FABRICATION OF SLURRY BASED Y-Si-Al-O ENVIRONMENTAL BARRIER COATING ON THE POROUS Si_3N_4 CERAMICS

摘要

The dense Y-Si-Al-O environment barrier coatings were fabricated on the surface of porous Si_3N_4 substrate by slurry spray method and then sintered at 1350°C-1450°C in N2 atmosphere. Results show that different phase composition and microstructure of coatings were formed due to the different sintering temperature. The Y-Si-Al-O powder melted and infiltrated into the porous substrate and formed a dense layer with a thickness of about 100p.m. The coating sintered at 1400°C is uniform and crack-free with a composition of β-Si_3N_4 and part of the glass phase. After sintering, the water absorption decreased significantly from 34.5% to only 2.6% and the flexural strength was improved by 15.6%. The dielectric constant and loss of specimen increased due to the decrease of the porosity after coating.