bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Substrate Properties on the Impact Resistance of WC Cermet Coatings
Authors: Osawa S. , Itsukaichi T. , Ahmed R.
Published: July 2022

This research delivers an integrated performance of generic coating-substrate systems under impact loading, and comprehends the understanding of underpinning failure mechanisms. This investigation thus benchmarks the coating design process for high impact stress applications. Repeated severe impacts to the coatings often result in poor performance by cracking and delamination from the coating-substrate interface. The durability and delamination resistance of coatings depend on the choice of coating and substrate materials, coating deposition process and service conditions. The design of overlay thermal spray coatings thus requires an optimization of these parameters. A thorough understanding of the underpinning failure mechanisms is thus critical for future coating developments. This investigation thus provides an insight to the role coating and substrate properties on the impact resistance of coated materials, and maps the relationship between the impact resistance of WC-Co and WC-CrC-Ni coatings on a variety of substrates. Results indicate that coating’s delamination resistance during impact loading not only depends upon the hardness and roughness of the substrate material, but more importantly, substrates with higher work-hardening coefficient indicate a higher delamination resistance during impact loading.
Solid Particle Erosion Resistance of Thermally Sprayed Functionally Graded Polymer/Ceramic Coatings
Authors: Ivosevic M. , Knight R. , Kalidindi S.R. , Palmese G.R. , Sutter J.K.
Published: July 2022

The use of polymer matrix composites [PMC's] in the gas flow path of advanced turbine engines offers significant benefits for aircraft engine performance, but their useful lifetime is limited by their poor erosion resistance. HVOF and flame sprayed polymer/cermet functionally graded coatings based on a polyimide matrix filled with varying volume fractions of WC-Co are being investigated to improve the erosion and oxidation resistance of polymer matrix composites. A study of the coating's effectiveness as erosion barriers was accomplished through a statistical analysis of the results of solid particle erosion testing of coated and uncoated PMC samples using a design of experiments [DoE] approach. Three coating systems and a control were evaluated in a randomized test matrix. The coatings were tested at room temperature and 250 °C, using an alumina erodent impacting the coatings at a speed of 100 m/s at angles of 20° and 90°. Erosion volume loss at 250 °C was approximately twice than at room temperature, but the maximum erosion volume loss did not exceed 0.30 mm3 at the elevated temperature. In general, as the angle of incidence of the eroding material increased from 20 degrees to 90 degrees the volume loss increased.
A Study of Gas and Particle Flow Characteristics in HVOF Thermal Spraying Process
Authors: Katanoda H. , Kuroda S. , Kawakita J. , Fukanuma H. , Matsuo K.
Published: July 2022

This paper analyzes the behavior of coating particles as well as the gas flow in a High-Velocity Oxy-Fuel (HVOF) gun by using numerical simulation. Special attention is paid to the particle behavior in turbulent boundary-layer inside the barrel.
Chemical Composition Optimization of Perovskite Coatings by Suspension Plasma Spraying for SOFC Cathodes
Authors: Monterrubio-Badillo C. , Ageorges H. , Chartier T. , Coudert J.F. , Fauchais P.
Published: July 2022

The purpose of this work is to optimise the chemical composition of perovskite coatings prepared by injecting a suspension of submicrometric LaMnO3 perovskite particles (d50 =~ 1 µm) in a direct current (d.c.) plasma jet. The perovskite powder composition, the particle size and the plasma parameters were modified in order to diminish the manganese evaporation. The process consists in mechanically injecting a well dispersed stable suspension of submicrometric perovskite particles in a dc plasma jet. In the process, large suspension droplets (~300 µm) are sheared into tiny ones (a few µm) by the plasma jet flow. Then the solvent is evaporated and the particles melt resulting in perovskite droplets of about 1 µm impacting on the substrate, the coating resulting from their layering. Such coatings are to be used as cathodes for the SOFCs (Solid Oxide Fuel Cells). Best results were obtained by injecting a stable suspension containing a 10 mol% MnO2 doped perovskite powder with 3 µm particle size in an Ar plasma forming gas and 300 A of current intensity.
Denser Ceramic Coatings Obtained by the Optimization of the Suspension Plasma Spraying Technique
Authors: Siegert R. , Döring J.-E. , Marqués J.-L. , Vaßen R. , Sebold D. , Stöver D.
Published: July 2022

The innovative suspension plasma spraying (SPS) technique, in which the carrier gas used to inject particles (10…100 µm) into the plasma jet is replaced by a liquid feedstock, is currently under development procuring denser ceramic coatings due to the use of submicron particles. The suspension properties, as well as the most relevant injection parameters - injection angle and liquid velocity - are adjusted to improve the coating quality at acceptable deposition rates. In addition, the plasma jet instabilities are studied and correlated to the coating properties. In the present work, a feasibility study is conducted addressing the key factors influencing the coating morphological properties such as the porosity, cracks, molten-fraction and amount of over-spray. The experimental setup is adapted to different DC plasma torch architectures (Sulzer-Metco F4 and Triplex) operating under atmospheric conditions with the aim of correlating the plasma jet qualities to the properties of the feedstock under consideration. The metallographic probes and fractured surfaces of the resulting yttria stabilized zirconia (YSZ, 5 wt. % Y2O3) coatings are analyzed by means of light microscopy and scanning electron microscopy (SEM).
Design of a Nozzle Extension for Thermal Spray Under Very Low Pressure Conditions
Authors: Bolot R. , Klein D. , Coddet C.
Published: July 2022

