Plasma Spraying Process Parameters Research Articles

Study on the Microstructure, Corrosion Resistance and Dielectric Properties of Atmospheric Plasma-Sprayed Y2O3 Ceramic Coatings

Atmospheric plasma spraying (APS) is one of the most efficient processes for the preparation of yttrium oxide (Y2O3) ceramic coatings. Changing the spraying process parameters can significantly improve the microstructure and enhance the coating properties. In this study, the combination of plasma-spraying process parameters (current, spraying distance, and argon (Ar) flow) was varied by Response Surface Methodology (RSM) with the help of Minitab 19 software. Applied to the design of experiments, improvement of errors, and prediction of microstructure property results, the optimization and validation of experimental parameters for attaining the desired microstructure of Y2O3 coatings, especially porosity, was achieved. Process parameters were optimized by RSM: current 613.64 A, Ar flow rate 46.92 L/min, spray distance 15.38 cm, and optimum porosity 1.8% after optimization. Electrochemical corrosion experiments and breakdown voltage experiments revealed that the corrosion resistance and dielectric properties increased significantly as the porosity of the coatings decreased. Therefore, by optimizing the plasma-spraying process parameters, the porosity of the coatings can be significantly reduced and the corrosion resistance and dielectric properties of Y2O3 coatings can be effectively improved.

Thermal plasma spraying of NiTi powder for thick coating of shape memory alloy

In this article, NiTi coating was fabricated via a thermal plasma process by tuning various parameters. The work aims to achieve shape memory behavior that could retained in the plasma-sprayed samples. Various plasma spraying process parameters such as plasma power, powder feed rate, spraying plan, and net powder spray were taken into consideration for the spraying. Microstructural, thermal, mechanical, and shape memory behavior was analyzed on the plasma-sprayed samples. Various phases austenite, martensite, and intermetallic phases such as NixTiy, Ni-Ti-O, Ni, and Ti were confirmed from the X-ray diffraction analysis. The presence of these phases in the samples contributes to the thermal transformation and mechanical behavior. A less heat-affected zone of 10 µm along the interface was confirmed without any diffusion of elements from the substrate to the coating layers. There was a homogenous distribution elemental composition of Ni and Ti throughout the coating layers. The shape memory behavior of the coating samples was confirmed by the thermo-mechanical analysis by performing the response in multiple cycles.

Influence of air plasma spraying process parameters on the thermal barrier coating deposited with micro- and nanopowders

Abstract This study investigates the optimal conditions to deposit a thermal barrier coating using micro- and nanopowders in the air plasma spraying (APS) process. The influence of the APS process parameters on the thickness, porosity and hardness of the yttria-stabilized zirconia (YSZ; ZrO2 × 8Y2O3) coatings deposited with a single-electrode plasma gun was determined. The temperature and velocity of melted particles were determined by the DPV diagnostic system to decrease the number of experimental processes. The current and H2 flow rate were changed in this research. Metco-6700 YSZ micropowder has already been used in plasma spray physical vapor deposition. The results of this study suggest the possibility of using it for APS. The particles of this powder are characterized by high temperature (2,700°C–2,900°C) and high speed (>380 m/s). The highest thickness of the coating was obtained with 6 NLPM (normal liter per minute) H2 flow and 800 A current. Difficulties were observed with the feeding of the powder particles at higher H2 flow. The results showed that using APS, deposition of Metco-6609, a nanopowder normally used in suspension plasma spraying, is possible. In this research, this powder was fed using a carrier gas. The coatings were around 40 μm thick and had high porosity. The lowest porosity of the coating was obtained at a current of 600 A and H2 flow rate of 12 NLPM. In the coatings, unmelted spherical particles were also visible.

Machine Learning-Assisted Design of Yttria-Stabilized Zirconia Thermal Barrier Coatings with High Bonding Strength.

As a high-quality thermal barrier coating material, yttria-stabilized zirconia (YSZ) can effectively reduce the temperature of the collective materials to be used on the surface of gas turbine hot-end components. The bonding strength between YSZ and the substrate is also one of the most important factors for the applications. Herein, the Gaussian mixture model (GMM) and support vector regression (SVR) were used to construct a machine learning model between YSZ coating bonding strength and atmospheric plasma spraying (APS) process parameters. First, GMM was used to expand the original 8 data points to 400 with the R value of leave-one-out cross-validation improved from 0.690 to 0.990. Then, the specific effects of APS process parameters were explored through Shapley additive explanations and sensitivity analysis. Principal component analysis was used to explain the constructed model and obtain the optimized area with a high bonding strength. After experimental validation, the results showed that under the APS process parameters of a current of 617 A, a voltage of 65 V, a H2 flow of 3 L min–1, and a thickness of 200 μm, the bonding strength increased by more than 19% to 55.5 MPa compared with the original maximum value of 46.6 MPa, indicating that the constructed GMM–SVR model can accurately predict the bonding strength of YSZ coating.

