Can Thermal Barrier Coatings be Sealed by Metal-Organic Chemical Vapour Deposition of Silica and Alumina?

Abstract

Thin AI2O3and Sio2films were deposited on thermal barrier coatings (TBC) by means of metalorganic chemical vapour deposition (MOCVD). The thermal barrier coatings consist of ZrO2, partially stabilised by MgO (Magnesium Zirconate Amdry 333) and a bond coat of NiAl (Amdry 956). Alumina films were deposited at low temperatures by low pressure MOCVD, carried out in nitrogen gas using aluminium-tri-sec-butoxide (ATSB) as the precursor. Silica films were deposited on the thermal barrier coatings by atmospheric pressure MOCVD with di-acetoxy-di-t-butoxy-silane (DADBS) as the precursor. Besides the deposition of thin oxide films on TBC, pre-oxidation experiments were performed at 600, 800 and 1000°C for 175 h. In order to evaluate the effectiveness of sealing and pre-oxidation, sulphidation experiments were carried out at 600°C for 200 h. Low pressure deposited alumina films did not show any increased “protective power”. Pre-oxidation of the TBC to form a dense and continuous alumina layer on the top of the bond coat also did not show any significant improvement of the protection against sulphide containing gases. © 1995, Walter de Gruyter. All rights reserved.