Corrosion Assessment and Characterization of Aerospace-Bearing Steels in Seawater and Ester-Based Lubricants

Abstract

The corrosion behavior of bearing steels was screened using potentiodynamic scans in seawater. The results of electrochemical testing provided a relative ranking of the bearing steels when tested in aqueous chloride-containing solution. The corrosion behavior of bearing steels in the lubricant environment has been observed to be quite different than in aqueous solution. Both the amount of water contamination in oil and chloride content of the water impact the observed corrosion rates in oil-water mixtures. All steel compositions tested demonstrated localized corrosion damage when exposed to oil with water added; however, inherently less corrosion-resistant alloys had more widespread shallow attack, whereas higher Cr-containing alloys displayed more localized severe attack. The mechanism of corrosion in the two-phase, oil plus aqueous phase system appears to be controlled by an aqueous corrosion process dependent on steel microstructure and emulsified or free water and likely limited by oxygen availability and amount of water (with aggressive ions) in the oil

Corrosion Initiation and Propagation on Carburized Martensitic Stainless Steel Surfaces Studied via Advanced Scanning Probe Microscopy

“…M50, a through-hardened carbon steel, was developed for aircraft engine bearing applications and has become the standard bearing steel used in the United States due to its ability to perform well at high temperatures while maintaining relatively high fracture toughness compared to earlier generation carbon steels, such as AISI 52100 (UNS G52986) [1,3,4]. In the case of sea-based or coastal aircraft operations however, open turbine engine systems can limit the ability of ester-based lubricants to provide wear and corrosion protection, as the surrounding environment introduces water and marine aerosols into the engine during both storage and operation [5]. The presence of water in the lubricant can then serve to initiate aqueous corrosion during engine cycling and downtime [5].…”

“…In the case of sea-based or coastal aircraft operations however, open turbine engine systems can limit the ability of ester-based lubricants to provide wear and corrosion protection, as the surrounding environment introduces water and marine aerosols into the engine during both storage and operation [5]. The presence of water in the lubricant can then serve to initiate aqueous corrosion during engine cycling and downtime [5]. Consequently, current aero-engine performance is limited by corrosion-enhanced wear of the metallic bearings and drive components, which leads to increased maintenance and premature failure [1,6,7,8].…”