bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Phenomena Occurring in Plasma Jet at Suspension Spraying of Hydroxyapatite Coatings
Authors: Delluc G. , Pateyron B. , Pawłowski L. , Calve N. , Denoirjean A.
Published: January 2023

The phenomena occurring after injection of water-ethanol suspension of fine hydroxyapatite powder are simulated numerically. The mathematical modeling starts with the calculation of the map of velocity and temperature of working plasma gases. The map is calculated by taking into account the evaporation of the liquids included in the suspension. The suspension is injected through a mechanical injector into the anode-nozzle of the SG-100 torch. The plasma was generated with the use of working gases composed of 45 slpm of Ar and 5 slpm of H2 and with the electric power input of 30 kW. The initial droplets of suspension were supposed to be spherical with a diameter equal to that of the injector, i.e., 500 µm. The trajectory of suspension was calculated until the evaporation of liquids. Then, the simulation of the movement and heating of solid hydroxyapatite (HA) started. The HA powder was home synthesized and exhibited a bimodal size distribution with two maxima around 3 and 10 µm. The equations describing the momentum and heat transfer from hot gas to the solids took into account the small size of solid particles. In particular, the thermophoresis force, as well as, the drag coefficient modified for non-continuum effect were used in the calculation of the trajectory of small particles. Similarly, the non-continuum effect was considered in the calculation of heat transfer. The obtained trajectories were tentatively correlated with the microstructure of the suspension plasma sprayed HA coatings.
Fabrication of Aluminum-Alumina Metal Matrix Composite Coatings Via Cold Gas Dynamic Spraying at Low Pressure Followed by Friction-Stir Processing
Authors: Hodder Kevin , Gerlich Adrian , Villafuerte Julio , McDonald André
Published: January 2023

Cold gas dynamic spraying (“cold spraying”) at low pressure (150 psig) was used to fabricate Al-Al2O3 metal-matrix composite (MMC) coatings onto 6061 Al alloy. The powder contained -45 µm Al stock powder admixed with -10 Al2O3 in fractions ranging from 0-90 wt%. Scanning electron microscopy (SEM), Vickers microhardness testing, and image analysis were conducted on the as-sprayed coatings. The coatings were then friction-stir processed (FSP) using a milling machine and a 12 mm diameter cylindrical tool. Microhardness testing, SEM, and image analysis were then repeated to study the effect that FSP had on the MMC coating hardness. Hardness increased with increasing fraction of Al2O3 in the feedstock powder, resulting in a maximum as-sprayed coating hardness of 85 HV when 90 wt% Al2O3 is used. After FSP, the hardness of the MMC fabricated from a 90 wt% Al2O3 powder blend increased to a maximum of 140 HV. SEM micrographs showed that the as-sprayed MMC coatings contained Al2O3 particles that had been trapped between the larger Al particles. FSP succeeded in redistributing the Al2O3 particles, decreasing the mean free interparticle distance and increasing the probability of load sharing between the reinforcing particles. It was suggested that this redistribution may be the primary reason for hardness improvement in the MMC coatings.
Deposition of Amorphous Aluminium Powder Using Cold Spray
Authors: Koh P.K. , Cheang P. , Loke K. , Yu S.C.M. , Ang S.M.
Published: January 2023

Deposition of amorphous aluminium powder using cold spray technology as a corrosion prevention measure was studied. Amorphous aluminium (Al-Ni-Ce) powder was successfully deposited on 7000-series aluminium substrates using cold spray parameters of 1.7 MPa under compressed air and temperature of 450°C. The coatings were subjected to tensile bond strength measurement and comparative studies with cold sprayed pure Al6061 coatings were conducted. The results obtained showed that the amorphous aluminium coatings exhibited better adhesive strength. In addition, salt-water immersion test was conducted. The Al-Ni-Ce coating not only demonstrated better corrosion resistance but also exhibited evidence of passivation of surface imperfections such as scratches in the coatings.
Research on Corrosion Behavior of Cold Sprayed Copper Coating on Aluminum Substrate
Authors: Guosheng Huang , Daming Gu , Xiangbo Li , Lukuo Xing , Hongren Wang
Published: January 2023

Due to its low processing temperature, cold-sprayed coatings tend to exhibit many advantages over traditional thermal sprayed coatings, such as, lower porosity, oxidation and residual stress levels. These characteristics impart the improved anti-corrosion performance of the cold-sprayed coatings. However, it is not known how much these factors influence the corrosion performance of them. In addition, there are few results on the electrochemical behavior difference between cold and thermally sprayed coatings. In this article, as-deposited cold-sprayed copper, aluminum bulk material, arc-sprayed copper and pure copper are tested with electrochemical methods to compare their electrochemical behaviors in natural seawater. The electrochemical methods included the potential-dynamic polarization curve and electrochemical impedance spectrum. The results indicated that there is no significant difference in the corrosion potential between cold-sprayed and bulk copper materials. The potential of cold-sprayed copper is much different from that of the arc-sprayed one. Polarization curves indicated that the corrosion rate is significantly higher for arc-sprayed copper. The electrochemical impedance spectrum shows that there is no difference in electrode interface structure between cold-sprayed and bulk copper materials. Based on these results it is inferred that the higher corrosion rate for arc-sprayed copper was caused by its high porosity level and oxidation degree.
Kinetic Metallization Repair of Alclad
Authors: Tapphorn R. , Gabel H. , Hashimoto K. , Crowe T.
Published: January 2023

