Thermal Plasma Spray Research Articles

Analysis of the ceramic layer microstructure influence on plasma spray thermal barrier coating performance

This paper outlines the results of analysis and describes the structure of the thermal protection coatings formed by atomic ion stream deposition in vacuum, and plasma thermal spraying method. Crystallite structure features are considered along with the crystallite dimensions, spatial orientation, and position of the boundaries between separate crystallites. Discontinuity, volume, and morphology of the pores has been evaluated. Experimental studies have been accomplished using various fractions of the powder-like material ZrO2 – 8%Y2O3. The influence of the coating microstructure on the coating performance has been analyzed, such as adhesive strength, thermal stability, and thermal conductivity.

A Confrontation of Lattice Boltzmann, Finite Difference and Taguchi Experimental Design Results for Optimizing Plasma Spraying Operating Conditions Toward Deposit Requirements

The aim of the present work is the confrontation of three numerical techniques results to optimize the operating conditions of thermal plasma spraying process. The Lattice Boltzmann method (LBM) is used to scrutinize dispersion effects of injection parameters on droplet impact characteristics when impacting substrate. The validation of the developed model shows good agreement with former findings. The results of spraying Zirconia particles give the values Kmin=88.2, Kmax=367.4, Kmean=273.8 and a standard deviation of 48.0 for the Sommerfeld number. The Taguchi experimental design study is conducted for five operating parameters of two levels. The ensuing retained factors combination give Kmean=258.9. To assess drawn conclusions, confirmation test was performed using the Jets&Poudres software. The results show that the prior way is to coat and particles of dp< 40.3 µm have evaporated, particles 40.3 = dp = 49 µm are fully molten and all particles of dp = 71.9 µm arrive fully solid.

Novel Approach in the Use of Plasma Spray: Preparation of Bulk Titanium for Bone Augmentations.

Thermal plasma spray is a common, well-established technology used in various application fields. Nevertheless, in our work, this technology was employed in a completely new way; for the preparation of bulk titanium. The aim was to produce titanium with properties similar to human bone to be used for bone augmentations. Titanium rods sprayed on a thin substrate wire exerted a porosity of about 15%, which yielded a significant decrease of Young′s modulus to the bone range and provided rugged topography for enhanced biological fixation. For the first verification of the suitability of the selected approach, tests of the mechanical properties in terms of compression, bending, and impact were carried out, the surface was characterized, and its compatibility with bone cells was studied. While preserving a high enough compressive strength of 628 MPa, the elastic modulus reached 11.6 GPa, thus preventing a stress-shielding effect, a generally known problem of implantable metals. U-2 OS and Saos-2 cells derived from bone osteosarcoma grown on the plasma-sprayed surface showed good viability.

The influence of HVOF spraying parameters on the microstructure, residual stress and cavitation resistance of FeMnCrSi coatings

Thermal spray processes can be used to apply erosion-resistant coatings to components. One of the most important is the HVOF (High Velocity Oxygen Fuel) process, which is characterized by lower temperatures and higher projection velocities than arc and plasma thermal spray processes. This study sought to analyze the influence of three process parameters (standoff distance, fuel/oxygen ratio and powder feed rate) on particle velocity, particle temperature, coating microstructure and residual stress formation in FeMnCrSi coatings deposited by a liquid-fuel HVOF process and the effect in turn of coating microstructure and residual stress on coating cavitation resistance. An increase in fuel flow and reduction in standoff distance resulted in increased particle velocity but did not significantly affect particle temperature. Varying the process parameters had a significant influence on the residual stress in the coatings. A correlation between compressive residual stress, increased hardness and reduced mass loss rate during ultrasonic cavitation testing was observed.

