Plasma Spray Deposition Research Articles

Nano-Micro-Structured 6%–8% YSZ Thermal Barrier Coatings: A Comprehensive Review of Comparative Performance Analysis

Beneficial properties achieved by nanostructuring effects in materials have generated tremendous interests in applications in surface engineering, especially in thermal barrier coatings (TBC). Limitations in conventional TBC processing for gas turbines and aero-propulsion systems have been exposed during past decades when rapid progress was made in nano-structuring coating research and developments. The present work is a comprehensive review of the current state of progress in nanostructured TBC (Ntbc) in reference to its microstructure, damage progression, failure mechanisms and a wide range of properties. The review aims to address the comparative performance analysis between the nanostructured and conventional (microstructured) 6–8 wt.% yttrium stabilized zirconia (YSZ) TBC systems. Oxidation resistance and sintering behavior in two TBCs are considered as the central focus of discussion. A few schematics are used to represent major microstructural features and failure progression. A performance analysis is performed for standard 2-layer, as well as functionally graded multilayer, TBC systems. A comparison of TBC characteristics processed by plasma spray and vapor deposition techniques is also made as reference. Compared to the sea of R&D efforts made for conventional TBC (Ctbc), limited experimental studies on Ntbc offers conflicting data, and prediction modeling and computational research are scarce.

Review of Various Hydroxyapatite Coating Methods on SS316L Foam for Biomedical Application

Metallic biomaterials such as 316L stainless steel (SS316L) are widely used as an implant to replace the function of damaged bone, especially in hip or knee applications. However, many of them fail during a short period or have complications. The biocompatibility issues are the main factor that caused this failure. Thus, coating the SS316L with bioactive and biocompatible material is one of the promising techniques to enhance the biocompatibility and lifetime of the implant. This paper provides an overview of the SS316L foam coated hydroxyapatite (HA). Various methods of HA coating such as sol-gel, dip coating, electrophoretic deposition, plasma spraying, and pulse laser deposition applied on SS316L foam and their coating characteristics were investigated based on recent literature. SS316L foam coated HA using different coating methods were compiled and their basic properties were reported. Therefore, this paper will benefit future works on SS316L foam coated HA in a biomedical application.

Plasma Spray vs. Electrochemical Deposition: Toward a Better Osteogenic Effect of Hydroxyapatite Coatings on 3D-Printed Titanium Scaffolds.

Surface modification of three-dimensional (3D)-printed titanium (Ti) scaffolds with hydroxyapatite (HA) has been a research hotspot in biomedical engineering. However, unlike HA coatings on a plain surface, 3D-printed Ti scaffolds have inherent porous structures that influence the characteristics of HA coatings and osteointegration. In the present study, HA coatings were successfully fabricated on 3D-printed Ti scaffolds using plasma spray and electrochemical deposition, named plasma sprayed HA (PSHA) and electrochemically deposited HA (EDHA), respectively. Compared to EDHA scaffolds, HA coatings on PSHA scaffolds were smooth and continuous. In vitro cell studies confirmed that PSHA scaffolds have better potential to promote bone mesenchymal stem cell adhesion, proliferation, and osteogenic differentiation than EDHA scaffolds in the early and late stages. Moreover, in vivo studies showed that PSHA scaffolds were endowed with superior bone repair capacity. Although the EDHA technology is simpler and more controllable, its limitation due to the crystalline and HA structures needs to be improved in the future. Thus, we believe that plasma spray is a better choice for fabricating HA coatings on implanted scaffolds, which may become a promising method for treating bone defects.

Beneficial osseointegration effect of hydroxyapatite coating on cranial implant - FEM investigation.