Conventional equipments used for low pressure plasma spraying are designed for a chamber pressure of a few tens of mbar. During the past three years, an increasing interest for thermal spray under very low pressure conditions (as low as 1 mbar) was encountered but no significant advances concerning the spray gun design was proposed. However, it is clear that actual tools do not allow providing uniform plasma jets and that the produced jets present successive expansions and constrictions due to a poor adaptation of the nozzle exit pressure regarding to the chamber one. In the present paper, the use of a nozzle extension is proposed. The holding nozzle is a lengthened F4 type one and the diverging part of the nozzle is formed by a fastened external extension. The design of the nozzle extension is a bell-contoured Laval type one and its dimensions (exit diameter and length) are much higher than for conventional diverging nozzles. An improvement in the jet homogeneity and uniformity is expected.
Development of High Quality Thermal Sprayed Metal Coating Process by Shielding Control
Authors: Sakakibara N. , Manabe Y. , Hiromoto Y. , Kobayashi Y.
Published: July 2022

The shielding controlled plasma spraying process is investigated to improve corrosion resistance of the metal surface. In this process, a shielding nozzle that covers just the spraying area is attached in front of the tip of a commercial plasma spray gun nozzle, and the environment surrounding the plasma jet is controlled by nitrogen flow. As the oxygen concentration in the shielding nozzle is maintained as low as 0.5%, the metal oxide contents in volume of CoNiCrAlY coating and the porosity of the coating reduced to 0.2% and 0.3% respectively under optimal spray particle size. The corrosion potential of CoNiCrAlY coating sprayed by this process in an acid solution including chloride ions is staying about -150 mV for 1000 hours, and no rust is observed during this test. On the other hand, that of the coating sprayed by atmospheric plasma spraying process changes from about -300 mV to about -500mV for 1000 hours, and the rust comes to the surface of the coating after 10 hours. Therefore the developed shielding controlled plasma spraying process is concluded to improve the corrosion of the metal.
Improved Design of de-Laval-type Nozzles for Atmospheric Plasma Spraying
Authors: Schwenk A. , Gruner H. , Zimmermann S. , Landes K. , Nutsch G.
Published: July 2022

An optimised de-Laval-type-contour for the Atmospheric Plasma Spraying (APS) with respect to the thermal and deposition efficiency as well as to the arc voltage fluctuations and the sound level of the plasma torch is presented. Investigations of the plasma gas dynamics and two different feedstock materials (Al2O3 (fused and crashed) and Cr2O3 (agglomerated and sintered)) have been done to promote the industrial utilization of convergent-divergent nozzles for the APS.
Arc Spraying with Dynamic Current Generators
Authors: Wilden J. , Bergmann J.P. , Jahn S.
Published: July 2022

Low running costs, high spray rates and efficiency make electric arc spraying a good tool for coating large areas with high production rates. The main applications are in the field of corrosion and wear protection of large structures, e. g. parts for bridges or offshore industry. New applications are expected for high quality coatings produced by cored wires. Disadvantages of the arc spraying process are that only electrically conductive wires can be processed and the lower particle velocity in comparison to other thermal spray processes like HVOF or APS. Depending on the process parameters the oxidation of particles has a negative effect on the mechanical and the electrochemical properties of the coating, too. In this paper some investigations with new and flexible power supply systems for arc spraying are presented. The particle size and the morphology of the coating can be optimised, due to the possibility of changing the current generator characteristic and modulating the power by pulsing up to 500 Hz. The oxidation of particles can be reduced by a lower heat input based on lower spray voltage. For a higher quality of the coating microstructure investigations with dynamic generators were performed for Zn, Al, ZnAl, 110MnCrTi8 and Al. An enhancement of the process stability was achieved, too.
Microstructure and Properties of Molybdenum Coatings Deposited by Microplasma Spraying Torch with a Novel Hollow Cathode
Authors: Li Chang-Jiu , Sun Bo
Published: July 2022

A microplasma spraying torch with a hollow cathode electrode is designed to melt completely the refractory materials and deposit coatings at plasma power level up to several kilowatts. The designed torch permits spray material to be fed into plasma arc jet through axial powder injection. In the present study, molybdenum is used as a typical refractory spray material. The effects of the main processing parameters including plasma arc power, plasma gas flow and spray distance on the particle velocity during spraying, and the microstructure and properties of the coatings are investigated. The microstructure of coating is characterized with optical microscopy and scanning electron microscopy. The properties of the coating are characterized by microhardness and abrasive wear tests. The particle velocity during in-flight is carried out using a particle velocity/temperature measurement system based on thermal radiation. The comparison of the microstructure and property of micro-plasma sprayed Mo coatings with those of the coating deposited by the conventional plasma spraying operated at a power of 42 kW is performed. The results show that the abrasive wear loss of the Mo coatings deposited by the micro-plasma spray torch is comparable to that of the coating deposited by the conventional plasma spraying disregarding the one order difference in the plasma operating power.
Interactions Between Molten Metal Splats Landing on a Substrate during Coating Formation
Authors: Dhiman Rajeev , Chandra Sanjeev
Published: July 2022

