Development of Corrosion-Hydrogen Cracking Resistant Aircraft Alloys from Mechanistic Understanding

An innovative science-based approach is needed to develop ultra-high strength steels that resist corrosion and associated hydrogen cracking in the severe maritime operating environment, specifically to reduce life-cycle cost and improve mission reliability for Navy aircraft components such as the landing gear and drive mechanism. This Phase I proposal integrates a fundamentally based experimental and modeling approach to develop steels with NAVAIR-required hydrogen environment cracking resistance. Emphasis is on AerMetTM100 and Custom 465 steels, processed to yield strengths at or above 1725 MPa. Work will establish the microstructural mechanism for transgranular hydrogen cracking. Cutting-edge experiments will characterize hydrogen cracking resistance of these steels with simple process changes implemented to test the importance of retained/reverted austenite. Experiments are designed based on mechanistic understanding to emphasize electrochemical polarization and crack tip strain rate/passive film stability that govern H uptake. Micromechanical modeling is proposed to interpret laboratory data and guide alloy/process development (e.g., estimating intrinsic H accumulation at a crack tip). Preliminary design concepts will be developed for JSF components (e.g., landing gear, weapons bay door drive system). An Option Phase will answer the questions that hinder transition of fundamental understanding of Phase I results to impact Navy aircraft applications.