EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Laser power bed fusion (L-PBF) of Ti-6Al-4V results in the formation of large directional prior-beta (β) columnar grains cooling down into brittle alpha/alpha prime (α/α’) phases with anisotropic properties and poor ductility. We have recently showed that it is possible to minimize microstructural anisotropy and control phase fractions by adding minor concentration of β stabilizer Fe (Metallurgy and Mater Transac A, 51.5, 2020). However, the particular role of β stabilizer on grain refinement and phase transformation is not fully understood in relation to various laser energy inputs and solute diffusivities. Operando X-ray diffraction experiments (Hocine et al., Materials Today, 34, 2020) are carried out on Ti-6Al-4V-3Fe and Ti-6Al-4V-3Cr, revealing phase evolution and temperature profiles during rapid cooling and repeated thermal cycling in L-PBF process. The powder is prepared by decorating the Ti-6Al-4V powder with pure Fe or Cr particles using the satelliting method (Simonelli et al., Materials Chara, 143, 2018). The operando diffraction shows that Fe is much more effective in stabilizing β-Ti phase than Cr during printing operations. Moreover, Fe can diffuse over larger areas and as such further stabilize β phase during thermal cycling of the layers underneath the newly printed surface layer. The obtained microstructures are characterized by electron backscatter diffraction (EBSD) and energy dispersive X-ray (EDX) spectroscopy and then discussed in terms of laser processing parameters during printing and thermal cycling.