Anode layer, as the main site for the reaction of fuel and removal of byproducts, plays an important role in anode-supported solid oxide fuel cell (SOFC). Generally, high electrical conductivity and gas permeability (porosity) of the anode materials are required to reduce the polarization loss of SOFC. This study focuses on the manufacturing of porous anode layers for SOFC. The NiO/8YSZ cermets anode coatings are fabricated by atmospheric plasma spray (APS) using the blended powder of nickel coated graphite (Ni-graphite) after oxidation (NiO-graphite) and 8mol%Y 2 O 3 -stabilized ZrO 2 (8YSZ). To increase the porosity and the uniformity of the coatings, nickel coated graphite with low density is used as the starting feedstock instead of the conventional pure Ni powder. To balance the conductivity (Ni), porosity (graphite), and structural stability (8YSZ) of the coatings, the effects of process parameters such as hydrogen (H 2 ) gas flow rate, spraying distance, and pore formation precursor (carbon black addition) on the microstructures of resulting coatings by APS are investigated. The results show that the NiO/8YSZ anode coatings with high conductivity, structural stability and porosity could be deposited by APS with moderate H 2 gas flow rate and short distance. The microstructure of the coating is mainly associated with the degree of melting of impact particles.

A group of blended and spray dried solid lubricants with the same nominal composition were deposited by atmospheric plasma spraying (APS). The wear resistance of two coatings formed at room temperature and 350°C was evaluated using a rig test to simulate actual application conditions. The results showed that the blended powder coating showed inferior mechanical and tribological properties due to its non-uniform microstructure, which were induced by the differences in the physical and thermophysical properties of each constituent phase. However, the nanostructured spray-dried feedstock coating showed a better wear resistance due to its lower porosity, higher hardness and higher bond strength. In addition, the friction coefficient decreased with an increase of the Ag fraction and the uniformity of the Ag solid lubricant in the coating.

This paper describes an initial development of oxidation resistant coatings for SOFC (solid oxide fuel cell) interconnectors using LaSrCoFe oxide (LSCF, (La 0.6 Sr 0.4 )(Fe 0.8 Co 0.2 )O 3 ). The process involved the development of hermetic coatings using a HVOF (high velocity oxy-fuel) spray process, specifically a θ-gun spray process. The X-ray diffraction of the powder and the coating is analyzed at first. To get the hermetic coating, numerous process parameters were chosen using design of experiments (DOE). The hermeticity of the coating was tested using a salt spray test. After these tests, a hermetic LSCF coatings was obtained with virtually no interconnecting pores.

The potential of post heat-treatment to improve the wear properties of nanostructured WC-Co coatings was investigated in the present study. Since the nanostructured coatings are more susceptible to the detrimental reactions during spraying than their conventional counterparts, there is certain limitation in optimization of coating properties by adjusting process parameters. Post heat-treatment of nanostructured coatings can thus offer one solution to achieve further improvement in coating performance. Nanostructured WC-Co coatings prepared by HVOF spraying were heat-treated under various temperatures and their wear properties were compared to those of the as-sprayed condition. The influence of the post heat-treatment was discussed in terms of changes in microstructure, composition and hardness of the coatings. These results demonstrate that the wear resistance of the nanostructured WC-Co coatings can be improved without any degradation of the substrate properties by proper post heat-treatment process.

Based on the previous studies of nanostructured WC based coatings, various improvement methods of the coatings were attempted. On of the method was to improve the feedstock materials via a partial flocculation method. This method uses a special technology to form spherical spray dried powders using nanostructured starting materials. According to this method, morphology and porosity level of the feedstock material was controlled. In addition, the basic principle of this method will be introduced. A few other methods are tried to improve the feedstock materials including carbon addition and a Co coating method. The coating morphology and characteristics are analyzed and wear performance is compared. The carbon contents, porosity, phases, and wear loss by a sand abrasion test will be presented in details. Abstract only; no full-text paper available.

WC-Co powders with nano-sized WC were deposited by dynamic powder deposition process. Microstructural characterization and phase analysis of feedstock powders with different compositions and as-deposited coatings with various substrates were carried out by SEM and XRD. The results show that there is no detrimental phase transformation and/or decarburization of WC by dynamic powder deposition. It is also observed that nano-sized WC in the feedstock powder is maintained in the deposited coatings. It is demonstrated that it is possible to fabricate the nano-structured WC-Co coatings with low porosity and very high hardness by dynamic powder deposition.

