bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Microstructure and Properties of Thermal-Sprayed Cermet Coatings Modified by Laser Remelting Post-Treatment
Authors: Yin Z. J. , Tan X. H. , Wang Q. X. , Xu S. H. , Hao R. L. , Deng Q. L. , Sun J. S.
Published: November 2022

In this study, carbide-based cermet (WC-Co, WC-NiCr, Cr3C2-NiCr) coatings were prepared by thermal spraying and efforts were made to explore the laser remelting effects on the coating microstructure, hardness, adhesion and tribological behavior under different conditions. Results obtained showed that under elected remelting parameters, laser-treated coatings exhibit denser structures and improved microhardness with smaller variability, as well as enhanced adhesion strength between coating and substrate arising from metallurgical element diffusion. In dry sling condition, HVOF sprayed WC-Co coating after laser remelting showed superior wear resistance, however, contrary to the lubricated condition, which may attribute to more lubricant stored in as-sprayed coatings with higher porosity. Solid particle erosion tests suggested that anti-erosion property of plasma sprayed Cr3C2-NiCr coating by laser remelting are increased, regardless of erosion velocity and angle. Additionally, the wear loss of laser-treated coating increased with erosion velocity, but due to its improved ductility shows no obvious relation to the erosion angle changing from 30 to 90 degree, which is accordance with the wear surface observation and tribological mechanism analysis.
Performance of HVOF and Cold Sprayed Ni-20Cr Coatings in Aggressive Molten Salt Environment at 900°C under Cyclic Condition
Authors: Bala N. , Singh H. , Prakash S.
Published: November 2022

Nickel-chromium alloys have been used as coatings to deal with oxidation environments at high temperature. The present work is a comparative study of HVOF and cold sprayed Ni-20Cr coating on a boiler steel (SAE 213-T22) in a molten salt environment of Na2SO4-60%V2O5 at 900°C under cyclic conditions. The weight change technique was used to establish the kinetics of corrosion. X-ray diffraction, surface and cross-sectional FE-SEM/EDS techniques were used to analyse the corrosion products. The hot corrosion resistance of both the coatings was better than the uncoated steel. This may be attributed to the formation of oxides and spinels of nickel and chromium in the coated steels. These oxides might have blocked the pores and splat boundaries, and acted as diffusion barriers to the inward diffusion of corroding species. Based upon the overall results and subsequent analysis of hot-corrosion data the cold spray process may be recommended as a better choice for the deposition of the Ni-20Cr coating on Mo-containing T22 steel in comparison with the HVOF spray process for hot corrosion protection.
Effect of the Substrate Temperature on Properties and Dissolution of Plasma Sprayed Wollastonite Coatings
Authors: Wang W. Z. , Liang J. C. , Xuan F. Z.
Published: November 2022

Wollastonite coatings were deposited on Ti6Al4V substrate at the substrate temperatures of room temperature, 200 °C, 400 °C and 600 °C by the atmosphere plasma spraying, respectively. The effect of substrate temperature on the microstructure, phase composition, mechanical properties and dissolution behavior of wollastonite coatings were investigated. The microstructure and phase composition of coatings were examined by SEM and XRD. The hardness and elastic modulus were obtained by the Knoop indentation tests. In addition, the dissolution behavior of coatings was evaluated by immersion in SBF solution. The results indicate that a slight decrement of porosity and an obvious increment of crystallinity were found with the substrate temperature. The hardness and elastic modulus of coatings increased with the substrate temperature up to 400 °C firstly, and then a decrement was observed with the temperature further increasing to 600 °C. The dissolution rate of coatings characterized by the pH changes and the released Ca, Si and P concentration in the SBF decrease with the substrate temperature, which is related to the porosity and crystallinity of coatings. It is revealed that through increasing the substrate temperature during plasma spraying is a feasible method to improve the mechanical properties and to decrease the dissolution of wollastonite coatings.
Excimer Laser Surface Treatment of Plasma Sprayed Coatings
Authors: Ibrahim A. , Shahrabi K. , Zoghi M. , Hung Y. , Ryu Y. , Berndt C. C. , Khonsari M.
Published: November 2022

Excimer laser annealing provides a rapid and efficient means for surface alloying and modification of ceramic materials. In this study, Alumina-13% Titania coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by Excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. The surface structure of the treated coating was examined by field emission scanning electron microscope and X-ray diffraction (XRD). A detailed analysis of the effects of various laser parameters including laser energy density (fluence), pulse repetition rate (PRR), and number of pulses on the morphology and the microstructure of the coatings are presented.
Local Corrosion Protection of Joints by Low Pressure Cold Spray
Authors: Dzhurinskiy D. , Maeva E. , Leshchynsky V. , Maev R. Gr.
Published: November 2022

The study of corrosion protection of magnesium and aluminum becomes increasingly important as the use of these alloys increases rapidly in the automotive and aerospace industries due to their advantages of light-weight, adequate mechanical properties and moderate cost. Corrosion, however, limits the application of magnesium and aluminum alloys. Fasteners, spot welds of dissimilar materials and their galvanic corrosion is of major concern in automotive applications. The paper presents first results of Low Pressure Cold Spray (LPCS) of Al based coatings for corrosion protection. The corrosion protection provided by these coatings was evaluated by electrochemical measurements in 1M NaCl electrolyte. The microstructures and electrochemical behavior of the coated joints were investigated. The electrochemical corrosion mechanisms of the coatings and microstructure were discussed.
Computational Analysis of Composite Powders Impacts to Evaluate Ceramic Coatings in Cold Spraying
Authors: Canales H. , Dolmatov A. , Markovich S.
Published: November 2022

