Microstructure and properties of tungsten carbide coatings sprayed with various high-velocity oxygen fuel spray systems

This article reports on a series of experiments with various high-velocity oxygen fuel spray systems (Jet Kote, Top Gun, Diamond Jet (DJ) Standard, DJ 2600 and 2700, JP-5000, Top Gun-K) using different WC-Co and WC-Co-Cr powders. The microstructure and phase composition of powders and coatings were analyzed by optical and scanning electron microscopy and x-ray diffraction. Carbon and oxygen content of the coatings were determined to study the decarburization and oxidation of the material during the spray process. Coatings were also characterized by their hardness, bond strength, abrasive wear, and corrosion resistance. The results demonstrate that the powders exhibit various degrees of phase transformation during the spray process depending on type of powder, spray system, and spray parameters. Within a relatively wide range, the extent of phase transformation has only little effect on coating properties. Therefore, coatings of high hardness and wear resistance can be produced with all HVOF spray systems when the proper spray powder and process parameters are chosen. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

Cold-Spray processing of a nanocrystalline Al−Cu−Mg−Fe−Ni alloy with Sc

This work describes recent progress in cold-spray processing of conventional and nanocrystalline 2618 (Al−Cu−Mg−Fe−Ni) aluminum alloy containing scandium (Sc). As-atomized and cryomilled 2618+Sc aluminum powder were sprayed onto aluminum substrates. The mechanical behavior of the powders and the coatings were studied using micro-and nanoindentation techniques, and the microstructure was analyzed using scanning and transmission electron microscopy (SEM and TEM). The influence of powder microstructure, morphology, and behavior during deposition on the coating properties was analyzed. This work shows that Al−Cu−Mg−Fe−Ni−Sc coatings with a nanocrystalline grain structure can be successfully produced by the cold-spray process. Inspection of the scientific literature suggests that this is the first time a hardness value of 181 HV has been reported for this specific alloy. The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and IIW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

Microstructures and characterization of zirconia-yttria coatings formed in laser and hybrid spray process

Hybrid plasma spraying combined with yttrium-aluminum-garnet laser irradiation was studied to obtain optimum zirconia coatings for thermal barrier use. Zirconia coatings of approximately 150 μm thickness were formed on NiCrAlY bond coated steel substrates both by means of conventional plasma spraying and hybrid plasma spraying under a variety of conditions. Post-laser irradiation was also conducted on the plasma as-sprayed coating. The microstructure of each coating was studied and, for some representative coatings, thermal barrier properties were evaluated by hot erosion and hot oxidation tests. With hybrid spraying, performed under optimum conditions, it was found that a microstructure with appropriate partial densification and without connected porosity was formed and that cracks, which are generally produced in the post-laser irradiation treatment, were completely inhibited. In addition, hybrid spraying formed a smooth coating surface. These microstructural changes resulted in improved coating properties with regard to hardness, high temperature erosion resistance, and oxidation resistance. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

Plasma Electrolytic Oxidation of Arc-Sprayed Aluminum Coatings

Different posttreatment methods, such as heat treatment, mechanical processing, sealing, etc., are known to be capable to improve microstructure and exploitation properties of thermal spray coatings. In this work, a plasma electrolytic oxidation of aluminum coatings obtained by arc spraying on aluminum and carbon steel substrates is carried out. Microstructure and properties of oxidized layers formed on sprayed coating as well as on bulk material are investigated. Oxidation is performed in electrolyte containing KOH and liquid glass under different process parameters. It is shown that thick uniform oxidized layers can be formed on arc-sprayed aluminum coatings as well as on solid material. Distribution of alloying elements and phase composition of obtained layers are investigated. A significant improvement of wear resistance of treated layers in two types of abrasive wear conditions is observed. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Characterization of Nanostructured WC-Co Deposited by Cold Spraying

Nanostructured WC-Co coating was deposited by cold spraying using a nanostructured WC-12Co powder. The critical velocity for the particle to deposit was measured. The coating microstructure was characterized by X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy. The coating hardness was tested using a Vickers hardness tester. The deposition behavior of single WC-Co particle was examined. WC particle size was measured for comparison of deposit properties to that of sintered bulk. The result shows that the nanostructured WC-Co coating can be successfully deposited by cold spraying using nanostructured powders. The coating exhibited a dense microstructure with full retention of the original nanostructure in the powder to the coating. The test of microhardness of the coating yielded a value of over 1820 Hv_0.3, which is comparable to that of sintered nanostructured WC-Co. The deposition behavior of WC-Co powders as superhard cermet materials in cold spraying and powder structure effects is discussed. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Air gas dynamic spraying of powder mixtures: Theory and application

