Striker T.
Published: September 2022

A solid oxide fuel cell is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. It involves ionic transport and electrochemical reactions where the electrolyte and electrode properties play a major role in performance, along with a range of complementary materials that need to ensure equally relevant functions across the cell. The lifetime of such functional materials is expected to reach many thousands of hours with minimal degradation. This article is centred around the process development, optimization and scale up of a thin plasma sprayed ceramic barrier layer to mitigate long-term performance degradation of metal-supported solid oxide fuel cells. The evolution from the proof of concept in a laboratory environment to the scale up toward large scale manufacturing production is discussed. The challenges associated with minimizing application time and lowering cost while maintaining high coating performance at high yield are discussed. Empirical observations such as microstructural analysis and in-flight particle monitoring are used to gain understanding of the plasma spray process and guide its development for high-volume production. Results show how this effort has led to the reduction of the coating deposition time by 94% to enable large-scale manufacturing at high yield.
Digital Process Chains for 3D Laser Cladding and LMD/DED Additive Manufacturing
Authors: Beccard R. , Bartling A.
Published: September 2022

Laser cladding or metal deposition (LMD/DED) is widely used for wear-resistant coatings, repair and additive manufacturing applications due to the excellent properties of the deposited material. However, processes on complex 3D surfaces are often a challenge because they require time-consuming programming. This is particularly the case when no CAD data is available for the parts on which metal coatings or structures have to be applied. As a solution, we describe a digital process chain that begins with a 3D scanning process within the laser cladding machine (either robotic or CNC type). Using special software, high-quality 3D models of the scanned parts are created. For coating applications, these models are visualized on a PC. The operator can define cladding areas with just a few clicks of the mouse. Based on predefined parameters, powerful software calculates all the required tool paths. An additional simulation step can be used to verify collision-free operation. Finally, robot or CNC programs are automatically generated that can be executed immediately. Similar software is used to create 3D parts directly from CAD files. Finally, by combining both approaches, 3D geometries can be printed directly onto existing 3D freeform parts using laser metal deposition/LMD, even if their shape is arbitrary and not well documented by CAD data.
Improvement of In-Flight Particles Diagnostic System to Monitor Process Stability in Thermal Spray Processes
Authors: Jibran W. , Nadeau A. , Desmarais C.
Published: September 2022

In the past 25 years, we have seen thermal spray processes such as Atmospheric Plasma Spray (APS), High Velocity Oxygen Fuel Spray (HVOF) and Suspension Plasma Spraying (SPS) transition from research and development towards mainstream production technology. Since thermal spraying is a multi-parameter and multi-response process, it is susceptible to process instabilities. Consistency and repeatability are of utmost importance in production lines that spray high volumes of coatings. Since process parameters such as feed rate, particle velocity, temperature, electrode wear and nozzle blockages can dramatically affect the coating properties, monitoring and controlling these parameters can significantly improve the process repeatability. This study presents an improvement in the online process monitoring sensor, the Accuraspray 4.0, to achieve repeatable coatings. The Accuraspray 4.0 introduces a new process stability measurement in order to quantify and control the variability in thermal spray processes and to make process monitoring more production friendly. The sensor includes a stability analysis tool which compares the real-time standard deviations of nominal plume parameters against bench-marked values found using statistical principles. This study details the theory behind the process stability measurement and presents a case study conducted in collaboration with an automotive production facility employing this new feature. It was found that monitoring the standard deviations of parameters being measured can allow the user to control stability in their thermal spray process to spray large volumes with higher confidence in the consistency of their coatings. This upgrade brings the Accuraspray 4.0 one step closer to becoming the industry standard for thermal spray production facilities.
Development of an Arc-Based Diagnostic Procedure for Process Characterization in DC Plasma Spraying
Authors: Thomas G. , Limburg M. , Mihm S. , Rupprecht C. , Gruner H.
Published: September 2022

The process properties for DC plasma spraying are affected by the arc as the source of energy for plasma generation. For instance, the position of the anode attachment point, the arc movement and the arc formation are significantly influencing process stability, reproducibility and coating quality. Following a qualitative and objective assessment of the complete arc movement and plasma generation is leading to an improved process characterization. Therefore, a preventive arc-based analytical method for DC plasma spraying is developed. Based on a representative data volume and realized by an automatic analysis of high-velocity recordings of the arc dynamics and correspondent arc voltage measurements, the evaluations are carried out. A developed software algorithm automatically detects for all images of the video sequence (at least 3200 images) the anode center axis, the arc orientation and the position of anode attachment point on the anode surface referring to the anode center, with simultaneous compensation of aberrations. This allows an objective assessment of the complete arc movement. In further investigations, the detection limit of the developed measuring system is determined and the effects on the arc behavior and the coating process could be quantified. Thus, the developed automated analysis of the arc dynamics in the DC plasma generator corresponds to an arc-based process characterization in DC plasma spraying process with relevance to developers (e.g. new anode nozzle designs) and end users (process control).
Importance of Evaluation Procedure of Particle State in Atmospheric Plasma Spraying
Authors: Hudomalj U. , Fallahi Sichani E. , Weiss L. , Nabavi M. , Wegener K.
Published: September 2022

In-flight particle state has been shown to play a crucial role in determining the properties of thermally sprayed coatings. Therefore, process control strategies have been suggested to keep the in-flight particle state constant in order to decrease the variability of coating quality. Such strategies are already used to some extent in industrial applications, where the particle state is measured before starting the coating of a part to make a go/no-go decision based on whether the values are inside a predefined process window. This paper shows the importance of the evaluation procedure of the in-flight particle state, with focus on process control applications. The paper demonstrates this on the example of atmospheric plasma spraying (APS) of yttria-stabilized zirconia (YSZ), using a commercially available sensor system Accuraspray for measuring the ensemble particle temperatures and velocities as descriptors of the in-flight particle state. It is concluded that the stabilization time of the particle jet might be different from what is practically considered. Moreover, the paper investigates an approach of monitoring the in-flight particle state during a coating run without having to install the sensor system on the robot arm.
Assessment of High Entropy Alloys as Thermally Sprayed Heating Elements
Authors: Bobzin K. , Heinemann H. , Schacht A.
Published: September 2022

An efficient temperature control on tool surfaces is essential in processes like injection moulding or die casting. A thermally sprayed heating coating could combine dynamic heating properties with a small assembly space as it is sprayed directly onto the cavity surface. With their intrinsically high electrical resistivity and low thermal expansion as compared with traditional alloys, High Entropy Alloys (HEA) show promising properties for the use as heating elements. Thus, the well-studied HEA Al0.5CoCrFeNi was used as a starting material for additional alloying with Zr and Si to force further lattice distortion in the solid solution. HEAs of differing compositions were melted and characterized. In the process, the potential of HEAs was assessed by characterizing their phase composition, thermal stability, and electrical resistivity. The characterized HEAs show a solid solution mainly consisting of fcc and bcc structure. Moreover, the composition Al0.5CoCrFeNiZr0.2Si0.2 was determined as stable after heat treatment at 600 °C for 324 h. In addition, the electrical resistivity was raised by over 20 % relative to the starting material. As a result, a hitherto unknown HEA composition was detected to possess superior properties to traditional alloys for the application as heating coating.