Interactions between multiple splats landing on a substrate was studied experimentally by photographing deformations of droplets as they land and freeze on the substrate, or previously solidified splats. Uniform-size molten tin droplets (550 µm diameter) were produced using a drop-on-demand generator. To achieve high impact velocities the stainless steel coupons used as substrates were mounted on the rim of a rotating flywheel and heated using cartridge heaters to vary substrate temperature. To hit a falling droplet with the substrate and photograph its impact, a timing circuit was used to synchronize the ejection of a droplet, triggering of the camera and a flash to provide illumination. The substrate temperature and substrate roughness significantly affected splat impact dynamics. Droplets hitting a smooth cold substrate splashed extensively whereas those hitting a hot substrate spread in the form of a smooth disc. The final splat shapes were dependent on the offset distance between the impacting droplet and the previously solidified splat. The size of fingers around the splat edge increased with the offset distance. Large pieces of metal detached from the droplet rim when the droplet hit a rough substrate whereas droplets hitting previously solidified splats splashed in a star-like shape with extremely long fingers.
High Powered Axial Injection Plasma Torch for Internal Surfaces
Authors: Young N. , Celler Z. , Dolomont D. , Burgess A.
Published: July 2022

Northwest Mettech Corporation has recently developed a new high power torch for spraying internal surfaces, the Axial III ID. The Axial III ID has been successfully operating at 135 kW while spraying inside a drum with an inner diameter of 34 cm. The three-electrode axial injection configuration of the new torch is based on the current Axial III torch. Various coatings were sprayed inside a drum while monitoring the torch temperature. The results of these experiments are presented in this paper.
Microplasma Wire Spraying
Authors: Borisov Yuri , Kislitsa Alesandr , Voynarovich Sergey
Published: July 2022

The method of microplasma spraying provides a small size of the spraying spot (a few millimeters), is characterized by small dimensions of relevant equipment and a low level of noise. A plasmatron with a device for feeding a wire has been designed to use wire as a material for coating spraying. Experiments on microplasma spraying of coatings were conducted using molybdenum, tungsten, titanium, nichrome, copper, brass, tin, aluminum, steel and stainless steel wires. The use has been made of wires with a diameter of 0.2-0.4 mm. Relationship between the wire material and diameter at a wire feed speed ensuring optimal conditions of the spraying process has been established. Structure and properties of coatings produced by the microplasma wire spraying method have been studied. Results of the studies are indicative of the possibility of thus producing the dense coatings at a spraying spot size of 3-8 mm.
Some Trials to Improve Uniformity of Film Thickness by Manual Thermal Spraying
Authors: Imai Norihiro , Seki Masao
Published: July 2022

In this article, three methods are studied to improve the uniformity of film thickness by manual thermal spraying. These methods are projection of personal computer graphics by the liquid crystal projector, irradiation of the laser ray, and on-line measurement of metal wire length for the thermal spraying.
Numerical Simulation of a Multi-Component Reacting Plasma Jet in Plasma Spraying
Authors: Fuchi Wang , Qunbo Fan , Lu Wang , Quansheng Wang
Published: July 2022

The present study is conducted to simulate the multi-component chemical reactions of a turbulent argon-hydrogen plasma jet flowing into the surrounding atmosphere under typical operating conditions. Based on the initial spraying process parameters, the temperature, velocity profiles and the basic chemical species at the nozzle exit are calculated, and then used for the boundary conditions of the next step, where the chemical reactions in the multicomponent plasma jet are calculated by employing the Eddy-Dissipation model and the Realizable k-ε turbulence model. As the result of the calculation, the distribution of the mole fractions of the products as well as the temperature and velocity distributions is discussed. The approach presented in this paper will be theoretically helpful to perform further analysis of the interaction between the plasma and the particles.
Computational Evaluation of Coating Characteristics in Ceramic Spraying
Authors: Sato T. , Solonenko O.P. , Nishiyama H.
Published: July 2022

Numerical simulation of a plasma spraying process from ceramic particle injection to a coating formation was conducted by integrating particle-laden plasma flow, ceramic splat formation and coating formation models. Velocity and temperature of both plasma flow and ceramic particles under an applied RF electromagnetic field were clarified by using the first model. Radial distributions of particle impact location, velocity and temperature were obtained based on both an unsteady effect of a plasma flow and distributions of particle size and injection velocity. Nextly, splat thickness and diameter of melted ceramic particles after impact on a substrate were clarified by using the particle impact velocity and temperature. Radial distributions of splat thickness and diameter became more uniform. Finally, coating thickness distributions were evaluated by using the last model. They were strongly influenced by particle size and injection velocity distributions.
Computational Model for the Prediction of the Temperatures in the Coating During Thermal Spray
Authors: Bao Y. , Zhang T. , Gawne D.T.
Published: July 2022

