Effect of Duplex Aging Heat Treatment on the Stress Corrosion Cracking Behavior of Ti-6Al-4V α+β Titanium Alloy in Methanol

The influence of duplex aging (DA) heat treatment and consequent microstructural changes in the stress corrosion cracking (SCC) resistance of Ti-6Al-4V α+β titanium alloy was examined through constant load SCC test and metallographic examination. The time for fracture (TFF) of duplex aged samples in the SCC test was compared with single aged samples TFF. The results of the constant load SCC test showed an improvement in corrosion resistance with the second stage of aging in the duplex aging heat treatment. Microstructural examination revealed a preferential path for SCC crack propagation through prior β grains (lamellar structure alternating α and β phases) which indicated that the bigger SCC resistance observed in DA samples is a consequence of greater β phase decomposition due to the second stage of aging. It wasn't observed a bigger grain growth in the DA heat treatment, in comparison with single aged (SA) samples. The observed fracture aspect was mixed (ductile-fragile) in peripheral regions and ductile in the interior of the body proofs, what indicate the major influence of SCC in the fracture mechanism.