Significant enhancement in yield strength for a metastable beta titanium alloy by selective laser melting

A β titanium alloy, Ti–10V–2Fe–3Al, was processed by pulsed selective laser melting. The as-fabricated sample was dominated by fibre-like columnar β grains and cellular structures which were embedded with a high density of nano-sized ω precipitates and dislocations. The samples demonstrated extraordinarily high yield strength (920–950 MPa) and high elongation (10–14%). After yielding, the samples showed nearly constant true stresses but changeable work hardening rates. Electron backscattered diffraction and transmission electron microscopy study on the deformed samples revealed that dislocation slipping has been the dominant deformation mechanism during tensile testing, which was accompanied by β→α′ martensitic transformation. The significantly high yield strength is attributed to the suppression of β→α′′ transformation and the fine grain and cell structures together with massive pre-existing dislocations. The abnormal increase in work hardening rate between 2.2% and 6% true strain is mainly attributed to the increased occurrence of stress induced β → α′ martensitic transformation.