Enhanced thick thermal barrier coatings that exhibit varying porosity

Thick thermal barrier coatings (TBCs) are defined within the current work as coatings that range from 1.5 to 2 mm in thickness. The microstructure and the porosity of the yttria partially stabilized zirconia (YPSZ) coating are controlled with respect to its resistance to thermal cycling fatigue (TCF). TBCs have been produced by means of a MCrAlY bond coat and YPSZ top coat, both sprayed by air plasma spray. Plasma spray experiments have been performed to obtain an appropriate coating microstructure. Ceramic coatings have been prepared at four levels of plasma jet energy to obtain different levels of porosity, with the aim of keeping the general ceramic coating microstructure constant. An analysis has been performed to develop a relationship between the surface roughness and internal porosity. Phase content in as-coated YPSZ coatings has been investigated by XRD and compared with the as-received powder to investigate the influence of the plasma spray process on the phase content of the coating. The samples have been submitted to TCF tests, according to the procedure of two OEMs. Post mortem analyses via XRD of the thermally cycled samples have been compared with the as-received samples. This study has enabled the determination of an appropriate TBC microstructure that demonstrates high TCF resistance, independent of the coating porosity. The deposition process is robust and the properties of the coating exhibit low sensitivity to slight changes in spray parameters that may occur within a high-volume production environment; thereby ensuring reliable performance of TBC's during their service life. (C) 2007 Elsevier B.V. All rights reserved.