The temperature of a substrate during thermal spraying may have a significant influence on the quality of coatings, especially for low-temperature materials such as polymers. The temperature must be high enough to thermally activate the interfacial bonding mechanisms but low enough to avoid degradation of the coating material or the substrate surface. It is thus necessary to understand and control the processes governing the temperature of the coating and substrate. However, thermal-spray deposition is a complex, dynamic process and the temperature distribution across the surface and through the thickness of the coating and substrate depends on many parameters. The scanning characteristics, the nature of the spray technique and the substrate dimensions are known qualitatively to influence the temperature profiles but the quantified inter-relationships are inadequately understood. It is difficult to characterize by experimental measurements the shifting patterns of temperature within the substrate because of the innumerable combinations of operating parameters. A computational model is therefore developed in this paper to simulate the temperature patterns during the deposition process. The influence of operating conditions, the spray technique and the dimensions of the substrate are taken into account in the computational model.
Modeling of Thermal Plasma Jets: A Comparison Between PHOENICS and FLUENT
Authors: Bolot R. , Li J. , Coddet C.
Published: July 2022

The modeling of thermal plasma jets is commonly used in order to obtain a better knowledge and understanding of the atmospheric plasma spray process. Many different software products are used in the literature at present but none of them present the same ease in integrating the plasma properties and none of them propose the same options: for example concerning turbulence modeling or concerning the implemented numerical methods. All that may result in differences in the converged solution and in the required computational time. For this reason, two different software products have been tested in the present study, namely the PHOENICS CFD code developed by CHAM (Wimbledon, UK) and the FLUENT CFD code developed by FLUENT Inc (Lebanon, NH, US). The comparisons concern different points such as the possibilities in implementing the plasma gas properties, the way the energy equation is considered, the available turbulence models or the implemented numerical methods. The conclusion indicates that some differences exist in the numerical results obtained using the two CFD packages.
Modelling of Plasma Jet and Particle Behaviour in Spraying Conditions
Authors: Delluc G. , Perrin L. , Ageorges H. , Fauchais P. , Pateyron B.
Published: July 2022

The numerical forecast constitutes an interesting way for plasma spraying to minimize the number of experiments to achieved the optimum spraying conditions. Many computational codes have been developed to predict the properties of the plasma jet (velocity, temperature) and the particles behavior within (temperature, velocity, melting state). According to the particle injection orthogonally to the plasma jet, the models have to be 3D. However, such codes need several hours if not several days of calculations to obtain the results of one condition. This is the main drawback of the existing sophisticated codes. The computing time is not compatible with industrial needs. Various clever numerical methods were developed in the past to simulate 2-D parabolic gas flows for laminar boundary layers or jets. For example, the Genmix 2-D axi-symmetric algorithm developed by Spalding and Patankar, and known as the Bikini method requires a very low-cost memory and computing time. This algorithm makes it possible, when using the proper thermodynamics and transport properties of plasma gases and the whole equation of Boussinesq-Oseen-Basset and taking into account the thermophoresis and non continuity effect for small particle, to predict in a fast and rather realistic way, the velocity and temperature fields of the plasma jet.
Numerical Simulation of Plasma-Sprayed Functionally Graded Coatings
Authors: Lu Wang , Qunbo Fan , Fuchi Wang , Quansheng Wang
Published: July 2022

Based on the mass flux distribution and dispersion rules of molten particles onto the substrate in plasma spraying, the 3-D shape and 2-D composition distribution map of functionally graded coatings are simulated by employing the grid method and Monte Carlo stochastic model. The models simulate the stochastic deposition according to an appointed stochastic operation number, allowing for the calculation of a large number of plasma spraying particles of different materials. In the analysis, the final mass distribution of the calculated coating is consistent with the initial mass flux distribution and reveals the process of coating formation, as well as the potential mechanism of the composition distribution.
Influence of Induction Plasma Gas Composition on Ti Coatings Microstructure and Composition
Authors: Shin D. , Gitzhofer F. , Moreau C.
Published: July 2022

Influence of induction plasma gas composition on Ti coatings microstructure and composition has been studied. Plasma sprayed Ti powder and coatings were prepared by using induction plasma system. Spheroidization of irregular shaped particles was observed in the powder collected after spraying with Ar-air plasma. Microstructures of the coatings were analyzed by a high-resolution scanning electron microscope. Image analysis of the backscattered images of the cross-sectional view of the coatings was used to calculate coating porosities. X-ray diffraction analysis was also performed to identify secondary phases, which have been formed in the coatings during plasma spraying. Partially induced nanostructures were observed in fractured areas in the coatings. The nanostructures were preferentially formed on the surface of splats. X-ray diffraction pattern reveals that a secondary phase has been formed in the coatings during spraying with air vol. at 16 % and 20 % in plasma gas. Changes of the coating density and thermal diffusivity were studied with respect to the formation of secondary phases and induced nanostructures.
Inductively Coupled Plasma Processing of Nano-Sized Calcium Phosphate Powders
Authors: Xu J.L. , Khor K.A. , Gu Y.W. , Cheang P.
Published: July 2022

