Analysis of Anisotropic Void Sytem in Electron Beam-Physical Vapour Deposited (EB-PVD) Thermal Barrier Coatings

Abstract

Thermal barrier coatings (TBCs) deposited by EB-PVD protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines increasing the combustion temperature and/or diminishing the air-cooling requirements. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task and to improve the turbine efficiency is to optimize the TBC properties by tailoring its microstructure and/or material. The different kinds of pores in EB-PVD TBCs influence their thermal conductivity according to their size, shape, orientation and volume. These pores can be open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization becomes very complex and requires the use of sophisticated methods. This work describes the analysis of the anisotropic and nano-sized pores in PYSZ-based TBCs by means of small angle neutron scattering (SANS) method. In order to differentiate and analyse 3D closed and open pores in 400 µm thick coatings, a contrast matching SANS technique has been employed. Thermal derived changes in crystal structure as well as pore size and morphology have been correlated with thermal conductivity.