In situ analysis of plasticity and damage nucleation in a Ti-6Al-4V alloy and laser weld

The present work addresses the mechanisms of plasticity and damage nucleation in a Ti-6Al-4V alloy and its laser weld. To this end, in situ tensile tests are performed in a Scanning Electron Microscope (SEM) equipped with a Electron BackScatter Diffraction (EBSD) camera. The slip activity is automatically analyzed using a modified Schmid analysis. It is shown that the slip activity of the base metal consists mainly in prismatic, basal and pyramidal slip. Damage nucleation in the vicinity of the beta phase and at alpha grain boundaries is also evidenced in the base metal. In the alpha' weld metal (a microstructure similar to the one often obtained in additive manufacturing Ti-alloy parts), plastic deformation results in a crystallographic rotation of the laths tending to align the < 10 (1) over bar0 > direction with the tensile axis. The rare events of crack initiation in the martensite are shown to occur along specific laths interfaces, former beta grain boundary or twinned martensite needles.