A novel thermal plasma process, based on inductively coupled plasma torch is employed for producing nano-sized calcium phosphate powders from spray-dried hydroxyapatite (HA) feedstock. The phases during plasma process of HA feedstock under different working conditions have been studied. It is revealed that amorphous calcium phosphate is predominant in the nano-sized powders. HA, α-TCP and CaO are also detected in the nano-sized powders. After heat treatment at 800 °C in air, β-Ca2P2O7 (β-DCP) and HA are found to dominate in the powders. The presence of β-DCP is attributed to the HA feedstock directly decomposed into DCP in the plasma flame, and this phase formed amorphous calcium phosphates region by the rapid quenching process. This region crystallized into β-DCP after heat treatment.
Characterization of Nanostructured and Conventional Cermet Coatings by Controlled Scratch Testing: Correlation with Abrasion and Hardness Tests
Authors: Marple B.R. , Hawthorne H.M. , Xie Y.
Published: July 2022

Controlled scratch testing, dry abrasion tests and hardness measurements were performed on WC-12Co coatings produced by the high velocity oxy-fuel spraying of nanostructured and conventional feedstock powders. The information obtained employing these different evaluation techniques was used to provide insight into coating behaviour and identify the most abrasion-resistant coatings. The results indicated a correlation between scratch hardness and the microhardness determined by Vickers indentation for the coatings. There was good agreement between the scratch test and the abrasion test in identifying the best coatings for use in dry abrasion. Observation of the scratched surfaces and wear scars indicated material removal by splat debonding and fracture. The results demonstrate the usefulness of the scratch test for assessing the abrasion resistance and wear behaviour of coatings.
Comparative Study of Nanostructured and Conventional WC-Co Coatings
Authors: Morks M.F. , Shoeib M.A. , Ibrahim A.
Published: July 2022

Conventional (micron size) and Nanostructured (multimodal) WC-Co powders were sprayed on Al alloys using JP 5000 HVOF system. The coating microstructural characteristics and phase composition were investigated using SEM and XRD. The morphology and microstructure of nano-powders were also analyzed by SEM and XRD. The crystal size of the different phases was also investigated. The results show that nano-structured coatings have additional phases of W2C beside WC phase. Abrasion and hardness resistance of the coatings were also investigated. The results show that the wear and hardness resistance of the nanostructured coating is higher than the Conventional coating.
Nanophase Partially Stabilized Zirconia Intermediate Layer for Strain Accommodation in a Multi-layer Thermal Barrier Coating
Authors: Guru D.N. , Palacio M. , Mook W. , Chambers M. , Heberlein J. , Gerberich W. , Racek O. , Berndt C.C.
Published: July 2022

Applying an environmental barrier coating (EBC) and a thermal barrier coating (TBC) on the next generation gas turbine structural materials such as silicon carbide matrix composites will lead to large stresses due to thermal expansion mismatch; thereby limiting the coating's effectiveness and lifetime. Nanostructured materials possess a large volume fraction of grain boundaries and are conjectured to partially relieve the strain in the coating structure. A Triple Torch Plasma Reactor (TTPR) was used to spray multi-layered TBCs consisting of a mullite EBC deposited either on a silicon carbide or a mullite substrate, a nano-phase partially stabilized zirconia coating (n- PSZ), and a yttria stabilized zirconia coating (YSZ) as the TBC. The nanostructure of the n-PSZ could be maintained during the deposition process. The coatings were heat treated at 1300°C and the change in microstructure and mechanical properties were analyzed using scanning electron microscopy (SEM), micro-indentation and scratch testing applied to the coating cross section. While a change in the microstructure was observed, in particular grain growth, the hardness and elastic modulus appeared to be little affected by the heat treatment giving a preliminary validation of the multilayer concept.
Nano Structured WC-12Co Coatings Sprayed by HVO/AF
Authors: Zha Bailin , Wang Hangong , Su Xunjia
Published: July 2022

A supersonic flame was produced in HVO/AF through the combustion of kerosene and the mixture of oxygen and air. The flame Temperature can be adjusted between 1400 and 2800 °C through changing the flux ratio of oxygen and air in the mixture. Three kinds of nanostructure WC-12Co coatings were sprayed by HVO/AF under three different spray conditions. Experiments results show that the coatings bond well with the substrates with very dense structure. The decarburization reduces with the decrease of flame temperature. Nanostructure coatings were much denser than microstructure coatings with about 0.4 to 0.5 times increase in microhardness.
The Relationship of Work Distortion and Surface Roughness on Grit Blasting Process
Authors: Abukawa S. , Kobayashi K. , Kobayashi Y.
Published: July 2022

In order to utilize the blasting process for preparing surfaces of precision products, the factors affecting the work piece distortion and the degree of the distortion were investigated. The long and flat shaped specimens of the different materials and the thickness were blasted, and the phenomena induced by the blasting were investigated. In the result, almost the linear relationship between the surface roughness and the maximum deflection existed. In addition, the equivalent load was applied to the simple model of the distortion, and the correlative expression among the maximum deflection, the specimen's size, and the equivalent load was deduced. The results made it possible to select and design beforehand the products, and to optimize the blasting condition.
New Developments in the PROTAL Process
Authors: Costil S. , Li H. , Coddet C.
Published: July 2022

