Plasma Spray Gun Research Articles

Structure and electrochemical behavior of coatings from complex concentrated alloys deposited by Metco Triplex Pro-210 gun

Complex concentrated alloys (CCAs) have gained a significant attention in the engineering and research community due to their unique phase structure and exceptional properties. CCAs are usually comprised of five or more principal alloying elements mixed in near-equimolar or equimolar ratio, which can derive their qualities from multiple principal elements owing to cocktail effect. In this study, atmospheric plasma spraying system equipped with a Metco Triplex Pro-210 gun was used to deposit CCAs designed coating compositions onto SS-316L steel substrate. The microstructure, mechanical and electrochemical behavior of the developed (CoCrFeNiMnx) CCAs were analyzed and compared to commercially used WC-17Co (Diamalloy 2005NS) and NiCr-75Cr2C3 (Metco 81NS) coatings deposited by APS Metco Triplex Pro-210 cascading arc plasma spray gun. The experimental results confirm that using Metco Triplex Pro-210 it is possible to manufacture a CCA coating layers with lower porosity, excellent phase stability in compare to conventional thermal spray processes. Coating characterization also reveals that the CCA coating’ grains experienced a significant amount of grain refinement as compared to those in as-received CCA feedstock powder materials due to the occurrence of shot peening effect and dynamic recrystallization caused by highly deformed splat boundaries during spraying process. The electrochemical results indicates that the CCA coatings have a lower corrosion rate in compare to its plasma sprayed counterparts.

Structural characteristics, oxidation performance and failure mechanism of thermal barrier coatings fabricated by atmospheric plasma spraying and detonation gun spraying

In recent years, thermal barrier coatings (TBCs) are widely applied to the surface of gas-turbine engines to prolong the service life of high temperature components. The increase in raw material requirements and costs has led to the search for an alternative, cheaper ceramic based material to yttria stabilized zirconia (YSZ), which is the traditional TBC top coating material. In this study, CoNiCrAlY metallic bond coating powders were deposited on Ni-based superalloy substrates by the detonation gun (D-gun) process. Commercial YSZ and blast furnace slag (industrial waste) powders were deposited on the bond coating by atmospheric plasma spraying (APS) technique. TBCs were subjected to isothermal oxidation tests for 8, 24, 50, and 75 h at 800 °C. The microstructural properties of the TBCs were evaluated comparatively using advanced characterization techniques before and after oxidation tests. It has been observed that the coatings produced using BFS material have a potential to be used in different types of industries as a low-cost and environmental solution against high temperature oxidation conditions.

Simulation of plasma spraying process based on Euler-Euler multi-phase model

According to the actual structure and size of plasma spraying gun, a simulation model based on the Euler-Euler multi-phase model was established with the parameters of medium energy in this study. The distribution nephogram of the temperature and velocity fields of tungsten powder particles and the working gas used in the spraying process were obtained. Additionally, through the mass distribution nephogram, the heating and melting processes of tungsten powder particles in the flame flow were analyzed, and the deposition behavior of the molten droplets of the tungsten powder was investigated. In order to verify the correctness of the simulation, an experiment is performed with the parameters of low energy, medium energy and high energy. This study was of significance in the development of spraying technology, as well as for the improvement on product performance.

Modeling of the Effect of Carrier Gas Injection on the Laminarity of the Plasma Jet Generated by a Cascaded Spray Gun

In this work, the plasma generated by the cascaded SinplexProTM plasma spray gun was studied by means of numerical simulation. Special attention is given to the laminarity of the plasma flow. The simulation part is divided into two parts: arcing simulation inside the spray gun and plasma jet simulation outside the spray gun. A laminar as well as a turbulent model is used in each case. The results show that, under the investigated conditions, the internal flow of the plasma torch can be considered as laminar with low turbulence and can, hence, be regarded as quasi-laminar flow. If carrier gas is injected into the plasma jet, the ideal laminar plasma jet is often greatly affected. However, the turbulent plasma jet with low turbulence intensity generated by the cascaded SinplexProTM plasma spray gun is less affected and can remain stable, which is beneficial to the plasma-spraying process.