Cladding is a common method of providing corrosion protection of aluminum alloys, which forms an anodic layer in direct and intimate contact with the alloy sheet during cold roll processing. A structural aluminum alloy is clad in a thin layer of a higher purity alloy that is more galvanically reactive. Common examples include 1230 clad on 2024, and 7072 clad on 6061 and 7075. If this clad layer is damaged or removed the underlying structural alloy is exposed and susceptible to corrosion and/or stress corrosion cracking. Kinetic Metallization is a low temperature deposition technique compliant with MIL-STD-3021 that enables repair or replacement of worn or damaged clad layers. Aluminum or Al-Trans coatings are deposited as a new clad coating, and can be subsequently polished to the same mirror finish as the original clad surfaces. This paper presents the techniques developed for repairing worn or damaged Al clad surfaces using the economical Kinetic Metallization process and the qualification tests performed to date for various feedstock powder formulations (Ref 1).
Phase Transformation of Cold-Sprayed Ni/Al-Al2O3 Composite Coatings during Post-Spraying Annealing Treatment
Authors: Yang G.-J. , Zhao S.-N. , Li C.-X. , Li C.-J.
Published: January 2023

NiAl-Al2O3 intermetallics based composite coatings were prepared by cold spraying of Ni/Al-Al2O3 composite powders followed by post-spraying annealing treatment. The phase transformation mechanism from Ni/Al mechanical alloy to intermetallics was explored to aim at controlling the microstructure of the composite coating. Results showed that, with the porous Ni/Al and Ni/Al-Al2O3 green compacts, self-propagating high-temperature synthesis (SHS) reaction was ignited at a temperature of 500-600°C. However, SHS reaction was not able to be ignited for the cold-sprayed dense Ni/Al alloy coating with or without substrate. SHS reaction was even not ignited for the Ni/Al-40vol.%Al2O3 composite coating, although the thermal conductivity of the coating was significantly decreased by the addition of Al2O3 ceramic particles. The phase transformation from Ni/Al mechanical alloy to NiAl intermetallics during post-spraying annealing can be evidently attributed to diffusion mechanism.
As Coated Compounding of Intermetallics from Feedstock of High and Low Melting Points by Cold Spraying
Authors: Ko K. H. , Choi J. O. , Lee H.
Published: January 2023

It is well known that the inlet temperature of the spray gas influences the impact velocity of particles which, in turn, affects the mechanical and chemical properties of the final coating. From cold spray of high- and-low-melting-point feedstock such as Cu-Sn, it was found that those effects can vary with changes in particle shape and size. Copper powder feedstocks with different shapes, such as and dendritic (under 25 μm), were selected for analysis. For spherical (under 10 μm) powders of Cu6Sn5, an intermetallic compound (IMC) of Cu-Sn was formed in the as-coated state at and above gas inlet temperatures of 100 °C. for A gas inlet temperature of at least 300 °C was needed for the dendritic Cu powders. As temperatures increase, another IMC, Cu3Sn, was also formed. The onset temperature for the formation of the additional IMC was 450 °C for both shapes. Below 300 °C, both Cu and Sn were in solid state and thermodynamic driving forces were drawn from impact energy. Therefore, the spherical particles had more stored energy (strains) than the dendritic particles to initiate IMC formation.
Corrosion Protection of Mg-Alloys with Cold Sprayed Composite Coatings
Authors: Maeva E. , Dzhurinskiy D. , Leshchynsky V. , Maev R.Gr.
Published: January 2023

Due to the demand for improved fuel economy as well as increased safety features, weight reduction is one of the major aims in the automotive industry. Future lightweight automotive components for the next car generation will probably use lots of magnesium alloy. These will form galvanic couples with other materials and may induce phenomena accelerating the corrosion rate of automotive components. The materials used were magnesium alloy AZ31B and several types of cold sprayed coating. The relative performance of each cold sprayed corrosion preventive compounds (CPC) was assessed in combination with the materials under several different electrochemical and accelerated corrosion tests. Baseline data for AZ31B with no CPC applied was also collected. CPC characteristics and properties are also included and discussed. The studies on bare Mg/Steel couples validated accelerated corrosion but found that CPC cold sprayed coatings mitigate corrosion rates. Thus Mg/Fe interfaces with defect-free cold sprayed coatings CPC can prevent buildup of corrosion products and reduce galvanic corrosion of automotive components.
Influence of Chemical Composition of WC Cermet Powders on Cold Spraying
Authors: Sato K. , Furukawa H. , Kitamura J. , Sato K. , Seo D. , Ogawa K.
Published: January 2023

