bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the Stand-Off Distance and Spray Angle on the Coating Formation and Properties During Three-Cathode Plasma Spraying
Authors: Bobzin K. , Zhao L. , Öte M. , Königstein T. , Oechsner M. , Siebers M. , Andersohn G. , Ellermeier J.
Published: November 2022

Three-cathode plasma spraying is characterized by high process robustness in terms of particle in-flight properties due to high stability of plasma jet. However, during coating parts with complex geometries, process parameters such as stand-off distance and spray angle usually cannot be kept at optimized conditions. In this study, the process robustness during three-cathode plasma spraying of a novel FeCrMnBC alloy was investigated by varying stand-off distance and spray angle to simulate spray conditions for complex geometries. A three-cathode plasma generator TriplexProTM-210 was used to spray FeCrMnBC powder with a fraction of -45 +20 µm onto substrates of cast iron EN-GJL-250. The stand-off distance and the spray angle were varied from d=90 mm to d=110 mm and between ø=90° and ø=60°, respectively, while the other process parameters were kept constant. The results revealed that the reduction of spray angle caused an about 15 % decrease of coating thickness, about 40 % porosity increase and about 15% increase of bond strength. In contrast, the variation of stand-off distance changed only insignificantly the coating thickness, porosity and bond strength. The variation of stand-off distance and spray angle did not result in significant changes in the coating microhardness. The reduction of spray angle resulted in significant worsening of the corrosion protection ability of the coating system.
Effect of Nozzle-Length, Powder Feed-Rate and Spray Distance on HIPOJET 2700 HVOF Sprayed Cr3C2-NiCr Coatings
Authors: Matthews S. , Woo J. , Daniel J.
Published: November 2022

The high wear resistance of Cr3C2-NiCr coatings is reliant on the formation of a dense coating containing a high percentage of carbide grains, with minimal carbide degradation. Such coating characteristics are typically achieved through the use of high velocity oxygen fuel (HVOF) spraying. The propane fuelled, manually operated HIPOJET 2700 HVOF system is one of a suite of smaller sized commercial HVOF systems recommended for smaller job shops. However, few works have characterised the properties of carbide composite coatings produced with this system. In this work a full factorial design of experiment analysis was used to assess the effect of key operating parameters on the quality of Cr3C2-NiCr coatings. The combustion parameters (fuel and oxygen flows) were fixed at the manufacturers recommended settings in order to focus on the effect of nozzle length, powder feed rate and, spray distance. The effect of these variables on the porosity/oxide content, carbide content, microhardness, coating thickness, and relative deposit efficiency is discussed.
An Experimental Approach to Gain Insight Into Cold Gas Spraying of Ceramics
Authors: Gutzmann H. , Irkhin I. , Gärtner F. , Klassen T.
Published: November 2022

In this study, an experimental approach to investigate basic dependencies on impact and bonding of agglomerated ceramic particles in cold spraying is presented. Single impact morphologies of ceramic particles obtained from wipe tests are correlated with data obtained from powder compression experiments with a modified nanoindenter. Different feedstock powders of agglomerated TiO2-nanoparticles were used and also partially heat treated. The powder shapes and sizes prior and after the compression tests were analyzed by confocal microscopy. The single particle impacts were characterized by SEM. Besides the expected influence of substrate material, substrate temperature, and spray conditions, the deformation and bonding of ceramic particles to metal substrates critically depend on the powder properties. To which degree particles fracture or contribute to layer formation upon the high-energy impact is highly correlated to their individual deformation behaviour in quasi-static compression tests.
Spray Pattern and Microstructure of Copper Coatings with the Optimized Rectangular Cross-Section Nozzle by the Computational Fluid Dynamics (CFD) in High-Pressure Cold Spraying
Authors: Sakaki K. , Arai S.
Published: November 2022

In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. There is a rectangular and a circular cross-sectional shapes on the cold spray nozzle. It has been reported that the rectangular nozzle provide a more uniform particle velocity across the exit of the nozzle. The circular exit nozzle is parabolic in shape. So spray pattern with the rectangular nozzle is wider than that with the circular spray nozzle. The goal of this investigation is to establish a design for the cold spray gun nozzle in order to gain more uniform spray profile of coatings. We have investigated the influence of expansion ratio, nozzle total length and the ratio of nozzle length of divergent section and parallel section of rectangular nozzle on behaviours of gas and particle by the computational fluid dynamics (CFD) in high pressure cold spraying. In this study, the spray pattern and microstructure of copper coatings with the rectangular cross-section nozzle optimized by CFD analysis in high-pressure cold spraying are reported. The optimized rectangular nozzle provide a more uniform spray profile of coatings. Relatively finer powder tended to deposit on the end of the coating.
Energy Efficient Production of Thermally Sprayed Coatings Through the Use of Modified Twin Wire Arc Spraying Processes – Final Results of a Bavarian Research Foundation Funded Project
Authors: Atzberger A. , Hartz-Behrend K. , Schein J. , Steiner E. , Blau L. , Mayr W. , Szulc M. , Zierhut J. , Krömmer W. , Lang F. , Aumiller M. , Abler E.
Published: November 2022

