Effect of Process Parameters on Microstructure of TiAl Alloy Produced by Electron Beam Selective Melting

Abstract

Pre-alloyed Ti-47Al-2Cr-2Nb powder was utilized to fabricate samples via electron beam selective melting. The microstructures of as-built components were characterized by optical microscopy, scanning microscopy and X-ray diffraction, while an electronic dispersive spectrometer was employed to study the chemical compositions. It is worth noting that the atomic percentage of aluminium decreased along with the increase of energy input. There appeared to be an element loss of aluminium up to 15% at the highest energy input. The microstructures consisted of lamellar α2-Ti3Al)/γ-TiAl, basket-weave α2 (Ti3Al) and B2 phase. With varied melting beam currents, different phase transformations resulted from different thermal cycles and varied element losses of aluminium. γ-TiAl was the main phase of Sample-1 with the lowest energy input, while α2-Ti3Al was the main phase of Sample-4 with the highest energy input. The thickness of lamellar α2 decreased as the cooling rate increased due to the increasing energy input.