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.     

Properties and Performance of High-Purity Thermal Barrier Coatings

It has been found that reducing the level of impurity oxides (particularly SiO₂ and Al₂O₃) in 7YSZ, from about 0.2 wt% to below 0.1 wt% raises the sintering resistance and the phase stability of plasma-sprayed coatings. The implications for the usage of these coatings at elevated temperatures are examined. It is concluded that using relatively high-purity powder of this type is likely to confer substantial benefits in terms of the thermomechanical stability of the coatings under service conditions. 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.     

Microstructure and Electrical Conductivity of Atmospheric Plasma-Sprayed LSM/YSZ Composite Cathode Materials

Yttria stabilized zirconia and lanthanum strontium manganate (YSZ/LSM) have been employed to fabricate the composite cathode layer for solid oxide fuel cells (SOFCs). In the present study, the YSZ/LSM composite coating was deposited by atmospheric plasma spray (APS) using the mechanical blending LSM and YSZ with ratios of 50:50, 40:60, and 20:80 wt.%. The electrical conductivity of the composite coating was measured by the means of direct current (DC) measurement in the temperature range of 500-900 °C. The electrical conductivity of the YSZ-50%LSM coating ranged from 2.17 to 3.60 S/cm along the direction parallel to the coating surface at the temperature range. For the same specimen, the electrical conductivity perpendicular to the plane is less than one-tenth of that in the plane. The anisotropy of the electrical conductivity is attributed to the phases of different properties in the composite coating and the APS coating structure characteristics. The results also showed that the electrical conduction of the composite was strongly influenced by the YSZ 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.     

Rapid and Continuous Deposition of Porous Nanocrystalline SnO2 Coating with Interpenetrating Pores for Gas Sensor Applications

In this article, we proposed a rapid and continuous process for the production of nanoporous coatings for functional applications. Experiments following two statistical designs were implemented to screen and investigate the spraying parameters’ effects on coating crystallinity and porosity in order to gain a better understanding. The spraying standoff distance, solution flow rate and power were identified as having significant effects on coating porosity and crystallinity. The result yielded a peculiar microstructure comprised of interpenetrating pores and layered structures with embedded pores. A deposition mechanism was postulated to explain this microstructure. Ethanol gas sensors that are constructed from the coatings had comparable sensitivities to those reported in the literature for thick-film coatings and had a maximum sensitivity near 200 °C. 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.     

Fabrication of Nano-TiO2 Coating for Dye-Sensitized Solar Cell by Vacuum Cold Spraying at Room Temperature

Deposition of nanocrystalline TiO₂ coating at low temperature is becoming more attractive due to the possibility for continuous roll production of the coating for assembly lines of dye-sensitized solar cell (DSC) at a low cost. In this study, porous nano-TiO₂ coating was deposited by vacuum cold spraying (VCS) at room temperature on a conducting glass substrate using commercial P25 nanocrystalline TiO₂ powder. The microstructure of TiO₂ coating was characterized by field emission scanning electron microscopy (FESEM) and nitrogen adsorption test. A commercial dye (N719) was adsorbed on the surface of TiO₂ particles within the coating to assemble a DSC. The cell performance was evaluated by employing simulated solar light at an intensity of 100 mW/cm². The results showed that TiO₂ coating was deposited by the agglomerates of nano-TiO₂ powders. The Brunauer-Emmett-Teller (BET) test of the as-sprayed TiO₂ coating yielded a porosity of 49% and an average pore size of 17 nm. The assembled solar cell yielded a short-circuit current density of 7.3 mA/cm² and an energy conversion efficiency of 2.4%. The test results indicate that VCS was a promising method to deposit nanocrystalline TiO₂ coatings at low temperature applied to DSCs. 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.     

Comparison of atmospheric plasma sprayed anode layers for SOFCs using different feedstock

Atmospheric plasma spraying (APS) is a cost-effective way to produce solid oxide fuel cell (SOFC) components. When using APS, therefore, sinter steps can be avoided, which is essential once a metallic support is used for the SOFC. Several properties are required regarding the microstructure of an optimized anode layer. Here, gas permeability, electrochemistry, electronic conductivity, coefficient of thermal expansion, as well as thermal shock resistance have to be considered. Different types of powder feedstock were investigated to develop an atmospheric plasma sprayed anode layer: (a) NiO or Ni together with YSZ as starting materials, (b) agglomerates in which NiO and YSZ are already mixed on a submicrometer range, (c) blended NiO/YSZ powder, and (d) separate injection of the individual NiO and YSZ powders, respectively, into the plasma by two separate powder lines. The performance of APS anodes are measured in single fuel-cell tests. Anode layers sprayed by a separate injection of the individual NiO and YSZ powders into the plasma show the best results. 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.     