The main goal of the project was to investigate the influence of different gas properties, in combination with different spraying parameters, on the wire arc spraying process. For this purpose, investigations with several gas compositions (pure nitrogen as well as nitrogen combined with hydrogen or ethene – compared to compressed air) have been carried out for different spraying materials which are currently being used in today’s industries, such as copper, carbon (St0.8) and stainless steels (316L). The preheating of the process gas as well as the variation of the gas pressure up to 1,400 kPa (14 bar) were also subject to research. The resulting coating properties have been analyzed in terms of oxide content, porosity and hardness as well as deposition efficiency and adhesive tensile strength. Additionally, in order to enhance the process stability, a system to detect the cause of cold shuts has been developed.
The Effect of Molybdenum Substrate Oxidation on Splat Formation
Authors: Wang J. , Li C.
Published: November 2022

Disk splats are usually observed when the deposition temperature exceeds the transition temperature, whereas thick oxide layer will reduce the adhesion resulting from high deposition temperature. In present study, single molybdenum splats were sprayed onto polished molybdenum substrates with different preheating processes to clarify the effect of surface oxidation on the splat formation. Three preheating processes included heating the substrate to 350 °C, 550 °C, and cooling the substrate from 550 °C to 350 °C, which were performed in argon atmosphere. The chemistry and compositions of substrate surface was examined by XPS. The cross sections of splats were prepared by focus-ion-beam (FIB), and then characterized by SEM. Nearly disc-shaped splat with small fingers in the periphery was observed on the substrate preheated to 350 °C. Perfect disc-shape splat was deposited at 550 °C. Flower-shaped splat exhibited a central core and discrete periphery detached by some voids on the substrate preheated to 350 °C (cooling down from 550 °C). The results of peeling off splats by carbon tape and morphology of FIB sampled cross-sections indicated that no effective bonding formed in the splat-substrate interface for the substrate ever heated to 550 °C, due to the increasing content of MoO3 on preheated molybdenum surface.
Characterization of Aluminum Based Coatings Deposited by Very Low Pressure Plasma Spray
Authors: Fan X. , Planche M.-P. , Darut G. , Kang N. , Montavon G.
Published: November 2022

The objective of this research is to investigate the changes of the microstructure and mechanical property of aluminum based coatings manufactured by VLPPS along the radial directions of the plasma plume. Aluminum powders were sprayed with a F4-VB low-power plasma gun under a working pressure of 150 Pa. Coatings deposition is studied at different distances from the plasma plume impact. Front of the plasma plume, in-situ reactions between aluminum and substrate elements (such as Fe, Cr, Ni) present in the base metal take places. It mainly forms aluminum based intermetallic Al3Fe coating according to the XRD. Based on the SEM observation, the packed columnar microstructure mixed with nanometer particles is formed with a majority of pure vapor condensation due to evaporated particles from the plasma jet and/or aluminum coating already made. For different distances relative to the center of plasma plume (i.e. from 10 mm to 110 mm along the radial directions), the deposited coatings exhibit a lamellar binary structure which was formed by the mixed deposition of vapor and molten droplets. The coatings morphologies vary from nearly dense to loose and highly porous. Finally, the hardness of typical coating is investigated. The Al based intermetallic AlxFey coating, on the center of the plasma plume, reached 448HV0.025, which is much higher than those obtained at other positions.
Open FOAM Modelling of Particle Heating and Acceleration in Cold Spraying
Authors: Leitz K.-H. , O’Sullivan M. , Plankensteiner A. , Kestler H. , Sigl L. S.
Published: November 2022

In cold spraying a powder material is accelerated and heated in the gas flow of a supersonic nozzle to velocities and temperatures that are sufficient to obtain cohesion of the particles to a substrate due to plastic deformation. The deposition efficiency of the powder particles is significantly determined by their velocity and temperature. The particle velocity correlates with the kinetic energy of the particles and thereby with the amount of energy that is converted to plastic deformation and thermal heating. The initial particle temperature significantly influences the mechanical properties of the particle. Velocity and temperature of the particles have nonlinear dependence on the pressure and temperature of the gas at the nozzle entrance. Whereas the particle velocity can easily be measured during the process, the particle temperature is not directly accessible by experimental techniques. Generally information about the particle temperature can be obtained based on theoretical models. In this contribution a simulation model based on the reactingParcelFoam solver of OpenFOAM is presented and applied for an analysis of the cold spray process. The model combines a compressible description of the gas flow in the nozzle with a Lagrangian particle tracking. The predictions of the simulation model are verified based on an analytical description of the gas flow, the particle acceleration and heating in the nozzle. Based on experimental data the drag model according to Plessis and Masliyah is identified to be best suited for OpenFOAM modelling particle heating and acceleration in cold spraying.
The High Temperature Wear and Oxidation Behavior of CrC-Based HVOF Coatings
Authors: Houdková Š. , Česánek Z. , Smazalová E.
Published: November 2022