Radiation Spectral Analysis and Particle Temperature/Velocity Measurement in Plasma Spray with One-Color Camera

A color camera optical diagnostic imaging system has been developed for the measurement of temperature and velocity of individual in-flight particles in thermal plasma spray, based on the principle of particle streak velocimetry and two-color thermometry. Radiation spectral analysis of the characteristic behavior of a particle-laden plasma plume was performed to identify an optimal spectral range for accurate temperature measurements over which the powder particles and the interfering thermal plasma gas are discernable. Calibration of the thermal imaging system was carried out using a blackbody furnace with uncertainties less than 1.8%. Extensive experimental measurements were taken with the optical imaging system to obtain the temperature and velocity distributions of YSZ particles in practical plasma spraying applications. The uncertainties of the measured temperature and velocity with a color camera system mostly fluctuate around ±10% in comparison with data obtained from a commercially available measuring system.

Fabrication of 100 Centimeter Square Metal-Supported Solid Oxide Fuel Cell Using Thermal Plasma Technique

In this study, the large-scale mold for compression molding process is prepared and a compression load of 120 ton is applied to form a porous alloy specimen with dimension of 12×12×1.2 cm. The carbon is used as pyrolyzable filler in the period of manufacturing processes in order to produce porous interconnected networks of molybdenum (Mo)-containing nickel (Ni)-based alloy. The specimens are sintered in hydrogen at the temperature of 1250°C to obtain porous alloy substrate. The flexural strength of porous alloy supporting component is measured in this work. The strength of porous alloy substrate (Sintered at 1250°C) in three-point flexure at 25°C and 750°C are 188 MPa and 76.5 MPa, respectively. Metal-supported solid oxide fuel cells (MS-SOFCs) are fabricated by thermal plasma spraying technique and the anode (Ce0.55La0.45O2-δ -NiO,LDC-NiO), electrolyte (La0.8Sr0.2Ga0.8Mg0.2O3-δ, LSGM) and cathode (Sm0.5Sr0.5CoO3- δ,SSC) functional layers are deposited onto porous alloy substrate. The 10×10 cm2 MS-SOFC with effective electrode area of 81 cm2 shows the open circuit voltages is 1.09 V at 700°C. The measured maximum output power densities (@0.76V) of this cell has reached 588 mW/cm2 at 700°C by employing hydrogen as fuel and air as oxidant.

Fabrication of 100 Centimeter Square Metal-Supported Solid Oxide Fuel Cell Using Thermal Plasma Technique

In this study, the large-scale mold for compression molding process is prepared and a compression load of 120 ton is applied to form a porous alloy specimen with dimension of 120×120×1.2 mm. The carbon is used as pyrolyzable filler in the period of manufacturing processes in order to produce porous interconnected networks of molybdenum (Mo)-containing nickel (Ni)-based alloy. The specimens are sintered in hydrogen at the temperature of 1250°C to obtain porous alloy substrate. The flexural strength of porous alloy supporting component is measured in this work. The strength of porous alloy substrate (Sintered at 1250°C) in three-point flexure at 25°C and 750°C are 188 MPa and 76.5 MPa, respectively. Metal-supported solid oxide fuel cells (MS-SOFCs) are fabricated by thermal plasma spraying technique and the anode (Ce0.55La0.45O2-δ-NiO), electrolyte (La0.8Sr0.2Ga0.8Mg0.2O3-δ) and cathode (Sm0.5Sr0.5CoO3-δ) functional layers are deposited onto porous alloy substrate. The 10×10 cm2 MS-SOFC with effective electrode area of 81 cm2 shows the open circuit voltages is 1.09 V at 700°C. The measured maximum output power densities (@0.76V) of this cell has reached 588 mW/cm2 at 700°C by employing hydrogen as fuel and air as oxidant.

Novel hardmetals with nano-grain reinforced binder for hard-facings

Ordinary hard-facings obtained by plasma spraying or thermal spraying are characterized by a combination of hardness, wear-resistance and fracture toughness inferior to that of conventional WC-Co hardmetals. Therefore, in the majority of applications they are incomparable with WC-Co materials and cannot substitute them. A fundamentally new approach to the fabrication of novel WC-based hardmetals in form of hard-facing obtained by PTA (plasma transferred arc) welding was elaborated. The microstructure of the novel hardmetals of the W-C-Fe-Cr-Si system depends on the plasma welding parameters and consists of carbide grains embedded in a Fe-based binder. The binder comprises hard nano-precipitates in form of nanoparticles of the η-type phases and mixed Cr-Fe carbides embedded in a Fe-based binder matrix. The wear-resistance of the novel hardmetals obtained in form of hard-facings is comparable with that of conventional WC-Co hardmetals fabricated by the powder metallurgy technology.

