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With the conventional gas or water atomization process of synthesizing metallic powders, it is difficult to obtain graphite structure in a gray cast powder particle because of rapid cooling of the molten droplets. In this work, a fabrication method of gray cast iron powder with graphite structure was proposed based on a structural transplantation route. In the fabrication process, the precursor powder was firstly prepared by mechanically separating from as-cast gray cast iron bulk, then the precursor powder was ball-milled with different ratios of ball-to-powder to obtain final powders. The profile, size distribution, and surface roughness of final powders were quantitatively characterized by circularity, particle uniformity level, and fractal dimension method, respectively. It was found that ball milling smoothed the sharp edges and corners of the precursor powder and reduced the size of the precursor powder. As a result, the ball-milled powders have a more regular shape, more uniform size distribution, lower surface roughness, and better flowability than the precursor powder for thermal spray applications.

Fe-based amorphous powder and shell-core-structured composite powder prepared by ball-milling Fe-based amorphous powder with 10 wt.% Ni/Al powder, were used to fabricate Fe-based amorphous coating and Fe-based amorphous composite coating by plasma spray process, respectively. X-ray diffraction (XRD) analysis results showed that the composite coating was comprised of multi-component amorphous Fe62.8Ni13.6Cr9.9Mo8.6Si1.6C2.3B0.9 layer and crystalline Ni3Al layer. Compared with Fe-based amorphous coating, the composite coating exhibited a more compact structure. The corrosion resistance of Fe-based amorphous coating, which was tested by potentiodynamic polarization method in 3.5 wt.% NaCl solution, was significantly improved by using shell-core-structured composite powder. The composite coating showed lower corrosion current density (12.5 μA/cm2) and passive current density (9.0 mA/cm2) than Fe-based amorphous coating. The improved corrosion resistance of the composite coating is attributed to the dense structure and the formation of passivation film.

In this study, the bonding formation of the cast iron splat deposited on a preheated aluminum substrate by atmospheric plasma spraying was investigated using a finite element method based on a heat transfer model built in a cylindrical coordinate system. To enhance the accuracy of calculations, thermal contact resistance (Rth) of the contact interface was incorporated into the calculation. A precise Rth value was obtained using a well-established relationship. The diameter of grains in the splat was determined by atomic force microscopy analysis. Furthermore, the physical parameters of the cast iron and the aluminum at different temperatures used in the simulation were calculated according to the composition of the materials. The calculations indicated that the interface temperature was below the substrate melting point during the entire observation period, confirming that no melting of the aluminum substrate had occurred. Thus, the formation of splat–substrate metallurgical bonding was attributed to the enhanced interface temperature and plastic deformation rather than the melting of the substrate surface.

The laser re-melting treatment was performed on the plasma-sprayed Fe-based amorphous coating to ameliorate the corrosion performance of the coating. The re-melting depth was about 200 μm which was mainly controlled by laser energy input, beam speed and facular dimension. The microstructure was characterized by scanning electron microscope (SEM), and X-ray diffraction (XRD). The corrosion property of the coatings was addressed via electrochemistry methods in a 3.5 wt.% NaCl solution. The results indicate that the plasma-sprayed coating becomes much denser after laser re-melting treatment. The connected porosity ratio in as-sprayed coating dramatically reduces from 16.3% to 2.4% after laser re-melting. The as-sprayed coating mainly contains amorphous and much limited crystal phase, and some amorphous phase in the as-sprayed coating crystalizes during laser re-melting. Polarization test demonstrated that the as-sprayed coating has a significantly dramatical effect for improving corrosion performance of carbon steel, while the laser re-melting process is a more efficient method. The influence level of the coating compactness in this study is roughly two times as big as that of amorphous in coating, in the term of improving corrosion resistance of carbon steel.

The properties of a thermally sprayed coating are primarily determined by the porosity and inter-lamellar bonding. In this work, three cast iron coatings were prepared by the atmospheric plasma spraying process. In the spraying process, the surface temperatures (deposition temperatures) of the coatings were controlled to be 50 ± 5, 180 ± 6, and 240 ± 8 °C. The microstructures of the coatings were characterized by field emission scanning electron microscopy. Both electrochemical polarization and immersion tests in 0.5 mol/L sulfuric acid solution were employed to evaluate the influence of deposition temperature on the corrosion behavior of the coatings. The results of these tests indicated that the coating deposited at high temperature shows a higher corrosion resistance than the coating deposited at low temperature, which was attributed to the reduced porosity of the coating resulting from the improvements in the flattening of the molten particles and the bonding between lamellae with raising the deposition temperature.