From the appearance of high velocity oxygen fuel (HVOF) thermal spray system in the 1980s, WC cermet coatings have been used as anti-wear coatings in many industrial manufacturing applications. Recently, WC cermet spray materials were applied using new thermal spray methods such as warm spray and cold spray, which are still in the research phase. In HVOF spraying, WC-Co and WC-Ni powders are regularly used as coating materials. On the other hand, using cold spray, WC-Fe alloy series can be deposited as dense and thick coatings, better than WC-Co. In this study, WC-Fe alloy powders were sprayed by cold spray to investigate the influence of binder metal on the coating properties and compared with those of HVOF WC-CoCr coatings. It was observed that the lower metal ratio and FeCrNi chemical composition exhibited improved results.
Atmospheric Plasma Sprayed Forsterite (Mg2SiO4) Coatings: An Investigation of the Processing-Microstructure-Performance Relationship
Authors: Cojocaru C.V. , Lamarre J.-M. , Legoux J.-G. , Marple B.R.
Published: January 2023

Evaluating and understanding the relationship between processing, microstructure and performance of a dielectric coating is essential for its practical usage and reliable application. In this study, the role of the powder feedstock on the properties of atmospheric plasma sprayed forsterite (Mg2SiO4) dielectric coatings was investigated by using different forsterite powder cuts. The microstructural and porosity characteristics of the coatings associated with the spray conditions employed were assessed via scanning electron microscopy (SEM) and image analysis. The phase composition of the coatings was studied via X-ray diffraction and their crystallinity index determined. The electrical insulating characteristics were investigated using the dielectric breakdown test. The obtained electrical properties were correlated with the microstructural characteristics. Ultimately, a performance comparison between forsterite and other dielectric coatings tested in similar conditions is presented.
Influence of Thermal Spray Parameters on Two-Wire Arc Aluminum Semiconductor Equipment Coatings
Authors: Watson M. , Gansert R.
Published: January 2023

Thermal spray metallic coatings are used for a range of applications in the semiconductor equipment industry including applications from particle reduction to precious metal reclaim in chamber operations during thin film deposition. Thermal spray coatings assist in reducing part costs, increasing product performance and lifetimes, and reducing chamber maintenance. The processing parameters in two-wire arc spraying of aluminum are traditionally used to provide a range of coating properties in industry from dense coatings for corrosion control applications- to rough texture coatings for anti-slip applications. Thus, the two-wire arc processing parameters selected for use for semiconductor applications are critical for surviving the semiconductor processing environment and increasing product performance. Important two wire processing parameters include current, voltage, atomizing air pressure, and stand-off distance between the gun and target (sprayed part). Secondary processing parameters including robotic traverse rate, air cooling, part manipulation (turntable speed, etc.) and others. Further, the specifics of the two-wire arc gun design (make/model), nozzle diameter, air caps, and wire diameter are also important variables. Current and voltage are important parameters for generating the electric arc for melting the aluminum wire. An optimum processing window exists for the range of current and voltage used for producing the aluminum coatings. The atomizing air pressure also has an optimum range for atomizing the molten aluminum produced from the electric arc. A range of atomizing air pressures are used to produce a range of coatings from dense to rougher textured coatings. Higher operating current increases the quantity of molten producing the coatings, and the lower operating current reduces the spray rates of the aluminum to be atomized. This paper examines the two-wire arc parameters producing aluminum coatings. Two-wire arc parameters to be examined include current, voltage, atomizing air pressure and stand-off distance varied to produce coatings. The coating produced from these parameter changes will be investigated in terms of microstructure and mechanical properties. The microstructural investigation will involve porosity analysis. Mechanical property testing will include tensile-adhesion bond strength. The surface roughness will also be investigated
Instability of the Arc Spraying Using Cored Wires
Authors: Tillmann W. , Abdulgader M.
Published: January 2023

Owing to the arc ignition in twin wire arc spraying (TWAS) the wire tips are heated in three different zones. The outer part of the wire tips (contact zone) is heated directly by the arc ignition (zone I). The wires material in this zone becomes fully liquefied. The heat propagation phenomenon raises the temperature of the area immediately adjacent (towards the fed wires) generating a doughy material (zone II). Next to the doughy zone (towards the fed wires) the transferred heat softens the wire material causing a permanent deformation (zone III). The deformation is due to the exerted aerodynamic forces of the atomization gas pressure. A high speed imaging system was used to observe the melting behavior, metal break up, and particle formation under different operating conditions. The liquidus metal in zone I is directly atomized in the form of smaller droplets. Their size is a function of the specific properties of the molten metal and the exerting aerodynamic forces. The doughy area (zone II) is the origin of the extruded metal sheets at the anode and cathode side. The extruded metal sheets in case of cored wires are shorter than the ones observed by solid wires. The extruded metal sheets support the re-ignition of the arc and therefore enhance the process stability in twin wire arc spraying. In this study the effects of adjustable parameters and powder filling on melting behavior, particle formation and process instability were revealed and a comparison between solid and cored wires was made. The findings can improve the accuracy of TWAS process modeling and enhance the atomization of metal droplets through the adoption of specific nozzle geometry modifications.
High Velocity Suspension Flame Spraying and Suspension Plasma Spraying of Oxide Ceramics
Authors: Killinger A. , Müller P. , Gadow R.
Published: January 2023