Cold Spraying, as a novel Thermal Spraying Technology can deposit a wide range of ductile materials on different substrates; a problem arises when the objective is to use this technology to deposit brittle materials such as ceramics in applications where melting must be avoided. One example is when spraying Bio-Ceramics, in which particle´s melting often leads to changes in physical and chemical properties and subsequently resulting in unknown variations in the coating´s biocompatibility. While Non-Ductile Materials can only be deposited if they are co-cold-sprayed with a ductile (matrix) material a Metal-Ceramic Powder Composite must be used for these objectives. The goal of this paper is to show a transient Non-Linear Dynamics Computational Analysis of a Metal- Ceramic Powders Composite impacting a metallic substrate by the means of Cold Spraying Technology; all this in order to understand the formation of cold sprayed composite coatings while comparing them with experimental results and using ANSYS-AUTODYN© to assess the suitability of this spraying technology for coating special application substrates.
Thermal Spraying of Advanced Zinc Alloys as an Addition to Hot-Dip Galvanizing
Authors: Bobzin K. , Schläfer T. , Warda T. , Schulz C.
Published: November 2022

Zinc coatings are widely adopted for cathodic corrosion protection. Mostly the process of choice is hot-dip galvanizing but due to limitations regarding component size and composition of the galvanizing bath it is not always practicable. In the present paper zinc coatings alloyed with Al, Sn, Mg and Cr are applied by twin wire arc spraying to enhance the corrosion protection ability of zinc thermal sprayed coatings. The alloys were characterized and investigated using salt spray test and by means of electrochemical corrosion. Corrosion damage and products were investigated by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and electron probe microanalysis (EPMA).
Correlation of the Particle Behavior, Microstructure and Phase Evolution During the Optimization of HVOF Sprayed WC-12Co Coatings by Means of DoE
Authors: Tillmann W. , Hagen L. , Baumann I. , Tolan M. , Paulus M. , Wieland F.
Published: November 2022

Due to their outstanding properties, WC-Co cermet coatings are widely used in the field of wear protection. It has been reported by many researchers, that their macroscopic and tribological behavior is largely determined by the process conditions and the feedstock powder characteristics respectively. Although the manufacturing route for high velocity oxy fuel(HVOF)flame sprayed WC-Co coating is in an advanced state, there is still a lack of knowledge about the complex relationships between the thermo-kinetic in-flight particle behavior, the microstructure formation and the phase evolution during the spray process. However, a fundamental understanding is not only necessary to provide coatings with optimized properties, but also to meet economic aspects with regard to the HVOF process. In this study the dependencies between the HVOF process parameters and characteristics (chamber pressure, thermal energy transferred to the coolant), the thermo-kinetic in-flight particle behavior (temperature, velocity and the spray particle size) with the microstructure formation (carbide content and size, free mean path of the binder phase, porosity), thermal phase reactions and the mechanical properties (hardness, toughness, roughness) were investigated. Statistical design of experiments (DoE) is utilized to enable a systematic analysis of several influencing factors along with their interactions on the coatings properties and to find optimized spray conditions. X-ray diffraction (XRD) applying high-energy synchrotron radiation has been used, not only to provide a phase analysis in deeper regions of the coating structure, but also to achieve more detailed information on phases which are not or hardly detectable by XRD using a conventional X-ray laboratory source. In addition the sliding and abrasive wear properties at optimized coating properties are studied.
Failure Mechanism of Non-Stoichiometric Mg-Al-Spinel Abradable Coatings under Thermal Cyclic Loading
Authors: Ebert S. , Steinke T. , Vaßen R. , Stöver D.
Published: November 2022

Plasma-sprayed ceramic coatings are often used as thermal barrier or abradable coatings in high-pressure stages of gas turbines. They are exposed to high thermo-mechanical loadings, due to the harsh operating conditions. Today, a material typically used in engines as thermal barrier coating material is yttria-stabilised zirconia (YSZ). This material has a low conductivity and a high thermal expansion coefficient, but a limited temperature capability of about 1200°C in long-term applications. For the use as abradable coatings, thicker coatings with a thickness above one millimetre are necessary. However with increasing coating thickness and limited cooling efficiency there is a risk of premature failure. As a result new ceramic materials have been developed. For the lifetime analysis they were tested by thermal gradient cycling tests. In the present work an APS ceramic double-layer topcoat composed of 7YSZ and a top layer of non-stoichiometric magnesia alumina spinel (Mg-Al-Spinel) was used. The layer was sprayed on disc-shaped IN738 superalloy substrates which were coated with a VPS bondcoat. Under specific thermal cycling conditions with temperatures above 1400°C, these samples showed a typical failure mechanism with exfoliation of thin coating lamellae, starting from the coating surface. This failure mechanism was analysed in detail, e.g. by scanning electron microscopy (SEM), X-ray diffraction, and chemical analysis. From these findings, a description of the failure mechanism was developed.
Development of Particle-Reinforced Nanostructured Iron-Based Composite Alloys for Thermal Spraying
Authors: Wielage B. , Lampke T. , Pokhmurska H. , Rupprecht C. , Drehmann R.
Published: November 2022