The 3 commercially available CrC-based powders with different kind of matrix (Cr3C2-25%NiCr; Cr3C2- 25%CoNiCrAlY and Cr3C2-50%NiCrMoNb) were deposited by HVOF JP-5000 spraying gun, evaluated and compared. The sliding wear resistance, measured at room and elevated (T=600°C) temperature according to ASTM G-133, the influence of heat treatment on the microstructure and properties, as well as the oxidation resistance in hot steam environment (p=24 MPa; T=610°C) were evaluated with respect to their potential application in steam power industry. The surface oxidation and microstructure changes were evaluated by SEM and XRD. The NiCr matrix proved to provide high oxidation and sliding wear resistance of the coating regardless volume content. On the contrary, the Cr3C2-25%CoNiCrAlY coating was subjected to massive oxidation of carbide particles. The low cohesive strength and high porosity of Cr3C2-25%CoNiCrAlY was identified responsible for its poor oxidation resistance in hot steam environment. The sliding wear resistance was found comparable at room temperature, regardless the matrix composition and content, while at elevated temperatures, the higher volume content of matrix led to higher wear of coating material.
Effect of Carbide Dissolution in the Metal Matrix of HVOF and HVAF Sprayed Cr3C2-NiCrMoNb Coatings on the Initial Stage of Chlorine High Temperature Corrosion
Authors: Fantozzi D. , Matikainen V. , Uusitalo M. , Koivuluoto H. , Vuoristo P.
Published: November 2022

Highly corrosion and wear resistant thermally sprayed chromium carbide (Cr3C2) based cermets coatings are nowadays a potential highly durable solution to allow traditional fluidised bed combustors (FBC) to be operated with ecological waste and biomass fuels. However, the heat input of thermal spraying processes causes carbide dissolution in the metal binder. This alters the coating structure and forms carbon saturated amorphous and nanocrystalline metastable areas, which can affect the behaviour of the materials under the corrosive chlorides containing environment of the flue gases. This study analyses the effect of carbide dissolution in the metal matrix of MMC coatings and its effect on the onset of chlorine induced high temperature corrosion. Four Cr3C2-NiCrMoNb coatings were thermally sprayed with high-velocity air-fuel (HVAF) and high-velocity oxygen-fuel (HVOF) spray processes in order to obtain microstructures with increasing amount of carbide dissolution in the metal matrix. The specimens were heat treated in an inert argon atmosphere at 700°C for 5 hours to induce secondary carbide precipitation. As-sprayed and heat-treated self-standing coatings were covered with KCl and their corrosion resistance was investigated with thermogravimetric analysis (TGA) at 550°C for 4 hours. High carbon dissolution in the metal matrix appeared to be a detrimental factor in the initial stage of corrosion. The microstructural changes induced by the heat treatment hindered the corrosion onset in the coatings. Moreover, an optimal amount of oxides and melting degree seemed beneficial.
Comparative Study of the Corrosion and Cavitation Resistance of HVOF and HVAF FeCrMnSiNi and FeCrMnSiB Coatings
Authors: Silveira L. L. , Pukasiewicz A. G. M. , Björklund S. , Nylén P. , Zara A. J.
Published: November 2022

Cavitation and corrosion on hydrodynamic components and systems reduces the operational efficiency. The use of wear resistant coatings have been studied as a solution to the problem of corrosion and cavitation in the industrial environment. Thermal spray processes are recognized as excellent technique to deposit coatings. The high velocity oxy-fuel process (HVOF) can produce high density and bond strength coatings. High velocity air-fuel process (HVAF) is an alternative process, shown to be superior regarding corrosion protection and production costs. HVAF can deposit coating with shorter dwell time and lower temperature, producing coating with lower oxide content. This paper presents the use of HVOF and HVAF process to deposit FeCrMnSiNi and FeCrMnSiB coatings, studying the resistance against corrosion and cavitation in comparison to 316L HVOF coating. Microstructure was analyzed by XRD, microscopic means and mechanical testing. Cavitation and corrosion behavior of the coatings were also studied comparatively. HVAF coatings presented lower porosity and oxide levels, as well as higher hardness values, compared with the coatings deposited by HVOF process. The HVAF process presented better cavitation resistance than HVOF coatings. The FeCrMnSiNi HVAF coating had the best corrosion protection performance between the developed alloys.
Large Size Fe-Based Bulk Metallic Glass Composite Prepared by Additive Manufacturing via HVOF Thermal Spraying
Authors: Wang W. , Zhang C. , Liu L.
Published: November 2022

Bulk metallic glasses (BMGs) are a novel class of metallic materials with disordering atomic structure and excellent mechanical and chemical properties, and are promising for various industry applications. BMGs are usually fabricated by copper-mould casting due to the requirement of fast cooling rate for the obtainment of amorphous structure. However, this casting approach has the limitation for preparation of large size samples (the biggest Fe-based BMG obtained so far is less than 16 mm diameter). In this work, the conventional high velocity oxy-fuel (HVOF) thermal spraying technique was utilized as a novel additive manufacturing route to create large size Fe-based BMGs and BMG composites. It will be reported that a large size of 20x20x20mm BMG (Fe48Mo14Cr15Y2C15B6 (at%) ) and big plate of 100×100×5 mm of Fe-based BMG composites reinforced with 50vol% 316L stainless steel powders was successfully prepared by HVOF thermal spraying. Both BMG and BMG composite showed very dense structure (porosity less than 0.4% ) and good mechanical properties, Especially, BMG composite reinforced with 316 L stainless steel exhibited a yield strength of 1.8 GPa and compressive plastic strain of 2%. More importantly, this Fe-based BMG composite exhibited good toughness of KJ=21 MPa m1/2, which is almost 4-times higher than that of as-cast BMG. This present work indicates that HVOF thermal spray can become a versatile technique for preparation of large size of bulk metallic glasses and composites with desired properties.
On the Validity of Continuum Computational Fluid Dynamics Approach in Very Low Pressure Plasma Spray Conditions
Authors: Ivchenko D. , Zhang T. , Mariaux G. , Vardelle A. , Goutier S. , Itina T.
Published: November 2022