Thermal spraying of oxide ceramic suspensions containing fine and ultrafine powder particles is a new approach for manufacturing ceramic coatings exhibiting a refined microstructure. Suspension sprayed coatings clearly differ from conventionally sprayed coatings regarding microstructure phase composition and resulting mechanical properties. Several industrial applications may take advantage in future; among these are thermal barrier structures, thermal shock protection, solid electrolytes, catalytically active surfaces and wear resistant coatings. Two methods, namely Suspension Plasma Spraying (SPS) and High Velocity Suspension Flame Spraying (HVSFS) are suitable to process suspensions but lead to rather different coating structures due to differences in the achievable particle velocities and temperature. Generally, HVSFS can lead to more dense coatings with low porosity values. With SPS on the other hand, coatings with a high volume fraction of porosity featuring a homogeneous pore structure are achievable. The presentation will compare SPS and HVSFS regarding the spray process, achieved properties of the oxide coatings and potential applications.
Robot Trajectory Planning for High Quality Thermal Spray Coating Processes on Complex Shaped Components
Authors: Floristán M. , Montesinos J. A. , García-Marín J. A. , Killinger A. , Gadow R.
Published: January 2023

Industrial robots are widely used in thermal spraying operations in order to assure process accuracy and reproducibility, as well as to increase worker´s safety. Robot path planning for the coating of free form geometries keeping constant the kinematic parameters can lead to complex robot paths and in some cases to unreachable robot configurations. An external rotational axis in coordinated movement with the robot can be used to manipulate complex shaped components during the spraying operation and to simplify the robot movement. Moreover, the robot kinematics, which define the spraying path, spray angle, spray distance and spray velocity, are key parameters to control the heat and mass transfer to the substrate during the coating deposition, and they influence therefore the development of residual stresses. The present work describes the off-line planning of robot trajectories for thermal spraying operations using an external rotational axis taking into consideration the heat transfer to the component.
Numerical Analysis of Solution Mixture and Torch Design in High-Velocity Suspension Flame Spraying
Authors: Dongmo E. , Wenzelburger M. , Gadow R.
Published: January 2023

High-velocity suspension flame spraying (HVSFS) is used for direct processing of submicron and nano-scaled particles to achieve dense surface layers in supersonic mode with a refined structure, from which superior properties are expected. The application of solutions as a carrier fluid for nano-particles in thermal spray systems is a new approach that requires some thermo-physical and chemical optimization. Three dimensional modeling and analysis of the combustion and gas dynamic phenomena of the three-phase HVSFS process is performed in this study for an industrial TopGun-G torch, based on a numerical model for a conventional HVOF process. Parameter analysis of the solution mixture (proportion between aqueous and organic solvent) in a suspension is performed as well as analysis of the variation of the combustion chamber depending on the torch design, leading to more homogeneous flow properties for an improved HVSFS torch.
Application of HVOF and HVSFS for High Performance Mass Transport Vehicle Chassis Components
Authors: Heyd S. , Manzat A. , Killinger A. , Gadow R.
Published: January 2023

Efficient transport is a key requirement for a powerful economy and will continue to gain importance leading to the necessity for high performance transport vehicles. A highly loaded major component of trains is the chassis. With increasing load, new materials and concepts have to be developed in order to increase the performance of these components. One approach to improving chassis components like bearings for chassis components is the deployment of thermally sprayed coatings by means of HVOF and HVSFS, which can significantly improve their wear resistance, prolong their life time and simultaneously reduce frictional losses. Using the example of spherical bearings, several HVOF sprayed metallic, cermetic and ceramic coatings have been tested for their ability to improve the properties of the components. In addition to metallographic investigations, extensive mechanical tests on test rigs have been carried out to determine the performance of the coatings under realistic conditions.
Military Adoption of Kinetic Metallization
Authors: Tapphorn R. , Gabel H. , Hashimoto K. , Wahl Weston , Crowe T.
Published: January 2023

The low temperature Kinetic Metallization (KM) deposition process is compliant with the recently revised MIL-STD-3021 standard for cold spray materials deposition. KM deposition process and equipment was supported through the US Military via multiple Small Business Innovative Research (SBIR) grants leading to delivery of KM deposition equipment to multiple branches. Coating application areas discussed in this paper include wear resistant tungsten-carbide and chromium-carbide hard-phase coatings. These are used for aircraft engines and landing gear surfaces with firm low temperature deposition requirements. Other areas include aluminum and magnesium dimensional restorations, in particular for Aircraft Mounted Accessory Drive (AMAD) gearboxes for F-18 platforms, and land vehicle housings and casings for the US Marines Corps.
Improved Coatings for Extended Design Life of 22%Cr Duplex Stainless Steel in Marine Environments
Authors: Paul S. , Lee C. M. , Harvey M. D. F.
Published: January 2023

