Microstructure modification of twin-wire directed energy deposition-arc fabricated γ-TiAl alloy via deposition current control

Abstract

Titanium aluminide has continuously attracted the attention of aerospace industry due to its low density and good performance at high temperatures. To overcome the room temperature brittleness induced manufacturing difficulty, additive manufacturing (AM) technology of titanium aluminide has been developing rapidly since last decade. Compared to powder-based AM methods such as electron beam melting (EBM), the twin-wire directed energy deposition-arc (TW-DED-arc) method for titanium aluminide fabrication possesses outstanding material deposition efficiency and much lower cost. However, because of the excessive arc deposition energy, the layer-band like microstructure of TW-DED-arc fabricated titanium aluminide is a great concern affecting the mechanical properties. In the present research, microstructure of as-fabricated TiAl alloy is modified by adjusting the deposition current of TW-DED-arc. Experimental results show that along with the increase of deposition current, the layer-band like microstructure consisting of dendritic grain region and fully lamellar colony region can be mostly homogenized. Although microhardness is decreased because of the inevitable lamella growth, tensile strength of TiAl deposit is on the other hand increased by eliminating the interdendritic γ-phase. In general, the present work has proved that deposition current adjustment is an effective method for homogenizing the microstructure of additively manufactured titanium aluminide.