Analysis of solid particle erosion in plasma sprayed alumina based coatings on SAE-347H steel

The erosion behavior of three different cermet coatings namely, Al2O3, Al2O3 + 3% TiO2 and Al2O3 + 13% TiO2 was studied in order to perform erosion analysis. The coatings were sprayed using Plasma spray gun in a simulated coal-fired boiler conditions on SAE-347H steel. An optical profilometer was put to use in order to find weight loss, erosion profiles and erosion rate (mm3/g) in term of volume loss. All the Plasma gun sprayed cermet coatings were able to protect SAE-347H steel from erosive wear at incident angles of 30°, 60° and 90°. In case of uncoated SAE-347H steel specimens the solid particle erosion (SPE) rate was highest at an incident angle of 30°, nominal at incident angle of 60° and lowest at incident angle of 90°.

Determination of residual stresses in thermal barrier coating due to the amount of CMAS infiltration

In this work, we present the effect of the amount of CMAS infiltration into YSZ of Thermal barrier coatings (TBC) on the magnitude of residual stresses. The (TBC) were deposited by thermal spraying of CoNiCrAlY (Bond Coat-BC) and YSZ (Top Coat-TC) powders. The deposition of the BC was through the high velocity oxygen fuel (HVOF) system. The TC was deposited via an atmospheric plasma-spraying gun (APS). The TBCs were heat treated at 1250 °C, with a CMAS attack at a concentration of 10 mg/cm².The attack exposure was for 2 and 4 hours respectively. In this evaluation, the measured parameter was the magnitude of the residual stress state in Yttria Stabilized Zirconia (YSZ). The residual stress profiles were obtained using the Modified Layer Removal Method for Duplex Coatings (MRCMRB) and the Noda equations. An increase of 26.446 MPa was determined for 2 hours of thermal treatment and 30.743 MPa for 4 hours.

COMPARISON OF Mo COATING DEPOSITED BY TWAS AND APS SinplexPro THERMAL SPRAY TECHNIQUES

The wear resistant Mo coatings were deposited using SmartArc Electric Arc Wire Spray System and advanced SinplexPro high throughput atmospheric plasma spray gun. The coatings were analyzed in terms of microstructure, mechanical properties and tribological characteristics, including wear rate and wear mechanism. It was shown that despite of the differences in deposition process principles, the properties of the coatings don’t differ with respect to their functional properties. Both coatings reached comparable hardness, microhardness, wear resistance and coefficient of friction. The economic aspects remain the main argument for the recommendation of the most suitable thermal spray deposition technique for the application of molybdenum coatings.

Hot corrosion behaviour of plasma and d-gun sprayed coatings on t91 steel used in boiler applications

Material degradation by salt induced hot corrosion is a serious threat to Coal fired Boiler components. Corrosion resistant thermal spray coatings is a proven solution for this problem. Thiswork compares the hot corrosion behaviour of a NiCoCrAlY coating on T91 boiler steel deposited using two different thermal spray methods namely Atmospheric Plasma Spray (APS) and Detonation Gun (D-Gun) spray. The coated samples were exposed to 650°C for 100 cycles (1 cycle being 1 hour holding plus 20 minutes cooling in air) in a thermal cycling furnace under a mixed deposit containing Na2SO4, K2SO4 and Fe2O3 to simulate the real time coal ash environment. The exposed coatings were examined using FESEM/EDS and XRD to analyze the extent and nature of corrosion attack. The results indicate that the D-Gun sprayed coatings provided superior corrosion resistance over their APS sprayed counterparts. NiO and Spinel oxide NiCr2O4 which offers corrosion resistance were formed in both the coatingswith the APS sprayed coatingbeing rich in the fast growing NiO which affected its corrosion performance. The enhanced corrosion resistance of the D-Gun sprayed coatings was attributed to its dense microstructure with minimal porosity and good intersplat bonding which minimized corrosion ingress.

Effect of Electromagnetic Boundary Conditions on Reliability of Plasma Torch Models

The cascaded-anode plasma torch makes it possible to get a longer and more stable plasma jet with higher specific enthalpy than conventional plasma torches. It is now used widely, but there are still few models of the cascaded-anode plasma torch. This study developed a 3-D time-dependent model that couples the gas phase and electrodes by encompassing the electromagnetic and heat equations both in the electrodes and gas phase. The model was applied to a commercial plasma spray gun equipped with a single cathode, single cylindrical anode and an inter-electrode insert to fix the average arc length. This paper examines the effect of the boundary conditions for the magnetic vector potential and electric current density on the electromagnetic, velocity and temperature fields of the plasma jet. The model predictions showed that, for such plasma torches where the arc is close to walls, the Biot and Savart formalism is required at the domain boundaries for the magnetic vector potential. They also showed that similar plasma fields could be obtained by imposing an electric current density profile at the cathode tip or by including the electrodes in the computational domain. However, this profile has to be chosen according to the specific design of the cathode, which is not obvious when the cathode has a design different from that of conventional plasma torches with sharp conical tip or rounded tip.