The radial injection gas dynamic spray (RIGDS) technology of powder coatings deposition was considered for this work. A coating was created by injecting powders with variable compositions into a supersonic air jet and depositing powder on the substrate. This study describes the preliminary analysis of an air gas dynamic spray method realized by a portable RIGDS apparatus with a radial injection of powder. Attention was given to shock compaction processes during the coating structure formation and examples of powder mixtures utilization in RIGDS. It was shown that the operational parameters of supersonic powder-gas jet have a significant influence on the coating's microstructure, thus defining the high performance of the coating. Compaction and bonding of particles were analyzed. The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

On the Role of Spraying Process on Microstructural, Mechanical, and Thermal Response of Alumina Coatings

Thermal spraying is a widely used technology for industrial applications to provide coatings that improve the surface characteristics. According to the specificities of processes (APS, VPS, flame, electric arc), any kind of material can be sprayed. Among materials, ceramic coatings present several interesting aspects such as wear resistance, corrosion protection as well as thermal or electrical insulation; particularly alumina coatings which appear as the most commonly used. From all spraying processes, atmospheric plasma spraying (APS) is a rather well-established process but some others can also be used with a lower economical impact such as the flame technology. The aim of this study was to analyze the alumina coating properties according to the technology employed such as APS or wire flame spraying using the Rokide™ and the Master Jet^? guns. After micrographic analyses by SEM, physical and mechanical properties were measured considering the thermal conductivity and the hardness. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Dependence of the Stabilization of α-Alumina on the Spray Process

A phase change from α-alumina (corundum) in the feedstock powder to predominantly other alumina phases, such as γ-alumina in the coating normally takes place, as a result of the spray process. It is expected that the prevention of this phase transformation will significantly improve the mechanical, electrical, and other properties of thermally sprayed alumina coatings. The results regarding the possibility of stabilization of α-alumina through addition of chromia published in the literature are ambiguous. In this work, stabilization using different spray processes (water-stabilized plasma (WSP), gas-stabilized plasma (APS), and high-velocity oxy-fuel spray (HVOF)) was studied. Mechanical mixtures of alumina and chromia were used, as were prealloyed powders consisting of solid solutions. The investigations focused on mechanical mixtures with both APS and WSP and on prealloyed powders with WSP. The coatings were studied by x-ray diffraction, including Rietveld analysis, and analysis of the lattice parameters. Microstructures were investigated by optical microscopy using metallographic cross-sections. It was shown that in the case of the mechanically mixed powders, the stabilization predominantly depends on the applied spray process. The stabilization of the α phase by use of the WSP process starting from mechanical mixtures was confirmed. It appears that stabilization exhibits a complex dependence on the spray process, the process parameters (in particular the thermal history), the nature of the powder (mechanically mixed or prealloyed), and the chromia content. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

HVOF-Sprayed Coatings Engineered from Mixtures of Nanostructured and Submicron Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> Powders: An Enhanced Wear Performance

In previous studies, it has been demonstrated that nanostructured Al₂O₃-13 wt.%TiO₂ coatings deposited via air plasma spray (APS) exhibit higher wear resistance when compared to that of conventional coatings. This study aimed to verify if high-velocity oxy-fuel (HVOF)-sprayed Al₂O₃-13 wt.%TiO₂ coatings produced using hybrid (nano + submicron) powders could improve even further the already recognized good wear properties of the APS nanostructured coatings. According to the abrasion test results (ASTM G 64), there was an improvement in wear performance by a factor of 8 for the HVOF-sprayed hybrid coating as compared to the best performing APS conventional coating. When comparing both hybrid and conventional HVOF-sprayed coatings, there was an improvement in wear performance by a factor of 4 when using the hybrid material. The results show a significant antiwear improvement provided by the hybrid material. Scanning electron microscopy (SEM) at low/high magnifications showed the distinctive microstructure of the HVOF-sprayed hybrid coating, which helps to explain its excellent wear performance. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

The modeling of coating thickness, heat transfer, and fluid flow and its correlation with the thermal barrier coating microstructure for a plasma sprayed gas turbine application

The plasma sprya deposition of a zirconia thermal barrier coating (TBC) on a gas turbine component was examined using analytical and experimental techniques. The coating thickness was simulated by the use of commercial off-line software. The impinging jet was modeled by means of a finite difference elliptic code using a simplified turbulence model. Powder particle velocity, temperature history, and trajectory were calculated using a stochastic discrete particle model. The heat transfer and fluid flow model were then used to calculate transient coating and substrate temperatures using the finite element method. The predicted thickness, temperature, and velocity of the particles and the coating temperatures were compared with these measurements, and good correlations were obtained. The coating microstructure was evaluated by optical and scanning microscopy techniques. Special attention was paid to the crack structures within the top coating. Finally, the correlation between the modeled parameters and the deposit microstructure was studied. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