Cermets like WC/Co or Cr3C2/Ni20Cr are well-established materials for thermally sprayed wear protection coatings. However, their high price and the adverse health effects of nickel and cobalt cause the motivation for the development of novel materials with excellent wear resistance. Within the AiF/DFG research cluster “Thermal Spraying”, a multi-institutional cooperation of various German research centres, the focus is put on particle-reinforced iron-based composite alloys. High-alloyed steels serve as matrix materials into which hard CrB2 particles are incorporated by means of high-energy ball milling (HEM). By adjusting appropriate milling parameters, the microstructure of the powder and its level of amorphisation can be influenced effectively. The high-velocity oxygen fuel process (HVOF) allows a transfer of the desired nanocrystalline structure from the particles to the coatings. The deposited coatings exhibit low porosity and high microhardness values of more than 1000 HV0.3. The wear resistance of the coatings was determined by means of Miller test (ASTM G75-01) and compared with conventional wear protection materials and coatings produced with agglomerated and sintered powders. The obtained outstanding results qualify particle-reinforced iron-based materials as a promising alternative for a wide range of applications.
Development of Ceramic Heating Elements Produced by Thermal Spray Technology
Authors: Toma F.-L. , Scheitz S. , Puschmann R. , Berger L.-M. , Sauchuk V. , Kusnezoff M.
Published: November 2022

In this work, completely ceramic heating elements have been developed by the combination of conductive and insulating thermally sprayed oxide coatings. These heating elements with a total thickness of less than 1 mm have been directly applied on metallic substrates. APS- and HVOF-sprayed Al2O3 and spinel (MgAl2O4) coatings were employed for insulation. A comparative analysis of the insulating properties (dielectric strength, electrical resistivity) of these coatings is presented. The HVOF-sprayed spinel coatings show better dielectric breakdown strength and higher electrical resistance stability. TiOx, TiO2-10%Cr2O3 and TiO2-20%Cr2O3 powders have been used to prepare the electrical conductive coatings. The thermal and oxidation stabilities at high temperature, as well the electrical properties have been investigated. Addition of Cr2O3 reduced the oxidation rate of titanium oxide and increased the operational temperature of the heating coating. A ceramic heater consisting of spinel coating as insulator and TiO2- 20Cr2O3 as conductor was sprayed on a metallic roller and the electrical stability during the long-term (300h) thermo-cycling (from RT to 300°C) was successfully tested.
Thermal Barrier Coatings for Rocket Engines
Authors: Schloesser J. , Bäker M. , Rösler J.
Published: November 2022

In rocket engine combustion chambers the cooling channels are subjected to extremely high temperatures and environmental attack. Because of the good heat conduction the inner combustion liner is made of copper. Thermal and environmental protection can be provided by Thermal Barrier Coating Systems. The performance of an APS-sprayed standard coating system for nickel based substrates (NiCrAlY and YPSZ) on copper substrates is investigated. Because mechanical and thermal properties (e.g. the coefficients of thermal expansion) of the two substrates are different, known failure mechanisms for nickel based substrates can not be directly transferred to the new application. Thermal cycling and laser shock testing is performed to identify possible failure mechanisms. The laser shock setup consists of a high-power diode laser (3kW) and realizes surface temperatures of up to 1500°C. Furthermore, it is possible to realize high thermal gradients inside the specimen, similar to those in real service. Delamination of the thermal barrier coating at the interface between bond coat and substrate is observed. Usually, this interface is not failing in standard applications, which gives an important hint for further research. Furthermore, FEM analysis confirms that stresses are maximal at this interface.
Effect of Bond Coat Material and Heat Treatment on Adhesion Strength and Characteristics of Thermal Barrier Coating System with CGDS, HVOF and APS Techniques
Authors: Lampke T. , El-Mahallawy N. , Grund T. , El-Araby I. , Karaoglanli A. C.
Published: November 2022

The most recent increase in turbine entry temperature (TET) can be obtained by the use of Thermal Barrier Coatings (TBCs) on cooled hot section components. The TBC systems are comprised of Ni-based super-alloy substrate which provides certain mechanical properties and blade geometry consisting of a ceramic top coat with low thermal conductivity applied to a metallic bond coat resulting in a significant temperature drop across the coating. The bond coat provides oxidation resistance and adherence of the top coat to the substrate. In this study different bond coat layers were applied on carbon steel substrates which were covered by yttria stabilized zirconia (YSZ) as a top coat layer using atmospheric plasma spray technique (APS). Al-12%Si and Al 99% were deposited by cold gas dynamic spray technique (CGDS) while Ni-5%Al layer was deposited by high velocity oxy fuel technique (HVOF). Heat treatment was performed on the samples under controlled atmosphere for 15 hrs. The microstructure and micro hardness of as sprayed and after heat treatment samples were investigated. Adhesion strength for top coat / bond coat interface and bond coat / substrate interface were investigated. The residual stresses for as sprayed and after heat treatment was estimated by XRD measurement on the top coat layer with different bond coat material. The results indicate that the adhesion strength either for as sprayed or after heat treatment was enhanced using this new bond coat materials compared to the traditionally as deposited Ni Co Cr Al Y bond coat material.
Preparation and Thermophysical Properties of La2(Zr0.7Ce0.3)2O7 Ceramic Material
Authors: Xiang J. Y. , Chen S. H. , Huang J. H. , Zhou G. D. , Liang W. J. , Wang R. J. , He Q.
Published: November 2022

