Effects of Sintering Aides on the Hydrothermal Oxidation of Silicon Nitride Spherical Rolling Elements

Authors

Allyssa Bateman, Boise State UniversityFollow
Abby J. Queale, University of Florida
Darryl P. Butt, Boise State University
Brian J. Jaques, Boise State UniversityFollow

Document Type

Article

Publication Date

2-2019

Abstract

Commercially available silicon nitride (Si₃N₄) spherical bearing rolling elements containing TiO₂, Y₂O₃, MgO and Al₂O₃ additives were evaluated for corrosion-resistance in high-temperature, high-pressure hydrothermal tests designed to simulate aero propulsion conditions. Spheres were exposed in an autoclave at 523–623 K and 5.2–16.5 MPa for 12–48 h and characterised using mass change and pH measurements, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy and inductively coupled plasma mass spectrometry. The oxidation resistance of the TiO₂/Y₂O₃/Al₂O₃-sinter-aided Si₃N₄ ceramic closely matches the Y₂O₃/Al₂O₃-doped Si₃N₄ and outperforms the MgO-sinter-aided Si₃N₄. Additional studies on the TiO₂/Y₂O₃/Al₂O₃ Si₃N₄ composition show pitting initiates around titanium-rich inclusions, due to a break in the protective hydroxide layer, accessible diffusion paths around inclusions and the catalytic nature of titanium. This study demonstrates that the addition of TiO₂/Y₂O₃/Al₂O₃ to hot pressed Si₃N₄ reduces corrosion rates in high-temperature, high-pressure, hydrothermal environments.

Publication Information

Bateman, Allyssa; Queale, Abby J.; Butt, Darryl P.; and Jaques, Brian J.. (2019). "Effects of Sintering Aides on the Hydrothermal Oxidation of Silicon Nitride Spherical Rolling Elements". Corrosion Engineering, Science and Technology, 54(1), 22-27. https://doi.org/10.1080/1478422X.2018.1523290