Development of Oxide-Based EBC for Silicon Nitride

• Published in: International journal of applied ceramic technology 2004-01, Vol.1 (4), p.362-373
• Main Authors: Ueno, Shunkichi, Jayaseelan, D. Doni, Ohji, Tatsuki
• Format: Article
• Language: English
• ISSN: 1546-542X; 1744-7402
• DOI: 10.1111/j.1744-7402.2004.tb00187.x

In search of a candidate EBC material for silicon nitride ceramics, water vapor corrosion test was performed for a series of monolithic materials such as Al2O3, TiO2, ZrO2, HfO2, Al2TiO5, Al6Si2O13, Lu4Hf3O12, Ln2Si2O7 (Ln = Yb and Er) and mullite/Lu2Si2O7 eutectic bulk at above 1300°C. Based on the high‐temperature water vapor corrosion test results and the resultant microstructures, the mechanisms of water vapor corrosion of these materials were discussed in this paper. In this present study, ZrO2 and HfO2 showed excellent resistance to water vapor corrosion at high temperatures. Among low‐thermal‐expansion materials, specifically silicate‐based materials, Lu2Si2O7 showed better results in the aspect of weight loss rate during the corrosion test, which also desirably has a coefficient of thermal expansion very close to that of silicon nitride. To verify the recession mechanism of Lu2Si2O7, a recession test was performed for this bulk in high‐velocity combustion gas flow at 1300‐1500°C. This material showed excellent recession resistance compared to Al2O3 and Si3N4. Different coating techniques, such as sputtering, sol‐gel, and reaction sintering, were employed to coat a high‐density Lu2Si2O7 EBC layer on a silicon nitride substrate. However, in polycrystalline Lu2Si2O7 phase, the grain boundary silica was prone to water vapor corrosion. It was observed that the corrosion resistance of a Lu2Si2O7/mullite eutectic bulk, without boundary silica, was more excellent than that of polycrystalline Lu2Si2O7 bulk.