Artificial neural network model of hardness, porosity and cavitation erosion wear of APS deposited Al2O3 -13 wt% TiO2 coatings

The aim of the article is to build-up a simplified model of the effect of atmospheric plasma spraying process parameters on the deposits’ functional properties. The artificial neural networks were employed to elaborate on the model and the Matlab software was used. The model is crucial to study the relationship between process parameters, such as stand-off distance and torch velocity, and the properties of Al2O3-13 wt% TiO2 ceramic coatings. During this study, the coatings morphology, as well as its properties such as Vickers microhardness, porosity, and cavitation erosion resistance were taken into consideration. The cavitation erosion tests were conducted according to the ASTM G32 standard. Moreover, the cavitation erosion wear mechanism was presented. The proposed neural model is essential for establishing the optimisation procedure for the selection of the spray process parameters to obtain the Al2O3-13 wt% TiO2 ceramic coatings with specified functional properties.

Investigation of Influence of Plasma Spraying Process Parameters on the Level of Residual Stresses

The method to determine thermal fields considering dependence of thermophysical and mechanical properties of coating materials and a base from the temperature, the running of plastic deformations and stresses relaxation at plasma spraying is suggested. The mathematical model of calculation of thermal field with moving boundary considering nonlinear feature of coating growth at layer-by-layer deposition and dependences from thermophysical properties of materials of the system «coating-base» is developed. The model application helps to estimate the effect of the parameters of plasma spraying process on the level of the residual stresses in the increased coatings.

Optimization of atmospheric low-power plasma spraying process parameters of Al2O3-50wt%Cr2O3 coatings

The work is focused on the effect of the processing parameters of Al2O3-50wt%Cr2O3 coatings manufactured by low-power plasma spraying systems on the microstructure, mechanical properties, and tribological behaviour. Design of experiments followed by an optimization process using desirability functions has been applied for the selection of the processing parameters. The results indicate that power is the crucial parameter that controls the microstructure and consequently, the mechanical response of the coatings. At high powers, the highest volume of hard phases is attained, which leads to the highest hardness values and the best wear resistance at high applied loads. On the contrary, at low powers, the highest volume of spinels (tough phases) is observed, resulting in the highest indentation fracture toughness values and the best wear response at low applied loads. Therefore, the mechanical properties are directly related to the contents of the tough and hard phases.

Current Progress in Solution Precursor Plasma Spraying of Cermets: A Review

Ceramic and metal composites, known also as cermets, may considerably improve many material properties with regards to that of initial components. Hence, cermets are frequently applied in many technological fields. Among many processes which can be employed for cermet manufacturing, thermal spraying is one of the most frequently used. Conventional plasma spraying of powders is a popular and cost-effective manufacturing process. One of its most recent innovations, called solution precursor plasma spraying (SPPS), is an emerging coating deposition method which uses homogeneously mixed solution precursors as a feedstock. The technique enables a single-step deposition avoiding the powder preparation procedures. The nanostructured coatings developed by SPPS increasingly find a place in the field of surface engineering. The present review shows the recent progress in the fabrication of cermets using SPPS. The influence of starting solution precursors, such as their chemistry, concentration, and solvents used, to the micro-structural characteristics of cermet coatings is discussed. The effect of the operational plasma spray process parameters such as solution injection mode to the deposition process and coatings’ microstructure is also presented. Moreover, the advantages of the SPPS process and its drawbacks compared to the conventional powder plasma spraying process are discussed. Finally, some applications of SPPS cermet coatings are presented to understand the potential of the process.