A firm connection of the bone-implant-fixation system is of utmost importance for patients with cranial defects. In order to improve the connection reliability, the current research focuses on finding the optimal fixation method, as well as selection of the implant manufacturing methods and the used materials. For the latter, implementation of bioactive materials such as hydroxyapatite or other calcium phosphates has also been considered in the literature. The aim of this study was to investigate the effect of gradual osseointegration on the biomechanical performance of cranial Ti6Al4V implants with a deposited HA coating as the osseointegration agent. This effect was assessed by two different computational approaches using finite element method (FEM) modeling. The values of key input parameters necessary for FEM were obtained from experimental plasma spray deposition of HA layers onto Ti6Al4V samples. Immediately upon implantation, the HA layer at the bone-implant contact area brought only a slight decrease in the values of von Mises stress in the implant and the micro-screws when compared to a non-coated counterpart; importantly, this was without any negative trade-off in other important characteristics. The major benefit of the HA coatings was manifested upon the modeled osseointegration: the results of both approaches confirmed a significant reduction of investigated parameters such as the total implant displacements (reduced from 0.050 mm to 0.012 mm and 0.002 mm while using Approach I and II, respectively) and stresses (reduced from 52 MPa to 10 MPa and 1 MPa) in the implanted components in comparison to non-coated variant. This is a very promising result for potential use of thermally sprayed HA coatings for cranial implants.

Preparation and performance of an Al/TiB2 + 10%Ti4O7/β-PbO2 as a composite anodic material for electrowinning of non-ferrous metals

Electrodes are the key material in the electrolysis of non-ferrous metals, and their selection and preparation can be a difficult problem in the hydrometallurgical industry. In this paper, starting from the selection of electrode materials and structural design, an Al/TiB2 + 10%Ti4O7-coating composite material was prepared by plasma spraying technology, and a β-PbO2 coating was prepared by electrochemical deposition. The phase composition of the coating was analyzed by X-ray diffractometer, and the structure of the coating was observed by scanning electron microscopy. Results show that the electrode prepared by electrodeposition at a current density of 0.03 A cm−2 has a more compact structure and more uniform grain size. Through steady-state polarization curve, cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy, the electrochemical performance of the electrode was studied. Through porosity measurements, it was found that the composite electrode material prepared by the plasma spraying method under the parameters of a spraying power of 36 kW, powder feeding rate of 30 g/min, spraying distance of 105 mm, and argon gas flow rate of 2.6 m3/h greatly reduces the charge resistance in the double-layer structure on the electrode surface, thereby accelerating the charge transfer rate. Plasma spraying and electrochemical deposition have been used to successfully prepare Al/TiB2 + 10%Ti4O7/β-PbO2 composite electrode materials with good corrosion resistance and electrochemical catalytic activity. Compared to Ti/β-PbO2 and Pb-(0.5 wt%)Ag/β-PbO2, the corrosion resistance and polarization potential increased by 83.6% and 93.0% and negatively shifted by 517.37 mV and 587.12 mV, respectively, and the catalytic activity was also significantly improved.

Thermal Barrier Coatings Overview: Design, Manufacturing, and Applications in High-Temperature Industries

Today’s competitive world economy is creating an indispensable demand for increased efficiency of engineering components that operate in harsh environments (i.e., very high-temperature, corrosive, or neutron irradiation environments), for applications in the energy, automotive, aerospace, electronics, and power industries. Increased research is being done on thermal barrier coatings (TBCs) for protecting such components, since the versatility of manufacturing techniques and the scale of deployment result in increased life, economics, performance, and durability. This review focuses on the advances that led to using TBCs for component life extension and, more recently, as an integral part of advanced component design for high-temperature and other types of harsh environments, such as those found in nuclear-related applications. Factors that led to state-of-the-art advanced coating-fabrication techniques [e.g., electron-beam physical vapor deposition (EB-PVD), plasma spray deposition, and electrophoretically deposited TBCs, as well as functionally graded material (FGM) manufacturing] have also been emphasized in current coating R&D. This review explores the current state of TBCs, i.e., the latest advances regarding their fabrication and performance, associated challenges, and recommendations for their future use in aerospace, nuclear, high-temperature, or otherwise harsh environments.

