The role of eta pockets resulting from Fe impurities in hydride formation in titanium
Abstract
The corrosion potential of commercially pure titanium in NaCl solutions is dramatically affected by trace Fe additions, which cause the appearance of submicron pockets of eta phase at grain boundary triple points. Furthermore, the low solubility of hydrogen in hexagonal close-packed α-Ti makes titanium alloys prone to subsequent hydride-associated failures due to stress corrosion cracking. We analyzed α-α and α-eta sections of the abutting grain boundary of a eta pocket in a Grade 2 CP-Ti, and the α-eta phase boundary. Fe and H partition to eta and segregate at the grain boundary, but no segregation is seen at the α-eta phase boundary. In contrast, a significant Ni (>1 at%) accumulation is observed at the α-eta phase boundary. We propose that the eta-pockets act as hydrogen traps and facilitate the nucleation and growth of hydrides along grain boundaries in CP-Ti.