High Ductility in a fully martensitic microstructure: a paradox in a Ti alloy produced by selective laser melting

Abstract

A fully martensitic Ti alloy consisting entirely of hexagonal-close-packed α′ was produced by selective laser melting (SLM), exhibiting an impressive combination of high strength and excellent ductility. A small quantity of body-centred-cubic β formed at some large primary α′ plates oriented at ∼45° to the tensile direction was found responsible for early fracture owing to α′/β strain incompatibility. Properly selected SLM parameters resulted in a β-free microstructure containing α′/α′ interfaces only, preventing premature fracture. Consequently, large plastic deformation was enabled, creating randomly oriented nano-α′ crystals. The investigation dispels the myth that α′ is inherently brittle.