The long-term stability of plasma spraying

The wear state of the different gun parts can affect the reproducibility of the plasma spray process. Indeed, this may influence the plasma characteristics and the energy transfer to the sprayed particles resulting in significant changes in the coating attributes. In this contribution, results from a detailed investigation on the stability of plasma spraying are presented.^[1] Specifically designed diagnostic tools were used to study the evolution of key parameters of a plasma spray process during a long-term experiment. A comprehensive analysis was carried out on the collected set of data, with an emphasis on the correlation that may exist among the data. Results show significant variations in the particle state and gun characteristics with spraying time. These variations are reflected in the microstructure of the sprayed coatings. The investigation also gives some indication about how the spray process could be controlled. This paper was presented at the International Thermal Spray Conference (ITSC 2000), May 8–11, 2000, in Montreal, Canada, and published in the proceedings, pp. 1233–1240.     

Microstructural Characterization of Cold-Sprayed Nanostructured FeAl Intermetallic Compound Coating and its Ball-Milled Feedstock Powders

It is difficult to deposit dense intermetallic compound coatings by cold spraying directly using the compound feedstock powders due to their intrinsic low-temperature brittleness. A method to prepare intermetallic compound coatings in-situ employing cold spraying was developed using a metastable alloy powder assisted with post-heat treatment. In this study, a nanostructured Fe/Al alloy powder was prepared by ball-milling process. The cold-sprayed Fe/Al alloy coating was evolved in-situ to intermetallic compound coating through a post-heat treatment. The microstructural evolution of the Fe-40Al powder during mechanical alloying and the effect of the post-heat treatment on the microstructure of the cold-sprayed Fe(Al) coating were characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy (TEM), and x-ray diffraction analysis. The results showed that the milled Fe-40Al powder exhibits lamellar microstructure. The microstructure of the as-sprayed Fe(Al) coating depends significantly on that of the as-milled powder. The heat-treatment temperature significantly influences the in-situ evolution of the intermetallic compound. The heat treatment at a temperature of 500 °C results in the complete transformation of Fe(Al) solid solution to FeAl intermetallic compound. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Influence of the Powder Size Distribution on the Microstructure of Cold-Sprayed Copper Coatings Studied by X-ray Diffraction

Two copper powders were deposited with CGT3000 cold-gas dynamic spray system on aluminum substrates. Mechanical properties have been studied using microhardness, nanoindentation, and bond strength measurements. The deposition efficiency has also been studied. The x-ray diffraction patterns allow the characterization of the microstructure such as grain size, strain in the coating, and dislocation densities. Both powders and coatings have been fully characterized. Three methods have been used to interpret the x-ray patterns: the Warren-Averbach method, the Hall-Williamson (H-W) method, and the modified H-W method. A comparison between the state of the powders before and after deposition will give an insight on the metallurgical processes that take place during the formation of the coating. The influence of the grain size distribution will also be discussed. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Oxidation/carbonization/nitridation and in-service mechanical property degradation of CoCrAlY coatings in land-based gas turbine blades

This article describes variations in the microstructure/composition and mechanical properties in plasma sprayed CoCrAlY coatings and a modified René 80 substrate of gas turbine blades operated for 21,000 h under liquefied natural gas fuels. Substantial oxidation/carbonization occurred in the near surface region of concave coatings, but not in the convex coatings. Aluminum and nickel/titanium-rich nitrides formed in near interface coatings and substrates of concave side of blades, respectively. Small punch (SP) specimens were prepared from the different blade location to examine the variation of the mechanical properties in the coatings. In SP tests, brittle cracks in the near surface and interface coatings of the concave side easily initiated up to 950 °C. The convex coatings exhibited higher ductility than the concave coatings and substrate and showed a rapid increase in the ductility above 800 °C. Thus it is apparent that the oxidation/carbonization and nitridation in the concave coatings produced a significant loss of the ductility. The in-service degradation mechanism of the CoCrAlY coatings is discussed in light of the operating temperature distribution and compared to that of CoNiCrAlY coatings induced by grain boundary sulfidation/oxidation. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

Preparation of perovskite powders and coatings by radio frequency suspension plasma spraying

Perovskite-type LaMnO₃ powders and coatings have been prepared by a novel technique: reactive suspension plasma spraying (SPS) using an inductively coupled plasma of approximately 40 kW plate power and an oxygen plasma sheath gas. Suitable precursor mixtures were found on the basis of solid state reactions, solubility, and the phases obtained during the spray process. Best results were achieved by spraying a suspension of fine MnO₂ powder in a saturated ethanol solution of LaCl₃ with a 1 to 1 molar ratio of lanthanum and manganese. A low reactor pressure was helpful in diminishing the amount of corrosive chlorine compounds in the reactor. As-sprayed coatings and collected powders showed perovskite contents of 70 to 90%. After a posttreatment with an 80% oxygen plasma, an almost pure LaMnO₃ deposit was achieved in the center of the incident plasma jet. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

