Effects of Sintering Aids on Hydrothermal Corrosion Behavior of Si3N4 Ball Bearings

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Student Presentation

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Darryl Butt


Silicon nitride (Si3N4) bearings are being incorporated into aeropropulsion applications that require high strength, hardness, and chemical stability at elevated temperatures. Sintering aids such as yttria (Y2O3), alumina (Al2O3), titania (TiO2) and magnesia (MgO) are added during processing to promote densification and enhance microstructure, but minor changes in composition can significantly alter corrosion behavior of monolithic Si3N4. The hydrothermal corrosion behavior of a silicon nitride bearing that includes TiO2, Y2O3, and Al2O3 additives was compared to more common Si3N4 composites. The bearings were corroded in an autoclave at 250-300°C and 750-2400 psi for 12-48 hours and subsequently characterized with scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and inductively coupled plasma mass spectrometry (ICPMS). The corrosion resistance of the TiO2/Y2O3/Al2O3-doped Si3N4 ceramic closely matches that of Y2O3/Al2O3-doped Si3N4 and outperforms Al2O3/MgO-doped Si3N4. This study demonstrates the stability of the TiO2/Y2O3/Al2O3-doped Si3N4 ceramic composition and verifies its potential as a bearing material in aeropropulsion applications.

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