Neutron diffraction of titanium aluminides formed by continuous electron-beam treatment

Ti-Al-based alloys were produced by hybrid electron-beam technologies. A composite Ti-Al film was deposited on a Ti substrate by electron- beam evaporation (EBE), followed by electron- beam treatment (EBT) by a continuously scanned electron beam. The speed of the specimens motion during the EBT were V-1 = 1 cm/sec and V-2 = 5 cm/sec, in order to realize two different alloying mechanisms - by surface melting and by electron- beam irradiation without melting the surface. The samples prepared were characterized by XRD and neutron diffraction to study the crystal structure on the surface and in depth. SEM/EDX analysis was conducted to explore the surface structure and analyze the chemical composition. Nanoindentation measurements were also carried out. No intermetallic phases were registered in the sample treated at velocity V-1, while the sample treated at V2 exhibited a Ti3Al/TiAl structure on the surface, transformed to Ti/TiAl in depth. The nanoindentation test demonstrated a significant negative hardness gradient from the surface to the depth of the sample.