Plasma-sprayed cast iron splats were deposited onto polished aluminum substrates preheated to different temperatures ranging from 25°C to 250°C. The morphology of single splat was observed by a field emission scanning electron microscope. Quantitative characterization methods, including fractal dimension (FD) and circularity analyses of the splat profile, were employed to identify the difference in morphology of the splats with the change of the substrate temperature. The results showed that the substrate temperature has a significant effect on the spreading of molten droplets and the morphology of resultant splats through changing the solidification rate of the droplets. With the increment of substrate temperature, the homogeneous and sufficient spreading of the droplets resulted from low solidification rate reduces the splashing of the droplets. In addition, the evaporation of adsorbed moisture on the substrate improves the wettability between the spreading droplet and the substrate, then benefits the homogeneous spreading of the molten droplet. As a result, a distinct decline in the FD value was observed. It was also suggested that the FD analysis could be used to characterize the morphology of the splat more effectively while the circularity method was heavily dependent on the area of the splat.

Atmospheric plasma spraying (APS) technique is employed to prepare Fe-based amorphous coatings on T91 steel substrate under various arc powers of 30 kW, 35 kW and 40kW. The morphology and microstructure of both Fe-based powders and amorphous coatings are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, the wear resistance and high-temperature oxidation resistance of the plasma-sprayed coatings at various arc powers are studied. It is found that with increasing the arc power, the content of the porosity and the amorphous phase in the coatings declines. Specifically, under 30 kW, 35 kW and 40 kW arc power, the porosity of the coatings is 7.96%, 6.13% and 5.75%. Correspondingly, the relative content of amorphous phase from the coatings is measured to be 96.07% (mass fraction), 73.89% and 65.54%. Moreover, under 40 kW arc power, it gives the coating the highest micro-hardness having more compact microstructure and more dispersive α-Fe grains. Besides, the coatings fabricated at high arc power exhibit less wear induced weight loss and less weight gain from high-temperature oxidation comparing with those fabricated at lower arc power.

The size of the grains formed in individual splats has a significant effect on the properties of a thermally sprayed coating. In this work, the grain size in a plasma-sprayed cast iron splat was predicted based on a known relationship between the grain size and the thermal contact resistance at the splat–substrate interface. A numerical calculation method, based on a 2D heat transfer model, was used to study the relationship between the thermal contact resistance and the melting depth on the substrate surface. The thermal contact resistance was evaluated according to the observed maximum melting depth from the field emission scanning electron microscope micrographs of the individual splats. The estimated grain size with a range 51.3-73.6 nm was in close agreement with the experimental observations.

Fe-based amorphous coatings are increasingly recognised as promising candidates for the protection of coal-fired boilers against corrosion. The present study prepared Fe-based amorphous coatings on a T91 substrate by plasma spraying technology. The corrosion behaviour of the coating in hot Na2SO4 + K2SO4 salts at 700°C was investigated, and measurements of the mean mass gain were performed after each cycle to establish the hot corrosion kinetics of the coatings using the thermogravimetric technique. The coated specimens, especially specimens with 380-μm-thick coatings, exhibited lower mean gain rates at all operating cycles as compared to the uncoated T91 samples. The highest hot corrosion resistance was a result of the amorphous composite microstructure and high Cr and Ni elemental contents, which contributed to the formation of the protective oxides of chromium and nickel such as Cr2O3, NiO and NiCr2O4.

During the plasma spraying process, the splat-substrate interaction is a key factor to understanding the formation of the coating-substrate adhesion. In the present study, both experimental and simulation methods were employed to analyse the splat-substrate interfacial bond and its formation. Individual cast iron splats were sprayed onto polished aluminum substrate surfaces, which were preheated to temperatures ranging from 25 °C to 240 °C. After spraying, polished cross sections of the collected splats were examined by scanning electron microscopy to identify the splat-substrate interface bonding characteristics. Furthermore, numerical simulation was conducted using a finite element method (FEM) to obtain quantitative information on heat exchange between the splat and the substrate. Results showed that the substrate preheating temperature (initial substrate temperature) significantly affected the splat-substrate bond formation. When the initial substrate temperature exceeded 190 °C, the formation of a metallurgical bond at the splat-substrate interface was detected. The results of the analysis based on both experimental and simulation data, demonstrated that the higher initial substrate temperature caused obvious plastic deformation of the substrate surface and atomic diffusion at the splat-substrate interface under the present conditions, which contributed to the formation of the metallurgical bond. Moreover, a barb-shaped structure was found at the periphery of the splat when the initial substrate temperature reached 240 °C, which was beneficial to the enhancement of the mechanical bonding between the splat and the substrate.

