The mechanism of element inhomogeneity in TW-DED-arc fabricated -TiAl alloy

The twin-wire directed energy deposition-arc (TW-DED-arc) method is a low-cost and efficient in situ alloying process for producing gamma-TiAl alloy, a new generation material for aero-engine blades. Its characteristic of "twin-wire-one-drop" can successfully avoid the phenomenon of discordant melting and ineffective mixing. In this study, the mixing effect of "twin-wire-one-drop" was analysed, and droplets of different diameters were used for fabricating Ti-48Al walls. It was found that the mixing effect in the droplet was great, but there were still local unmixed areas, and a completely uniform Ti-48Al wall could be obtained by using small droplet mode. Meanwhile, incompletely mixing regions with composition difference greater than 5% appeared in many places on the sides of the Ti-48Al wall in huge droplet mode. A numerical model is established to simulate the mixing process after the droplet enters the molten pool. It is found that the secondary droplets generated in huge droplet mode are the main reason for the element inhomogeneity phenomenon. Therefore, keeping the droplet interval short and uniform is beneficial to the element in situ alloying.