Microstructural Changes in Aerospace Bearing Steels under Accelerated Rolling Contact Fatigue Life Testing

摘要

Operating in the extreme environment of a turbine engine, aerospace bearings must endure high thrust loads and very high rotational speeds. Subsurface fatigue damage is often observed as stressed zones, dark etching regions, light etching regions, and white etching regions. American Iron and Steel Institute (AISI) 52100 bearing steel is widely studied for microstructural changes and has been reported in the literature. Microstructural changes in a large test matrix of advanced materials for aerospace applications have not been studied. In this study, one through-hardened (VIM-VAR AISI M50) and four case-hardened materials (M50 NiL, M50 NiL Nitrided, Pyrowear® 675 High Temperature Temper, and Pyrowear® 675 Low Temperature Temper) were tested with silicon nitride balls under accelerated life conditions on a ball-on-rod rolling contact fatigue bench tester. Microstructural changes were characterized by light optical microscopy and scanning electron microscopy in radial and axial cross-section views. White etching cracks and white etching regions were observed in M50, M50-NiL, and M50-NiL (N) with shorter average fatigue lives as compared to either version of Pyrowear® 675.