Rheological and chemical interaction between volcanic ash and thermal barrier coatings

Combustion temperatures (>1200 °C) in gas turbines cause softening and eventually melting of ingested volcanic ash particles. In the downstream section, lower temperatures lead to droplet deposition onto the thermal barrier coatings (TBCs) of the turbine blades. The intensity of interaction (wetting and chemical interaction) depends on the ash and TBC chemistry as well as the TBC structure. We have determined the spreading behavior of five different volcanic ash melts on four types of TBCs. The TBCs differed in their composition - yttria-stabilized zirconia (YSZ) and gadolinium zirconate (GZO) – and in their fabrication - air plasma spraying (APS) and electron-beam physical vapor deposition (EB-PVD). The spreading properties have been parameterized on the basis of four parameters, 1) the CaO-SiO 2 -ratio, 2) optical basicity, 3) the R b/a ratio and 4) the viscosity of the volcanic ash melts. Infiltration efficiency of the melts into the TBCs and corrosion characteristics have been determined via electron microprobe analysis of cross sections. In this study, the highest damage potential was found following interaction with basaltic melt, as its low viscosity is favorable to extensive spreading and high chemical reactivity. • Basaltic (SiO 2 -lean) silicate melts show the most extensive spreading on TBC surfaces and the most intense chemical reaction with the TBC materials • Spreading of silicate melts on APS TBCs is enhanced over EB-PVD TBCs and spreading on GZO TBCs is enhanced over YSZ TBCs • Spreading ability of silicate melts can be estimated based on a parametrization deduced from our spreading experiments

Plasma spraying of transition metal oxide coatings

ABSTRACTThe rapid increase in the world population has drastically increased the generation of organic solid waste. Currently, this is disposed of mainly in landfills, leading to environmental pollution that necessitates the development of new treatment technologies. Catalytic wet oxidation has been proven to be an effective technology for solid waste destruction and the elimination of hazardous organic compounds. The aim of this work is to explore the production of NiO, MnO2, Fe2O3 and CuO as transition metal oxide catalyst coatings using plasma spraying. Little, if any, literature has been presented on the plasma spray deposition of these materials, so this work provides the first proof of concept and benchmark for future development. The coating compositions were quantified from XRD patterns and the coating thickness measured from cross-sectional optical images. The optimal coating from each composition was analysed by scanning electron microscopy to determine the coating microstructure and phase distribution.

Recent advances in the thermal barrier coatings for extreme environments

Thermal barrier coatings (TBCs) are gaining tremendous research interest for protecting aircraft turbine blades, power plants, and other applications from high-temperature exposure. This opinion spotlights on those recent progresses that have directed to the use of TBCs for component life addition and, lately, as an essential part of advanced components design for high temperatures and related harsh environments, such as applications in the nuclear industries. Development of this coatings has been driven by results obtained from laboratory and industrial testing, corroborated by engine and gas-turbine testing and related high-temperature application experience. Factors that have led to the choice of current high-tech advanced coating fabrication methods–such as plasma spray deposition (PSP), electron-beam physical vapor deposition (EB-PVD), and electrophoretically fabricated thermal barrier coatings, have also been highlighted in current coating research and development. Here, we provide a short review on the present status of TBCs, their latest advances in fabrication and performance, drawbacks associated with them, as well as recommendations for their futuristic use in harsh high-temperature environments.

Fabrication of NiAl intermetallic alloy integrated materials chips with continuous one-dimensional composition gradients by plasma spray deposition and laser remelting

Integrated materials chips (IMCs) contain a multitude of discrete materials with varying compositions on a single substrate to enable the rapid screening of material properties, and therefore offer the potential for accelerating the speed of materials research and development. The present work proposes a combinatorial technology based on conventional plasma spray (PS) deposition and laser remelting (LR), and employs the proposed technology to develop Ni-Al intermetallic alloy IMCs with a continuous composition gradient yielding various homogeneous compositions with unique microstructures and microhardness values along the length. The experimental results demonstrate that the proposed technology can effectively promote the discovery of relationships between the composition, microstructure, and the inherent properties of materials.