In this paper evaluation of sealed and unsealed thermally sprayed aluminum (TSA) for the protection of 22%Cr duplex stainless steel (DSS) from corrosion in aerated, elevated temperature synthetic seawater is presented. The assessments involved general and pitting corrosion tests, external chloride stress corrosion cracking (SCC), and Hydrogen induced stress cracking (HISC). These tests indicate that DSS samples which would otherwise fail on its own in a few days do not show pitting or fail under chloride SCC and HISC conditions when coated with TSA (with or without a sealant). TSA-coated specimens failed only at very high stresses (>120% proof stress). In general, TSA offered protection to the underlying or exposed steel by cathodically polarizing it and forming a calcareous deposit in synthetic seawater. The morphology of the calcareous deposit was found to be temperature dependent and in general is of duplex nature. The free corrosion rate of TSA in synthetic seawater was measured to be ~5-8 µm/year at ~18°C and ~6-7 µm/year at 80°C.
Utilizing Computational Metallurgy to Design Amorphous and Nanocrystalline Coatings for Wear and Corrosion Resistance
Authors: Cheney J. , Kusinski G.
Published: January 2023

Computational metallurgy is a technique being used and developed in the field of bulk alloys to design and develop novel amorphous and nanocrystalline materials. This technology can be transitioned to develop chemistries for both wear and corrosion resistant thermal spray coatings. Using computational metallurgy and small scale laboratory experiments, nanostructured and amorphous chemistries can be designed to specifically accommodate one of the many environmental conditions challenging the oil and gas industry. This study reviews the design procedures behind developing three unique chemistries intended to function in different environments: 1) an Fe-based chemistry designed for metal to metal sliding wear resistance, 2) an Fe-based chemistry containing elevated refractory content intended specifically for spray and fuse applications to resist sulfurous corrosion, and 3) a Ni-based chemistry similar to Alloy C276 for high temperature corrosion resistance. All three alloys were designed using computational techniques and eventually manufactured into cored wires for use within the twin wire arc spray (TWAS) process. The fine grained structure provides unique benefits to each application including 1) high hardness, 2) ability to rapidly form protective scale, 3) low melting temperature and creep resistance.
Multi-Response Optimization of Process Parameters for Low-Pressure Cold Spray Coating Process Using Taguchi and Utility Concept
Authors: Goyal Tarun , Walia R.S. , Sidhu T.S. , Sidhu H.P.S.
Published: January 2023

In this research work, an approach based on a Utility theory and Taguchi quality loss function (TQLF) has been applied to low-pressure cold spray (LPCS) process to deposit copper coatings, for simultaneous optimization of two potential response parameters i.e. coating thickness (CT) and surface roughness (SR). Utility values based upon these response parameters have been analyzed for optimization by using Taguchi approach. The selected input parameters of powder feeding arrangement, air stagnation pressure, air stagnation temperature and stand-off distance except substrate material, significantly improves the Utility function (raw data and S/N ratio) comprising of quality characteristics (coating thickness and surface roughness). The percentage contribution of the parameters to achieve a higher value of utility function is: stand-off distance (55.86%), air stagnation temperature (16.58%), air stagnation pressure (14.20%), powder feeding arrangement (5.12%) and substrate material (0.16%) respectively.
Knudsen Effect on the Computed Effective Thermal Conductivity of Thermal Spray Coatings
Authors: Qiao J.H. , Bolot R. , Liao H.L. , Coddet C.
Published: January 2023

To implement image-based numerical modeling of the thermal conductivity of coatings, a YSZ coating was considered as a network of two phases, namely the coating material and pores. The variation of the thermal conductivity of the gas trapped within the pores caused by their small size was considered by complying with the Knudsen law. In the present work, the quantification of the Knudsen effect on the effective thermal conductivity of coatings was achieved with the help of image analysis. The thicknesses of the pores were determined by combining the use of the Scion image software with a new in-house algorithm coded in C language. The Knudsen effect was quantified by applying a finite-difference model for both 2D images and a 3D image. In both cases, a decrease of the computed thermal conductivity was found while considering the Knudsen effect. Furthermore, the Knudsen effect was also taken into account in a finite-element model applied on the same images. Despite differences were noticed on the computed thermal conductivities obtained with the two methods, a quite similar decrease was calculated by comparing with data computed with the FDM method.
Fabrication of Porous Stainless Steel through Semi-Molten Spray Particles Deposition by Flame Spraying
Authors: Yao J.-T. , Li C.-J. , Yang G.-J. , Li C.-X.
Published: January 2023

Porous materials possess many unique properties. Many processes have been employed to fabricate porous materials. Recently, it was found that a porous deposit can be created through controlling the deposition of semi-molten spray powder particles. In this study, porous 316L stainless steel deposits were prepared by flame spraying under different spray conditions to aim at controlling deposit porosity. During deposition the temperature of the substrate and/or deposit surface was kept at 600°C to ensure bonding formation between the spray particle and underlying particle. To understand the deposition process mechanism, the velocity of spray particles was quantitatively measured and the morphology of deposited isolated particles was characterized by scanning electron microscopy to estimate the melting degree of spray particles before impact. The microstructure of porous 316L stainless steel deposits was characterized by scanning electron microscopy and deposit porosity was estimated from its cross section by image analysis. It was found that pores were uniformly distributed in the deposit. The results showed that porosity of the 316L deposits changed from 20% to 50% with the change of spray particle melting degrees, resulting from the change of spray parameters. The examination showed that 3D through-deposit pore-net structure was created by viscoplastic flowing of the molten fraction of semi-molten particles which forms the bonding between necks of particles. The present results clearly demonstrated that a porous ferrous alloy based material can be formed by spray deposition through controlling the melting degree of spray particles.
Effect of Powder Structure on the Adhesion and Electrical Properties of TiN Coatings Deposited by Vacuum Cold Spray
Authors: Wang Y.-Y. , Zhang Y.-J. , Liu Y. , Li C.-J. , Yang G.-J
Published: January 2023

