High temperature oxidation studies of sputtered and EB-PVD Si-bond coated EBC system on SiC-SiCf substrates

Abstract

Rare earth disilicates RE2Si2O7 (REDS) are currently being used as environmental barrier coatings (EBCs) to protect the ceramic matrix composite (CMCs) against environmental degradation. Atmospheric plasma spray (APS) method is the widely accepted state of the art methodology to deposit EBCs and Si-bond coat. However, novel processing methods are needed to produce crystalline and phase pure EBCs to overcome the draw backs of APS method. Oxidation of Si-bond coat at high temperatures and the corresponding SiO2 oxide scale growth rate is a life limiting factor for the EBCs. In this work, two different coating deposition methods were used and namely magnetron sputtering and electron beam physical vapor deposition (EB-PVD) to deposit Si bond coat on SiC-SiCf substrates. A multi-layer Yttrium disilicate (15 µm)/Yttrium monosilicate (15 µm) coating was deposited on top of bond coated substrates by means of magnetron sputtering method. High temperature isothermal oxidation tests as well as furnace cycle tests were done at 1250°C up to 1000h. The oxide scale growth rates for both sputter and EB-PVD bond Si-bond coats were calculated and its influence on the life time of EBC system will be presented.