Characterization of flame sprayed and furnace fused NiCrBSiC alloy coatings with two different carbon contents and 15~45 wt.% WC-Co addition is described in terms of microstructure, microhardness, and differential thermal analysis. Microstructural development of these coatings before and after fusing treatment is discussed to identify the precipitates in the coatings. Optimum fusing conditions (time and temperature) for wear testing sample are investigated in terms of microhardness and porosity of the coatings. Wear performance of these coatings is also investigated by two-body and three-body abrasive and dry sliding wear experiments. Optimum tungsten carbide content of the coatings is also selected to improve wear performance and thus enhance the service life of the process roll for cold rolling steel plant. Finally, microstructure and microhardness of the furnace and induction fused coatings are compared with emphasis on the interface between the coating and the steel substrate.

Silicon nitride and sialons are very attractive materials for thermal spaying, but the high temperatures of spray processes lead to their decomposition instead of melting. Therefore, the use of these materials as protective coatings has been very restricted. Nevertheless, researchers have tried to provide silicon nitride-based coatings using metallic or oxide binders. Oxide binder additions to silicon nitride have been quite successful. In this paper, mixtures of silicon nitride and oxides were prepared for the thermal spraying of silicon nitride-based materials by using a detonation gun. Powders for the spraying were prepared through mixing, sintering, crushing and sieving. To get an oxide binder of low melting point, three components of oxides, Al 2 O 3 -ZrO 2 -TiO 2 , were selected; the ratio of oxides was determined to have a low melting point. When the sintering temperatures were below 1400°C, phases of the powders and coating layers were composed of α-Si 3 N 4 and oxides and any of sialon phases were not found. By sintering at the temperatures between 1400 and 1600°C in a nitrogen gas environment, χ(chi)-sialon (Si 6 Al 10 O 21 N 4 ) and β’-sialon (Si 3 Al 3 O 3 N 5 ) were formed. The ratio of β’-sialon increased as the sintering temperature increased. TiO 2 was transformed to a nitride, TiN. During the spraying procedure χ-sialon was decomposed to amorphous binder, but β’-sialon was not totally decomposed. Finally a coating layer composed of tetragonal-zirconia and β’-sialon was made.

A continuous galvanizing line (CGL) has a zinc pot, which is filled with molten zinc for zinc coating. In a zinc pot there are pot rolls to guide steel strip. Usually WC-Co thermal sprayed coatings are used for protection of the pot rolls from severe corrosion by molten zinc. Authors analyzed WC-Co coatings used in a zinc pot of a CGL for 33 and 56 days. On the surface of a WC-Co coated roll, many kinds of deposits were observed including top dross, Fe2Al5 inter-metallic compound, which might induce dross defect on the surface of galvanized steel. Diffusion depth of zinc into the WC-Co coating used for 33 days was only within 10µm but some areas were severely attacked along cracks within the coating layer. Usually molten zinc contains small amount of aluminum about 0.12 - 0.2%. Through SEM study, we observed that not only zinc but also aluminum diffused into the WC-Co coating after service in the zinc pot for 56 days. Al-Fe rich layers were observed on the surface of the spray coating for some cases. The phase of those layers might be Fe2Al5 since their chemical compositions are similar to Fe2Al5 top dross.

High temperature corrosion is a serious problem on tlie heat exchanger tubes of recuperators because they encounter an corrosive environment at maximum temperature around 900°C. These tubes were found to be corroded via oxidation, sulfidation and molten salt corrosion. Particularly molten salt corrosion could be the most severe corrosion mechanism. As a protective coating for recuperators, nickel and cobalt based self-fluxing alloys, iron based amorphous alloy and chromium carbide cermet coatings were considered. These coatings were prepared by an arc spray and or/not fusing or a HVOF spray. Their molten salt corrosion resistance was tested, and the high temperature corrosion resistance in a SO2 containing atmosphere was examined. Also microstructures of the coatings were studied after corrosion tests.

To maintain surface roughness of process rolls in cold rolling steel plants, WC-Co coatings have been known to be effective ones. In this study, a high pressure/high velocity oxygen fuel (HP/HVOF) process was used to obtain WC-Co coatings. To get the best quality of coatings, WC-Co coatings are sprayed with numerous powders made by various processes. These powders include agglomerated sintered powders, fused-crushed powders, extra high carbon WC-Co powders and (W 2 C, WC)-Co powders. After spraying, properties of coatings such as hardness, wear resistance. X-ray diffraction, and microstructures were analyzed. For coatings produced by agglomerated-sintered powders, hardness of the coating increased as power levels and the number of passes were increased. In case of the coatings produced by fused-crushed powders, a very low deposition rate was obtained due to a low flowablity of the powders. In addition, the WC-Co coatings sprayed with extra carbon content of WC-Co did not show improved hardness and wear resistance. Also, some decomposition of WC was observed in the coating. Finally, the coatings produced by (W 2 C, WC)-Co powders produced higher hardness and lower wear resistance coating.