Sub-micro-structured titanium nitrides (TiN) coatings on Al2O3 substrates were fabricated by vacuum cold spray (VCS) process using ceramic powders, which were ball-milled at room temperature. The microstructure features and crystal structures of the VCS TiN coatings were analyzed by scanning electron microscopy and X-ray diffraction. The adhesion between the coating and the substrate was evaluated with a scratch tester. The sheet resistance of the VCS TiN coatings was measured by using a four-point probe method. The effects of nozzle traverse speed on the microstructure, adhesion to substrate and electrical properties of the coatings were investigated. It was found that the adhesion improves greatly with the nozzle traverse speed increasing from 5 to 15mm/s, and the electrical resistivity levels of the coatings is decreased significantly. The resistivity of sub-micron-structured TiN coatings is substantially lower than those of nano-structured ones fabricated by the same VCS process. And a minimum resistivity of 1.16×10-4 Ω·m is achieved.
Bilayer Plasma-Sprayed Alumina for Optical Applications
Authors: Marthe J. , Meillot E. , Enguehard F. , Jeandel G.
Published: January 2023

Materials with fine-scale structures are recognized to exhibit technologically efficient mechanical or thermal properties. Thermal sprayed nanostructured media could also be interesting in the optical field thanks to the diffusion interaction between short wavelength radiations and submicron-sized pores. One difficulty of the Suspension Plasma Spray (SPS) technique is to provide a sufficiently thick coating and to maintain efficient mechanical properties when the coating is removed from the substrate. The aim of this study was to spray a reflective and diffusive self-supporting alumina bilayer. The first coating was obtained by Atmospheric Plasma Spraying of micron-sized powders in order to obtain a thick layer and the second coating was sprayed by SPS onto the first one with strong adhesion. An oxide ceramic material with high scattering reflectance in a large band of wavelengths was thus obtained.
Study on the Mechanism of Adhesion Improvement Using Dry-Ice Blasting for Plasma-Sprayed Al2O3 Coatings
Authors: Dong S.-J. , Song B. , Liao H.-L. , Coddet C. , Hansz B.
Published: January 2023

A previous study indicated that improved adhesions of plasma-sprayed Al2O3 coatings have been achieved by using dry-ice blasting. Therefore, it is important to understand the mechanisms involved. In this study, the surface roughness of different substrates treated by dry-ice blasting was firstly examined. And then the surface wettability was characterized in order to clarify the effect of dry-ice blasting on the substrate surface properties. The effect of dry-ice blasting on Al2O3 splat morphology with different treatment times was investigated. The residual stress of plasma-sprayed Al2O3 coatings using dry-ice blasting was measured and compared with that of coatings deposited with conventional air cooling. Based on these numerous assessment tests, it could be concluded that the cleaning effect of dry-ice blasting on different organic substances adsorbed on the substrates was the most important influence on the adhesion improvement of Al2O3 coatings.
A Simplified Model for Prediction of HVOF NiCr Coating Properties through Experimental Design and Diagnostic Measurements
Authors: Zois D. , Wentz T. , Sampath S.
Published: January 2023

An empirical model was built for the prediction of HVOF sprayed NiCr in-flight particle properties based on the spraying parameters. The employment of factorial design in process parameter development, allowed determination of the contribution of the key process variables, such as flame energy (combustion pressure and O2/F ratio), spray distance and feed rate, on the resultant particle velocities and surface temperatures. The significance of each parameter was used to compose a simple model which enabled the description of the particles’ in-flight properties. Particles with velocities ranging as much as 300 m/s and temperatures ranging up to 350 °C were used to produce a range of coatings on an in situ curvature sensor enabling the determination of evolving and residual stress. These diverse particle states combined with the effect of flame impingement on the substrate, resulted in coatings of similar thickness, but significantly different stress states. Real time evolving stresses during deposition were interrelated to particle in-flight properties and, consequently, to spraying parameters.
Multiple-Approach Evaluation of WSP Coatings Adhesion/Cohesion Strength
Authors: Musalek R. , Vilemova M. , Matejicek J. , Pejchal V.
Published: January 2023

Adhesion/cohesion testing represents one of the most common methods for benchmarking and optimization of thermal spray coatings. However, due to the inhomogeneous coating microstructure, such testing may be quite troublesome. In this study, adhesion/cohesion strength of representative metallic and ceramic coatings deposited by Water Stabilized Plasma (WSP) spraying was evaluated by different methods, namely Tensile Adhesion Test (TAT), newly utilized pin test and Tubular Coating Tensile (TCT) test. Combination of various methods enabled the evaluation of the splat bonding quality in different loading modes. Limitations and benefits of each method for testing of WSP coatings are demonstrated. Dominating failure micromechanisms were determined by supplementary fractographic analysis.
Adhesion Properties of Sprayed Coatings on Substrate Blasted by Multiangle Blasting
Authors: Maruyama T. , Kishita T.
Published: January 2023

