Plasma Spray Deposition Research Articles

Numerical study of molten and semi-molten ceramic impingement by using coupled Eulerian and Lagrangian method

Large temperature gradients are present within ceramic powder particles during plasma spray deposition due to their low thermal conductivity. The particles often impinge at the substrate in a semi-molten form which in turn substantially affects the final characteristics of the coating being formed. This study is dedicated to a novel modeling approach of a coupled Eulerian and Lagrangian (CEL) method for both fully molten and semi-molten droplet impingement processes. The simulation provides an insight to the deformation mechanism of the solid core YSZ and illustrates the freezing-induced break-up and spreading at the splat periphery. A 30μm fully molten YSZ particle and an 80μm semi-molten YSZ particle with different core sizes and initial velocity ranging from 100 to 240m/s were examined. The flattened degree for both cases were obtained and compared with experimental and analytical data.

The Influence of Overaluminizing on TGO Formation on Thermal Barrier Coatings Deposited by Low Pressure Plasma Spraying and Chemical Vapour Deposition Methods on Rene 80 Nickel Superalloy

The paper presents results of research into isothermal oxidation test of thermal barrier coatings characterized by high oxidation resistance and hot corrosion. Bondcoats were deposited by overaluminizing of MeCrAlY–type coating deposited by LPPS method. The outer ceramic layer of yttrium oxide stabilized zirconia oxide (Metco 6700) was deposited by plasma spray physical vapour deposition (PS-PVD). For comparison purposes additionally LPPS-sprayed were MeCrAlY bondcoats, which were not subsequently aluminized.. The isothermal oxidation test at 1100oC for 1000h shown that thickness of the TGO layer in overaluminized bondcoat was significantly thicker in comparison with conventional LPPS-sprayed MeCrAlY bondcoats.

Microstructure of Thermal Barrier Coatings Deposited by Low Pressure Plasma Spraying and Chemical Vapour Deposition Methods on Rene 80 Nickel Superalloy

The paper presents results of research into thermal barrier coatings characterized by high oxidation resistance and hot corrosion. Bondcoats were formed by overaluminizing of an MeCrAlY–type coating deposited by low pressure plasma spraying. The outer ceramic layer of yttrium oxide stabilized zirconia oxide (Metco 6700) was deposited by plasma spray physical vapour deposition (PS-PVD). For comparison purposes additionally LPPS-sprayed were MeCrAlY bondcoats, which were not subsequently aluminized. Used as base material was Rene 80 nickel superalloy. The research has shown that as a result of aluminizing by the CVD method there was formed in the bondcoat a deposit zone built of the β-NiAl phase which protects from oxidation. Preserved below increased chromium content ensures resistance to hot corrosion. The outer ceramic layer was characterized by columnar structure similar to that obtained in the EB-PVD process.

Plasma spray-deposited lanthanum phosphate coatings for protection against molten uranium corrosion

Lanthanum phosphate is recommended as an effective barrier against molten uranium and its alloys. LaPO4 has a high melting point, is inert towards reactive metals and has low thermal conductivity, which make it an ideal candidate for corrosion barrier coatings in molten metal environment. Studies on plasma deposition of lanthanum phosphate, its characterization and interaction with molten uranium are reported in this paper. Lanthanum phosphate was synthesized by chemical route and the as-synthesized powder was converted to free flowing powder for plasma spray deposition. Lanthanum phosphate coatings were prepared on stainless steel substrates and the deposits were characterized for phase composition using X-ray diffraction (XRD), Raman spectroscopy and Fourier transformed infrared spectroscopy (FTIR). Results showed that the coatings retained the monazite structure of LaPO4 precursor powder. Microstructure of the coatings and interface by scanning electron microscope (SEM) revealed good bonding between the phosphate layer and substrate. Porosity of the coatings was observed to decrease with the increase in deposition power from 10kW to 20kW. Adhesion strength of the coatings was found to increase with deposition power. Corrosion studies of coated LaPO4 in molten uranium showed that lanthanum phosphate does not chemically react with molten uranium and LaPO4 coating offers adequate resistance to the substrate against corrosion attack by molten uranium.