Effect of APS process parameters on high-temperature wear behavior of nickel–graphite abradable seal coatings

It has been a while since abradable coatings have been used in turbine engines to seal the gap between rotating and stationary components to protect these parts and increase the efficiency of engines. The properties of these coatings should satisfy the need of low wear resistance to seal the gap without any damage to the parts involved, and high erosion resistance against compressed air trying to pass through the gap. Many parameters are involved in order to tailor the coatings' properties to the needs; in this work, the effect of atmospheric plasma spraying (APS) process parameters such as hydrogen flow rate as the secondary plasma gas and spraying distance on wear behavior of nickel-graphite (Ni-G) abradable seal coatings at 400°C have been investigated. The results showed these parameters have a direct impact on the hardness, adhesion strength, coefficient of friction and consequently wear resistance of the coatings.

The Influence of LPPS Process Parameters on Porosity and Microstructure of MCrAlY Coatings

In present article the influence of Low Pressure Plasma Spraying (LPPS) process parameters on microstructure of MCrAlY coatings was studied. Nowadays the Atmospheric Plasma Spray (APS) is the most widely used process to obtain MCrAlY-type coatings. The LPPS process may be consider as an alternative technology for deposition of this type coatings which have less porosity and smaller amount of oxides compared to APS coatings. This features are important to obtain coatings with better hot corrosion and oxidation resistance. In order to determine and optimize the process parameters the microscopic investigations were carried out. Assessment of microstructure, thickness of coating and porosity level was conducted as well. Correlation between LPPS parameters and obtained microstructure have been found. It has significant meaning for deposition of MCrAlY coatings which could be applied as a bond coat in thermal barrier coating (TBC).

Optimization of the Atmospheric Plasma Spray Parameters using Design of Experiments for Coatings on AISI 410 Stainless Steel

ABSTRACTIn this work, the effect of three principal and independent parameters of Atmospheric Plasma Spray on the properties of coatings deposited using mixtures of commercial powders of titanium dioxide (TiO2) and chromium oxide (Cr2O3) was studied. The results of this work are used for special applications on turbomachinery components such as wear protection in sliding seals and in steam valves for turbines, chemical protection for centrifugal compressor members, and special seal applications.The design of experiments (DoE) technique has proved to be very useful to study the influence factors and optimization. Pierlot et al. [1] demonstrated that the application of the Hadamard and two factorial design techniques are useful for the optimization of thermal spray processes. An example of the application of the DoE is the one mentioned by Murugan et al. [2]. In their work, a factorial design was used to study the interactions between gas flow, oxygen flow, powder rate and spray distance on the percentage of porosity and hardness of TiO2- Cr2O3composite coatings generated by High Velocity Oxy-Fuel.The ½ fractional two-level factorial DoE technique was used to analyze and optimize the Atmospheric Plasma Spray process parameters. In the current research, experiments were conducted varying the deposition velocity, gas flow and stand-off distance. The effect of these process variables were evaluated by thickness, hardness and microstructure analysis. In this study, an empirical relationship between process variables and response parameters was developed. The entire relationship was made using the results of the DoE.

Plasma sprayed hydroxyapatite coatings: Understanding process relationships using design of experiment analysis

Abstract The biocompatibility and osteoconductivity of hydroxyapatite (HA) coatings have led to their use in a wide range of applications in dentistry and orthopaedics. One such application is for the uncemented fixation of implants, where coatings are commonly applied to titanium implants using a plasma thermal spraying process. The spraying process is affected by a large number of parameters leading to highly complex process–property–structure relationships. In a step forward from one-at-a-time analyses, this study used Design of Experiment (DOE) methodology to investigate the simultaneous effects of key plasma spray process parameters on hydroxyapatite coatings for biomedical applications. The effects of five plasma spray process parameters (current, gas flow rate, powder feed rate, spray distance and carrier gas flow rate) on the roughness, crystallinity and purity of hydroxyapatite coatings was determined using a fractional factorial design. The results of this study enabled identification of consistent and competing influences within the process and the identification of some first order interactions. In particular, the diffuse particle size of the HA feedstock powder was found to influence the responses observed within the parameter range investigated. The roughness of HA coatings was found to relate to the particle velocity and the degree of particle melting occurring, with higher coating roughness resulting when current was high, gas flow rate was low and powder feed rate was high. Highest coating crystallinity resulted at high current, low spray distance and low carrier gas flow rate. Under these conditions deposition of larger HA particles resulted leading to higher amounts of bulk crystalline material and the low spray distance increased the substrate temperature allowing amorphous material to recrystallise. Coating purity relates directly to thermal decomposition of the particles within the plasma jet with a high purity coating resulting at low particle temperatures i.e. at the lower ranges of powder feed rate, spray distance and carrier gas flow rate. This study thus brings greater clarity on the effects of plasma spray process parameters on the properties of resultant hydroxyapatite coatings.