AZO photocatalytic coating deposited by plasma thermal spraying with shell-type feedstock powder

Aluminum zinc oxide (AZO) was deposited on a glass substrate using plasma spraying technique. Hierarchical nanostructured morphology is observed, for the first time, in plasma spraying coatings. Nanorod and nanosphere adhere to micro spherical particle to form hierarchical structure, however, is only reported by chemical synthesis method. Through XRD and SEM analysis, it is found that the morphology of coating can improve the formation of defects greatly. After UV-A light testing, photocatalytic efficiency of coating was analyzed using UV–vis spectrometer. Combined with photoluminescence and X-ray photoelectron spectroscopy analysis, the results indicates that AZO coating is with good enhanced photocatalytic properties. This phenomenon suggests that AZO crystallites consist of multiple facets with high surface-energy planes. The measured water contact angle of about 7° indicates that AZO coating is with high hydrophilic characteristic and has very good practical applications in industry. This study thus paves a new way for environmental pollution control.

Production of Metal-Supported Solid Oxide Fuel Cell Using Thermal Plasma Spraying Technique

Metal-supported solid oxide fuel cells (MS-SOFCs) are prepared by the high-temperature plasma spraying technique in this paper. The positive electrolyte and negative functional layers are deposited onto porous alloy substrate using thermal plasma in the air. The porous alloy supporting component is produced by molding ( $6 \times 6$ cm2), pressing (35 ton), and sintering (e.g., 1000 °C, 1100 °C, 1200 °C, and 1250 °C). The $5 \times 5$ -cm2 MS-SOFC with an effective electrode area of 16 cm2 shows that the open-circuit voltages are 0.95 V (Cell-1100), 1.09 V (cell-1200), and 1.08 V (Cell-1250) at 650 °C. In addition, the maximum power at a cell potential of 0.6 V is 5.7 W (Cell-1100), 11.5 W (Cell-1200), and 12.1 W (Cell-1250) at 650 °C. Thermal expansion coefficient of porous alloy supporting component is also measured in this paper. MS-SOFCs without cracking and deforming following thermal plasma spraying process have good electrical performance. Atmospheric plasma spraying method is revealed as a suitable deposition technique for manufacturing MS-SOFCs.

Sea water corrosion behavior of plasma sprayed abradable coatings

Aluminum based abradable coating is used for sealing purpose in compressor casing of aero engines to withstand up to a service temperature of 450°C. Al-BNSiO2 composite coating is deposited using thermal plasma spray technique. Coating thickness measured and porosity of the coating is evaluated.Coating morphology is observed and EDSanalysis is done with SEM (Jeol make). The effect of time on the sea water corrosion behavior of the coating is evaluated. It is observed that, there is a sharp increase in weight gain of the coating up to six weeks of immersion. This behavior is attributed to the adsorption/deposition of other elements/reactions taking place during interaction with sea water.

The Influence of Anode Inner Contour on Atmospheric DC Plasma Spraying Process

In thermal plasma spraying process, anode nozzle is one of the most important components of plasma torch. Its inner contour controls the characteristics of plasma arc/jet, determining the motion and heating behaviors of the in-flight particles and hence influencing the coating quality. In this study, the effects of anode inner contour, standard cylindrical nozzle, and cone-shaped Laval nozzle with conical shape diverging exit (CSL nozzle) on the arc voltage, net power, thermal efficiency, plasma jet characteristics, in-flight particle behaviors, and coating properties have been systematically investigated under atmospheric plasma spraying conditions. The results show that the cylindrical nozzle has a higher arc voltage, net power, and thermal efficiency, as well as the higher plasma temperature and velocity at the torch exit, while the CSL nozzle has a higher measured temperature of plasma jet. The variation trends of the plasma jet characteristics for the two nozzles are comparable under various spraying parameters. The in-flight particle with smaller velocity of CSL nozzle has a higher measured temperature and melting fraction. As a result, the coating density and adhesive strength of CSL nozzle are lower than those of cylindrical nozzle, but the deposition efficiency is greatly improved.

