ABSTRACT
A Ti-6Al-4V alloy is one of important titanium alloys used for aerospace, power
generation, chemical and biomedical applications. The alloy is available in two grades;
commercial grade (0.16mass% (%)-0.2% oxygen) and extra-low interstitial (ELI) grade
(0.10%-0.13% oxygen). In this study, effect of tempering on microstructure and
hardness of the Ti-6Al-4V ELI alloy was investigated. The alloy was heat-treated at
temperature of 1323K for 3.6ks for solution treatment at a bcc (β) phase region. The
alloy is subsequently quenching into the water to promote a martensitic transformation,
and then tempered at temperatures from 923K-1123K for various times from 0.6ks to
7.2ks. Microstructure of quenched specimen is a martensitic structure, which exhibits a
needle-like structure. On the other hand, the microstructure of the tempered specimens
are hcp+bcc (α+β) dual-phase. It is observed that the β phase increases as the
tempering temperature increases or time prolongs. Hardness measurement shows that
the hardness of the tempered specimen gradually increased as the time and the
temperature increase. It is thought that the increase in hardness of the tempered
specimen is due to precipitation hardening of the β phase.