Saint-Gobain engineers from France and the United States prepared an evaluation of next-gen environmental barrier coatings made of rare earth silicates for presentation at the cancelled ASM International ITSC 2020 conference.
They reported that, in order to increase fuel efficiency of jet engines, ceramic matrix composites (CMC) have been introduced into new designs. Silicon based CMCs enable higher service temperatures and reduced weight, which translates into reduced fuel consumption and emissions. These CMCs, however, face steam-induced corrosion that must be mitigated by a protective environmental barrier coating.
Saint-Gobain has long history of developing such EBC materials as powders for thermal spraying. The first generation BSAS-based coatings have evolved to current rare-earth mono- and di-silicates. Specially designed fusion processes have been improved over the years to provide the most uniform powders, in terms of both chemistry and phase.
Yttrium and Ytterbium disilicates have become a widely used reference material for studies and new developments. More recently, interest has increased for scandium silicates. These powders have been developed and thermally sprayed on silicon-based substrates for evaluation.
Researchers compare the features of these powders in the coating process and investigated the as-sprayed and heat-treated coatings. Water vapor corrosion tests were done to quantify the protection provided by scandium disilicate versus other more common solutions. Preliminary CMAS exposure tests have been completed and additional tests are planned on CMAS resistance.
Title: Aviation Industry I: Evaluation of next generation rare earth silicate EBC coatings
Authors: Alain Allimant, Saint-Gobain C.R.E.E., France
Tim Vitorino, Saint-Gobain, USA