La2(Zr0.7Ce0.3)2O7(LZ7C3) ceramic was prepared by solid state reaction method at 1400 °C for 12h using La2O3, ZrO2, and CeO2 as starting reactants. The phase composition and microstructures were studied by XRD and SEM technology. The thermal conductivity and linear thermal expansion coefficient were investigated by laser-flash method and pushing-rod method respectively. XRD results revealed that LZ7C3 is a mixture of pyrochlore and fluorite, and the pyrochlore is the main phase which is a small solid solution of La2Ce2O7 (LC) in La2Zr2O7 (LZ). The thermal conductivity of LZ7C3 decrease gradually with the increase in temperature until 1200°C, and the value is 0.79 W⋅m-1⋅K-1, which is almost 50% lower than that of LZ. The linear thermal expansion coefficient which is 11.6 × 10-6 K-1 at 1200°C is larger than that of LZ. These results show that LZ7C3 ceramic material can be explored as a novel prospective candidate material for use in new thermal barrier coating systems in the future.
Study of Plasma Sprayed Mullite Coating Using Mullite and a Mixture of Alumina and Silica Powder Particles
Authors: Salimi Jazi H. , Hosseini M. , Shafyei A. , Samadi H. , Pershin L. , Coyle T. W. , Mostaghimi J.
Published: November 2022

Plasma sprayed ceramic coatings are widely used for thermal barrier coating applications. Commercially available mullite powder particles and a mixture of mechanically alloyed alumina and silica powder particles were used to deposit mullite ceramic coatings by plasma spraying. Microstructure and morphology of both powder particles as well as coatings were investigated by using scanning electron microscopy (SEM). Phase formation and degree of crystallization of coatings were analyzed and estimated by using X-ray diffraction technique. Differential thermal analysis (DTA) method was used to study the phase transformation of coatings. Results indicated that the porosity level in the coating deposited using mullite as initial powder particles was lower than that deposited using the mixed powder particles. The crystallization degree of the coating deposited using the mixed powder particles are higher than that deposited using mullite powder particles. DTA curves of coatings deposited using the mixed powders have showed some phase transformation due to the crystallization of the retained amorphous phases such as mullite and alumina in the coatings. The degree of crystallization of both as sprayed coatings was significantly increased after post deposition heat treatments.
Optimization of Plasma Spray Processing Parameters for Deposition of YSZ+Al2O3 Coating
Authors: Altuncu E. , Tozkoparan D. , Okumus S. C. , Ustel F.
Published: November 2022

Plasma sprayed yttria stabilized zirconia (YSZ) coatings are being increasingly used as thermal barrier coatings(TBCs) for gas turbine parts. However oxidation problems are critical for durability of TBC. Al2O3 addition to YSZ is considered as an oxygen barrier microstructure at elevated temperature. Therefore it helps to the growth rate of the thermally grown oxide layer between top coat and bond coat. Spray properties and rapid solidification determine the final characteristics of the coating. Plasma current, plasma gas flow rate and spray distance factors have main effect on occurrence of microstructure. Therefore plasma spray parameter optimisation is required for TBC manufacturing. Statistical designs of experiments have been shown to provide efficient approaches to systematically investigate the process parameters of plasma spray process. In this study Al2O3-YSZ particle composite TBC deposited with different plasma spray process parameters by using Taguchi method for optimisation.
Effect of the Grit Blasting Exposure Time on the Adhesion of Al2O3 and 316L Coatings
Authors: Vilemova M. , Siegl J. , Matejicek J. , Musalek R.
Published: November 2022

The effect of grit blasting exposure time on the adhesion of plasma sprayed Al2O3 and 316L stainless steel coatings was studied in the present work. The steel substrates were grit blasted prior to the coating deposition. Two sets of substrates with exposure time of 1 and 4 seconds were prepared. Both types of coatings were deposited using Water Stabilized Plasma (WSP) torch. Adhesion strength was evaluated using standardized pulloff test. The obtained results showed a slight improvement in the adhesion strength for the blasting time of 4 s. Failure processes taking place in the coatings during the pull-off tests were described based on the detailed fractographic analysis.
Cold Spray Ultrasonic Monitoring and Modeling
Authors: Maev R. Gr. , Titov S. , Dech J. , Leshchynsky V.
Published: November 2022

To fully understand particle interactions with both substrate and neighboring particles in Cold Spray (CS), ultrasonic monitoring and acoustic emission of particle agglomerate impact were studied. The results obtained show the influence of particle agglomeration density on stress and strain distribution in the particles and at the particle interfaces. The results are compared with metallographic structures of real coatings. The development of monitoring procedure is made using acoustic methods, specifically testing during the actual spray process itself. It is shown that the final thickness as well as the dynamics of buildup can be evaluated. Cross sections of the coating thickness are also easy to obtain and show true profiles of the coating. Comparisons of real thickness and acoustically estimated thickness show a close linear relationship.
The Tensile and Shear Strength of Thermally Sprayed Coatings
Authors: Kašparová M. , Zahálka F. , Houdková Š. , Volák J.
Published: November 2022

