Phase microstructure engineering in laser powder bed fusion: A case study in TiTa alloys

TiTa alloys exhibit a low elastic modulus and exceptional biocompatibility, making them ideal for biomedical load-bearing applications. However, the relatively low yield strength and severe compositional segregation in TiTa alloys, caused by the large melting point difference between Ti and Ta, can initiate crack formation and mechanical failure under low-cycle fatigue conditions. The phase structure plays a vital role in determining alloy properties. To further enhance the strength of TiTa alloys, both the formation of a composite-phase structure and the high solubility of Ta in the Ti matrix are essential. In this work, dense Ti-60 (wt%) Ta specimens featuring cellular β-phase matrices and an intragranular network-like α″ phase with excellent formability were successfully fabricated using the laser powder bed fusion (LPBF) technique. The results reveal a homogeneous and refined microstructure, with an average grain size of ∼4.16 μm. The LPBF TiTa alloys exhibited an elastic modulus of 73.64 ± 4.8 GPa, a tensile yield strength of 1131.89 ± 27.01 MPa, and an elongation of 12.68 ± 1.17 %, outperforming other LPBF multi-element biomedical β-phase titanium alloys. The excellent mechanical properties are attributed to the refined constructure, solution strengthening, and the unique network-like composite phase. This work presents the composite-phase TiTa alloys with promising performance and elucidates the homogeneous microstructure and strengthening mechanisms.