Significant α-phase growth confinement in Grade 4 titanium and substantial β-phase refinement in Grade 7 titanium

Significant alpha-phase growth confinement in Grade 4 titanium (Ti) and substantial beta-phase refinement in Grade 7 Ti were observed during hightemperature annealing. The mechanism for each observation was identified through detailed microstructural investigation assisted with phase diagram analyses. The former observation was due to the pinning effect of Fe-stabilized grain boundary (GB) beta-Ti phases in Grade 4 Ti. The latter observation resulted from the redistribution of Fe and, palladium (Pd) in particular, in Fe-stabilized and Pd-containing GB beta-Ti phases in Grade 7 Ti. Pd was found to exist mainly in two forms in cold-rolled Grade 7 Ti, i.e. Fe-stabilized GB beta-Ti phases and an occasionally observed orthorhombic Ti88Pd9 Fe3 phase. The latter is close to the Ti2 Pd3 intermetallic phase in terms of the crystal structure.