To avoid constraints due to the conventional surface preparation before thermal spraying (degreasing and sandblasting), the PROTAL process was developed implementing a Q-switched Nd-YAG laser to prepare the surface simultaneously to the coating build-up. The original system was designed with a single laser head and could meet with some limitations versus the thermal spray plume size, for example in the case of HVOF or twin wire arc spraying. In this work, a device with two laser heads was implemented thus increasing the size of the surface area which is prepared to receive the impinging material droplets. Then, after a presentation of the integration of such laser system in the thermal spray environment, some results will be presented. No significant surface topography modification can be noticed after the laser beam impact, this paper aims at clarifying the bonding mechanisms of thermal spray coatings manufactured implementing the PROTAL process. The case of a metallic coating deposited on a metallic substrate is especially discussed.
Pack Boronizing of HVOF-Sprayed WC-Co Coatings
Authors: Niinobe K. , Watanabe S. , Itakura K. , Sakoda N. , Tajiri T.
Published: July 2022

The effect of pack boronizing on microstructure and hardness of WC-12wt%Co coating sprayed on a low carbon steel (SS400) was studied using two kinds of HVOF-sprayed WC-Co coatings consisting of a single phase of WC and several phases of WC, W2C and Co3W3C, respectively. Pack boronizing was applied at 1273K for 3.6ks under an argon flow atmosphere, using 5%B4C, 5%KBF4 and 90%SiC powders. Microstructures obtained were characterized by X-ray diffraction, SEM and EDX analyzer. After boronizing, WC and CoW2B2 phases were detected in the both sprayed WC-Co coatings. This suggests that not only WC but also W2C and Co3W3C of WC-Co coatings decomposed by boronizing, resulting in the development of CoW2B2. However, many porosities with a size of more than 10µm were formed on the coating consisting of WC, resulting in a low hardness of HV600. On the contrary, the coating with W2C and Co3W3C has little porosity and a high hardness of HV2600.
The Influence of Post Heat Treatment Processes on Thermal Fatigue Resistance of Thermally Sprayed Coatings
Authors: Abdel-Samad Abdou , Lugscheider E. , Bobzin K. , Maes M.
Published: July 2022

Die-casting moulds are subjected to severe conditions of cyclical thermal and mechanical loads, as well as chemical and mechanical wear. Dies mostly fail due to a combination of wear mechanisms. Heat checking, erosion, melt corrosion and soldering often lead to complete die failure. Ceramic plasma-sprayed coatings have a great potential for die protection, since they are chemically inert, and show high form stability at elevated temperatures. Furthermore, they show good resistance against thermal shock due to the porous state of the coated layer and low Young’s modulus. In the present study, the influence of hot isostatic pressing on thermal fatigue resistance of plasma spraying coatings is investigated. Thermal and thermomechanical tests were applied to characterise their ability to protect dies. The coatings were evaluated by residual stress measurements, metallography, hardness test and X-ray diffraction.
Effects of Sealing on Electrochemical Characteristics of WC-NiCr HVOF Sprayed Coatings
Authors: Koga Yoshito , Obata Hiroaki , Noguchi Masahiro , Tarumi Kiyohiro , Ogi Keisaku
Published: July 2022

The effects of resin sealing on WC-NiCr HVOF sprayed coatings were studied using the anodic polarization measurements and the potentiostatic polarization measurements in sulfuric acid aqueous solution. Three types of coatings, without sealing, with sealing applied once and twice were prepared. Regarding the anodic polarization measurements the current densities of the coatings with sealing were less than that of the coating without sealing in the potential range of 0.1 V to 1 V (vs. Ag/AgCl, sat. KCl). According to the potentiostatic polarization measurements the current densities of the coatings with sealing were also less than that of the coating without sealing. Fe was detected in the electrolyte which the coating without sealing was immersed in on the potentiostatic polarization measurements. This meant that the substrate dissolved into the electrolyte because the coatings contain Fe less than 0.13 wt%. In addition, the coating sealed once were compared with that sealed twice. And it became clear that sealing effectively prevents substrates from dissolving and improves corrosion resistance of coating in sulfuric acid aqueous solution, which agreed with the result of salt spraying test.
Strengthening Alumina Protective Layer on MCrAlY Atmospheric Plasma Sprayed Coating by Chromate Processing
Authors: Teratani T. , Suidzu T. , Tani K. , Harada Y.
Published: July 2022

The high temperature oxidation resistance behavior of atmospheric plasma sprayed CoNiCrAlY coating with a thin layer of Cr2O3 employing chromate treatment was investigated. The high-temperature oxidation test was performed at 1423K for 7.2, 14.4 and 32.4ks, respectively. The formation of the oxide layer on the CoNiCrAlY coatings with Cr2O3 thin layer by chromate treatment was compared with that of the non-Cr2O3 thin layer. The oxide layer formed on the both types of MCrAlY coatings grows with increasing the elevated temperature and the holding time. Also, the thickness of the oxide layers was proportional to the square root of time. The thickness of the oxide layer on CoNiCrAlY coatings with the thin layer of Cr2O3 was only 60% as compared with that of the non-Cr2O3 thin layer in high temperature oxidation tests at 1423K.
Effect of Measurement Technique on Particle Temperature and Velocity Values in a Plasma Spray Jet
Authors: Hussary N. , Outcalt D. , Craig J. , Parker R. , Heberlein J.
Published: July 2022

