Abstract
The plasma spray–physical vapor deposition (PS–PVD) process has received considerable attention due to its non-line of sight deposition ability, high deposition rates, and cost efficiency. Compared with electron beam–physical vapor deposition (EB–PVD), PS–PVD can also prepare thermal barrier coatings (TBCs) with columnar microstructures. In this paper, yttria-stabilized zirconia (YSZ) coatings were fabricated by PS–PVD. Results showed that the as-deposited coating presented a typical columnar structure and was mainly composed of metastable tetragonal (t′-ZrO2) phase. With thermal exposure, the initial t′ phase of YSZ evolved gradually into monoclinic (m-ZrO2) phase. Significant increase in hardness (H) and the Young’s modulus (E) of the coating was attributed to the sintering effect of the coating during the thermal exposure, dependent on exposure temperature and time. However, the values of H and E decreased in the coatings thermally treated at 1300–1500 °C for 24 h, which is mainly affected by the formation of m-ZrO2 phase.
Highlights
In recent years, to improve the service temperature of the hot section of an aircraft engine, besides cooling gas film, thermal barrier coatings (TBCs) consisting of an oxidation-resistant metallic bond coat and a thermally insulating ceramic topcoat of yttria-stabilized zirconia (YSZ) have been applied due to their low thermal conductivity and high thermal expansion coefficient [1,2,3,4]
The columnar structure can provide a high strain tolerance due to the gaps between the columns, which is similar to the electron beam–physical vapor deposition (EB–PVD) coatings [23]
The results indicate that the main phase of the as-deposited coatings was t-ZrO2, which indicates that the coating was mainly formed by vapor mixture of zirconia and yttrium oxide
Summary
To improve the service temperature of the hot section of an aircraft engine, besides cooling gas film, thermal barrier coatings (TBCs) consisting of an oxidation-resistant metallic bond coat and a thermally insulating ceramic topcoat of yttria-stabilized zirconia (YSZ) have been applied due to their low thermal conductivity and high thermal expansion coefficient [1,2,3,4]. Air plasma spraying (APS) and electron beam–physical vapor deposition (EB-PVD) are the two main technologies that are used for TBC deposition [5]. Both of the above technologies exhibit limitations. Different from the APS case, TBCs with super strain tolerance and improved spallation lifetime with high thermal conductivity can be obtained through the EB–PVD process. This is because of the columnar microstructure with an inter-columnar gap that is perpendicular to the top-coat/bond-coat interface [7,8]
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