The work deals with the evaluation of strength characteristics of thermally sprayed coatings. The main aim was concentrated on the tensile and shear loading of HVOF (Stellite Alloy 6, Tribaloy 400) and arc sprayed (13%Cr, CuAl8) coatings. The investigation of the coatings behaviour on the coating-substrate interface is important for the evaluation of one of significant coating mechanical properties that influence properties of the whole coating-substrate system. The magnitude of the coating bond strength during tensile and shear stresses predicates the coating stability, reliability, impact resistance, resistance against failure and mostly operating lifetime. The determination adhesive-cohesive strength was performed according to EN 582 and EN 15340 Standards.
Thermal Shock Resistance of Plasma-Sprayed Thermal Barrier Coatings
Authors: Takahashi S. , Hirano N. , Kojima Y. , Harada Y. , Kawasaki A. , Ono F.
Published: November 2022

The thermal shock resistance of plasma-sprayed thermal barrier coatings (TBCs) with different top coats was investigated according to the Japanese Industrial Standard "Testing methods for thermal cycle and thermal shock resistance of thermal barrier coatings" (JIS H 8451:2008). Three types of ceramics powders, namely, Al2O3, 8 mass % Y2O3-stabilized ZrO2 (YSZ) and La2Zr2O7 (LZ) were used in the top-coat spray. After the specimens were subjected to a thermal shock, the tensile adhesive strength of the TBCs was measured and the thermal shock resistance as defined in JIS H8451 was determined. The thermal shock properties of the TBCs were found to depend strongly on the chemical composition of the top-coat material. For TBCs with Al2O3 and LZ, the adhesive strength decreased with increasing thermal shock temperature difference (ΔT). On the other hand, little change in the adhesive strength was observed with increasing ΔT for YSZ TBC. From these results, the thermal shock resistance, ΔTc, was determined to be 480 °C for Al2O3, 680 °C for LZ and more than 880 °C for YSZ TBC. Furthermore, the influence of thermal shock on the adhesive strength of TBCs was investigated in detail through observations of cross-sectional microstructures and fracture surfaces after adhesive testing.
Electrical Resistivity of Thermally Sprayed Cr2O3-TiO2 Coatings
Authors: Trache R. , Berger L.-M. , Toma F.-L. , Stahr S. , Lima R. S. , Marple B. R.
Published: November 2022

In this study, the influence of spray parameters on the electrical resistivity of thermally sprayed ceramic coatings from the system Cr2O3-TiO2 was investigated. Fused and crushed feedstock powders with contents of 10 wt. % and 20 wt. % chromium oxide were deposited by APS and HVOF. Temperature and velocity of the particles in the spray jet as well as the coating surface temperature were analyzed during the deposition process. Impedance spectroscopy was used to investigate the electrical resistivity of the coatings and the results were correlated to coating microstructure and phase composition. It was found that phase transformations occur during the spray process. In the coatings a high temperature phase (n-phase) and rutile were observed. Though, the ratio of rutile depends on the spray methods employed for coating deposition. The electrical resistivity of coatings obtained by HVOF can be correlated to the content of chromium oxide. Furthermore, the surface temperature of the coating during deposition also shows some influence. Concerning the coatings resulting from APS, the different mixtures of the plasma gases (Ar-H2 and Ar-N2) are supposed to have the most important influence on the electric resistivity.
Solidification of Plasma Transferred Arc Coatings
Authors: Bond D. , D’Oliveira A. S. C. M.
Published: November 2022

Plasma Transferred Arc is the only thermal spray process that results in a metallurgical bond with the substrate. When compared with other welded coatings finer microstructures are observed after PTA processing, which have been associated with the faster solidification rate imposed by this technique. However, the powdered/atomized material used that forms the thermal spray, can play an important role in the solidification of coatings depending on their chemical composition and their grain size. This study analyzed the solidification of PTA coatings processed with an atomized cobalt based alloy (Stellite 6) with different average grain sizes. Typically, solidification of a welded coating follows solidification principles regarding the nucleation and growth of their microstructure determined mainly by the solidification rate. The role of the powdered feedstock in the solidification of coatings is analyzed based on the assumption that solidification is influenced by the initial interface energy of the atomized grains that melt in the plasma arc before reaching the melt pool. A commercial atomized Stellite 6 alloy was divided in two groups according to their grain size, below and over 125 microns, and deposited with the same processing parameters. Coatings were characterized by laser confocal microscopy and Vickers microhardness. Differences in coatings hardness and microstructure of coatings were associated with the grain size of the deposited alloy and subsequent solidification.
Numerical Study on the Role of Substrate Size in Supersonic Jet Flow and Substrate Preheating Process in Cold Spraying
Authors: Yin S. , Wang X.-F. , Li W.-Y. , Xie R.
Published: November 2022

