Interfacial characterization and reaction mechanism of Ti/Al multi-material structure during laser powder bed fusion process

Abstract

Laser powder bed fusion (LPBF) process is a promising additive manufacturing technique to manufacture multi-material integrated parts with complex structures. In this paper, the multi-material structure of Ti6Al4V/AlSi10Mg is fabricated by LPBF, the interfacial characterization, interfacial reaction mechanism and mechanical properties of Ti/Al structure are investigated. Results show that continuous and excellent metallurgical bonding between Ti6Al4V and AlSi10Mg is obtained, and the width of interface zone is about 100 μm. The equiaxed grains of aluminum alloy at the interface show random crystallographic orientation, which is attributed to the thermal dynamics in the melt pool, thermal cycles during LPBF process and lower thermal conductivity of titanium alloy. The interfacial reaction layers are orderly from titanium alloy to the aluminum alloy consisting of Ti 3 Al, TiAl with nanoparticles Ti 5 Si 3 and rod-like TiAl 3 . The segregated Si atoms react with the dissolution of Ti atoms in-situ to form Ti 5 Si 3 , meanwhile, a mass of Al atoms also react with Ti atoms to form TiAl. Namely, the TiAl phase forms in thin layer shape embedded with nanoparticles Ti 5 Si 3 through eutectic reaction near the fusion line at the interface. At the wall of eutectic production, the TiAl 3 phase nucleation and grow opposite to the heat dissipation direction and vertical to the fusion line. Outside the fusion line, the supersaturated solid α-Ti transforms to Ti 3 Al through the diffusion of Al atoms in the part of titanium alloy. During the interfacial reaction, in-situ generated nanoparticles Ti 5 Si 3 could improve the joint strength, and the tensile strength of Ti6Al4V/AlSi10Mg specimens reached 264.8 ± 22.4 MPa. The tensile specimens exhibit brittle fracture and two typical fracture morphologies appear on the fracture surface. • Ti/Al samples were fabricated by laser powder bed fusion (LPBF), and the microstructure at the interface was affected by the extremely fast cooling rate and thermal cycles of LPBF • The interfacial phases are formed by different mechanisms and they are orderly from titanium alloy to the aluminum alloy consist of Ti 3 Al, TiAl with nanoparticles Ti 5 Si 3 and rod-like TiAl 3 . • The tensile strength of Ti/Al specimens reached 264.8 ± 22.4 MPa due to the in-situ generated nanoparticles Ti 5 Si 3 .