The History, Technical Specifications and Efficacy of Plasma Spray Coatings Applied to Joint Replacement Prostheses

Thermal plasma sprayed coatings are designed to improve both the biocompatibility and durability of implantable medical devices, and include pure titanium, cobalt/chrome alloy and hydroxyapatite. Coated joint replacements have now been in continuous clinical use for thirty years and are applied to products manufactured or used in Europe, North America, South America, Africa, Asia and Australasia. Prostheses incorporating such coatings have been successfully implanted into several million of patients worldwide and to date there have been very few reports of any failure of an implant which could be attributed to problems with, or failure of, the coating. This paper summarises the early history of cementless prostheses and subsequent development, specification, validation, regulatory requirements and clinical performance of thermal plasma spray coatings provided by Accentus Medical.

Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas

In order to develop a low cost oxide film deposition process with short duration time, a 1 kW class Atmospheric thermal plasma spray (APS)/Atmospheric solution precursor plasma spray (ASPPS) dual mode thermal spray equipment was manufactured and film depositions of alumina (Al2O3) and titania (TiO2) by APS and titania film deposition by ASPPS were carried out. Consequently, though intensive fluctuation with intensive abrasion of electrodes occurred during plasma jet generation in case of N2 working gas, the plasma jet was stabilized and the abrasion was dramatically diminished by slight addition of Ar to N2 working gas. Since the suction type feedstock feeder could be confirmed to be available not only for powder feedstock but also solution precursor feed stock. In the case of APS, lamellar structure alumina and titania films could be deposited. However, in the case of titania films deposited by APS, a phase transformation from anatase to rutile occurred partially during film deposition. Also in the case of ASPPS, titania films including rutile and anatase were deposited. From these results, the developed equipment was proved to be available as an APS/ASPPS dual mode thermal spray equipment and this technique was found to have high potential for a low-cost oxide film deposition process.

Oxidation resistance of Si-coated TZM alloy prepared through combined process of plasma spray and laser surface melting

Plasma thermal spraying of Si coating layer on titanium–zirconium–molybdenum (Ti–Zr–Mo), TZM alloy, was conducted for the surface protection of the Mo substrate that is unstable in air at high temperatures. Although the plasma thermal spraying alone could protect the Mo alloy from oxidation at a high temperature for a short time, the post laser surface melting process further improved the oxidation resistance of Si-coated alloy. In the case of the post laser treated specimen, MoSi compounds, mainly MoSi2 phases, were formed during the additional annealing process, and the oxidation resistance could be even further enhanced. The corrosion behaviors of Si-coated specimens in 3.5% NaCl solution were also investigated; however, no significant variations with respect to the post treatment procedure were found.

Surface characterization and fatigue performance of a chemical-etched Ti-6Al-4V femoral stem for cementless hip arthroplasty

Abstract This work investigated the influence of a two-step chemical etching (H 3 PO 4 + NaOH) on the surface characteristics, coating properties and fatigue performance of a finished Ti-6Al-4V femoral stem early coated with Ti powder by thermal plasma spraying (namely TPS). Two further groups of stems were used as control: coated with TPS itself and coated with TPS followed by electrochemical deposition of CaP. The surface roughness and the coating properties based on ASTM F1854-15 were respectively evaluated by confocal laser scanning microscopy and scanning electron microscopy, whereas the fatigue performance was assessed according to the protocols given in ISO 7206-4:2010 standard and subsequent penetrant liquid testing. The two-step chemical etching produced a coral-like nanotopography and a finer, flatter and less porous surface, with an outward projected surface, in comparison to the CaP coating. All stems survived the fatigue tests (no fracture after 5 × 10 6 loading cycles) and no cracks were identified. The results indicated that two-step chemical etching may be suitable for modifying the surface of femoral stems used in cementless hip arthroplasty.