Ti-6Al-4V alloy has been widely used as an important structural material in aerospace, automotive, and chemical and biomedical industries due to its high specific strength and excellent corrosion resistance. However, the poor tribological properties and low resistance to high temperature oxidation limit extensive applications of the alloy. Plasma surface diffusion treatments, including plasma carbonizing, plasma nitriding, and plasma alloying treatments, contribute to improve wear resistance and the anti-oxidation property of the alloy by introducing other elements into the surface of the alloy to form hard surface layers under low pressure conditions. In this review article, the developments in microstructure and properties of the layers generated by the three techniques were reviewed systematically. In particular, the development in the phase determination of the plasma-nitrided layer was analyzed. New approaches in accelerating the diffusion of atoms and optimizing process were analyzed in detail.

Amorphous coating technology is an attractive way of taking advantage of the superior properties of amorphous alloys for structural applications. However, the limited bonds between splats within the plasma-sprayed coatings result in a typically lamellar and porous coating structure. To overcome these limitations, the as-sprayed coating was treated by a laser-remelting process. The microstructure and phase composition of two coatings were analyzed using scanning electron microscopy with energy-dispersive spectroscopy, transmission electron microscopy, and x-ray diffraction. The wear resistance of the plasma-sprayed coating and laser-remelted coating was studied comparatively using a pin-on-disc wear test under dry friction conditions. It was revealed that the laser-remelted coating exhibited better wear resistance because of its defect-free and amorphous-nanocrystalline composited structure.

To understand the effects of spray parameters on the splashing, cast iron particles were plasma-sprayed onto polished surfaces of aluminum substrate to form single splats. Various plasma arc powers and spray distances were applied to adjust the morphology of the splats which was studied using a field emission scanning electron microscope (FESEM). The experimental results showed that the splashing of impinging droplets was significantly restrained for the splats deposited with high arc power (30 kW) and short spray distance (80 mm). This finding would be beneficial to improving the adhesive strength of the coating.

In the plasma-sprayed coatings, the morphology of the splats plays an important role in optimizing the microstructure and performance of the coating. Especially, the splashing of impinging droplets during deposition weakens the splat–substrate/intersplat bonding and increases the porosity of the coating. Consequently, the integration of the coating is deteriorated. In the present study, cast iron particles were plasma-sprayed on the surface of polished aluminum substrate to form a single splat. During spraying, the surface of aluminum substrate was preheated in a temperature range from 25 °C to 320 °C. The impact of the substrate preheating temperature on the morphology of the splats was studied using a field emission scanning electron microscope. Results showed that the substrate temperature had significant effects on the morphology of splats. At room temperature, the splats mainly exhibited a splash type with network or radial lines on the splat periphery. While, the splashed splats deposited onto a high temperature substrate showed a star shape on the splat periphery. When the substrate was preheated to 130 °C, the mean percentage of the splashed splats decreased to a minimum value of 18.4% and the disk-like splats prevailed. With the increase of the substrate temperature from 130 °C to 290 °C, the mean percentage of the splashed splats increased monotonically to 78.3%. When the substrate temperature reached to 320 °C, the mean percentage of the splashed splats slightly reduced to 76.6%.

Fe-based amorphous and nanocrystalline coatings were fabricated by air plasma spraying. The coatings were further treated by laser remelting process to improve their microstructure and properties. The corrosion resistance of the as-sprayed and laser-remelted coatings in 3.5wt% NaCl and 1 mol/L HCl solutions was evaluated by electrochemical polarization analysis. It was found that laser-remelted coating appeared much denser than the as-sprayed coating. However, laser-remelted coating contains much more nanocrystalline grains than the as-sprayed coatings, resulting from the lower cooling rate in laser remelting process compared with plasma spraying process. Electrochemical polarization results indicated that the laser-remelted coating has great corrosion resistance than the as-sprayed coating because of its dense structure.

