Evaluation of Protection Schemes for Ultrahigh-Strength Steel Alloys for Landing Gear Applications.

摘要

The use of ultrahigh-strength steel alloys is required to meet the performance and weight requirements for landing gear. Historically, there has not been a corrosion resistant alloy available that meets the strength requirements and provides adequate corrosion protection. Therefore, the use of cadmium coatings has been the preferred method of corrosion protection in landing gear systems for decades. In recent years, a new ultrahigh-strength corrosion resistant alloy has been developed (UNS S10500) that has potential to reduce or eliminate the use of cadmium coating within landing gear systems. A comparison of various protection schemes (primer and paint only, zinc-nickel, and cadmium) for this new alloy were compared to other ultrahigh-strength steels (UNS G43400, UNS K44200, UNS K92580, and UNS K91973) using their currently recommended protection schemes for landing gear (primarily cadmium). Salt fog testing per ASTM B117 using scribed panels was the basis for this study. Scribe widths of approximately 0.5 mm and 2.5 mm were exposed for times of 100 and 500 hours. Results indicate that the cadmium coating starts to break down at approximately 100 hours, and small areas of iron oxide corrosion product are present on the low-alloy steels, while no rust is observed for the high-alloy and corrosion-resistant alloy. The zinc-nickel coating evaluated provides adequate corrosion protection up to 500 hours, but experiences blistering. The prime and paint only scheme of the corrosion resistant alloy showed localized pitting and rust product, while other areas of the exposed region were protected by a passive chromium-oxide layer.