In this study, Cu-based bulk metallic glass coatings were deposited by atmospheric plasma spraying with different hydrogen flow rates. The crystallization and oxidation of the coatings is assessed along with corrosion resistance. As thermal energy in the plasma jet increases, the melting fraction and oxidation of particles in the coating increases as does porosity. All of these factors have an effect on the corrosion resistance of Cu-based bulk metallic glass coatings and their relative impact is discussed.

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 adhesion at the interface between coating and substrate is a key factor for the reliability and performance since the main problem in the application of coating systems is the delamination at the interface. Finite element models are developed to find a way to predict the adhesion strength of a thermal sprayed coating system from simply designed indentation test. Large depth indentation behavior is simulated to study shear induced delamination beneath the indenter. The interface between the coating and the substrate is modeled by three different bonding characters to investigate the effect of interfacial bonding on indentation test. Pressure-strain relations based on Tabor’s suggestion are observed for various combinations of material properties and interfacial bonding characteristics. The growth of a crack in the interface plane leaves a clear imprint on indentation load-depth curve in case of soft coating on hard substrate. Tabor curve also shows potential ability to detect interface bonding strength under indentation test.

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.