Adhesion properties on the substrate blasted by multi-angle blasting with white alumina grit were examined. The low carbon steel substrates were blasted at two blasting angles (high and low angles) in a multi-angle blasting process. The sprayed coating of zinc alloy was evaluated by an adhesion test. The surface roughness levels after the multi-angle blasting were lower than those in the case of normal blasting. The multi-angle blasting was an effective blasting process to obtain improved adhesive properties. The low blasting angle may have contributed for removing contamination from the substrate surface. The high blasting angle may have contributed for an effective surface roughness to enhance the adhesive properties.
Cladding by Plasma Transferred Arc Process: Effect of the Process on Plasma Parameters Behavior and Molten Bath
Authors: Lucas H. , Denoirjean A. , Vardelle M. , Furlani A.M.
Published: January 2023

Coatings, a few-millimeter thick, are widely used to protect new mechanical parts against abrasion and erosion or rebuild worn parts. The plasma transferred arc process is a commonly used process to deposit such coatings. It makes it possible to bring about a metal bath inside which melted powders are introduced to form an alloyed coating between the feedstock material and substrate material with metallurgical adhesion. The main parameters of the process are the arc current intensity, plasma and shrouding gas flow rates, distance between the cathode tip and piece, velocity of plasma torch displacement; they all have a notable effect on the produced coating. This study investigates the plasma behavior and properties of the clad by using a design of experiments. The properties of the coating are the dilution level, porosity, and efficiency of material deposition, heat flux transferred to a water-cooled calorimeter, and the hardness in the clad and the substrate to estimate the thermally affected area.
Erosion and Abrasion Resistance of Fe2B-Based Arc-Sprayed Coatings and Weld Overlays Containing Chromium and Carbon
Authors: Dallaire S.
Published: January 2023

Earlier works have demonstrated that Fe2B-based arc-sprayed coatings and weld overlays present outstanding dry erosion resistance when compared to other carbide-based coatings and overlays. The present work was undertaken to examine their wear resistance, particularly their slurry erosion resistance. Cored wires containing chromium (2-20 wt%) and carbon (0.2-1.2 wt%) additives were deposited by arc spraying and gas metal arc welding (GMAW). The abrasion, particle erosion and slurry erosion resistances of these (Fe-B-Cr-C) coatings and overlays were evaluated in laboratory. The results demonstrate that both differences in cored wire composition and variations in the deposition process must be considered in order to obtain the best wear properties.
The Influence of Process Equipment on the Properties of Suspension Plasma Sprayed Yttria-Stabilized Zirconia Coatings
Authors: Marr M. , Waldbillig D. , Kesler O.
Published: January 2023

Suspension plasma sprayed YSZ coatings were deposited at lab-scale and production-scale facilities to investigate the effect of process equipment on coating properties. The target application for these coatings is SOFC electrolytes, so dense microstructures with low permeabilities were desired. Both facilities had the same torch but different suspension feeding systems, torch robots and substrate holders. These differences meant that the lab facility had higher torch-substrate relative speeds compared to the production facility. When using porous stainless steel substrates with relatively smooth surfaces, permeabilities and microstructures were comparable for coatings from both facilities, and no segmentation cracks were observed. Coating permeability could be further reduced by increasing substrate temperatures during deposition or reducing suspension feed rates. On rougher substrates representative of SOFC cathodes, production facility coatings had higher permeabilities and more segmentation cracks compared to lab coatings. The increased cracking may be due to larger heat impulses with each torch pass at the production facility caused by its lower torch-substrate relative speed. This work highlights some of the challenges associated with scaling up the spray process from the lab to production.
Thermal Diffusivity and Conductivity of Yttria Stabilized Zirconia Coatings Obtained by Suspension Plasma Spraying
Authors: Łatka L. , Pawłowski L. , Valette S. , Pateyron B. , Lecompte J.P. , Denoirjean A. , Cattini A. , Kumar R.
Published: January 2023

Plasma generated by an SG-100 torch was applied to a spray suspension formulated with the use of ZrO2+8 wt% Y2O3 (8YSZ) solid phase. The solids had a mean size of about 4.5 μm and were obtained by milling of commercial Metco 204 NS powder. The suspension was formulated with 20 wt% solid phase, 40 wt% water and 40 wt% ethanol. The plasma spray parameters were optimized with the electric power equal to 40 kW, working gases composition Ar 45 slpm and H2 5 slpm, spray distance varying from 40 to 60 mm, and torch scan linear speed varying from 300 to 500 mm/s. Coatings with thicknesses ranging from 51 to 106 μm were sprayed onto stainless steel substrates. The porosity of the samples was found from the image analysis of metallographically prepared cross-sections of the samples to be in the range of 8 to 12%. Thermal diffusivity was measured with the use of the commercial NanoFlash system in the temperature range from room temperature to 523 K. The measurements were made with the use of the coatings sprayed on the substrate, and a 2-layer numerical model was developed to determine thermal diffusivity of the coatings. The diffusivity was in the range from 0.196 × 10-6 to 0.352 × 10-6 m2/s in room temperature depending on the spray parameters. The obtained data were then associated with the literature data of density and specific heat and experimental porosity to find thermal conductivity, which was in the range of 0.47 to 0.86 W/(mK) at room temperature, depending on the spray run.
Process Conditions and Microstructures of Ceramic Coatings by Gas Phase Deposition Based on Plasma Spraying
Authors: Mauer G. , Hospach A. , Zotov N. , Vaßen R.
Published: January 2023