Plasma Spray Physical Vapor Deposition aims to substantially evaporate a powder in order to produce coatings with microstructures ranging from lamellar to columnar. This is achieved by the deposition of fine melted powder particles and nanoclusters and/or vapor condensation. The deposition process typically operates at pressure ranging between 10 and 200 Pa. In addition to experimental works, numerical works help to better understand the process and optimize the experimental conditions. However, the combination of high temperature and low pressure with the appearance of shock waves resulting from the supersonic expansion of the hot gas in the low pressure medium, makes questionable the suitability of the continuum approach for modelling such a process. This work deals with the study of (i) the effect of the pressure dependence of the thermodynamic and transport properties on the CFD predictions and (ii) the validity of the continuum approach for thermal plasma flow simulation under very low pressure conditions. It compares the flow fields predicted with a continuum approach (ANSYS Fluent CFD code) and a kinetic-based approach using a Direct Simulation Monte Carlo method (DSMC, SPARTA code). It also shows how presence of flow gradients can contribute to the errors in the results for typical PS-PVD conditions.
Cold Spraying of WC-Co-Ni Coatings Using Porous WC-17Co Powders
Authors: Yin S. , Lupton T. , Meyer M. , Lupoi R. , Ekoi E. , Dowling D.
Published: November 2022

Cold spray has been successfully used to produce WC-Co coatings in recent years, showing great potential. However, due to the lack of sufficient Co matrix phase for plastic deformation, the fabrication of cold sprayed WC-Co coating naturally requires expensive propulsive gas or very high working parameters, significantly increasing the manufacturing difficulty and cost. This paper aims to use conventional high pressure cold spray to fabricate high-performance and cost-effective WC-Co-Ni coatings, and to clarify its formation mechanism. To achieve this objective, mechanically mixed porous WC-17Co and dense Ni powders were selected as the feedstock with different WC mass fraction, F1 (41.5 wt.%), F2 (64.5 wt.%) and F3 (74.7 wt.%). Working parameters were set at a moderate level (nitrogen, 3.0MPa and 350°C) to control the experimental cost. Experimental results showed that WC reinforcements had no phase transformation and were completely retained in the WC-Co-Ni coatings. The highest WC mass fraction was present in the F3 coating, reaching approximately 75% (equivalent to the feedstock), quite close to the cold sprayed WC-25Co coating. Fracture of WC-Co particles during the deposition process was found to be the reason for such high WC retainability, dominating the coating formation mechanism.
Fatigue Strength of Mg Alloy Coated with Al Coatings via In-Situ Shot-Peening Assisted Cold Spray
Authors: Wei Y. , Luo X. , Li C. , Li C.
Published: November 2022

In this study, pure Al coatings were deposited on ZK60-T5 Mg alloy substrates via in-situ shot-peening assisted cold spray in order to study the effect of the Al coating on fatigue behavior of coated samples. Fatigue behavior of the coated and un-coated samples has been investigated through experimental tests. The size and shape distribution of powders, microstructural characteristics of coatings and fractography of fatigue test samples have been studied using scanning electron microscopy. The average microhardness of pure Al coating is higher than 70 HV50. In order to obtain the fatigue S-N diagram for each set, coated and un-coated samples have been tested in a load-controlled condition. The tension-compression fatigue experiments reveal that the fatigue property of ZK60-T5 alloy coated with pure Al coatings has significantly deteriorated compared with un-coated samples.
Coupled Thermo-Mechanical Analysis of the Ceramic Thermal Barrier Coatings
Authors: Kokot G. , Jasik A. , Moskal G. , Białecki R. , Adamczyk W. , Kruczek T.
Published: November 2022

The paper is devoted to thermal and thermo-mechanical analysis of the plasma sprayed thermal barrier coatings (TBC). The temperature and stress distribution using the finite element method in the microscopic scale is presented. The finite element model is based on the microscopy scan (dimension 5mmx3.5mm) and represent three levels of barrier structure: basement AMS 5599,undercoat NiCrAlY and ceramic layers of ZrO2×8Y2O3, Gd2Zr2O7 and DCL (double ceramic layer) Gd2Zr2O7/ZrO2×8Y2O3 type. The layers material properties are fully temperature dependent and coupled thermo-mechanical analysis is performed. The numerical results will be compared with the experimental one.
An Investigation of the Corrosion and Cavitation Resistance of Different Thermally Sprayed Coatings in River and Marine Environments
Authors: Fedorova M. , Baldaev L. , Baldaev S. , Baldaev N. , Akhmetgareeva A. , Martyanova V.
Published: November 2022