Measurement of residual stress in thermal barrier coating using GIXRD

Abstract Inconel alloys are widely used in aerospace industry for various components of the gas turbines. These materials have excellent mechanical properties at high temperatures, but they do not provide suitable protection against hot corrosion and oxidation at high temperature. YSZ based Thermal barrier coating (TBC) system is the most widely used in the industry to enhance the life of the alloy. The low thermal conductivity of the YSZ TBC reduces the operating temperature of the alloy to achieve this. But even with YSZ TBC fail at temperatures above 1200⁰C. In order to overcome these limitations YSZ is doped with Gadolinium oxide Gd2O3 in varying compositions. The Inconel 718 alloy was selected as the substrate to be coated and 4 different composition and combinations were coated. There are residual stresses present in the coatings which can be either beneficial or detrimental. Residual stresses will be generated during plasma spray deposition and influence on the coating properties. Residual stresses can cause cracking in the surface coatings which leads to decreased durability of the top coat. As a result, the oxidation and corrosion resistance of the alloy decreases at higher temperatures. Residual stress analysis was done on the coatings to find the internal stresses in the coatings using GIXRD process.

Cold spray deposition of Inconel 718 in comparison with atmospheric plasma spray deposition

Inconel 718 is a Ni-based superalloy which has been widely used in aerospace industry. Repairing of Inconel 718 components has been usually carried out using atmospheric plasma spray (APS) and high velocity oxy fuel (HVOF) spray techniques. Cold spray (CS) is a relatively new thermal spray technique, which relies more on powders’ kinetic energy and less on their thermal energy to impact powders onto the substrate, where the powders undergo severe plastic deformation and subsequently adhere to the substrate surface as coatings. In this work, high pressure CS using dry N2 as propellant gas has been deployed to deposit Inconel 718 powders as thick coatings for structural restoration application. The coating’s surface morphology, cross-section microstructure, crystallinity, residual stress and mechanical properties were subsequently characterized and compared with the Inconel 718 coating deposited by APS in order to elaborate the unique features of the Inconel 718 coatings deposited by both spray techniques.

Plasma Spray Deposition of HA-TiO2 on β-phase Ti-35Nb-7Ta-5Zr Alloy for Hip Stem: Characterization of Bio-mechanical Properties, Wettability, and Wear Resistance

In this work, a biomimetic coating of hydroxyapatite (HA)-and titania (TiO2) was deposited on low elastic β-phase Ti-35Nb-7Ta-5Zr (β-TNTZ) alloy by plasma spray deposition technique for orthopedic applications. The effect of TiO2 reinforcement on microstructure, mechanical properties, and bioactivity was investigated. The morphology, coating thickness, elemental composition, and phase composition of the developed coatings were characterized. The biomechanical behavior of the deposited coatings was investigated in terms of surface hardness, elastic modulus, and adhesion strength. It was found from the morphological investigation that the TiO2 reinforcement improves the microstructure and prevents the formation of defects in the coating. The biomimetic HA-TiO2 coated surface possessed pores, size ranging from 200 nm–600 nm that benefits the apatite growth and osseointegration. The EDS spectrum, mapping, and XRD analysis show that the deposited layer β-TCP, CaO, TTCP, TiO2 phases. The HA-TiO2 coating exhibits a very dense and thick layer of 100 µm–125 µm that exhibits excellent adhesion strength to offer mechanical interlocking to prevent delamination. The alloying of TiO2 improves the hardness from 1.67 GPa to 2.95 GPa that enhances the wear resistance. It was found that HA-TiO2 coating exhibits better hydrophilic and biocompatible surface as compared to HA-coating.

High-temperature oxidation behavior in YSZ coated Cr2AlC and CoNiCrAlY substrates

Yttria-stabilized zirconia (YSZ) was applied as a ceramic top coat on the Cr2AlC and CoNiCrAlY substrates using atmospheric plasma spray (APS) deposition technique and the high-temperature oxidation behavior of these coating systems examined at 1100 °C. The high-temperature performance of coated samples was studied using techniques such as scanning electron microscopy (SEM) to observe the microstructure, energy dispersive spectroscopy (EDS), elemental mapping, and X-ray diffraction (XRD) analysis to examine the phase composition before and after oxidation tests. According to the results, the high-temperature oxidation resistance of Cr2AlC/YSZ was much better than CoNiCrAlY/YSZ. In Cr2AlC/YSZ system, the thermally grown oxide (TGO) formed by the outward diffusion of aluminum and inward diffusion of oxygen. In this system, the thickness of TGO was about 7.6 μm after 350 h and crack nucleated due to the formation of a porous Cr7C3 layer. In CoNiCrAlY/YSZ samples, TGO consisted of Al2O3 and spinel oxides and the thickness of TGO increased up to approximately 5.3 μm after 150 h of oxidation test (failure time). The better oxidation behavior of Cr2AlC/YSZ can be attributed to the decrement of internal stresses due to the lower mismatch of CTE values between this substrate and the TGO layer.

