Y₂SiO₅ environmental barrier coatings for niobium silicide based materials

Abstract

The oxidation behaviour of Nb silicide based alloys, considered as potential ultra-high temperature material for gas turbine engine applications, can be improved by chromia–silica forming coatings with M₇Si₆ structure. To stabilise the protective oxide scales against water vapour corrosion in combustion atmospheres, environmental barrier coatings (EBCs) of yttrium silicate were deposited on an FeB modified M₇Si₆ based bond coat using magnetron sputtering. The 15–20 μm thick ceramic top coats with an approximate chemical composition of 25Y–13Si–62O (at.-%) were dense and amorphous after deposition. They were annealed in vacuum to get a crystalline structure with the predominant phase Y₂SiO₅. Samples with this EBC system were tested in rapidly flowing water vapour at temperatures between 1100 and 1300°C for up to 16 h. At 1100 and 1200°C, significantly reduced mass gains were determined for samples with yttrium silicate top coat in comparison to those coated only with FeB containing layers. The EBC partially transformed into the Y₂Si₂O₇ phase and exhibited microporosity. At 1300°C, the yttrium silicate layer decomposed forming yttrium oxides.

Keywords:

• Niobium silicide
• M₇Si₆ based bond coat
• Yttrium silicate
• Environmental barrier coating
• Magnetron sputtering
• Water vapour corrosion

Acknowledgements

The support of the EU-funding by the 7th framework program is highly acknowledged (grant agreement number: 266214). The authors thank Mr D. Bindert for manufacture of the yttrium silicate coatings by magnetron sputtering and Mr A. Handwerk for performing the annealing treatments in vacuum.