Bulk CoNiFe-SiB Amorphous and Nanostructured Alloys Produced by Plasma Spray Deposition and Dynamic Compaction: Formation of Soft Magnetic Properties

The bulk nanostructured Co58Ni10Fe5B16Si11 alloys were prepared by dynamic compaction and plasma spray deposition techniques. The investigation of structure and magnetic properties of bulk samples was carried out by X-ray diffraction, electron microscopy and correlation magnetometry. The bulk samples produced by both methods can be characterized as a heterophase system. The highest value of permeability 20 · 103 for plasma spraying coating is achieved when volume fraction of nanocrystalline phase with Curie temperature Tc ∼ 640 K is increased to 30%. The magnetic characteristics, such as the saturation magnetization, the Bloch constant, the local magnetic anisotropy field, the ferromagnetic resonance linewidth, and the coercivity remain unchanged after both compaction techniques. It was shown that the plasma spraying method allows to obtain bulk magnetically soft materials with magnetic parameters that are not inferior to the characteristics of a thermally treated rapidly quenched ribbon with the same composition.

Comparative Study of Creep Resistance of a Ti-6Al-4V Alloy with Metallic and Ceramic Coatings

Titanium and its alloys are largely used for many industrial applications due to their high mechanical and corrosion resistance and low specific mass. Ti-6Al-4V alloy is the most used in aerospace industry and it is applied for the manufacturing of aircraft blades and steam turbines. This alloy has high affinity with oxygen which constrains its application at high temperatures due to creep resistance reduction. Methods to increase creep resistance of Ti-6Al-4V alloys includes the use of metallic coatings and its combination with ceramic thermal barrier coating deposition on the material surface. The aim of this work is to compare the creep behavior of Ti-6Al-4V alloy in three different conditions: uncoated, metallic coated, metallic + ceramic coated specimens. The metallic coating layer (CoNiCrAlY) and the ceramic coating (ZrO2 + 8wt%Y2O3) are both applied by plasma spray deposition technique. The specimens were submitted to constant load creep tests at 600oC and stress conditions of 125, 250 and 319MPa. Specimens of metallic + ceramic coating have presented higher creep resistance, longer lifetime and lower stationary creep rate when compared to uncoated and metallic coated specimens.

Mo–Si–B Coating for Improved Oxidation Resistance of Niobium

A Mo–Si–B based coating was applied to niobium that produced a coating structure composed of molybdenum and niobium silicides. Oxidation tests at 1000 °C and 1200 °C showed that the Mo–Si–B coating provided enhanced oxidation protection of niobium due to the formation of a protective aluminosilica layer. The coating performance was identified to be limited by the formation of NbB2 during the pack cementation process. A revised coating treatment was implemented using TiB2 as the boron source to reduce the NbB2 formation. The Mo–Si–B coating utilizing plasma spray deposition of Mo and a revised pack cementation exhibited a mass change of 0.44 mg cm−2 after TGA testing at 1300 °C for 24 h.

Design of durability and lifetime assessment method under thermomechanical stress for thermal barrier coatings

A durability testing method under thermo-mechanical stress for thermal barrier coatings (TBC) specimens was designed by a combination of an electric furnace and a tensile testing machine, which was done on TBCs on NIMONIC 263 substrates by an atmospheric plasma spraying (APS) deposition method. The testing conditions were chosen according to a preliminary experiment that identified the elastic deformation region of the top coating and the substrate during mechanical loading. Surface cracking and a decrease in the thickness of the top coating, which are typical degradation behaviors under conventional thermal shock testing, were observed after the designed thermal fatigue test, and delamination at the top coating-bond coating interface occurred by the mechanical load. Lifetime assessment was conducted by statistical software using lifecycle data which were obtained after the thermal fatigue test.

Plasma spray deposition of yttrium oxide on graphite, coating characterization and interaction with molten uranium

Yttrium oxide coatings on graphite substrates were prepared by atmospheric plasma spray technique. Temperature and velocity of the yttrium oxide particles during the plasma spray process were measured by ‘spraywatch’ diagnostics system. Coatings were characterized for phase composition, microstructure and thermal stability. Dense adherent coatings could be deposited at 24 kW power. Corrosion behaviour of the coatings in molten uranium was studied by using differential thermal analysis (DTA) up to 1473 K. The results showed that the coatings offered sufficient protection to graphite against corrosion by molten uranium.