Ti-6Al-4V (TC4) alloys were plasma carbonized at different temperatures (900, 950, and 1 000 °C) for duration of 3 h. Graphite rod was employed as carbon supplier to avoid the hydrogen brittleness which is ubiquitous in traditional gas carbonizing process. Two distinguished structures including a thin compound layer (carbides layer) and a thick layer with the mixed microstructure of TiC and the α-Ti in carburing layer were formed during carburizing. Furthermore, it was found that the microstructure and the properties of TC4 alloy were significantly related to the carbonizing temperature. The specimen plasma carbonized at 950 °C obtained maximum value both in the hardness and wear resistance.

Microarc oxidation (MAO) was used to prepare TiO 2 + ZrO 2 composite coatings on Ti6Al4V alloy in Zr-containing electrolytes. The high temperature oxidation resistance and oxidation mechanism of MAO coatings were investigated and discussed. The composite ceramic coatings exhibit a porous structure with small pores (0.4–1 μm in diameter) on the inner wall of larger pores, and consist of m-ZrO 2 and ZrTiO 4 . In the case of static oxidation at different temperatures, the high temperature oxidation resistance of Ti6Al4V is improved 2–10 times after MAO treatment. The coated samples oxidized at different temperatures present various oxidation behaviors. A porous TiO 2 layer forms after exposing oxidation at 500 °C for 300 h, while a continuous TiO 2 layer forms after oxidation at 600 °C for 75 h. However, when the coated samples oxidized at 700 °C and 800 °C, a multilayer structure of MAO coating/transitional layer/TiO 2 layer/TiN layer forms on Ti6Al4V with the combined effect of interface migration of MAO coating and air diffusion inward, and the diffusion of substrate elements outward. Especially, it is found that a TiN layer with preferential growth towards (111) lattice planes forms in the multilayer structure in coated samples, which is much different from the oxidation behavior of Ti6Al4V at 700 °C and 800 °C. The presence of multilayer structure can provide an efficient diffusion barrier, which restrains the growth of TiO 2 and TiN.

Fe-based and Fe/Mo composite amorphous coatings were deposited on the surface of plain carbon steel substrates by atmospheric plasma spraying (APS). With increasing the Mo alloy content, the microstructure of the coatings revealed more dense structure. The porosities of composite coating were all less than those of Fe-based coating due to Mo alloy self-bonding performance. The ME-10 friction and wear tester was employed to investigate the wear behaviors of the coatings under dry sliding conditions. It was found that the mass loss of the resultant coatings decreased with increasing Mo-based powders into the feedstock. This was attributed to the reduction of the delaminations resulting from improved intersplat bond with Mo addition.

Controllable formation of splat bonding in thermally sprayed coatings is essential to fulfill requirements of versatile coating applications, because the bonding influences most of the coating properties. The splat bonding formation in single-layered and multi-layered Al 2 O 3 and YSZ splats was examined at different deposition temperatures to reveal the factors dominating the splat bonding formation. Results show that the splat interface bonding was significantly influenced by the deposition temperature. There is a critical bonding temperature for the formation of the effective splat interface bonding in plasma-sprayed ceramic coating. The critical bonding temperature depends on coating materials. It is found that the critical bonding temperature is ~ 300 °C or ~ 600 °C for Al 2 O 3 or YSZ, respectively. It will be shown that the critical bonding temperature concept can be used to explain qualitatively reasonably the lamellar bonding formation during multi-splats and coating deposition.

Ti–6Al–4V alloy was treated by plasma carburizing process at 950 °C for different durations of 1 h, 2 h, 3 h, and 4 h. Plasma carburizing was performed in pure Ar gas under 32 ± 2 Pa. Graphite rod was employed as carbon supplier. Optical microscope (OM) observations showed a carburizing layer formed after carburizing. Further FESEM examinations and XRD analysis confirmed that the carburizing layer consists of a TiC/α-Ti mixed layer and a thin compound (TiC) layer on the mixed layer. With increasing the carbonizing time, the thickness of the carburizing layer increased and the specimen treated at 950 °C for 3 h obtains maximum values of the hardness.