This study investigates the effect of substrate conditions on supersonic jet flow pattern, particle acceleration and substrate preheating process in cold spraying. Computational fluid dynamic (CFD) approach is employed in the present work to achieve this objective. The simulated results show that substrate diameter has some effects on gas flow regime and thus particle acceleration. When the substrate diameter is smaller than the nozzle exit diameter, the size of the bow shock formed in front of the substrate is rather small, which contributes to increase the particle impact velocity. With increasing the substrate diameter gradually, the flow regime becomes more and more insensitive to the substrate diameter and the pattern becomes uniform. Moreover, the current numerical work also reveals that substrate preheating process can be significantly influenced by substrate thickness. With the increment in substrate thickness, the preheating effect becomes increasingly undesirable and the substrate surface temperature presents a downward trend.
Effects of Spray Nozzle Design on Cold Sprayed Magnesium Alloy Coating and its Composite
Authors: Suo X. K. , Guo X. P. , Li W. Y. , Planche M. P. , Bolot R. , Liao H. L. , Coddet C.
Published: November 2022

In this paper, a commercial AZ91D magnesium alloy powder and its mixture with 30 vol.% SiC powder were used to deposit coatings by cold spraying. Two types of converging-diverging nozzles with different cross-sectional shapes were employed. The velocity and temperature of in-flight particles under different operating conditions were simulated using the FLUENT software. The simulated results show that the particle velocity through the rectangular cross-section nozzle is the same with that through the circular one. However, the coating observation shows that the AZ91D coating and its composite could only be deposited using the rectangular cross-section nozzle. The increase of gas temperature has little effect on the coating microstructure, porosity and microhardness. Furthermore, the observation of the composite coating produced under the gas temperature of 600°C shows that the SiC content in the composite is about 23 vol.%. The microhardness of the composite is improved to about 140 HV0.3 due to the enhancement of SiC particles, compared to that of about 100 HV0.3 for the AZ91D coating.
Iron Boride Coatings Produced by Cold Spray Processes
Authors: Ozdemir I. , Ogawa K. , Sato K. , Seo D.
Published: November 2022

Iron based coatings have recently gained much attention as they have favorable mechanical, frictional, and corrosion properties. The coatings possessed a high content of iron borides are particularly valuable for satisfying engineering needs. Boron and iron form two major boride phases, FeB and Fe2B, with different mechanical and thermal properties. Orthorhombic boride FeB is considered to be viable candidate to enhance the surface hardness and wear resistance of components, since it has high hardness. Producing of such coating by cold spray method is considered to be an alternative for boronizing method which is a conventional thermochemical surface hardening process. In this work, the crushed ferroboron (FeB) powders of Fe-17.9B-0.4C-1.6Si-0.3Al (wt. %) were deposited onto low carbon steel substrate by cold spraying. However, low and high pressure cold spraying allowed depositing very thin and single layer on the substrate, due to the intrinsic brittleness of the powder. Therefore, several contents of Al, Ni and Fe metallic powder and their combinations were added to FeB powder to obtain thick coating via cold spray processes. Post heat treated coatings at a temperature of 700 °C resulted in increase of the hardness, possibly the formation of hard phases such as intermetallic compound.
Microstructural Changes During Heat Treatment of Cold Sprayed Pure Titanium Coatings
Authors: Wong W. , Irissou E. , Legoux J.-G. , Yue S.
Published: November 2022

This research systematically examines the effect of heat treatment on the microstructural properties of cold sprayed titanium coatings. Heat treatments were performed on as-sprayed coatings at 200, 400, 600, and 800°C for four hours under argon atmosphere. Vickers microhardness, microstructural investigation using FEG-SEM, structural characterization using XRD, and porosity evaluation using SEM image analysis were performed on as-sprayed and heat treated coatings. Results demonstrated that static recovery and static recrystallization may have occurred for heat treated coatings at 600 and 800°C. In addition, for the heat treated coating at 800°C, significant oxidation occurred and a slight decrease in porosity took place. Furthermore, a thin metallic layer characteristic of a solid solution or an intermetallic compound, was found at the coating/substrate interface.
Corrosion Resistance of Thermally Sprayed Coatings and Welded Overlays in Waste Incineration Environments
Authors: Pokhmurska H. , Wielage B. , Durham R. N. , Schütze M. , Franik D. , Gebert A.
Published: November 2022

Several model Fe- and Ni-based alloys with increased content (up to 30 at.-%) of protecting scale forming elements were developed. High temperature corrosion resistance of bulk alloys as well as thermally sprayed coatings and welded overlays were investigated under the waste power plants simulated atmosphere (500 °C, 100 hours, 75N2-20O2-4.9Ar-0.1Cl2). Arc and HVOF spraying as well as PTA overlay welding were used to produce the coatings. After an exposure the samples were examined with electron probe micro-analysis (EPMA). It was shown that the protection behaviour of overlay welds depends on the content of alloying elements, although the last is limited because of weldability decrease by high alloying level. High temperature corrosion resistance of thermally sprayed coatings is determined by their porosity, which can be varied over a very broad range depending on the applied spray method. The arc sprayed coatings need an additional post-treatment to close a porosity. Two methods were applied, pre-oxidation treatment in the air and sealing with the commercial sealant. Newly developed iron-based coatings with increased aluminium content (< 20 wt- %) sprayed with HVOF-spraying with powders obtained by means of high energy ball milling demonstrate high corrosion resistance. Selected coatings were evaluated for 1000 h exposure under chlorine-containing salt deposits at the higher temperature (600 °C).
Suspension Plasma Spraying (SPS) of Manganese-Cobalt Spinel Coatings
Authors: Puranen J. , Hyvärinen L. , Lagerbom J. , Kylmälahti M. , Koivuluoto H. , Vuoristo P.
Published: November 2022