Plasma Spraying of Ceramics with Particular Difficulties in Processing

Emerging new applications and growing demands of plasma-sprayed coatings initiate the development of new materials. Regarding ceramics, often complex compositions are employed to achieve advanced material properties, e.g., high thermal stability, low thermal conductivity, high electronic and ionic conductivity as well as specific thermo-mechanical properties and microstructures. Such materials however, often involve particular difficulties in processing by plasma spraying. The inhomogeneous dissociation and evaporation behavior of individual constituents can lead to changes of the chemical composition and the formation of secondary phases in the deposited coatings. Hence, undesired effects on the coating characteristics are encountered. In this work, examples of such challenging materials are investigated, namely pyrochlores applied for thermal barrier coatings as well as perovskites for gas separation membranes. In particular, new plasma spray processes like suspension plasma spraying and plasma spray-physical vapor deposition are considered. In some cases, plasma diagnostics are applied to analyze the processing conditions.

Thermal Conductivity Analysis and Lifetime Testing of Suspension Plasma-Sprayed Thermal Barrier Coatings

Suspension plasma spraying (SPS) has become an interesting method for the production of thermal barrier coatings for gas turbine components. The development of the SPS process has led to structures with segmented vertical cracks or column-like structures that can imitate strain-tolerant air plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD) coatings. Additionally, SPS coatings can have lower thermal conductivity than EB-PVD coatings, while also being easier to produce. The combination of similar or improved properties with a potential for lower production costs makes SPS of great interest to the gas turbine industry. This study compares a number of SPS thermal barrier coatings (TBCs) with vertical cracks or column-like structures with the reference of segmented APS coatings. The primary focus has been on lifetime testing of these new coating systems. Samples were tested in thermo-cyclic fatigue at temperatures of 1100 °C for 1 h cycles. Additional testing was performed to assess thermal shock performance and erosion resistance. Thermal conductivity was also assessed for samples in their as-sprayed state, and the microstructures were investigated using SEM.

Invited: Microplasma Spray Deposition of Nanostructured Films for Catalytic, Magnetic, and Photonic Applications

We present a hybrid plasma spray deposition technique, based on geometrically-confined, supersonic microplasma jets, which can realize a wide range of metal oxide/sulfide nanoparticles and nanostructured thin film materials (e.g., CuO/CuS, ZnO, SnO2, NiO/NiFe2O4) on virtually any surface. Organometallic precursors are dissociated in a hollow cathode microplasma jet under different reducing/oxidizing atmospheres at high pressure (10-100 torr), creating a directed flux of active metal and oxide species for the subsequent growth of nanostructured films. Interaction of the jet afterglow with the background gas can create additional species (e.g., excited neutrals, radicals, etc.) which participate in film growth. By varying supersonic jet flow characteristics, plasma current, precursor flux, source distance, and deposition time, deposits ranging from isolated nanoparticles to films of fibers, aggregates, nanowires, and dense columns can be realized. The talk will highlight our recent efforts [1-5] in oxide/sulfide nanomaterial synthesis via microplasmas with emphasis on the physics of the jet source, dynamics of the growth process, and applications such as solar cell electrodes, photo(electro)catalysis, and nanogranular films for magnetic exchange bias applications.[1] T. Koh and M.J Gordon, J. Phys. D: App. Phys. 46, 495204 (2013).[2] T. Koh, I. Chiles, and M.J Gordon, Appl. Phys. Lett. 103, 163115 (2013).[3] T. Koh and M.J Gordon, JVST A 31, 061312 (2013).[4] T. Koh and M.J. Gordon, J. Crystal Growth 363, 69 (2012).[5] T. Koh, E. O'Hara, and M.J. Gordon, Nanotechnology 23, 425603 (2012).