To evaluate the corrosion resistance of various coatings applied by the flame spraying method, and to compare their protective properties in sweet- and sea-water samples with seven types of coatings were made, one of them is paint, used to coat ship’s bottom. SEM, Neutral spray salt, according to ASTM B117, erosion-corrosion (E-C) tests in sweet- and sea-water were carried out. The test results showed that coatings based on zinc alloys and polymer are much more effective than standard epoxy coatings and can be compared with expensive zinc-filled paints, because the latter require frequent repairs and repainting. Moreover, the developed coatings are supposed to protect against fouling. At the moment, the fouling tests are continuing.
A Review of Utilization of Niobium and Tantalum for the Enhancement in Corrosion Resistance and Biocompatibility of Bio-Implants
Authors: Singh G. , Singh Sidhu B. , Singh B.
Published: November 2022

A bio-implant is a medical device used to support, replace or enhance a biological structure. Bio-implants have incalculable importance for mankind due to their crucial applications in situations like heart diseases, joint replacements, bone fixation and bone replacements etc. The materials which are used to manufacture bio-implants are generally called biomaterials. Corrosion and biocompatibility of biomaterials are the two issues, which are needed to be addressed to enhance the life span of the bio-implants. Various strategies were used to enhance the performance of biomaterials; however surface modification and alloying are the two main strategies among them. To employ these two strategies; various ceramic, metallic and composite materials were utilized as coatings and alloying elements with different biomaterials. Among all these materials, Niobium and Tantalum metals are studied by various researchers and proved to improve the corrosion resistance as well as biocompatibility of the bioimplants. This article gives a systematic overview of research work carried out in the area of bio-implants by utilizing Niobium and Tantalum for the enhancement of corrosion resistance and biocompatibility.
Plasma Processing of AB2 Alloy as Negative Electrode Material for NiMH Batteries
Authors: Onur Şahin E. , Eyovge C. , Öztürk T.
Published: November 2022

The present work deals with a Laves phase C14 AB2 alloy, namely (TiZr)(VNiMnCrSn)2. The alloy in many ways is a good alternative to a rare earth AB5 alloy with a superior capacity reaching a value of 400 mAh/g. A drawback with this alloy is that it is difficult to activate and therefore it is desirable to develop processing techniques which would readily activate the alloy. In this study we have plasma processed the alloy so as to see if this processing would exercise a positive effect on activation. AB2 powder was therefore fed to plasma torch with 25 kW power. The powders of -325 mesh had a range of particles sizes, the finer ones were evaporated and condensed into nanoparticles less than 100 nm in size. The larger ones spheroidized and were collected in the form of two groups of powders. We have characterized all three groups of powders both chemically and the latter two in terms of electrochemical performance.
Microstructural and Mechanical Investigations of Dissimilar Metal Joints of T91 and T22 Ferritic Steels
Authors: Mittal R. , Singh Sidhu B.
Published: November 2022

Ferritic steels are commissioned as one of the preferred structure materials for the boilers of nuclear and thermal power plants. The mechanical characterization and microstructural evolution of shielded metal arc welded dissimilar joint between ferritic SA213T91 (T91) and ferritic SA213T22 (T22) steels has been investigated by virtue of microstructures, micro-hardness, XRD and SEM/EDS analysis. Comparative performance of distinctive zones in the weldment i.e. heat affected zone, base metal and weld pool has been explored. The T91 HAZ and T22 HAZ zones of the weldment are observed to have high micro-hardness by virtue of martensitic morphology along with the presence of delta ferrite in T91 HAZ and carbide as well as intermetallics in T22 HAZ.
The Effect of Splats Morphology and Post-Treatment on the Microstructure of Sprayed Coating
Authors: Pakseresht A. , Shahbazkhan A.
Published: November 2022

In the thermal spray process, particulate materials can be melted by plasma atmosphere due to its high local temperature from 8700 °C to 15,000 °C. Therefore, the material powders turn into droplets after being melted by injection into the hot flame. Molten droplets are accelerated toward a substrate and form the splats which quickly solidify; finally, the film is formed by pile-up splats. Splat morphology and post treatment can determine the microstructure, mechanical and physical properties of the coating. In this study, BaTiO3 films were deposited onto a mirror polished stainless steel substrates kept at room temperature and 500 °C. At the elevated temperatures, the desorption of adsorbates and condensate at the substrate surface are the most important factor which change the morphology of the splats, from irregular- splash morphology to disk-like shape. Splat morphology can determine deposit microstructure and improve the coating properties. The morphology of individual splats and the post treated films were studied using scanning electron microscopy. Results indicated that the porosity in the film produced at room temperature was higher than that in the film deposited on the heated substrates. Also, post heat treatment can improve coating properties
Influence of Bondcoat Surface Characteristics on Lifetime in Suspension Plasma Sprayed Thermal Barrier Coatings
Authors: Gupta M. , Markocsan N. , Li X.-H. , Kjellman B.
Published: November 2022