Effect of experimental parameters on the micro hardness of plasma sprayed alumina coatings on AZ31B magnesium alloy

Abstract Surface treatment of engineering materials has recently become important for serviceable engineering components. Many techniques such as thermal and thermo chemical surface treatments have been used to develop surface characteristics of materials. Hardness is the most important property, which influences considerably service life characteristics of coatings. In this investigation, alumina coatings were deposited by atmospheric plasma spray technique under different levels of power, stand-off distances and powder feed rates. Empirical relationship was developed to predict the micro hardness of alumina coatings by incorporating the plasma spray process parameters. The input power and the stand-off distance appeared to be the most significant two parameters affecting the hardness of the coating among the three investigated process parameters. Further, correlating the spray parameters with coating properties enables the identification of characteristics regime to achieve desired quality of coatings.

Optimization of the process parameters in generic thermal barrier coatings using the Taguchi method and grey relational analysis

The purpose of this paper is to develop 7 wt% yttria stabilized zirconia (7YSZ) thermal barrier coatings by optimization of the atmospheric plasma spraying process parameters. Multiple-performance characteristics, such as coating thickness and surface roughness were considered for optimization. Eighteen experimental runs based on the L18 orthogonal arrays of the Taguchi method were used to show the best conditions among the plasma spraying parameters. Thereafter, best possible process parameters were obtained by the analysis of variance using grey relational analysis as the quality guide. Results signify the application possibility of the grey-based Taguchi technique for continuous development of quality coating in the area of advanced manufacturing technology.

Atmospheric Plasma-Sprayed Metal-Supported Solid Oxide Fuel Cells with Varying Cathode Microstructures

Metal-supported solid oxide fuel cells (SOFCs) use less expensive materials than traditional anode-supported or electrolyte-supported SOFCs. The active layers of a metal-supported SOFC can be manufactured by plasma spraying without the need for high-temperature sintering. Plasma spraying is a rapid-fabrication process that is scalable for large cell areas and for mass production. Porous ferritic stainless steel (Sanergy HT, Sandvik, Sweden) supports were manufactured from powders by pressing and sintering pellets. The active cell layers consisted of a composite nickel - yttria-stabilized zirconia (YSZ) anode, a YSZ electrolyte, and a La0.6­Sr0.4Co0.2Fe0.8O3-δ (LSCF) – Ce0.8Sm0.2O1.9 (SDC) cathode. Plasma spraying produces unique microstructures, as the cell layers are built up by the rapid solidification of molten (or semi-molten) splats. These microstructures were tailored by adjusting the plasma spray process parameters and the ingredients in the feedstock. Dense electrolytes were made using a high-power plasma, a very high torch pass speed (to minimize the plasma heat impulse to the substrate), and a feedstock consisting of YSZ suspended in a mixture of water, ethanol, and ethylene glycol. Cathodes with four different microstructures were produced by varying the plasma spray parameters and mixing carbon or starch-based pore forming agents into the ceramic feedstock powders. Resultant microstructures are shown in Figure 1. Electrochemical performances of metal-supported button cells with varying cathode microstructures were measured. At 750°C, the cells had open circuit potentials of up to 1.057 V and peak power densities as high as 562 mW/cm². Electrochemical impedance spectra were measured at an operating point of 0.7 V, varying the cathode gas with different air-nitrogen mixtures. With 100% air as the cathode gas, the lowest cell polarization resistance was 0.29 Ωcm² at 750°C. Equivalent circuit modeling was performed to analyse how the cathode microstructure affected the cell performance. Figure 1

Study of the Microstructure and Mechanical Properties of Pbsn Alloys Deposited on Carbon Fiber Reinforced Epoxy Composites

In this paper, four groups of the plasma spray process parameters (g1, g2, g3 and g4) of PbSn coatings deposited on carbon fiber reinforced epoxy composites (CFRE composites) were examined. The microstructure and phase composition of the as-sprayed coatings have been examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The bonding strength of the coatings to the substrates was detected on a RGD-5 tensile testing machine. Results indicate that the melting extent and the bonding strength of the coatings were evidently improved and the porosity decreased with the g3 parameters. However, the phases and the content of crystalline of PbSn coatings were slightly changed with all of the parameters.