The distributions of spray particle velocity and temperature were determined with two different instruments, the SpectraViz (Stratonics, Laguna Hills, CA) and the DPV2000 (Tecnar Automation, Montreal, Canada). Experiments were performed with three different powders and a Praxair SG 100 plasma spray torch. The instruments differ by the method they use in imaging the jet ultimately allowing for measurements of velocities and temperatures. The average particle temperature values obtained are very close, indicating that different ways of imaging do not influence the measurement value. The values for the average velocities are in good agreement for two of the powders tested (Al2O3 and CrO2), however, for the YSZ powder a consistent difference in velocity values was found. It appears that for obtaining average values e.g. for process control, both instruments are equivalent.
Particle Diagnostics in Wire-Arc Spraying System
Authors: Pourmousa A. , Abedini A. , Mostaghimi J. , Chandra S.
Published: July 2022

Diagnostics of particles produced from Value-Arc 100 twin-wire-arc spraying system was found using DPV2000 monitoring tool. Effect of different operating parameters on the diagnostics of the particles, namely, temperature, velocity, and size distributions, were experimentally studied and discussed. It was found that the particle characteristics are not symmetric about the center line of the plume. It was also found that the divergence angle in the plane parallel to both wires is less than the divergence angle in the symmetry plane of the wires, which is observed in the actual oval-shape coating structure and is explained by the geometry of the system. Size distribution and volumetric size distribution of particles are also analyzed and compared with log-normal distribution function. It is shown that the size distribution consists of two different peaks believed to be associated with anodic and cathodic particles in the process.
Tribological Properties and Microstructure of Plasma Sprayed High Silicon Aluminium Alloy Coatings
Authors: Mori H. , Nakanishi K. , Tachikawa H.
Published: July 2022

Plasma spraying was carried out on aluminium alloy substrates using high silicon aluminium alloy powders (Al- 40Si-Cu-Mg) to improve the wear resistance of the aluminium alloy. The coating exhibits superior more wear resistant to cast A390, and a low friction coefficient ranging from 0.2 to 0.25. The sprayed coating is much higher hardness of HV260 compared with that of cast A390, because of its quenched microstructure with sub-micron size silicon particles. The coating hardness does not decrease as annealing temperature up to 573 K, above 573 K it decreases rapidly. This drop in coating hardness is related to the coarsening of silicon particles and thus expanded interparticle distance. The wear resistance of coatings after annealing is inferior to that of sprayed coating. This is attributed to decrease in hardness value and coarsening of the microstructure. After annealing, the friction coefficient of the coatings shows a remarkable increase with increasing sliding distance. Since the plasma sprayed coating is in a non-equilibrium state, it maintains low friction coefficient even with a long sliding distance. Therefore, improvement in tribological properties is considered here to be due to change in wear mechanism brought by the formation of film-like layer, which prevents coating surface from adhering to iron.
Abrasion Behavior of Nanostructured and Conventional Titania Coatings Thermally Sprayed via APS, VPS and HVOF
Authors: Lima R.S. , Leblanc L. , Marple B.R.
Published: July 2022

Nanostructured and conventional titania feedstocks were thermally sprayed using APS, VPS and HVOF techniques to study the effects of processing, microstructure and properties on the abrasion behavior. The in-flight characteristics (temperature and velocity) of the APS and HVOF-sprayed particles were also investigated. For the nanostructured coatings, a process map was developed relating the in-flight particle characteristics during coating deposition to the abrasion resistance. This map showed that the particle velocity and particle temperature had an important influence on the volume loss in abrasion tests. Coatings were characterized using SEM to investigate the microstructural features, image analysis to measure coating porosity and Vickers indentation to determine hardness. The abrasion behavior of the coatings was evaluated using the ASTM standard dry sand/rubber wheel test. The abrasion results indicated that the VPS and HVOF-sprayed nanostructured titania coatings exhibited the highest abrasion resistance among the 14 coatings studied.
Abrasion and Erosion Behavior of WC and CrC Cermet Coatings
Authors: Legoux J.G. , Bouaricha S. , Marcoux P.
Published: July 2022

The abrasion and erosion resistance of six different coatings were evaluated in relation to their microstructure. The coatings were produced from six different powders: four containing WC and two containing CrC. Microstructural analysis highlights the relationship between the starting powder morphology and chemistry and the spray conditions in the development of the final coating microstructure. The wear performance of the coatings was evaluated according to the ASTM G-65 standard for the abrasion resistance and a slurry containing 0.66% of 180 μm alumina particles flowing at 20 m/s for wet erosion resistance. The results show that for all tested coatings the abrasion wear resistance is mostly governed by the hardness distribution. For the chrome carbide, coatings having the lowest hardness are the lest abrasion resistant. For the WC containing coatings, carbide debonding and pullout is the main wear mechanisms. The most resistant material being the WC-6Co-8Cr. All the coatings performed better than the D2 tool steel reference sample. The erosion wear resistance is controlled by the local hardness, the matrix properties and the droplet debonding. The most wear-resistant materials are the WC-Co-Cr cermets. The least wear-resistant materials are the clad CrC-20(NiCr) and the WC-Ni cermets.
The Microstructure and Tribology Behavior of NiTiZrSiSn Bulk Amorphous HVOF Coating
Authors: Lee Sangyong , Choi Hanshin , Yoon Sanghoon , Lee Changhee
Published: July 2022

