Surface transformation of Ti–45Al–2Nb–2Mn–1B titanium aluminide by electron beam melting

Microstructure and phase evolution on the surface of Ti–45Al–2Nb–2Mn–1B (at.%) gamma based titanium aluminide was investigated by a series of electron beam melting with different beam energies and scanning speeds. X-Ray Diffraction (XRD), Glow Discharge Spectroscopy (GDS), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were performed to characterize the phase modification and morphology after the EBM treatment.At beam energies of 250 W and scanning speed of 16 mm s−1, the lamellar structure of Ti–45Al–2Nb–2Mn–1B transformed into a dendritic structure composed of initial α2 (Ti3Al) dendrites and an interdendritic phase of the γ (TiAl). While at higher energies of 350 W and lower beam speeds of 7 mm s−1, mainly B2 and α2 (Ti3Al) phases with higher titanium formed on the surface.All Phase transformations increased the hardness of the surface to a maximum of 600 HV if compared to 330 HV for untreated material. Lower energies and higher speeds induced cracks in the surface layers, while higher energies and lower speeds produced hard surface layers without cracking.