Trajectory control and parameter optimization of plasma robot gun

A plasma robot model with redundant freedom is proposed for the shortage of flexibility in the complex working environment of plasma robot. The existence of redundant degrees of freedom leads to the complex motion characteristics of the plasma robot joints. The trajectory of the end of the spray gun is difficult to describe. Therefore, a trajectory optimization algorithm based on fitness function is proposed. In the plasma robot joint space, a parabolic linear fitting is adopted. The error between the actual trajectory and the desired trajectory is taken as fitness function. Genetic algorithm is applied to find the optimal solution for the parameters in trajectory planning. The orthogonal experimental model of the parameters of the plasma spray gun is set up. The optimum working parameters of the spray gun are obtained through the analysis and study of the power, atmospheric pressure and the distance of the gun. Finally, the rationality of the proposed method is proved by simulation and test.

Effects of Gun Scanning Pattern on the Structure, Mechanical Properties and Corrosion Resistance of Plasma-Sprayed YSZ Coatings

Due to the non-symmetric distribution of sprayed particle plume in conventional plasma spraying caused by the radial injection of feedstock powder into a plasma jet, significant influence of the gun scanning pattern can appear in the structure of the sprayed coatings. Especially, the portion of poorly treated powder flux can be a cause of horizontal cracking as well as poor coating adhesion. In this study, three different scanning patterns of an air plasma spray gun were adopted with a commercial ZrO2-8 mass% Y2O3 (YSZ) powder. The cross sections of the obtained YSZ coatings were observed by SEM, while interfacial fracture toughness was measured by the indentation method, and hot corrosion testing was conducted. It was found that by modification of the gun scanning pattern, it is possible to decrease the possibility of horizontal weak bonding between spray passes and improve the coating adhesion and corrosion resistance.

Wear behaviour of plasma sprayed WC−12%Cο and Al2O3−13%TiO2 coatings on ASTM A36 steel used for I.D. fans in coal fired power plants

Erosion is a major problem for the power generation plants for any country. A very high cost induced per annum accounting for the downtime of replacement/repair of boiler components of coal fired power plants due to oxidation and erosion.Thermal spray coating technique is a method used for coating the mechanical components in order to enhance the surface properties of the base material like resistance to corrosion, wearand erosion. In the present study, the cermet powders and coatings (wt% age) are applied on steel substrate with the help of plasma spray gun technique. Techniques like XRD, SEM/EDX and EPMA analysis have been used for characterization of the coatings. These coated materials were subjected to a Pin-on-Disc wear testing.The coated samples have shown almost negligible wear loss as compared to the uncoated samples. Further sliding wear resistance of is almost double of that of coated samples.

Optimizing of hardness, microstructure and adhesive strength of plasma-sprayed FeSiAl coatings using orthogonal analysis

The traditional high-efficiency absorber FeSiAl has gradually achieved the attention at high temperature. The paper focuses mainly on the preparation and characterization of plasma-sprayed FeSiAl coatings. The plasma-sprayed FeSiAl coatings were prepared through the Praxair 100HE high enthalpy plasma spray gun on stainless steel 316 substrate by orthogonal experiment. The cross-section and properties of sprayed coatings were analyzed. The results reveal that the best parameters of sprayed coatings can be represented by C3B2A3D2 for microhardness, i.e., 30 SCFH, 140 mm, 50 KW, 3 PRM. The optimal parameters can be expressed as C3D1B3A3 for adhesive strength, i.e., 30 SCFH, 2 PRM, 200 mm, 50KW. The cross-section of sprayed coatings is composed of fattening FeSiAl particles (pale gray) and oxidation phase of FeSiAl (dark). The percentage of disorder structure reduces in FeSiAl coatings.

