Microstructural Inhomogeneity and Mechanical Properties of Ti-6.4Al-3.3Mo-1.6Zr-0.2Si Alloy Fabricated by Laser Metal Deposition

Laser metal deposition (LMD) additive manufacturing has gained growing interest in the aerospace industry. Herein, a Ti-6.4Al-3.3Mo-1.6Zr-0.2Si (TC11) titanium alloy is produced by LMD. The inhomogeneity of multiscale grain morphology and mechanical properties are systematically investigated. The results indicate that the melting pool (MP) morphology can be divided into three areas: melting pool center (MPC), melting pool boundary (MPB), and heat-affected zone (HAZ), respectively. The widths of & alpha; laths in MPB are larger than that in HAZ and MPC, which result in a lower microhardness in MPB than that in MPC. Besides, the columnar grains are generally distributed along the deposition direction. The average widths of the & alpha; laths in the top and bottom MPC regions are about 0.58 and 0.67 & mu;m, respectively. Correspondingly, the ultimate tensile strength and fracture elongation of the top and bottom samples are 1,053.5 MPa, 16.7%, and 1,011.5 MPa, 20.7%, respectively, which suggest the inhomogeneity of mechanical properties. The initiation fracture sites of both the top and bottom samples are presumed to be the & alpha; lath inside the MPB according to stress distribution analysis. The formation mechanisms of inhomogeneous grain structures and their influences on mechanical performance are also discussed.