Performance of Zirconia Composite Coatings Produced by Gas Tunnel Type Plasma Spraying as a Thermal Barrier Coating(Physics, Processes, Instruments & Measurements)

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Zirconia (ZrO_2) formed by the plasma spray method is widely used industrially as a thermal barrier coating (TBC). But it still has problems such as spallation and cracking inside the coating. The solution may be found through the development of new spraying processes. The zirconia-alumina (ZrO_2-Al_2O_3) composite coating formed by gas tunnel type plasma spraying at short spraying distances, also has a high hardness layer at the surface side of the coating, which shows a graded functionality of hardness. In this paper, the performance of such high hardness ZrO_2-Al_2O_3 composite coatings under different spraying conditions was investigated and their merits as TBC clarified. For the enhancement of the graded functionality of such composite coatings, the Vickers hardness of the high hardness layer near the coating surface increased as a result of the thermal process of the high energy plasma, and corresponded to the result that the coating became denser. Also, the effect of alumina mixing on the microstructure of this composite coating was examined. The combination of high hardness of Al_2O_3 with the low thermal conductivity of ZrO_2 resulted in the development of high functionally graded TBC. By a calculation using laminate theory, the thermal conductivity of such ZrO_2-Al_2O_3 composite coatings in the thickness direction was proved to be much smaller than in the longitudinal direction. Moreover the adhesive strength of such high hardness zirconia composite coatings was investigated as well as their mechanical properties. The adhesive strength of such high hardness coatings to the substrate was weakened with an increase in the alumina content of the spraying powder.

著者

Kobayashi Akira
Osaka Univ. Jpn

Performance of Zirconia Composite Coatings Produced by Gas Tunnel Type Plasma Spraying as a Thermal Barrier Coating(Physics, Processes, Instruments & Measurements)

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