Densification of Plasma Sprayed SOFC Electrolyte Layer Through Infiltration With Aqueous Nitrate Solution

Electrolyte of the solid oxide fuel cells deposited by atmospheric plasma spraying of 8 mol.% yttria (8YSZ), is not applicable in as sprayed condition. Optimization of the plasma spraying process parameters or application of feedstock powder, consisting of 8YSZ and 5wt.% alumina improves the problem of gas leakage through electrolyte layer, whereas provides no solution to the problem of electrodes short-circuiting. Infiltration of deposited electrolyte layer with a thin aqueous solution of nitrate precursors of 8YSZ for one time is a solution to high gas permeability; however three infiltration cycles are required to omit the risk of electrodes short circuiting thoroughly.

Parametric study of suspension plasma spray processing parameters on coating microstructures manufactured from nanoscale yttria-stabilized zirconia

A parametric study was conducted to determine the effect of suspension plasma spray (SPS) processing parameters, including plasma torch standoff, suspension injection velocity, injector location, powder loading in the suspension, and torch power, on the final microstructure of coatings fabricated from 80 nm diameter yttria-stabilized zirconia (YSZ) powders. Coatings made with different conditions were analyzed via stereology techniques for the amount of unmelted powder and spherical particles, which are undesirable features in a thermal barrier coating. Observation of unmelted powders, generally in the form of submicron-sized clusters of nanometer-sized powders, indicated insufficient plasma enthalpy or time in the plume to evaporate the liquid carrier in the fragmented droplet and melt the remaining powders. For coatings produced with a 4 cm standoff, a suspension injection velocity of 23 m/s, or a torch power of 21 kW, unmelted powders covered between 20 and 50% of the surface area. The presence of micron-sized spherical particulates was an indication of either partial powder melting or complete melting and re-solidification of a YSZ powder cluster prior to impact with the substrate. A 6 cm standoff, suspension injection velocity of 15 m/s, or 10 wt.% YSZ powder suspension each yielded coatings in which spherical particles comprised more than 8% of the coating surface area. The parametric study findings and the plasma-spray literature were employed to further modify the SPS experimental parameters to produce coatings that minimize unmelted powder and spherical particulates. The improved spray parameters for 80 nm diameter YSZ particles were found to be suspensions comprised of 8 wt.% YSZ powder, a 21 m/s suspension injection velocity (corresponding a ~ 50 ml/min volumetric flow), a 5 cm standoff, and a torch power of 50 kW. With these conditions less than 2% of the coating top surface area was covered by unmelted powder and spherical particulates.

Effect of suspension plasma spraying process parameters on YSZ coating microstructure and permeability

Suspension plasma spraying (SPS) is a modification of plasma spray processes that uses small feedstock powders suspended in a liquid to rapidly produce fully sintered, thin ceramic coatings with good microstructural control and no need for post-deposition heat treatments. This technique has been proposed as a potential next generation manufacturing method to fabricate metal supported solid oxide fuel cells (SOFC). This study produced SPS YSZ layers and characterized the effect of torch power and particle velocity on coating physical properties that are relevant to SOFC electrolyte performance such as density and permeability. The highest density (> 95% dense), lowest permeability coatings were produced from conditions with large plasma gas flow rates and small nozzles; however, these conditions resulted in low deposition efficiency. Coatings produced from conditions with slightly lower plasma gas flow rates and small nozzles were also fairly dense (93% dense) and had fairly low permeabilities, but had 70% higher deposition efficiency compared to the densest coatings.

Controlled Introduction of Anelasticity in Plasma‐Sprayed Ceramics

Recent studies on the mechanical compliance measurements of plasma‐sprayed ceramic coatings have revealed anelastic response, i.e. the stress–strain relations are nonlinear and hysteretic, collectively. The anelasticity stems from the “brick” layered assemblage of spray‐deposited droplets along with the presence of porosity and other geometric discontinuities. This anelastic response is reproducible and can provide a quantitative description on the mechanical properties of the sprayed ceramic coating. In this paper, we have examined strategies to manipulate and control these anelastic characteristics through plasma spray processing parameters as well as through extrinsic modifications of the defect interfaces. Plasma‐sprayed ceramic coatings are fabricated under various conditions and their unique anelastic parameters are computed. These results reveal that the novel properties are tunable via process and material manipulation, opening up opportunities for microstructural design and optimization of mechanical compliance in industrially relevant coating systems.