Hot Salt Stress Corrosion Cracking Behavior of Ti-6242S Alloy

The hot salt stress corrosion cracking behavior of Ti-6A1-2Sn-4Zr-2Mo-0.1Si (Ti-6242S) alloy was studied in the temperature range from 523.15 K to 673.15 K (250 degrees C to 400 degrees C). The alloy showed marginal susceptibility at 573.15 K (300 degrees C), and the extent susceptibility found to increase significantly at higher test temperatures. The specimens did not fail in long-term (1000 hours) hot salt constant load exposure tests carried out at 623.15 K and 673.15 K (350 degrees C and 400 degrees C), even at the stress levels more than the 80 pct of their ultimate tensile strength. However, the salt exposure in both stressed and unstressed conditions found to significantly impair the room-temperature ductility. The study shows that pitting and formation of slip step were the precursor events for SCC initiation; and the cracks were found to grow in transgranular manner in the primary-alpha phase and discontinuous-faceted manner in the transformed beta colony. Furthermore, the XRD analysis of hot salt-exposed specimens revealed the presence of titanium hydride phase, which could be responsible for the embrittlement. (C) The Minerals, Metals & Materials Society and ASM International 2015