Suspension plasma spraying (SPS) is regarded as a promising way to produce new coating structures with improved properties. In this study, SPS was studied as a possible manufacturing process for producing thin MnCo2O4 spinel coatings for used as protective coatings in metallic interconnector plates of SOFC’s. Suspension of nanosized MnCo2O4 powder and ethanol was thermally sprayed by using an F4-MB plasma gun with radial suspension feeding. The influence of spraying parameters, such as plasma gas composition, total gas flow, current and spraying distance for coating architecture was studied by using field-emission scanning electron microscopy (FESEM) and X-ray diffraction method (XRD). Spraying parameters had a strong influence on the coating structure and composition. Coating with the most homogenous structure were formed when sprayed with the low energy spraying parameters whereas high energy parameters resulted in formation of a columnar microstructure containing larger cobalt rich areas.
Correlation between Process Parameters and Thermal Cycling Lifetime for Thermal Barrier Coatings
Authors: Altuncu E. , Ustel F.
Published: November 2022

With the modification of plasma spray parameters, porosity ratio of top coat can control along the cross-section. This improves the thermal cycle resistance and decrease the thermal conductivity. Plasma sprayed ZrO2/8 wt.–% Y2O3–NiCrAlY TBC systems which have different porosity (%8-12) and range of 250-350µm thicknesses of top coats, during thermal cycling tests with different hold times at 1350 °C have been performed. The main failure modes: delamination cracking, TGO growth rate and phase transformation are strongly dependent on the hold temperature and time. The correlation between TBC thermal cycle lifetimes and duration of high temperature hold time per cycle is shown and discussed with depending on thickness and porosity ratio.
Isothermal Oxidation Behavior of NiCoCrAlTaY Coating Deposited by High Velocity Air-Fuel Spraying
Authors: Yang G.-J. , Xiang X.-D. , Xing L.-K. , Li D.-J. , Li C.-J. , Li C.-X.
Published: November 2022

The performance of a thermal barrier coating is influenced by the high temperature oxidation behavior of bond coat. In this paper, NiCoCrAlTaY bond coat was deposited by high velocity air-fuel (HVAF) spraying, and the microstructure and surface morphology of the bond coat before and after oxidation were examined. Results show that the HVAF sprayed NiCoCrAlTaY coating presented a dense microstructure and some partially melted particles in a near spherical morphology were deposited on the coating surface. A uniform α-Al2O3 oxide was formed on the HVAF sprayed MCrAlY coating surface after the pre-oxidation treatment in an argon atmosphere. A small fraction of nodular-shaped mixed oxides was formed when the MCrAlY coating was oxidized at 1000°C for 100 h. The amount of the mixed oxides did not significantly increase after 200 h oxidation. The large particles on the bond coat surface maintained homogeneous α-Al2O3 oxide scale in 200 h oxidation at 1000°C in air. A model is proposed to explain the formation of nodular-shaped mixed oxides.
Durability of Low Pressure Plasma Sprayed MoB/CoCr Coating in Molten Al-12.07wt%Si Alloy
Authors: Chen X.
Published: November 2022

MoB/CoCr, a novel material for thermal spraying, with high durability is used to resist erosion by molten Al-12.07wt%Si alloy. The durability of the MoB/CoCr coating prepared by low pressure plasma spraying (LPPS) has been investigated using a molten-metal immersion tester. The test revealed that the MoB/CoCr coating has much higher durability without dissolution in the molten Al-12.07wt%Si alloy. Little change of crystal structure, mainly composed of ternary borides of Co2MoB2 and CoMoB, is observed after the immersion test, suggesting that the ternary borides have much higher durability.
Using of CFD Simulations for Increasing Speed and Temperature of Flame Spray Technology
Authors: Zabransky T.
Published: November 2022

This paper describes computational fluid dynamics (CFD) simulations for state-of-the-art flame-spray processes and experimental validation of these simulations. Alternative nozzle designs are presented along with analysis of their impact on flow-field and flame parameters. Validated CFD models are used for performance prediction of these nozzles. Several variants are compared and the possibility of improvement of technology parameters is analyzed.
Basic Physics and Engineering Program System SPLAT – SPRAY DEPOSIT for Computer-Aided Design of Coatings Formation
Authors: Solonenko O. P. , Blednov V. A. , Iordan V. I.
Published: November 2022