Influence of Feedstock on the Microstructure of Sm2Zr2O7 Thermal Barrier Coatings Deposited by Plasma Spraying

Four Sm2Zr2O7 (SZO) powders with different morphologies were deposited by atmospheric plasma spraying on superalloy substrates using the same spraying parameters. Both the particle size distribution and microstructure of the powders had an important effect on the coating microstructure. SZO thermal barrier coatings (TBCs) deposited using the powder with a narrow particle size distribution showed a better “molten state” and exhibited a higher average bonding strength compared with the SZO TBCs deposited using the powder with a wide particle size distribution. The dense microstructure of the calcined powder sintered at high temperature and of the powder spheroidized by plasma spraying gun (SF) improved the melting capacity of the powders, and the resulting coatings showed a compact microstructure with unique bimodal structures. Furthermore, the SF SZO TBCs presented an excellent “molten state” with a smooth surface and exhibited a high bonding strength of 29.6 ± 0.15 MPa.

Experimental study of the dynamic indentation damage in thermally shocked granite

This paper presents an experimental procedure to study the effects of pre-existing cracks and damage on the rock behavior under dynamic indentation. To gain better understanding on the mechanism involved in percussive-rotary drilling procedure, a modified Split Hopkinson Pressure Bar device was used to carry out dynamic indentation tests, where rock drill buttons were impacted on rock samples with dimensions of 30 cm × 30 cm × 30 cm. Before the mechanical testing, the samples were thermally shocked using a plasma spray gun for periods of 3, 4, and 6 seconds. The plasma gun produces a powerful heat shocks on the rock sample, and even short exposures can change the surface structure of the samples and provide samples with different crack patterns and surface roughness for experimental testing. The effects of the heat shock damage on the dynamic indentation behavior of the rock were characterized with single- and triple-button indentation tests. The specific destruction work was used to characterize the effects of heat shocks on the material removal during dynamic indentation. The results show that the force-displacement response of the rock does not change much even if the rock surface is severely damaged by the heat shock, however, the destruction work decreases significantly. This means that the same loading removes more volume if the material surface is pre-damaged, and that the efficiency of the indentation process cannot be evaluated from the bit-rock interaction forces alone. The presented experimental framework can be a useful tool for the verification of numerical models where the rock microstructure and especially the microcracks are essential.

Bonding Strength and Thermal Insulation Property of Thermal Barrier Coating with Nanometer Alumina Coated Zirconia

The thermal barrier coating samples of different thickness with alumina coated zirconia and zirconia as coating materials were prepared on the surface of heat resistant alloy steel substrate after activation treatment with NiCoCrAlY as adhesive transition layer by plasma spraying method and spray gun quick spraying process. The bonding strength and thermal insulation property of two kinds of ceramic coating with the same thickness were compared by the test results of bonding strength, high temperature heat insulation and microstructure, and the relationship between the coating thickness and heat insulation effect were investigated. The results indicate that the structure and property of thermal barrier coating using nanoAl2O3coated ZrO2-Y2O3powder are superior to that using single zirconia powder. The thermal insulation property of the thermal barrier coating increased with the increasing of coating thickness, and the advantage is more obvious with temperature increasing.

Failure Analysis of Multilayered Suspension Plasma-Sprayed Thermal Barrier Coatings for Gas Turbine Applications

Improvement in the performance of thermal barrier coatings (TBCs) is one of the key objectives for further development of gas turbine applications. The material most commonly used as TBC topcoat is yttria-stabilized zirconia (YSZ). However, the usage of YSZ is limited by the operating temperature range which in turn restricts the engine efficiency. Materials such as pyrochlores, perovskites, rare earth garnets are suitable candidates which could replace YSZ as they exhibit lower thermal conductivity and higher phase stability at elevated temperatures. The objective of this work was to investigate different multilayered TBCs consisting of advanced topcoat materials fabricated by suspension plasma spraying (SPS). The investigated topcoat materials were YSZ, dysprosia-stabilized zirconia, gadolinium zirconate, and ceria–yttria-stabilized zirconia. All topcoats were deposited by TriplexPro-210TM plasma spray gun and radial injection of suspension. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. Microstructure analysis of as-sprayed and failed specimens was performed with scanning electron microscope. The failure mechanisms in each case have been discussed in this article. The results show that SPS could be a promising route to produce multilayered TBCs for high-temperature applications.