Suspension plasma spray deposition of CoxNi1-xO coatings

Suspension Plasma Spray (SPS) process was used for the deposition of cobalt-nickel oxide solid solutions as potential coatings for inert anodes in primary aluminum production. The effects of SPS process parameters (plasma power, standoff distance, gas mixture, and substrate temperature) on the structure and composition of coatings were investigated. X-ray diffraction measurements, coupled with Rietveld refinement analysis, and scanning electron microscope (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) analyses were performed. It was shown that substrate temperature is the single most important parameter affecting the nature of the coating, and that uniform, adherent and non-porous CoxNi1-xO coatings made of a single solid solution phase are obtained when the substrate temperature is above 950 °C. Metallic Ni is observed in coatings prepared at lower temperatures and, in that case, the composition of the solid solution phase deviates from that of the starting materials. This work also discusses possible causes for the formation of metallic nickel during spraying.

Microstructure and magnetic properties of Co58Ni10Fe5B16Si11 and Co58Ni10Fe5B16Si11–Al2O3 bulk amorphous coatings prepared by plasma spraying

The bulk soft magnetic glassy Co58Ni10Fe5B16Si11 alloy specimens have been prepared by plasma spray deposition. In order to increase resistivity of the material, the bulk Co58Ni10Fe5B16Si11–Al2O3 composite materials were fabricated. The investigations of structure and magnetic properties of the bulk samples were carried out by X-ray diffraction, electron microscopy and magnetic measurements. The relation of the structural features and magnetic characteristics of the bulk coating to the main parameters of the deposition regimes was determined. Optimized plasma spray deposition parameters allowed obtaining bulk glassy samples with magnetic parameters that are not inferior to the characteristics of a thermally treated rapidly quenched ribbon with the same composition. It was found that the bulk amorphous coatings can be characterized as a heterophase system. The relaxation annealing of the Co58Ni10Fe5B16Si11 bulk coating leads to a phase transition in this alloy in the precrystallization temperature range. The magnetic properties of the both kinds of coatings are correlated with changes in the microstructure. The appearance of nanocrystalline phase with TC˜640 K during relaxation heat treatment leads to a decrease of the coercivity and to an increase of the permeability. A comparison between the magnetic properties of the CoNiFe-BSi coating and (CoNiFe-BSi)–Al2O3, composite coating is carried out.

Deposition of HA-TiO2 by plasma spray on β-phase Ti-35Nb-7Ta-5Zr alloy for hip stem: Characterization, mechanical properties, corrosion, and in-vitro bioactivity

This research work presents the deposition of titanium oxide (TiO2) reinforced hydroxyapatite (HA) on Ti-35Nb-7Ta-5Zr alloy by plasma spray deposition technique for Hip-stem application. The effect of TiO2 reinforcement (15 and 30 wt%) in HA has been studied on coatings morphology, microstructure, mechanical properties, corrosion resistance, and in-vitro bioactivity was investigated. The microstructure, elemental composition, and phase composition were characterized by FE-SEM, EDS, and XRD. The morphology analysis showed that of HA-coating contains micro-cracks and splats like structure with large globules. The reinforcement of TiO2 in HA improved the microstructure, prevents the formation of micro-cracks, and formed a dense structure. The cross-section morphology shows that HA-15%TiO2 (HA-Tx) and HA-30%TiO2 (HA-Ty) coatings (thickness 185–200 μm) were mechanically bonded with the substrate as compared HA-coatings, that helps in enhancing implant stability. Results also show that microhardness and adhesion strength of HA/TiO2 coatings improved with the reinforcement of TiO2 and HA-30%TiO2 possessed high micro-hardness and adhesion strength (1.35 GPa and 32.5 MPa) in comparison with HA-coating (0.63 GPa and 18.5 MPa). The electron dispersive spectroscopy (EDS) analysis and X-ray diffraction analysis (XRD) results show that HA-TiO2 coatings contain HA and TiO2 phases that prevent the formation of amorphous contents. In contrast, HA-coating contains amorphous content (CaO, β-TCP, and TTCP). The HA-TiO2 coatings exhibit excellent corrosion resistance as compared to HA-coating because of the presence of TiO2 lamellar structure in the HA matrix that acted as a barrier to corrosion and improves the corrosion resistance. The TiO2 reinforcement in HA/TiO2 coating not only increase the corrosion resistance but also help in promoting chemical integration of MG-63 osteoblastic cellular structure through the formation of apatite on the surface of the implant. Furthermore, the in-vitro bioactivity analysis results showed that Mg-63 osteoblastic cells have excellent adhesion and growth on the HA-30%TiO2 coated substrates.

