Microstructure and hardness of electron beam melted Ti-6Al-4V titanium alloy in dependence of the scanning speed

The effect of the beam scan velocity upon microstructure and hardness of Ti-6Al-4V titanium alloy produced by means of Electron Beam Melting (EBM) was investigated in this work. Five levels of scan velocity were used during the experimental campaign, ranging from 121 to 697 mm/s, and keeping all other process parameters fixed. It was found that a finer microstructure is generated with the increase of the beam speed, since the characteristic dimensions of both the prior columnar b grains and of the α laths decrease for higher beam speeds. In particular the finer microstructure was observed at a scan speed of 697 mm/s while the coarser at 121 mm/s. On the other side, the hardness of the EBMed samples increase with the increase of the scanning speed and a maximum hardness of about 400 HV was measured at a scan speed of 697 mm/s. This value is strictly associated to the finer microstructure that was obtained at this value of the scan speed. In particular, it was observed a 17% increase of the hardness going from a scan speed of 121 to one of 697 mm/s.