Spatially-resolved velocities of thermally-produced spray droplets using a velocity-divided Abel inversion of photographed streaks

Droplet velocities of thermal spray are known to have profound effects on important coating qualities, such as adhesive strength, porosity, and hardness, for various applications. For obtaining the droplet velocities, therefore, the TOF (time-of-flight) technique has been widely used, which relies on observations of emitted radiation from the droplets, where all droplets along the line-of-sight contribute to signals. Because droplets at and near the flow axis mostly contribute coating layers, it has been hoped to get spatially resolved velocities. For this purpose, a velocity-divided Abel inversion was devised from CMOS photographic data. From this result, it has turned out that the central velocity is about 25% higher than that obtained from the TOF technique for the case studied (at the position 150 mm downstream of the plasma spray gun, where substrates for spray coatings are usually placed). Further implications of the obtained results are discussed.

Thermo-electrical properties of the alumina coatings deposited by different thermal spraying technologies

Abstract Thermal and electrical properties of alumina (Al 2 O 3 ) coatings produced via Atmospheric Plasma Spraying (APS) and Detonation Gun Spraying (DGS) were investigated and compared in this study. A combination of Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) analysis, image analysis and X-ray Diffraction analysis (XRD) were used to better understand microstructural characteristics of as-sprayed alumina coatings. Microstructure formation of coating layers and its main features such as splats, pores, and boundaries were experimentally observed for both deposited coatings. The measurement of splats average thickness indicated that splat sizes, as building blocks of coatings were approximately similar for both coatings. The XRD showed that feedstock was pure α-Al 2 O 3 , but both deposited alumina coatings contained the mixture of α-Al 2 O 3 and γ-Al 2 O 3 phases. However, the amount of α-Al 2 O 3 phase was two times higher in DGS deposited coating. The DGS deposited coatings were also had a higher hardness compared to APS deposited one. The electrical properties of alumina coatings were measured using the pseudo two-contact impedance spectroscopy method that allowed separation of the electrical resistivity of splats and their boundaries within the coating microstructure. The obtained results showed significant difference between these two features in terms of electrical resistivity, namely splats had 5 orders of magnitude smaller resistivity compared to the splat boundaries. In addition, DGS deposited coating was characterized with higher electrical resistivity of splats and splat boundaries compared with APS coating. Finally, the experimentally measured thermal conductivities of alumina coatings showed higher thermal conductivity in DGS deposited coatings compared to the APS ones. These values were validated using analytical models and Finite Element Analysis (FEA).

Low power consumption suspension plasma spray system for ceramic coating deposition

Suspension plasma spraying (SPS) is a modification of conventional plasma spray techniques that has been developed to overcome the challenge of using nano-sized particles in plasma spray processes. The novel feature of using nano-sized particles in the form of a suspension makes the SPS process promising for several applications and for improving the performance of plasma spray coatings. The focus of this study is to develop a new SPS system that consumed low power and gas to deposit ceramic coatings.Several ceramic coatings, such as titanium dioxide (TiO2), aluminum oxide (Al2O3), yttrium oxide (Y2O3), and yttria-stabilized zirconia (8YSZ), were successfully fabricated using only Ar as the plasma gas at a low power of 27kW with the new SPS system. The new system is characterized by lower power and gas consumption (only Ar as plasma gas) and axial injection. It is a unique SPS system based on a twin-cathode-type plasma spray gun. The gun has three plasma torches, the main one is called a P-torch (anode) and the two sub-torches are called N-torches (cathodes). The main plasma torch has a reversed polarity (with a cathode nozzle and an anode electrode). The two sub-torches have normal polarity (with an anode nozzle and a cathode electrode). During operation, electric power is supplied between the anode of the P-torch and the two cathodes of the N-torches, so that the so called hairpin-shape of the plasma jet can be maintained. The system requires only argon as the plasma gas (without using any other gases). The voltage (enthalpy of the plasma jet) with Ar is high enough (150V) for melting ceramic powders, which results in a gas consumption SPS system compared to the other available SPS systems. Furthermore, the electrode of the main torch (P-torch) is a hollowed anode, so that axial feeding of spraying materials could be carried out in this system, which is the best method for spraying. In this configuration, the particles are injected into the center of the plasma jet along the axis of its flow. Therefore, the feedstock suspension would be fully entrapped and melted within the plasma before deposition on the substrate surface.