Microstructure Effects on Electrochemical Characteristics for Plasma Spray Deposited LiFePO4 Films

The electrochemical behavior of composite electrodes used in Li ion batteries is influenced by factors such as microstructural characteristics (e.g. particle size, crystallinity, porosity etc.) and composition. For optimal performance of electrodes these factors are of utmost concern and serve as motivation for research in this field. In this report, we investigated LiFePO4 films synthesized by a novel plasma spray deposition method, which has capability for direct deposition of LiFePO4 films with carbon. This enables electrode characterizations to be carried out at the film level, without recourse to steps involving powder material handling. In this report microstructure and electrochemical properties of LiFePO4 films were investigated to elucidate their unique characteristics. Our studies show that factors such as porosity and microstructure of the films affect the electrochemical properties. The mechanical compression and thermal annealing experiments are shown to affect the electrochemical characteristics of LiFePO4 films. We show that annealing treatment leads to a drastic improvement in impedance and charge-discharge capacities for the LiFePO4 films. These treatments could serve to improve the electrode properties of porous film based materials for Li ion batteries and help us develop new film based materials for energy storage applications.

Plasma spray deposition of fly ash onto mild steel substrates using a fractional factorial design approach

In this study, fly ash was used as a feedstock material for atmospheric plasma spray deposition onto commercial marine-grade mild steel substrates. The experiments were conducted according to a fractional factorial design with four process parameter variables: the primary and carrier gas pressures, the powder feed rate and the plasma power. The results obtained indicate that the primary gas pressure was the most significant factor affecting the thickness and surface roughness of the deposited coatings, whereas the microhardness was affected by the primary gas pressure, the plasma power and the interaction between the primary gas pressure and the powder feed rate.

Automatic Event Detection in Noisy Environment for Material Process Monitoring by Laser AE Method

Laser acoustic emission (AE) method is a unique in-situ and non-contact nondestructive evaluation (NDE) method. It has a capability to detect signals generated from crack generation and propagation, friction and other physical phenomena in materials even in high temperature environment. However, laser AE system has lower signal-to-noise ratio compared to the conventional AE system using PZT sensors, so it is difficult to apply this method in noisy environment. A novel AE measurement system to detect events in such difficult environments was developed. This system could continuously record all AE waveforms and enable unrestricted post-analyses. Noise reduction filters in frequency domain coupling with a new AE event extraction using multiple threshold values showed a good potential for AE signal processing. This system was successfully applied for crack monitoring of plasma spray deposition process of ceramic coating.

Plasma spray deposition of tri-layer environmental barrier coatings

Abstract An air plasma spray process has been used to deposit tri-layer environmental barrier coatings consisting of a silicon bond coat, a mullite inter-diffusion barrier, and a Yb 2 SiO 5 top coat on SiC substrates. Solidified droplets in as-deposited Yb 2 SiO 5 and mullite layers were discovered to be depleted in silicon. This led to the formation of an Yb 2 SiO 5 + Yb 2 O 3 two-phase top coat and 2:1 mullite (2Al 2 O 3 *SiO 2 ) coat deposited from 3:2 mullite powder. The compositions were consistent with preferential silicon evaporation during transient plasma heating; a consequence of the high vapor pressure of silicon species at plasma temperatures. Annealing at 1300 °C resulted in internal bond coat oxidation of pore and splat surfaces, precipitation of Yb 2 O 3 in the top coat, and transformation of 2:1 mullite to 3:2 mullite + Al 2 O 3 . Mud-cracks were found in the Yb 2 SiO 5 layer and in precipitated Al 2 O 3 due to the thermal expansion mismatch between these coating phases and the substrate.

Decreased Staphylococcus aureus and increased osteoblast density on nanostructured electrophoretic-deposited hydroxyapatite on titanium without the use of pharmaceuticals.