Mechanical Characteristics of Al-Co-Ce Coatings Produced by the Cold Spray Process

Gas atomized feedstock particles of an Al-13Co-26Ce alloy system were sprayed using the Cold Spray deposition technique. The microstructures of the coatings produced are examined and the mechanical characteristics, in particular the bending fatigue and the bond strength, of the Al-Co-Ce coatings are reported. The results show that the Al-Co-Ce coatings improved the fatigue behavior of AA 2024-T3 specimens when compared to uncoated and Alclad specimens. During the bond strength tests, the bonding agent failed and no delamination of the coating from the substrate occurred. The microstructural features of the feedstock powder were also found in the coatings. It is suggested that the increase in the fatigue properties of the specimens can be attributed to the residual compressive stresses induced in the coatings and to the high adhesion strength of the coatings to the substrates. 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.     

Effect of Powder Injection Location on Ceramic Coatings Properties When Using Plasma Spray

The effect of powder injecting location of the plasma spraying on spraying properties was studied. Three different powder-injecting methods were applied in the experiment. In the first method, the particles were axially injected into the plasma flow from the cathode tip. In the second method, the particles were radially injected into the plasma flow just downstream of the anode arc root inside the anode nozzle. In the third method, the particles were radially injected into the plasma jet at the nozzle exit. The alumina particles with a mean diameter of 20 μm were used to deposit coatings. Spraying properties, such as the deposition efficiency, the melting rate of the powder particles, and the coating quality were investigated. The results show that the spraying with axial particle injecting can heat and melt the powder particles more effectively, produce coatings with better quality, and have higher deposition efficiency. 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.     

Sliding Wear Properties of HVOF Thermally Sprayed Nylon-11 and Nylon-11/Ceramic Composites on Steel

Polymer and polymer/ceramic composite coatings were produced by ball-milling 60 μm Nylon-11 together with nominal 10 vol.% of nano and multiscale ceramic reinforcements and by HVOF spraying these composite feedstocks onto steel substrates to produce semicrystalline micron and nanoscale reinforced polymer matrix composites. Room temperature dry sliding wear performance of pure Nylon-11, Nylon-11 reinforced with 7 nm silica, and multiscale Nylon-11/silica composite coatings incorporating 7-40 nm and 10 μm ceramic particles were characterized using a pin-on-disk tribometer. Coefficient of friction and wear rate were determined as a function of applied load and coating composition. Surface profilometry and scanning electron microscopy were used to characterize and analyze the coatings and wear scars. The pure Nylon-11 coating experienced less wear than the composites due to the occurrence of two additional wear mechanisms: abrasive and fatigue wear. 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.     

Tribological and Corrosion Behavior of Vacuum Plasma Sprayed Ti-Zr-Ni Quasicrystalline Coatings

This investigation deals with a study of the friction, wear, and corrosion behavior of vacuum plasma sprayed quasicrystalline (QC) Ti_41.5Zr_41.5Ni₁₇ coatings. During pin on disc experiments, a change in the mode of wear has been found to occur with corresponding changes in normal load and sliding velocity. The low thermal conductivity of quasicrystals and its brittleness play a vital role in determining the friction and wear behavior of such materials. When these coatings are subjected to rubbing for a longer period of time, wear occurs by subsurface crack propagation, and subsequent delamination within the coated layer. By comparing the QC to its polycrystalline counterpart during potentiodynamic measurements according to ASTM G 31, higher currents were found over the whole range of potentials for QC when immersed in 1 M HCl solution. 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 microstructure of Nano-TiO2 coating deposited by vacuum cold spraying

Control of the microstructure of TiO₂ coatings through preparation methods significantly influences the coating performance. In this study, a vacuum cold-spray process, as a new coating technology, is used to deposit nanocrystalline TiO₂ coatings on conducting glass and stainless steel substrates. TiO₂ deposits were formed using two types of nanocrystalline TiO₂ powders with mean particle diameters of 200 and 25 nm. Coating microstructures were characterized by scanning electron microscopy and x-ray diffraction analysis. Results demonstrate that a thick nanocrystalline TiO₂ coating can be deposited by the vacuum cold-spray process. The coating was found to consist of particles stacked as agglomerates that build up to several hundred nanometers. The coating also presents a mesoporous microstructure that could be effective in such applications as photocatalytic degradation and dye-sensitized solar cells. 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.     

Yttria-Stabilized Zirconia Thermal Barriers Sprayed Using N<Subscript>2</Subscript>-H<Subscript>2</Subscript> and Ar-H<Subscript>2</Subscript> Plasmas: Influence of Processing and Heat Treatment on Coating Properties

Thermal barrier coatings were produced using both Ar and N₂ as the primary plasma gas. Various aspects of the process and the coatings were investigated. It was found that higher in-flight particle temperatures could be produced using N₂, but particle velocities were lower. Deposition efficiencies could be increased by a factor of two by using N₂ as compared to Ar. Coatings having similar values of porosity, hardness, Young’s modulus, and thermal diffusivity could be produced using the two primary gases. The coatings exhibited similar changes (increased hardness, stiffness, and thermal diffusivity) when heat-treated at 1400 °C. However, the N₂-processed coatings tended to have lower values of Young’s modulus and thermal diffusivity following such treatment. The results point to the potential advantage, in terms of reduced powder consumption and increased production rate, of using N₂ as compared to Ar as the primary plasma gas for TBC deposition. 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 YSZ solid oxide fuel cells electrolyte deposited by atmospheric plasma spraying and low pressure plasma spraying