The Fe-based amorphous coatings were produced by air plasma spraying. The as-sprayed coatings were heat-treated at the temperature of 573, 873, and 1 023 K, respectively. The crystallization and wear behavior of the heat-treated amorphous coatings were investigated. It was found that the amorphous-nanocrystalline transformation appeared when the as-sprayed coatings were treated at 853 K. The crystallization process had completed and a coating with microcrystallines was formed when the treatment temperature reached 1 023 K. The resultant amorphous and nanocrystalline composite coatings exhibited superior wear resistance compared to crystalline coating. It is attributed to fine grain strengthening of formed nanocrystallines.

Alumina coatings were prepared by atmospheric plasma spraying through controlling the surface temperature of the coatings during spraying. Both the polished and fractured cross-section microstructures of the coatings were characterized by scanning electron microscopy (SEM). The phase structures of the coatings and the feedstock were analyzed by X-ray diffraction technique (XRD). The microstructure and phase structure of the coatings prepared at different substrate temperatures were examined. SEM observations show that the intersplat bonding within the coatings was significantly improved by increasing the substrate temperature. The fracture toughness of the deposits was measured by indentation methods. For the coatings prepared at low substrate temperatures, the fracture toughness increased with the substrate temperature due to the improvement in the intersplat bonding. However, a significant decrease in the fracture toughness was found for the coatings prepared at high substrate temperatures. The change in phase structure of the coatings suggested that the residual tensile stress mainly resulted from phase transformation from γ-alumina to α-alumina at high substrate temperature should answer for the decline in the fracture toughness.

Three kinds of cast iron coatings were prepared by atmospheric plasma spraying. During the spraying, the mild steel substrate temperature was controlled to be averagely 50, 180, and 240°C, respectively. Abrasive wear tests were conducted on the coatings under a dry friction condition. It is found that the abrasive wear resistance is enhanced with the substrate temperature increasing. SEM observations show that the wear losses of the coatings during the wear tests mainly result from the spalling of the splats. Furthermore, the improved wear resistance of the coatings mainly owes to the formation of oxides and the enhancement in the mechanical properties with the substrate temperature increasing.

Fe/Mo composite coatings were prepared by air plasma spraying (APS) using Fe-based and Mo-based amorphous and nanocrystalline mixed powders. Microstructural studies show that the composite coatings present a layered structure with low porosity due to adding the self-bonded Mo-based alloy. Corrosion behaviors of the composite coatings, the Fe-based coatings and the Mo-based coatings were investigated by electrochemical measurements and salt spray tests. Electrochemical results show that the composite coatings exhibit a lower polarization current density and higher corrosion potentials than the Fe-based coating when tested in 3.5wt% NaCl solutions, indicating superior corrosion resistance compared with the Fe-based coating. Also with the increase in addition of the Mo-based alloy, a raised corrosion resistance, inferred by an increase in corrosion potential and a decrease in polarization current density, can be found. The results of salt spray tests again show that the corrosion resistance is enhanced by adding the Mo-based alloy, which helps to reduce the porosity of the composite coatings and enhance the stability of the passive films.

Alumina coatings are prepared by atmospheric plasma spraying through controlling the substrate temperature during spraying. The changes in microstructure and mechanical properties ol the coatings prepared at different substrate temperatures are examined. The hardness and the elastic modulus of the coatings are measured by indentation methods. The results show that interlamellar bonding in the coatings is significantly improved with increasing the substrate temperature. Moreover, long through-thickness columnar grains form in the coatings when the substrate temperature reaches above 430°C. As a result, the cross-sectional hardness and the elastic modulus perpendicular to the coating surface increase with increasing the substrate temperature.

The effects of CuO, TiO2 and B2O3 oxides and nanocrystalline Al2O3+ TiO2 particles on the sintering of Al2O3 glass-ceramics were investigated by X-ray diffraction and scanning electron microscopy. The CuO and TiO2 oxides can effectively facilitate the formation of CuO–Al2O3–TiO2 glass ceramic. The CuO, TiO2 and Al2O3 oxides can form the new phase Cu2Ti4O and CuAl2O4. They wrapped the Al2O3 grains tightly, so the density ceramic was fabricated successfully sintered at 1300°C. Analyzing the fracture surface morphology, the ceramic added CuO, TiO2 oxides shows the mixed mode of intergranular and transgranular fracture. However, after added B2O3 oxides the B2O3-CuO–Al2O3–TiO2 glass ceramic shows the mode of intergranular fracture. The ceramic added nanocrystalline Al2O3 + TiO2 was more density and fine organization. The fracture mode is as same as the ceramic added CuO, TiO2 oxides.