Development of TBCs allowing higher combustion temperatures in gas turbines is of high commercial interest since it results in higher fuel efficiency and lower emissions. It is well known that TBCs produced by suspension plasma spraying (SPS) have lower thermal conductivity as compared to conventional systems due to their very fine porous microstructure. Moreover, columnar structured SPS TBCs are significantly cheaper to produce as compared to the conventionally used electron beam – physical vapour deposition (EB-PVD). However, SPS TBCs have not yet been commercialised due to low reliability and life expectancy of the coatings. Lifetime of a TBC system is significantly dependent on topcoat-bondcoat interface topography. The objective of this work was to study the effect of topcoat-bondcoat interface in SPS TBCs by changing bondcoat spray parameters and bondcoat surface heat treatment. High velocity air fuel (HVAF) spraying was used for bondcoat deposition while axial-SPS was used for topcoat deposition. Same topcoat spray parameters were used for all samples. Lifetime was examined by thermal cyclic fatigue and thermal shock testing. The influence of surface roughness on lifetime has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition to achieve long lifetime SPS TBCs.
Investigation of Interfacial Microstructures between LZ Splats and YSZ Substrate by HR-TEM
Authors: Chen L. , Yang G.-J. , Li C.-X.
Published: November 2022

Thermally-sprayed LZ/YSZ double-layer coatings are promising candidate for the next generation thermal barrier coatings (TBCs) due to exceedingly low thermal conductivity and superior high-temperature phase stability. However, a delamination failure at LZ and YSZ interface were widely observed during TBCs service. Till today, the interfacial microstructure between LZ and YSZ remains unclear. In the present study, LZ splats were deposited on YSZ substrate to serve as a LZ/YSZ interface. The interfacial microstructure was explored by focused ion beam (FIB) and high-resolution transmission electron microscope (HR-TEM). The interfacial defects at splat interface were clearly observed and thoroughly discussed. These results would shed light on deeply understanding the interfacial failure of double-layer LZ/YSZ coatings.
Comparison of Oxidation Resistance and TGO Zone Morphology of NiCrAlY Plasma Sprayed Coating and Sintered Alloy
Authors: Niemiec D. , Moskal G. , Białecki R. , Adamczyk W. , Kruczek T. , Szymański K.
Published: November 2022

The basic aim of presented article is related with comparison of internal morphology of atmospheric plasma sprayed NiCrAlY coating and sintered alloy obtained from the same feedstock powder. This part of investigations consisted characterization of phases composition and internal morphology characterization by SEM/EDS method. The second level of this comparing process is characterization of oxidation process in both cases. In order to properly perform these tests the top surfaces of sintered sample was sand blasted to the roughness level adequate to surface condition after plasma spraying process. The oxidation tests were performed at temperature 1000 and 1100°C during the time to 1000h of exposure in air. The specimens after determined intervals were moving out from the furnace and characterized by visual inspection of top surface as well as by SEM/EDS method and XRD analysis to characterization of phases generated during oxidation. The special emphasis was on the characterization of TGO zone on cross sectioned samples where detailed assessment of oxides zone morphology was made by SEM/EDS method. The oxide thickness was measured as well with dividing of overall oxides zone thickness on the sublayers related with alumina and spinels formation.
The Influence of Deposition Temperature and Thermal Conductivity of the Substrate on Splat Formation
Authors: Wang J. , Li C.-J.
Published: November 2022

Ni20Cr splats were sprayed onto polished substrates at different preheating temperatures in an argon atmosphere by Low Pressure Plasma Spray to reveal the dominating factor on the effective interface bonding formation. The splat morphology, microstructure and splat-substrate interface bonding were characterized by SEM and EBSD. The interface for examination of typical splats was prepared by FIB. Disk splats were obtained on AISI 304 stainless steel substrates preheated to temperatures of 100 °C (cooling from 350 °C), 350 and 550 °C. Moreover, typical distinct two-zone microstructure feature was observed on the splat surface by SEM and EBSD, including central coarse grain and marginal fine grain. When the preheating temperature was higher than 350 °C, effective bonding formed only in the entire central coarse zone, whereas no effective bonding was observed in the fine grain zone. By using glass, copper, nickel and 304 SS as substrates, it was found that increasing thermal conductivity of metallic substrates has little effect on splat diameter and morphology and however decreased the area fraction of central coarse grain zone. It was revealed that the melt/substrate interface temperature plays a crucial role on the interface bonding formation.
Performance of CoCrAlSiY Alloy Powder
Authors: Zhang S. , Du K. , Peng R. L. , Shi J. , Liu J.
Published: November 2022

The CoCrAlSiY alloy powder with Si mass concentrations of 0, 2% and 5% was prepared in this work. The oxidation kinetics curves of all three kinds of powders after 300 h oxidation at 1000 °C were plotted. In addition, the phase constitution of alloy powder and the distribution of β phase were analyzed by SEM and EDS. Furthermore, the effect of Si-addition on the melting temperature and oxidation resistance of the alloy powder were investigated by DSC-TG from the room temperature to 1400 °C. And the element concentrations at the grain boundary of alloy powder with Si addition of 2% were also analyzed. The results show that the melting temperature of alloy powder decreases as increasing Si content, which indicates that adding Si element could influence on the selective oxidation of Al and Cr elements in the alloy system, and improve the oxidation resistance of CoCrAlY powder. In addition, the weight gain of powder with Si addition of 2% is lowest. And Si element has a enrich tendency in the grain boundary. Therefore, the higher Si content would have a negative effect on the high temperature oxidation resistance of powder.
Effect of Thermal Aging on Properties and Microstructure of AlSi-hBN Coating
Authors: Liu J. , Yu Y. , Liu T. , Yang S. , Cheng X.
Published: November 2022

