Scale effect on mechanical properties of titanium aluminide alloy additively manufactured by electron beam melting

TiAl (titanium aluminide) has been applied to turbine blades in aerospace industry, because it is a promising lightweight material with high strengths at high temperatures. In recent years, the production method of TiAl by additive manufacturing has been studied. In this research, the effect of dimensions of TiAl specimens by additive manufacturing had on the tensile and creep properties was studied. It was confirmed that the near-net specimen showed higher tensile strengths and lower creep resistance and life than those of the specimen cut from the block with larger cross section and volume than near net specimen. The results showed that the difference of the mechanical properties was because of the different microstructure caused by the powder melting process including hatching to melt inside the cross section and contouring perimeter. The difference in microstructure is considered to be due to the energy density. The energy density of contours is nearly 4 to 10 times higher than that of hatching. Therefore, it is considered that rapid heating and rapid cooling occur in the contour process, resulting in a fine structure.