In view of huge destructibility of the near-fault ground motions, structures with long natural vibration period are liable to fall into nonlinear reaction stage. Based on a full understanding of the near-fault seismic spectrum characteristics, the out-of-plane seismic response of a long span concrete-filled steel tube (CFST) arch bridge was studied in depth, and the research result could offer a reference for near-fault aseismic design.

In this work, three cast iron coatings were produced by atmospheric plasma spraying. During spraying, the surface temperature of three coatings (substrate temperature) was controlled to be averagely 50oC, 180oC and 240oC by changing the processing parameters. X-ray diffraction (XRD) was employed to analyze the phase structure of the starting powder and the coatings. The results showed that the powder was mainly composed of (Fe,Cr)7C3 and martensite and both the spraying processing and the substrate temperature exerted no influence on coating phase structure. An optical microscope (OM) was used to characterize the microstructure of the cross-section and surface of the coatings. It was found that the cross sectional hardness increased with the increase of the substrate temperature due to the improvement in interlamellar bonding.

A composite layer was prepared on the surface of Ti-6Al-4V alloy by nitriding-sulfurizing composite treatment, and its microstructure and phase structure were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The tribological performance was measured to investigate its dependence on the nitriding-sulfurizing composite treatment process. The results indicated that the composite layer was mainly comprised of Ti2N, TiN, and TiS2. It was found that the composite layer exhibited superior tribological properties under dry friction and absolute sliding conditions due to the formation of sulfides with self-lubricating function.

A composite layer was prepared on the Ti-6Al-4V alloy surface by ion nitriding, magnetron sputtering Mo and ion sulfurizing composite treatment technique. The phase structure, morphology, and cross-sectional element distribution of composite layer were analyzed. Friction and wear properties of composite layer were tested by MM-200 laboratory tester. XRD analysis showed that the composite layer was mainly comprised of Ti, Mo, MoS2, TiN, and transition layer. This composite layer is perfect wear-resistant surface due to existence of self-lubricating MoS2 on hard Mo and TiN layers with good anti-friction ability. Thereby, the results of friction and wear test showed that anti-wear performance of Ti-6Al-4V alloy after composite treatment was remarkably improved under dry and sliding conditions. Both the friction coefficient and the wear loss of the nitriding-Mo plating-sulfurizing layers were lower than that of the nitriding layer due to the formation of the MoS2 layer on Mo and TiN layers.

Three composite coatings were prepared by nitriding-sulfurizing processing of Ti-6Al-4V alloy at different sulfurizing temperatures. The microstructure and phase structure of the coatings were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Furthermore, the hardness of the coatings was measured. The effect of the sulfurizing temperature on microstructure of coatings was investigated. The results indicated that the composite coating was mainly comprised of titanium nitrides, titanium sulfides, and titanium. It was found that the phase composition of composite coating changed with the variation of the sulfurizing temperature.

In this work, an experiment was performed to demonstrate the possibility of the metallurgical bonding in plasma-sprayed cast iron coatings at high substrate temperature. A quantitative analysis of splat cooling and rapid solidification of cast iron splat is then presented. The effect of the substrate temperature on the development of melt undercooling within the splat is investigated in detail. The results indicated that the initial substrate temperature has a profound effect on the development of melt undercooling in a splat, the splat bottom melt temperature, and the substrate surface temperature. A high initial temperature of the substrate restrains the cooling of the splat and leads to a high melt temperature that may promote the grain growth directly on cast iron substrate surface to form the metallurgical bonding.

Yttria-stabilized zirconia (YSZ) deposits were prepared by an atmospheric plasma spray (APS) on a stainless-steel substrate preheated to different temperatures from room temperature to 1100°C. The microstructure of the deposits was characterized from polished and fractured cross sections by scanning electron microscopy (SEM). The ionic conductivity of the deposits was measured using both DC and AC methods, and the relationship between ionic conductivity and microstructure of deposits was examined. SEM observation revealed that the YSZ deposits exhibit different microstructures with different deposition temperatures. With the increase of the deposition temperature, the columnar grain growth across lamellar interfaces was enhanced and subsequently the intersplat bonding ratio in the deposit was improved. The ionic conductivity of YSZ deposits at the direction perpendicular to the deposit surface was significantly increased through the microstructure development on increasing the deposition temperature. However, it was found that the intergrain resistance changed little despite a remarkable change of the deposition temperature. A microstructure model is proposed to correlate the relative conductivity to the mean lamellar interface bonding ratio. The increase in ionic conductivity of the YSZ deposit with the deposition temperature can be attributed to the increase in the lamellar interface bonding ratio.