A bulk amorphous NiTiZrSiSn produced using an inert gas atomization was sprayed onto the Cu substrate. As the oxygen to hydrogen gas fraction was increased, oxide phase fraction was increased at the expenditure of amorphous phase fraction. The phase evolution was mainly due to the in-flight particle oxidation according to flame gas composition. Tribological behaviors were investigated in view of friction coefficient and weight loss by a pin-on-disc dry sliding test. Both friction coefficient and weight loss were largely dependent on the phase composition of the coating. As the amorphous phase fraction was increased, the friction coefficient was decreased with the increase of the transfer film formation. On the other hands, major weight loss mechanism was changed from transfer film formation to pull-out of coat material as the amorphous phase fraction was decreased.
Properties of HVOF Sprayed Multi-Scale Polymer/Silica Nanocomposite Coatings
Authors: Twardowski T. , Bhargava V. , Knight R.
Published: July 2022

The high velocity oxy-fuel (HVOF) combustion spray technique previously has been shown to be an excellent solution for depositing nano-reinforced thermoplastic polymer coatings. Dense polymer coatings can be produced regardless of ceramic particle size with little change in the spray parameters. Composite powders with multiple scales of silica reinforcement, ranging from 12 nm to 100 µm, have been created. Preliminary testing was begun using melt processing. The multiple scales have shown improved scratch resistance relative to single-scale reinforcements.
Delamination Crack Growth in Thermal Barrier Coatings
Authors: Brodin H. , Li X.H.
Published: July 2022

Thermal barrier coatings (TBC) in general fail by delamination of the ceramic partially stabilised Zirconia (PSZ) top coat (TC) from the underlying metallic bond coat (BC). The process is initiated by crack initiation and growth either in the TC or in the thermally grown oxide (TGO) that will form at the interface between top and bond coat. The aim of the present paper is to describe the degradation due to crack growth in such a way that data can be used for FEM modelling work. Flat rectangular test coupons have been subjected to thermal cyclic fatigue (TCF) in air with a temperature range from 100°C to 1100°C. Identical samples were removed from the TCF furnace at different times of thermal cycling in order to achieve material with different degree of damage. After mounting, cutting and sectioning the specimen were investigated by light optical microscopy (LOM) and scanning electron microscopy (SEM) together with an energy dispersive spectrometer (EDS). Image analysis of LOM micrographs was used for measurement of crack distribution and degree of TC damage. A method for crack growth measurement based on the degree of TC / TGO damage has been developed. Furthermore, a measure of TBC damage as a function of elapsed fatigue cycles was introduced. The TBC material shows a mixed black and white fracture surface after TCF cycling. Delamination crack growth data are presented. Delaminated TC/BC interface surface as a function of fatigue cycles follows an S-curve behaviour.
Performance of Thermal Barior Coatings Formed by Gas Tunnel Type Plasma Spraying
Authors: Kobayashi Akira
Published: July 2022

Zirconia (ZrO2) coating formed by plasma spray method is widely used industrially as a thermal barrier coating (TBC). But it has still problems such as spallation and cracks inside the coating. The solution will be given by the development of new spaying processing. The zirconia-alumina (ZrO2-Al2O3) composite coating formed by gas tunnel type plasma spraying has a high hardness layer at the surface side of the coating, which shows the graded functionality of hardness, and is superior as a TBC. In this paper, the performance of such high hardness ZrO2- Al2O3 composite coating was investigated and the merit as TBC was clarified. The Vickers hardness of the high hardness layer near the coating surface increased by the thermal process of high energy plasma, which corresponded to the result that the coating became denser. Also, the effect of alumina mixing was discussed about the microstructure of this composite coating. The combination of high hardness of Al2O3 with the low thermal conductivity of ZrO2 resulted to the development of high performance TBC. The thermal conductivity of such ZrO2- Al2O3 composite coatings was proved to be much smaller than that in the longitudinal direction. Moreover the adhesive strength of such high hardness zirconia composite coatings was investigated as well as its mechanical properties. The adhesive strength of such high hardness coatings to the substrate was weakened as the increase in the coating thickness.
Intrinsic Properties of Thermal Sprayed Single Splats on Substrates
Authors: Li Li , Gouldstone Andrew , Sampath Sanjay
Published: July 2022

Splats are the building blocks of thermal sprayed coatings, and thus the mechanical properties of such coatings are directly related to splat behavior. Elastic and elastoplastic properties of coatings have been measured on the macro-scale, but are not yet quantitatively predictable using process parameters as inputs. Coating mechanical properties represent contributions from intrinsic splat properties, splat-splat interfaces, and other microscopic defects. In this study, we investigated the intrinsic properties of Ni and Ni based alloy splats on substrates, for a variety of process methods and input parameters. Residual stresses were measured via X-ray microdiffraction and elastic and elastoplastic properties were studied via nano-indentation. From a purely scientific standpoint, splat studies provide insight into rapidly cooled small-volume structures that often exhibit extra ultrafine- or nano-crystalline structure. Thus, accordingly, nano-indentation response was also compared to the prediction for bulk counterparts of the splat materials.