Process optimization, interfacial characteristics, and mechanical properties of titanium-tantalum multi-material structures fabricated via laser powder bed fusion

Abstract

To fully exploit the biomechanical properties of titanium (Ti) and biocompatibility of tantalum (Ta), Ti-Ta multi-material structures with different printing sequences were fabricated using laser powder bed fusion (LPBF). The interfacial characteristics, mechanical properties, formation mechanisms, and influence of process parameters on bonding strength at the Ti/Ta (Ta printed on Ti) and Ta/Ti (Ti printed on Ta) interfaces were investigated. At the Ti/Ta interface, a wide diffusion zone led to microstructure evolution along the building direction: coarsened lath α′ grain → refined α′ + β grains → columnar β + cellular β grains. This evolution was attributed to keyhole formation and differences in material density that promoted element diffusion. On the other hand, at the Ta/Ti interface with a narrow diffusion zone, direct microstructure evolution occurred from columnar β + cellular β grains to lath α′ grains due to limited solid-state diffusion and compromised element diffusion caused by gravity and heat dissipation. Optimal bonding strengths of 548.11 MPa and 285.42 MPa were achieved for the Ti/Ta and Ta/Ti interfaces, respectively. During LPBF processing of Ti-Ta multi-materials, reducing scanning speed significantly enhanced bonding strength, indicating its significant impact on interfacial bonding. These findings offer novel insights and references to fabricate Ti-Ta multi-material structures with great potential for biomedical implants through LPBF.