Ni–Al 2 O 3 cermet supported tubular solid oxide fuel cell (SOFC) was fabricated by thermal spraying. The anode, electrolyte and cathode were deposited by plasma spraying and the Ni–Al 2 O 3 cermet support was deposited by flame spraying to aim at reducing manufacturing cost. The test cell was assembled employing scandia stabilized zirconia (ScSZ) and yttria stabilized zirconia (YSZ) deposits as the electrolyte and influence of electrolytic Ohmic polarization on cell's performance was investigated. The results showed that the maximum output power density increased through reducing the electrolyte thickness and increasing the electrical conductivity of electrolyte. The maximum output power density reached 0.89 W/cm 2 with ScSZ electrolyte of 40 µm thick at 1000 °C in comparison of 0.76 W/cm 2 obtained with YSZ electrolyte. The present results clearly revealed that the controlling polarization was electrode polarization for the plasma-sprayed single cell assembled with a thin APS ScSZ electrolyte of 40 µm thick. This fact indicates that the design and preparation of effective electrode in the SOFC assembled using thin electrolyte are more important to improve cell performance.

The development of a cost-effective fabrication method for stabilized zirconia electrolyte for the most advanced tubular solid oxide fuel cell (SOFC) remains the most important challenge for the commercialization of an SOFC power generation system. Atmospheric plasma spraying is expected to be a promising alternative to other costly electrolyte processing methods. The problem with the plasma-sprayed ceramic coating is the limited interface bonding of the lamellar structure, which reduces the ionic conductivity of stabilized zirconia deposits to one-fifth of the comparable bulk. Continuous growth of columnar grains across splat–splat interfaces has been achieved through control of the substrate surface temperature which affects spreading of molten droplets. These cross-splats columnar grains lead to improved bonding between lamellae. Measurements over the temperature range of 600–1000 °C have shown that the microstructural changes result in a significant increase of ionic conductivity of the yttria-stabilized zirconia deposit (by a factor of about 3). A change in activation energy at about 750 °C was observed for coatings deposited with two different sets of spray conditions. This change is associated with a switch of the predominant ion conduction path from grain boundary to intragrain with increasing temperature.

Sc 2 O 3 stabilized ZrO 2 (ScSZ) coating in free standing planar shape was prepared by atmospheric plasma spraying (APS) using ScSZ powder consisting of 10 mol% Sc 2 O 3 . ScSZ powder was prepared by solid phase reaction followed by sintering and screening processes. The coating microstructure was characterized using X-ray diffraction and scanning electron microscopy. The electrical conductivity of ScSZ coating was measured using both DC and AC approaches. The electrical conductivity of the as-sprayed ScSZ coating was about 0.07 S/cm at 1000 °C. It is one-fourth that of the sintered one. This result is due to the lamellar structure feature with the limited interface bonding which dominates the electrical conductivity of APS coatings. The activation energy of the as-sprayed coating was 1.31 eV at temperature range less than 750 °C and 0.97 eV at above 750 °C. The change of activation energy indicates that the ion transportation dominants are changed with temperature. This fact is due to higher activation energy of the grain boundary than that of intragrain.

Novel Ni–Al2O3 cermet-supported tubular SOFC cell was fabricated by thermal spraying. Flame-sprayed Al2O3–Ni cermet coating played dual roles of a support tube and an anode current collector. Y2O3-stabilized ZrO2 (YSZ) electrolyte was deposited by atmospheric plasma spraying (APS) to aim at reducing manufacturing cost. The gas tightness of APS YSZ coating was achieved by post-densification process. The influence of YSZ coating thickness on the performance of SOFC test cell was investigated in order to optimize YSZ thickness in terms of open circuit voltage of the cell and YSZ ohmic loss. It was found that the reduction of YSZ thickness from 100 μm to 40 μm led to the increase of the maximum output power density from 0.47 W/cm2 to 0.76 W/cm2 at 1000 °C. Using an APS 4.5YSZ coating of about 40 μm as the electrolyte, the test cell presented a maximum power output density of over 0.88 W/cm2 at 1030 °C. The results indicate that SOFCs with thin YSZ electrolyte require more effective cathode and anode to improve performance.

