Suspension plasma spray (SPS) is a novel process for producing nano-structured coatings with metastable phases using significantly smaller particles as compared to conventional thermal spraying. Considering the complexity of the system there is an extensive need to better understand the relationship between plasma spray conditions and resulting coating microstructure and defects. In this study, an alumina/ 8 wt.% yttria-stabilized zirconia was deposited by axial injection SPS process. The effects of principal deposition parameters on the microstructural features are evaluated using the Taguchi design of experiment. The microstructural features include microcracks, porosities, and deposition rate. To better understand the role of the spray parameters, in-flight particle characteristics, i.e., temperature and velocity were also measured. The role of the porosity in this multicomponent structure is studied as well.The results indicate that thermal diffusivity of the coatings, an important property for potential thermal barrier applications, is barely affected by the changes in porosity content.

Good performance of optical coatings depends on the appropriate combination of optical and mechanical properties. Therefore, successful applications require good understanding of the relationship between optical microstructural and mechanical characteristics and film stability. In addition, there is a lack of standard mechanical tests that allow one to compare film properties measured in different laboratories. We give an overview of the methodology of mechanical measurements suitable for optical coatings; this includes depth-sensing indentation, scratch resistance, friction, abrasion and wear testing, and stress and adhesion evaluation. We used the techniques mentioned above in the same laboratory to systematically compare the mechanical behavior of frequently used high- and low-index materials, namely, TiO2, Ta2O5, and SiO2, prepared by different complementary techniques. They include ion-beam-assisted deposition by electron-beam evaporation, magnetron sputtering, dual-ion-beam sputtering, plasma-enhanced chemical-vapor deposition, and filtered cathodic arc deposition. The mechanical properties are correlated with the film microstructure that is inherently related to energetic conditions during film growth.

Amorphous and crystalline phase formation during suspension plasma spraying of the alumina zirconia composite Tarasi, F.; Medraj, M.; Dolatabadi, A.; Oberste-Berghaus, Jorg; Moreau, C.Contact us / Contactez nous: nparc.cisti@nrc-cnrc.gc.ca.

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Amorphous phases are commonly found in nanostructured plasma‐sprayed coatings. Nonetheless, the role of these phases in the resulting coatings’ properties has remained uninvestigated until now. In the present work, pseudo‐eutectic coatings—based on alumina and 8 wt% yttria‐stabilized zirconia (YSZ)—containing amorphous phases are produced using a suspension‐plasma‐spray process. These composite materials are a potential choice for thermal‐barrier coating applications. The role of the amorphous phase on the performance of the coatings is investigated before and after heat treatment. Results show that, although the amorphous phases in untreated coatings reduce the thermal conductivity, they impair the mechanical properties. However, treatment above the crystallization temperature leads to better mechanical properties as well as enhanced high‐temperature stability of the resulting nanostructure. Moreover, the role of alumina as a stabilizer of high‐temperature YSZ phases (tetragonal and cubic) is confirmed and the high‐temperature phase stability of the alumina–YSZ composite is demonstrated. The amorphous phases are found to crystallize into their corresponding high‐temperature stable phases; i. e., α‐alumina and tetragonal zirconia.