Environmental fatigue crack propagation in Ti-6A1-4V sheet: Revised Edition

Abstract

A study was made of environmental fatigue crack propagation in 2.5 mm thick Ti-6A1-4V sheet conforming to AMS 4911, and 2.2 mm thick IMI 3l8 conforming to BS TA 10. The environments were dry argon, normal air, distilled water and 3.5 ^ aqueous NaCl. There were three alloy/orientation combinations: Ti-6A1-4V L-T, IMI 3l8 L-T and IMI 318 T-L. Test frequencies were 30 and 50 Hz, at which there was a general trend of higher crack growth rates in the order: argon, air, distilled water, 3.5 ?^ aqueous NaCl. For both dry argon and 3.5 ^ aqueous NaCl there were large differences in crack growth rates at low AK values between the three types of specimen. There was a correlation between the texture and cleavage fracture and Crack growth rates in 3.5 ^ aqueous NaCl. This result is of considerable practical importance. For dry argon the ranking of specimen types could be explained by the relative importance of mechanical and environmental crack growth, using the structuresensitive to structure-insensitive transition concept of Irving and Beevers.