Ni-Al2O3 cermet supported tubular SOFC was fabricated by thermal spraying. Flame-sprayed Al2O3-Ni cermet coating plays dual roles of a support tube and an anode current collector. 4.5mol. % yttria-stabilized zirconia (YSZ) and 10mol.% scandia-stabilized zirconia (ScSZ) coatings were deposited by atmospheric plasma spraying (APS) as the electrolyte in present study. The electrical conductivity of electrolyte was measured using DC method. The post treatment was employed using nitrate solution infiltration to densify APS electrolyte layer for improvement of gas permeability. The electrical conductivity of electrolyte and the performance of single cell were investigated to optimize SOFC performance. The electrical conductivity of the as-sprayed YSZ and ScSZ coating is about 0.03 and 0.07 S·cm−1 at 1000 °C, respectively. The ohmic polarization significantly influences the performance of SOFC. The maximum output power density at 1000 °C increases from 0.47 to 0.76 W·cm−2 as the YSZ electrolyte thickness reduces from 100 μm to 40 μm. Using APS ScSZ coating of about 40 μm as the electrolyte, the test cell presents a maximum power output density of over 0.89 W·cm−2 at 1000 °C.

4.5 mol% yttria-stabilized zirconia (YSZ) deposit was prepared by atmospheric plasma spraying (APS) using an agglomerate-sintered YSZ powder. Two samples were continuously deposited at two spray distances of 80 mm and 90 mm without intermittence during spraying. The measurement showed that the ionic conductivity of the YSZ deposit at 1000 °C significantly decreased from 0.06 S/cm to 0.033 S/cm with increasing spray distance from 80 mm to 90 mm. The deposit microstructure exhibited distinct interfaces between consecutive pass layers in the deposit sprayed at long spray distance. The decrease of ionic conductivity can be ascribed to change of the bonding ratio between consecutive passes resulting from decrease of deposition temperature with the increase of spray distance.

To enhance the wear properties of function structure, Al 2 O 3 -13%TiO 2 (AT13) coatings were plasma sprayed on 45 steel functional structure using micro and nano powders. The microstructures and phase compositions of the coatings were investigated by scanning electron microscopy and X-ray diffraction, respectively. Results show that the nano powder coating consists of fully-melted region and partially-melted region. The fully-melted regions show a lamellar structure, while the partially-melted regions retain the powders structure. The phases of coatings are α -A1 2 O 3 and TiO 2 .The wear test was carried out on a ML-10 friction and wear tester under dry sliding condition. It is found that the wear resistance of the micro powder coating is higher than that of nano powder coating. This is mainly ascribe to the breakage of the nano powder coating resulted from low agglomerated binding force.

In many applications, it will be beneficial if the plasma-sprayed Yttria stabilized zirconia (YSZ) coatings exhibit epitaxial growth. Early experiments in plasma spray have shown that a high initial substrate temperature may help develop epitaxial growth from the previous deposited splats. This paper has performed an experiment to demonstrate the possibility of epitaxial growth in plasma-sprayed YSZ coatings at high substrate temperatures. A quantitative analysis of splat cooling and rapid solidification of the YSZ splat is then presented. The analysis is based on a one-dimension heat transfer model of a thin liquid YSZ layer in contact with an YSZ substrate at fairly high initial temperature. The model calculations indicate that equilibrium solidification may take place on the YSZ substrate but with a solidification temperature that is much higher than the YSZ substrate temperature. Such equilibrium solidification requires nucleation of new crystalline YSZ and therefore only leads to non-epitaxial growth. Epitaxial growth, on the other hand, requires a large melt undercooling so the YSZ crystalline can grow directly from the substrate surface, which is at a much lower temperature than the equilibrium melting point. The effect of the substrate initial temperature on the development of melt undercooling within the splat is investigated in detail. Some interesting observations have been made which may explain the physics of epitaxial growth in YSZ coatings.Copyright © 2007 by ASME