Atmospheric-Pressure Plasma Spray Deposition of Silver/HMDSO Nanocomposite on Polyamide 6,6 with Controllable Antibacterial Activity

Novel coatings containing silver nanoparticles (AgNPs) with strong bonding and controllable antibacterial activity on polyamide 6,6 fabric were produced by dielectric barrier discharge (DBD) plasma-assisted deposition at atmospheric pressure and hexamethyldisiloxane (HMDSO) layers. Silver ion release was tuned using a "sandwich" coating structure to prolong the antibacterial effect. The novel spray-assisted deposition increased deposition rates of AgNPs using atmospheric pressure DBD plasma treatment when an HMDSO layer was applied. An increase in AgNPs deposition in plasma treated samples and antimicrobial activity against Gram-negative (Escherichia coli) for samples with an additional HMDSO layer was observed. These coatings allow the development of new and safe wound dressings able to switch the antimicrobial effect against Gram-positive and Gram-negative bacteria by washing the dressing at high temperature (75 °C) before application.

A solar-responsive zinc oxide photoanode for solar-photon-harvester photoelectrochemical (PEC) cells.

A highly efficient, nanostructured, solar-responsive zinc-oxide (SRZO) photoanode has been achieved by utilization of a versatile solution precursor plasma spray (SPPS) deposition technique. For the first time, it is demonstrated that a front-illumination type SRZO photo-anode fabricated with a ZnO/stainless steel (SS-304) configuration can generate an enhanced photo-electrochemical (PEC) current of 390 μA cm−2, under solar radiation from a solar simulator with an AM1.5 global filter (∼1 sun). The SRZO electrode displayed a solar-to-hydrogen (STH) conversion efficiency of 2.32% when investigated for H2 evolution in a PEC cell. These electrodes exhibited a maximum peak efficiency of 86% using 320 nm photons during incident photon-to-current conversion efficiency measurement. Interestingly, the film lattice of SRZO showed a significant red-shift of 0.37 eV in the ZnO band gap thereby providing solar photon absorptivity to SRZO. Further, an enhanced charge transport property by virtue of increased donor density (∼4.11 × 1017 cm−3) has been observed, which is higher by an order of magnitude than that of its bulk counterpart. Efficient optical absorption of solar photons and higher donor-density of SRZO have been thus attributed to its superior PEC performance.

Experimental investigation and parametric optimization of HA-TiO2 plasma spray coating on β-phase titanium alloy

In the present research work, experimental investigation and parametric optimization plasma spray deposition process have been carried out to deposit a nature-inspired biomimetic coating of hydroxyapatite (HA)-and titania (TiO2) on low elastic β-phase Ti-35Nb-7Ta-5Zr alloy for orthopedic application. The effect of powder mixture ratio, gas flow rate, and powder feed rate on the surface hardness and adhesion strength was investigated. The experiments were conducted as per the L-9 orthogonal array. The morphology, coating thickness, elemental composition, and phase composition of the developed coatings were characterized and analyzed using field emission-scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) technique. It has been found from the morphological investigation that the coated surface contained splats like morphology, globules, and craters. The best optimal condition to obtain the maximum surface hardness is the high level of powder ration (50%HA-50%TiO2), high level of gas flow rate, and low level of powder federate. The best optimal condition to obtain the maximum adhesion strength is the medium level of powder ration (70%HA-30%TiO2), low level of gas flow rate, and a high level of powder federate.