Plasma spraying at very low pressure (50-200 Pa) is significantly different from atmospheric plasma conditions (APS). Applying powder feedstock it is possible to defragment the particles into very small clusters or even to evaporate the material. As a consequence, the deposition mechanisms and the resulting coating microstructures could be quite different compared to conventional APS liquid splat deposition. Thin and dense ceramic coatings as well as columnar-structured strain-tolerant coatings with low thermal conductivity can be achieved offering new possibilities for application in energy systems. To exploit the potential of such a gas phase deposition from plasma spray-based processes, the deposition mechanisms and their dependency on process conditions must be better understood. Thus, plasma conditions were investigated by optical emission spectroscopy. Coating experiments were performed, partially at extreme conditions. Based on the observed microstructures, a phenomenological model is developed to identify basic growth mechanisms.
Influence of the Spray Angle on the Characteristics of HVOF Sprayed Coatings Processed by Means of Fine WC-12Co (2–10 μm) Powders
Authors: Tillmann W. , Baumann I. , Hollingsworth P. , Laemmerhirt I.-A.
Published: January 2023

The application of fine powders in the thermal spray technology represents an innovative approach to apply dense and smooth near-net shape coatings on tools with complex geometry. However, this aim can only be achieved, as long as the influence of the handling parameters of the spray process such as the spray angle are sufficiently understood. In this study the influence of the spray angle on the deposition rate as well as on the coating properties (microhardness, roughness and porosity) of HVOF-sprayed, fine-structured coatings is investigated. A fine agglomerated and sintered WC-l2Co powder (agglomerate size: 2-10 pm, WC-particle size: FSS = 400 nm) was used as feedstock material. It has been shown that HVOF spraying of fine powders is less susceptible to an alteration of the spray angle than most other thermal spray processes such as plasma- or arc-spraying. The reduction of the spray angle results in a decrease of the deposition rate, while no significant degradation of the coating properties was found up to 30°. However, at spray angles below 30° the coating strength is negatively affected by the formation of pores and cracks.
Characterization of Yttria Coatings Synthesized by Conventional DC Plasma Spray and a Novel Plasma Torch
Authors: Saeidfar M. , Salimijazi H. R. , Emadi R. , Mostaghimi J. , Pershin L. , Coyle Thomas W.
Published: January 2023

Yttrium oxide (Y2O3) can be used in different applications such as corrosion resistance, high temperature applications and semi-conductor production equipment due to its very high thermal and chemical stability. In the current research, yttria coatings were processed using a new type of DC plasma gun consisted of molecular gases CO2+CH4. Physical and structural properties were compared with the coating made by SG-100 plasma torch. Gas mixture of CO2+CH4 improves the torch efficiency due to its high thermal enthalpy and conductivity which leads to increased particle temperature and complete fusion of the sprayed particles during the process of coating. SEM study of the structure revealed that the coating has higher density and lower porosity compared to the coating produced by SG-100 torch. No unmelted particles can be observed in the coating. XRD analysis of the coating showed that the coating contains no amount of harmful metastable monoclinic phases. This all proves the better quality of the coatings deposited by CO2+CH4 gas mixture in comparison to the conventional coatings.
APS TriplexPro-200/-210 and HVOF K2: Comparison of Two Modern Thermal Spray Systems with Regard to Particle In-Flight and Coating Properties Using Iron Based Feedstock Materials
Authors: Bobzin K. , Schläfer T. , Warda T. , Petkovic I. , Schäfer M. , Landes K. , Forster G. , Zimmermann S. , Marques-Lopez J. , Kirner S. , Kauffeld M. , Schein J.
Published: January 2023

New developments in the field of thermal spraying systems (increased particle velocities, enhanced process stability) are leading to improved coating properties. At the same time innovations in the field of feedstock materials are supporting this trend. The combination of modern thermal spraying systems and new material concepts has led to a renaissance of Fe-based feedstocks. Using modern APS or HVOF systems, it is now possible to compete with classical materials for wear and corrosion applications like Ni basis (e.g. NiCrBSi) or metal matrix composites (MMC, e.g. WC/Co or Cr3C2/NiCr). The work described in this paper focuses on that combination and intends to give an analysis of the in-flight particle and spray jet properties achievable with two different modern thermal spraying systems (kerosene driven HVOF system K2, 3- cathodes APS system TriplexPro-200/-210) using Fe-based powders. The velocity fields are measured with the Laser Doppler Anemometry (LDA). Additionally, resulting coatings are analyzed metallographically with regard to their properties and a correlation with the particle in-flight properties is given. The experimental work is accompanied by computational fluid dynamics (CFD) simulations of spray jet and particle velocities, leading to a comprehensive analysis and characterization of the achievable particle properties with state-of-the-art HVOF and APS systems.