Miniature lightweight X-ray optics (MiXO) for surface elemental composition mapping of asteroids and comets

The compositions of diverse planetary bodies are of fundamental interest to planetary science, providing clues to the formation and evolutionary history of the target bodies and the Solar system as a whole. Utilizing the X-ray fluorescence unique to each atomic element, X-ray imaging spectroscopy is a powerful diagnostic tool of the chemical and mineralogical compositions of diverse planetary bodies. Until now the mass and volume of focusing X-ray optics have been too large for resource-limited in-situ missions, so near-target X-ray observations of planetary bodies have been limited to simple collimator-type X-ray instruments. We introduce a new Miniature lightweight Wolter-I focusing X-ray Optics (MiXO) using metal-ceramic hybrid X-ray mirrors based on electroformed nickel replication and plasma thermal spray processes. MiXO can enable compact, powerful imaging X-ray telescopes suitable for future planetary missions. We illustrate the need for focusing X-ray optics in observing relatively small planetary bodies such as asteroids and comet nuclei. We present a few example configurations of MiXO telescopes and demonstrate their superior performance in comparison to an alternative approach, micro-pore optics, which is being employed for the first planetary focusing X-ray telescope, the Mercury Imaging X-ray Spectrometer-T (MIXS-T) onboard Bepicolumbo. X-ray imaging spectroscopy using MiXO will open a large new discovery space in planetary science and will greatly enhance our understanding of the nature and origin of diverse planetary bodies.

Thermal plasma spheroidization and spray deposition of barium titanate powder and characterization of the plasma sprayable powder

In this paper, atmospheric plasma spray method was used to produce dense plasma sprayable powder and thick barium titanate film. In this regard, the commercially feedstock powders were granulated and spheroidized by the organic binder and the thermal spray process, respectively. Scanning electron microscopy was used to investigate the microstructure of the produced powders and the final deposits. X-ray diffraction was also implemented to characterize phase of the sprayed powder. The results indicated that spheroidized powder had suitable flowability as well as high density. The micro-hardness of the film produced by the sprayed powders was higher than that of the film deposited by the irregular granules. Additionally, relative permittivity of the films was increased by decreasing the defects from 160 to 293 for film deposited using spheroidized powder. The reduction in the relative permittivity of deposits, in comparison with the bulk material, was due to the existence of common defects in the thermal spray process.

Effect of Laser Surface Treatment on the Corrosion Behavior of FeCrAl-Coated TZM Alloy

The current study involves the coating of Titanium-Zirconium-Molybdenum (TZM) alloy with FeCrAl through plasma thermal spraying which proved effective in improving the oxidation resistance of the substrate. A post-laser surface melting treatment further enhanced the surface protection of the TZM alloy. Oxidation tests conducted at 1100 °C in air indicated that some Mo oxides were formed at the surface but a relatively small amount of weight reduction was observed for FeCrAl-coated TZM alloys up to 60 min of treatment. The post-laser surface treatment following the plasma thermal spray process apparently delayed the severe oxidation process and surface spalling of the alloy. It was suggested that the slow reduction in weight in the post-laser-treated specimen was related to fewer defects in the coating layer. It was also found that a surface reaction layer formed through the diffusion of Fe into the Mo alloy substrate at high temperature. The layer mainly consisted of Fe-saturated Mo and FeMo intermetallic compounds. In order to observe the corrosion behavior of the laser-treated alloy in 3.5% NaCl solution, electrochemical characteristics were also investigated. A proposed equivalent circuit model for the specimen indicated localized corrosion of coated alloy with some permeable defects in the coating layer.

Fatigue performance of a Ti-6Al-4V femoral prosthesis modified by thermal plasma spray

Fatigue performance of a Ti-6Al-4V femoral prosthesis modified by thermal plasma spray