Functionally graded properties in directed-energy-deposition titanium parts

Abstract

The directed energy deposition (DED) process can directly build full-density, high-performance, complex metal parts by melting metal powder with laser scanning. Functionally graded properties are characterized by gradual property variations over the volume according to the designed pattern. This study investigated the functionally graded properties obtained from DED of titanium powder. The formation of titanium nitride in the laser-melted layer has a strong potential to increase the hardness of the titanium alloy. Thus, the hardness of the deposited part was controlled by changing the concentration of nitrogen in the shielding gas. Furthermore, the effect of laser surface remelting on the deposited layer was investigated to control the surface qualities of the part, such as the roughness, hardness, and surface colour. From the analysis, a functionally graded part having variable hardness was obtained on a trial basis, and the proposed method is shown to be feasible with a high degree of reliability.