BackgroundPlasma-spray deposition of hydroxyapatite on titanium (Ti) has proven to be a suboptimal solution to improve orthopedic-implant success rates, as demonstrated by the increasing number of orthopedic revision surgeries due to infection, implant loosening, and a myriad of other reasons. This could be in part due to the high heat involved during plasma-spray deposition, which significantly increases hydroxyapatite crystal growth into the nonbiologically inspired micron regime. There has been a push to create nanotopographies on implant surfaces to mimic the physiological nanostructure of native bone and, thus, improve osteoblast (bone-forming cell) functions and inhibit bacteria functions. Among the several techniques that have been adopted to develop nanocoatings, electrophoretic deposition (EPD) is an attractive, versatile, and effective material-processing technique.ObjectiveThe in vitro study reported here aimed to determine for the first time bacteria responses to hydroxyapatite coated on Ti via EPD.ResultsThere were six and three times more osteoblasts on the electrophoretic-deposited hydroxyapatite on Ti compared with Ti (control) and plasma-spray-deposited hydroxyapatite on Ti after 5 days of culture, respectively. Impressively, there were 2.9 and 31.7 times less Staphylococcus aureus on electrophoretic-deposited hydroxyapatite on Ti compared with Ti (control) and plasma-spray-deposited hydroxyapatite on Ti after 18 hours of culture, respectively.ConclusionCompared with uncoated Ti and plasma-sprayed hydroxyapatite coated on Ti, the results provided significant promise for the use of EPD to improve bone-cell density and be used as an antibacterial coating without resorting to the use of antibiotics.

Plasma spray deposition and characterization of strontium zirconate coatings

Strontium zirconate has been deposited on stainless steel substrates by atmospheric plasma spray technique. In-flight temperature and velocity of strontium zirconate particles were measured by the ‘spraywatch’ particle diagnostics system. The coatings have been characterized by x-ray powder diffraction and scanning electron microscope. Results indicated that the coating microstructure, porosity and deposition efficiency could be correlated with torch input power and spray distance in terms of the particle temperature and velocity. Adherent coatings with low porosity could be obtained at 24kW power and 80mm standoff distance.

Influence of a powder feed rate on the properties of the plasma sprayed chromium carbide-25% nickel chromium coating

The plasma spray process is a leading technology of powder depositing in the production of coatings widely used in the aerospace industry for the protection of new parts and for the repair of worn ones. Cermet 75Cr3C2 - 25Ni(Cr) coatings based on Cr3C2 carbides are widely used to protect parts as they retain high values of hardness, strength and resistance to wear up to a temperature of 850°C. This paper discusses the influence of the parameters of the plasma spray deposition of 75Cr3C2 - 25Ni(Cr) powder on the structure and mechanical properties of the coating. The powder is deposited using plasma spraying at atmospheric pressure (APS). The plasma gas is He, which is an inert gas and does not react with the powder; it produces dense plasma with lower heat content and less incorporated ambient air in the plasma jet thus reducing temperature decomposition and decarburization of Cr3C2 carbide. In this study, three groups of coatings were deposited with three different powder feed rates of: 30, 45 and 60 g/min. The coating with the best properties was deposited on the inlet flange parts of the turbo - jet engine TV2-117A to reduce the influence of vibrations and wear. The structures and the mechanical properties of 75Cr3C2 - 25Ni(Cr) coatings are analyzed in accordance with the Pratt & Whitney standard. Studies have shown that powder feed rates have an important influence on the mechanical properties and structures of 75Cr3C2 - 25Ni(Cr) coatings.

플라즈마 용사 및 전자빔 물리기상 증착법으로 제조된 4YSZ 코팅의 고온마찰마모 거동

Department of Materials Science and Engineering Korea University, Seoul 136-701, Korea(Received December 6, 2013 ; revised December 14, 2013 ; accepted December 20, 2013)Abstract4 mol% Yttria-stabilized zirconia (4YSZ) coatings are fabricated by Air Plasma Spray (APS) and ElectronBeam Physical Vapor Deposition (EB-PVD) with top coating of thermal barrier coating (TBC). NiCrAlYbased bond coat is prepared as 150 µm thickness by conventional APS (Air Plasma Spray) method on theNiCrCoAl alloy substrate before deposition of top coating. Each 4YSZ top coating shows different tribologicalbehaviors based on the inherent layer structures. 4YSZ by APS which has splat-stacked structure shows lowerfriction coefficient but higher wear rate than 4YSZ by EB-PVD which has columnar structure. For 4YSZby APS, such results are expected due to the sliding wear accompanied with local delamination of splats.