Yttria doped zirconia has been widely used as electrolyte materials for solid oxide fuel cells (SOFC). Plasma spraying is a cost-effective process to deposit YSZ electrolyte. In this study, the 8 mol% Y₂O₃ stabilized ZrO₂ (YSZ) layer was deposited by low pressure plasma spraying (LPPS) and atmospheric plasma spraying (APS) with fused-crushed and agglomerated powders to examine the effect of spray method and particle size on the electrical conductivity and gas permeability of YSZ coating. The microstructure of YSZ coating was characterized by scanning electron microscopy and x-ray diffraction analysis. The results showed that the gas permeability was significantly influenced by powder structure. The gas permeability of YSZ coating deposited by fused-crushed powder is one order lower in magnitude than that by agglomerated powder. Moreover, the gas permeability of YSZ deposited by LPPS is lower than that of APS YSZ. The electrical conductivity of the deposits through thickness direction was measured by potentiostat/galvanostat based on three-electrode assembly approach. The electrical conductivity of YSZ coating deposited by low pressure plasma spraying with fused-crushed powder of small particle size was 0.043 S cm⁻¹ at 100 °C, which is about 20% higher than that of atmospheric plasma spraying YSZ with the same powder. 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.     

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.     

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.     

Influence of Annealing on Photocatalytic Performance and Adhesion of Vacuum Cold-Sprayed Nanostructured TiO2 Coating

Composite powder was prepared using primary nanoTiO₂ powder and polyethylene glycol (PEG). The nanoTiO₂ coating was deposited through vacuum cold spray using both the composite powder and the primary nanopowder. The influence of annealing on the coating adhesion and photocatalytic activity was investigated. The coating adhesion was evaluated through erosion test by water jet. The photocatalytic performance of the coatings was evaluated through photodegradation of phenol in water. Results showed that annealing of the coating at a temperature from 450 to 500 °C yielded both higher activity and better adhesion. The adhesion of the coating deposited using the composite powder was better than that using the primary nanoTiO₂ powder. It was found that the TiO₂ coating, resulting from the composite powder, presented much higher activity than that deposited with the primary nanopowder. The better activity is attributed to the existence of large pores resulting from the stacking of composite powder, which benefits the reactants’ transportation through the porous 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.     

Oxidation and Hot Corrosion Resistance of HVOF WC-NiCrFeSiB Coating on Ni- and Fe-based Superalloys at 800 °C

The present work evaluates the oxidation and hot corrosion resistance of high velocity oxy-fuel (HVOF) sprayed WC-NiCrFeSiB coating deposited on Ni-based superalloy (Superni 75) and Fe-based superalloy (Superfer 800H). The coated as well as uncoated specimens were exposed to air and molten salt (Na₂SO₄-25% NaCl) environment at 800 °C under cyclic conditions. The thermogravimetric technique was used to establish the kinetics of corrosion. The corrosion products were characterized using the combined techniques of x-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe micro analyser (EPMA). The WC-NiCrFeSiB coating provides necessary resistance against oxidation and hot corrosion to both the nickel and iron-based superalloys in the given environmental conditions at 800 °C. The oxides of active elements of the coatings, formed in the surface scale as well as at the boundaries of nickel and tungsten rich splats, have contributed for the oxidation and hot corrosion resistance of WC-NiCrFeSiB coatings, as these oxides act as barriers for the diffusion/penetration of the corrosive species through the coatings. 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.     

Thermomechanical behavior of nanostructured plasma sprayed zirconia coatings

Retaining nonmelted nanoparticles of zirconia in nanostructured coatings has been a challenge in the past. Recently an air plasma spray process was developed to produce coatings that retain up to 30–35% by volume nonmelted particles, resulting in a unique structure. The creep/sintering behavior of such thermal barrier coatings deposited from nanostructured feedstock has been measured and compared with deposits produced from hot oven spherical particles (HOSP). Both feedstocks contain 6–8 wt.% Y₂O₃ as a stabilizer. Flexure and compression creep testing were conducted under several different loads and temperatures to obtain creep exponents and parameters. 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.     

Corrosion Behavior of Arc Sprayed Nickel-Base Coatings

In this study, nickel-base cored wires were prepared by using NiCr strip to wrap metal powders of nickel (Ni), chromium (Cr), molybdenum (Mo), and chromium boron (CrB). Nickel-base coatings were prepared by electric arc spraying. Microstructures of Ni-Cr-Mo and Ni-Cr-B coatings were investigated using scanning electron microscopy (SEM), energy-dispersive analysis (EDAX), and x-ray diffraction (XRD) analysis. The coatings have a compact surface and presented a bonding strength higher than 40 MPa. Potentiodynamic polarization measurements and salt-spray test were carried out to determine the corrosion behavior of the coatings. The results showed that Ni-base coatings containing Mo (5%) or B (2-4%) had better antichlorine ion corrosion performance than that of Ni-base coatings without Mo element, and PS45 (Ni-Cr-Ti) coating. The antichlorine ion corrosion coatings could be used for resolving the corrosion protection problem of the equipment and piping contacting sour, alkali, salt liquid in petrochemical engineering applications. 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.