In our previous publications the preference was given to develop the theoretical fundamentals which could be used for rapid and sufficiently accurate prediction of thickness and diameter of splat vrs the key physical parameters (KPPs), i.e. temperature, velocity and size of droplet, and substrate temperature. Theoretical solutions derived have permitted to obtain the number of practically useful consequences are of interest for thermal spray technology in context of sensitivity analysis and establishing the inverse link between the splat characteristics and KPPs. For constructive solution of the feedback problem, there are formulated the essence of this notion. The natural basis is the requirements imposed on splats as elements of the mesostructure, from which the coating is formed in the course of spraying. This approach, realized as subsystem “SPLAT”, allows one at the first stage of designing a coating to concentrate the attention on the space-time characteristics of splat formation. After comprehensive evaluation of the operation room of KPPs, providing the formation of splats required, subsystem “SPRAY DEPOSIT” allows one at the second stage of designing a coating to predict its lamellar structure and functional characteristics (porosity, adhesion, cohesion etc.) taking into account a variable surface topology at splat by splat deposition.
Atomization of Water Droplets in Atmospheric Plasma Jets
Authors: Soysal D. , Ansar A.
Published: November 2022

Liquid injection plasma spraying is of growing interest for thermal spray applications like thermal barrier coatings and solid oxide fuel cells, since finely structured coatings offer improved properties over conventionally spray ones, for example lower thermal diffusivity and higher catalytic activity. One challenge is the optimization and understanding of the injection process. With a new high speed shadowgraphy setup, the injection and atomization of individual drops was observed and described in detail in this work which is, to our best knowledge, not reported before. A drop atomization cone model is derived from observations. A new modelling approach is developed which allows the prediction of the drop atomization cones by analytical calculations. The simulations are compared to measurements and deviations are explained by neglected effects which will be included in further developments of this model.
Adhesion of Ceramic Coating on Thin and Smooth Metal Substrate: A Novel Approach with a Nanostructured Ceramic Interlayer
Authors: Vert R. , Carles P. , Laborde E. , Mariaux G. , Meillot E. , Vardelle A.
Published: November 2022

The adhesion of plasma-sprayed coating is to a large extent controlled by the cleanness and roughness of the surface on which the coating is deposited. So, most of the plasma spray procedures involve surface pretreatment by grit-blasting to adapt the roughness of the surface to the size of the impacting particles. This preparation process brings about compressive stresses that make it inappropriate for thin substrates. The present works aims to elaborate a ceramic coating on a thin metal substrate with a smooth surface. The coating system is intended for use in a generation–IV nuclear energy system. It must exhibit a good adhesion between the ceramic topcoat (about 0.5-mm thick) and the smooth metal substrate (1-mm thick) to meet the specifications of the application. Our approach has consisted in depositing the ceramic layer on a few micrometers thick ceramic layer made by suspension spraying. We have observed the interface between both ceramic layers by transmission electronic microscope and studied the adhesion of the nanostructured layer by the Vickers Indentation Cracking technique and that of the coating system by tensile test.
Effect of Dispersed TiC Content on the Microstructure and Thermal Property of Shrouded-Plasma-Sprayed FeAl/TiC Composite Coatings
Authors: Tian L.-H. , Li C.-X. , Li C.-J. , Yang G.-J.
Published: November 2022

FeAl intermetallics matrix composites reinforced by ceramics particles such as titanium carbide have attracted much attention in recent years. In this study, shrouded plasma spraying with nitrogen as a protective gas was employed to deposit TiC particles dispersed FeAl/TiC composite coatings. Fe-35Al powder and Fe-35Al/TiC composite powders containing 35 vol.% and 45 vol.% TiC prepared by mechanical alloying were used as feedstock powders. The microstructure of the ball-milled powders and the as-sprayed coatings was characterized by scanning electron microscopy and X-ray diffraction. The mean coefficient of thermal expansion (CTE) of FeAl and FeAl/TiC was measured. The results showed that dense FeAl and FeAl/TiC coatings with low oxide inclusions were deposited by shrouded plasma spraying. The mean CTEs calculated based on the Reuss formula are reasonably consistent with those measured in the present study. As a result, the CTE of FeAl-based composite coating can be properly controlled by adjusting TiC content in the composite coating to match with that of the substrate.
Spraying of Metallic Powders by Hybrid Gas/Water Torch and the Effects of Inert Gas Shrouding
Authors: Kavka T. , Matějíček J. , Ctibor P. , Hrabovský M.
Published: November 2022

A hybrid DC arc plasma torch, combining water and gas stabilization, offers a high flexibility in plasma characteristics. These can be controlled in a wide range by the torch operational parameters, such as arc current and secondary gas flow rate. In this study, their influence on plasma spraying of tungsten and copper was investigated. To suppress the in-flight oxidation of the metals, inert gas shrouding was applied. In-flight particle diagnostics, analysis of free-flight particles and coatings was performed for spraying experiments in the open atmosphere and with argon shrouding. Both in-flight particle behavior and coating properties were found to be sensitive to the torch parameters. The application of shrouding was found to affect particle in-flight parameters, reduce the oxide content in the coatings and generally improve their properties, such as thermal conductivity. However, different degree of these effects was observed for copper and tungsten.
Development of Optical Monitoring of the Thermal Spraying
Authors: Chivel Yu. , Smurov I.
Published: November 2022

A new approach has been made in monitoring of the thermal spraying. Monitoring of the process is based on visualization of particles movement using both high speed video camera and wide-band high intensive illumination and measurements of particles temperature velocity and size and their distribution. Synchronously with the registration of the particles parameters surface temperature of the coating has been measured with 2-channel pyrometer with a high spatial and a temporal resolution. The results of investigations of the Cold spraying and D-gun spraying are presented.