A commercial abradable coating AlSi-hBN was fabricated by atmospheric plasma spraying and was thermal aged at 450 °C in the atmospheric environment for 1000h. Thermal aging effect on coating abradability, hardness, bond strength and microstructure were evaluated. It was found that coating abradability increased obviously after 2h thermal aging and slightly decreased for extended thermal aging time. A sharp decrease in both coating hardness and bond strength were found after 2h thermal aging and a slow increase occurred with the extended aging time. Relationships between coating properties and microstructure were studied. Decomposition of organic binder and sintering of AlSi matrix metal generated by thermal aging were found to be reasons for coating properties changes.
The Influence of Size and Speed of Drops on the Structure and Properties of Electric-Arc Sprayed Coatings
Authors: Pokhmurs’ka H. , Student M. , Hvozdetskyi V. , Stupnytskyi T. , Posuvailo V.
Published: November 2022

Increase of the pressure of air flow from 0.6 to 1.2 MPa provides the growth of its speed from 300 to 600 m/s. The increase of air flow speed reduces the flight time of drop from the arc to the substrate and them against the prepared surface at higher temperatures. Increase of the pressure of air provides reduction the size of drops and oxides between lamellas as well as improves the mechanical characteristics.
Post Deposition Heat Treatment of Cold Sprayed C355 Deposits for Repair: Microstructure and Mechanical Properties
Authors: Zuccoli M. V. , Sabard A. , Guagliano M. , de Villiers Lovelock H.L. , Hussain T.
Published: November 2022

Cold gas dynamic spray is increasingly used for dimensional repair in the aerospace sector as it is capable of producing dense, oxide-free deposits of significant thickness and with good levels of adhesion and inherent mechanical strength. There is significant interest in extending the application of cold spray deposits to include structural, load-bearing repairs. However, particularly for high strength aluminium alloys, cold spray deposits can exhibit high levels of porosity and micro-cracks, leading to mechanical properties that are inadequate for most load bearing applications. In this work, heat treatment was investigated as a potential means of improving the properties of a cold sprayed Al alloy C355 deposit. C355 alloy deposits were produced using two process gas temperatures (350°C and 500°C) and three gas pressures (40, 50 and 60 bar) using a commercially available HPCS system. Microstructural analysis of the coatings revealed that the optimal microstructure (ca. 1% porosity) was obtained at 500°C and 60 bar. Therefore, coatings produced with process conditions of 500°C and 60 bar were heat treated at 175, 200, 225, 250°C for 4h in air and the evolution of the microstructure and microhardness was analysed. The results show that heat treatment at 225°C can decrease porosity (<0.2%) and retain high hardness (105 HV0.05 vs 130 HV0.05 as-sprayed). Further investigation was performed on as-sprayed and 225°C heat treated deposits. The results show that this heat treatment can halve residual stress (-50 MPa vs -100 MPa as-sprayed), and improve tensile properties (UTS). Therefore, this work has demonstrated that the heat treatment of C355 cold sprayed deposits at 225°C can significantly improve their properties.
Development of High-Performance Cold-Sprayed Nanostructured NI-20Cr Coatings for Harsh Environment of Power Plant Boilers
Authors: Kumar M. , Singh H. , Singh N. , Chavan N. M. , Kumar S. , Joshi S. V.
Published: November 2022

In the current work, Ni-20Cr coatings have been developed for potential use in harsh environments of power plant boilers. A pre-synthesized Ni-20Cr nanocrystalline powder was deposited on T22 boiler steel using cold-spray process. The high temperature oxidation behavior of the coating was investigated under cyclic conditions at 900° C for 50 cycles, so as to understand the kinetics of oxidation. Moreover, high temperature erosion-corrosion (E-C) behaviour of the coating was ascertained under cyclic conditions in an actual boiler at 740 ± 10°C for 1500 hours. The oxidized and eroded-corroded samples were characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) analyses. The microhardness, oxidation and E-C data for the developed coating was compared with an earlier reported cold-spray Ni-20Cr coating, which was developed by using a commercially available micron-sized Ni-20Cr powder. The results showed that the developed coating was found to have 33% high microhardness in comparison with the microstructured Ni-20Cr coating. The oxidation and E-C rates of the steel were found to decrease significantly after the application of the developed coating by 89% and 68% respectively. Moreover the nanostructured coating outperformed the corresponding micro-structured Ni- 20Cr coating with regard to high temperature oxidation and E-C resistance to boiler steel by a significant fraction. The investigated coating was found to have oxidation protective oxides such as Cr2O3 and NiO in its oxide scale and was found to be spallation-free.
High Temperature Hot Corrosion Behavior of Selected Thermally Sprayed Coatings in an Aggressive Environment
Authors: Česánek Z. , Houdková Š. , Schubert J.
Published: November 2022

Cr3C2-25%NiCr, Stellite 6, NiCrBSi and Hastelloy C-276 coatings were deposited on substrate material P91 by HP/HVOF (High Pressure / High Velocity Oxygen Fuel) thermal spraying technology. The resistance against high temperature corrosion was evaluated exposition of coatings to corrosive-aggressive environment in the form of molten salts mixture with composition of 60% V2O5 and 40% Na2SO4 at temperature of 750 °C. Further, coatings were exposed to cyclic conditions. After the corrosion tests, all coatings were analyzed using scanning electron microscope (SEM), and analysis of elemental composition (EDX). Alloys-based coatings showed very similar corrosion mechanism in the selected aggressive environment and the same can be stated about cermet coatings. The obtained results prove that HVOF deposited coatings can replace current surface protection of components in power equipment such as nitriding.
Cold-Gas Sprayed Deposition of Metallic Coatings Onto Ceramic Substrates Using Laser Surface Texturing Pre-Treatment
Authors: Kromer R. , Danlos Y. , Costil S.
Published: November 2022