Effect of Particle Size Distribution on Isothermal Oxidation Characteristics of Plasma Sprayed CoNi- and CoCrAlY Coatings

The effect of particle size distribution on the degradation behavior of plasma sprayed CoNi- and CoCrAlY coatings during isothermal oxidation was investigated, in terms of the oxygen content, porosity, surface roughness, and oxide scale formation. The results show that the degradation of both coatings was considerably influenced by the starting particle size distribution. It also shows that in the as-sprayed vacuum plasma spray (VPS) coatings the oxygen content on the coating surface increased significantly with decreased average particle size. But after thermal exposure, the difference of the oxygen contents between the coatings with different particle size was decreased. The powder with various particle size resulted in low porosity inside the coatings during the deposition process. The surface roughness of the coatings increased with increased particle size. The small particles produced a relatively smooth surface, and the oxide growth in the coating deposited by small particle was slower than that in the large particle coating. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Thermal Fatigue Behavior of Thick and Porous Thermal Barrier Coatings Systems

High-temperature thermal fatigue causes the failure of thermal barrier coating (TBC) systems. This paper addresses the development of thick TBCs, focusing on the microstructure and the porosity of the yttria partially stabilized zirconia (YPSZ) coating, regarding its resistance to thermal fatigue. Thick TBCs, with different porosity levels, were produced by means of a CoNiCrAlY bond coat and YPSZ top coat, both had been sprayed by air plasma spray. The thermal fatigue resistance of new TBC systems and the evolution of the coatings before and after thermal cycling was then evaluated. The limit of thermal fatigue resistance increases depending on the amount of porosity in the top coat. Raman analysis shows that the compressive in-plane stress increases in the TBC systems after thermal cycling, nevertheless the increasing rate has a trend which is contrary to the porosity level of top coat. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Tungsten carbide coatings with different binders prepared by low power plasma spray system

Thermal spraying of cermet coatings is widely used for protection of machining parts against wear and corrosion. These coatings consist of WC particles in metal binders such as Co, Cr and Ni. Three kinds of WC powders with different metal binders (Co, NiCr and CoCr) were sprayed by low power plasma spray system on Al-Si-Cu alloy substrate. Fundamental aspects of sprayed cermet coatings, including (i) the effects of binder type on the coating structure, (ii) the hardness and (iii) the microstructure, were investigated. All cermet coatings have the same phase structure such as WC and W2 C. However, the intensities of these phases are different in each coating, mainly due to the difference in solidification rate in each case. Moreover, the hardness measurements are found to be different in each coating. The results show that, binder type has a significant effect on the physical and mechanical properties of the sprayed coatings.     

Suspension plasma spraying of nanostructured WC-12Co coatings

Nanostructured WC-12% Co coatings were deposited by suspension plasma spraying of submicron feedstock powders, using an internal injection plasma torch. The liquid carrier used in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to thin coatings with a fine surface finish. A polyethylene-imine (PEI) dispersant was used to stabilize the colloidal suspension in an ethanol carrier. In-flight particle states were measured for a number of operating conditions of varying plasma gas flow rates, feed rates, and standoff distances and were related to the resulting microstructure, phase composition (EDS, SEM, XRD), and Vickers hardness. High in-flight particle velocities (>800 m/s) were generated, leading to dense coatings. It was observed that the coating quality was generally compromised by the high temperature and reactivity of the small particles. To compensate for this shortcoming, the suspension feed rate was adjusted, thereby varying the thermal load on the plasma. Results showed that a slightly larger agglomerate size, in conjunction with low particle jet temperatures, could somewhat limit the decomposition of WC into brittle W₂C/W₃C and amorphous cobalt containing binder phases. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Investigation of Al-Al2O3 Cold Spray Coating Formation and Properties

Coating build-up mechanisms and properties of cold-sprayed aluminum-alumina cermets were investigated using two spherical aluminum powders having average diameters of 36 and 81 μm. Those powders were blended with alumina at several concentrations. Coatings were produced using a commercial low-pressure cold spray system. Powders and coatings were characterized by electronic microscopy and microhardness measurements. In-flight particle velocities were monitored for all powders. The deposition efficiency was measured for all experimental conditions. Coating performance and properties were investigated by performing bond strength test, abrasion test, and corrosion tests, namely, salt spray and alternated immersion in saltwater tests. These coating properties were correlated to the alumina fraction either in the starting powder or in the coating. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.