Cold spraying consists in depositing a variety of metals as dense coatings onto metal surfaces. Indeed, copper, stainless steel, nickel, chromium, aluminum, cobalt, titanium, niobium and other metals can all be deposited, as well as metal alloys according to these base-metals and braze powders. The particle-substrate contact time, contact temperature and contact area upon impact are parameters influencing physico-chemical and mechanical bonds. The resultant bonding arose from plastic deformation and temperature at the interface which illustrates why metal coating cannot be sprayed onto rough ceramic substrates. Laser surface texturing has been used as prior treatment to create specific topography. Metal-ceramic has demonstrated a non-deformation of the substrate minimizing intimate bonds. Particle compressive states indicate anchoring mechanisms for laser textured surfaces. Consequently, cold spraying parameters depend on the target material and a methodology can be established with particle parameters (diameters, velocities, temperatures) and particle/substrate properties to adapt the surface topography. Mechanical adhesion is a key issue in cold spray process. As a result, laser surface texturing is a promising tool to adapt the surface to improve adhesion. Metallization process can be achieved.
Modelling of Heating the Particles of Powders in the New Detonation System
Authors: Rigin A. , Maximov A. , Maximova O. , Parygina S.
Published: November 2022

Detonation spraying is used for applying metal, cermet, polymer and ceramic coatings. The advantages of this technology include good adhesion and density of coatings. Minimal residual stresses in the spray process give the possibility to apply coatings to thin-walled parts and foil. Numerical modeling methods for energy parameters of powder particles give the possibility to predict the interaction of powder particles with the gas flow in and properties of coatings depending on spray parameters. In many cases, existing advantages such as high quality of coatings, little heating of the substrate, efficient and economical use of the powder, make the detonation spray process more attractive in comparison with other spray methods. The new design of D-Gun and software gives the possibility to overcome these limitations and significantly increase the productivity. This result was obtained due to a new design of the valve head, new computer control system, electronics and software that allows the firing rate frequency to be increased, ensure the reliability and extend the maintenance-free lifetime. The paper discusses the results of modeling of acceleration and heating the particles of powders in the new detonation system and also methods of computer simulation of the formation of adhesive contact between powder particles and metal surface.
Adhesive-Corrosion Resistance of High Velocity Metal Droplet on Atmospheric Plasma Sprayed Ni-WSe2-BaF2·CaF2-Y-Ag-hBN Solid Lubricant Coatings
Authors: Yuan X.-J. , Chen X.-H. , Zha B.-L. , Yao C.
Published: November 2022

Adhesive-corrosion resistance is an important issue for the application life of solid lubricant coatings. With abundant metal droplets deposited on the surface of a solid self-lubricating coating, the coefficient of friction of the coating changes and results in adhesive wear. In this paper, a new method for evaluating the adhesive resistance for solid self-lubricating Ni-WSe2-BaF2·CaF2-Y-Ag-hBN coatings was reported. The microstructures and anti-adhesive characteristics under different angles of aluminum metal droplets obtained with an arc supersonic nozzle were investigated for high temperature solid self-lubricating coatings produced by plasma spray. The results demonstrate that the friction coefficient of Ni-WSe2-BaF2·CaF2-Y-Ag-hBN solid self-lubricant coatings is distributed between 0.086 and 0.299 at 25-800℃. The effect of molten metal drops on the coating adhesive-corrosion rate increases with the deposition angle. At 90°, the deposition rate of metal droplets on the coating and substrate surface is maximized, and the hexagonal boron nitride (hBN) self-lubricating coating deposition rate is only 58 mg/(cm2·s). This work demonstrates that hBN can effectively decrease the adhesive layer of the coating by the rate of the polishing and stripping.
Influence of Substrate Properties on the Formation of Suspension Plasma Sprayed Coatings
Authors: Zhao Y. , Yu Z. , Planche M.-P. , Lasalle A. , Allimant A. , Montavon G. , Liao H.
Published: November 2022

In this study, YSZ coatings were deposited on different substrate materials (stainless steel and aluminum) using suspension plasma spray (SPS) technique. The effects of substrate properties (material, surface topology, temperature, and thickness) on the formation of coatings were investigated. The results showed that, with the identical spray parameters, the porosity is higher for the coatings deposited on aluminum than that on stainless steel due to the high thermal transfer ability of the former substrate material. The SEM results revealed that the microstructure of as-prepared coatings could be tailored from the vertical cracked structure to the columnar structure by increasing the substrate surface roughness and their formation mechanisms were discussed. The substrate preheating temperature has an influence on the microstructure of the coatings, especially in the interfacial region and increasing the substrate temperature is an effective means for reducing the interface defects in the coatings. With the increase of the substrate thickness, the quantity of the vertical cracks in the coatings is reduced and their width becomes narrower.