Fatigue performance of beta titanium alloy topological porous structures fabricated by laser powder bed fusion

Abstract

The performance of porous β-titanium alloys is crucial for their diverse applications, with fatigue characteristics playing a pivotal role in shaping the design of these porous structures. While topological configurations have exhibited exceptional property, a systematic understanding of their fatigue performance is lacking in recent literature. This study reveals that at a porosity level of ∼75%, designed topologically optimized (TO) structures surpass rhombic dodecahedron (RD) structures in compressive yield strength by ∼4 times (149 ± 3 MPa vs. 38 ± 1 MPa). Furthermore, post-heat treatment further enhances the yield strength of TO structures by ∼15%, reaching 172 ± 3 MPa due to grain refinement and β phase stabilization. Moreover, the as-printed TO structure exhibits exceptional compressive fatigue endurance, enduring stress approximately ∼5 times higher than the as-printed RD structure at a cycle count of 106. Microstructure analysis after fatigue testing reveals a reduction in the α'' martensitic phase and an increase in stress-induced ω phase in the heat-treated TO structure, contributing to a slight improvement in fatigue strength compared to the as-printed TO structure. The exceptional fatigue performance observed in LPBF-built beta-type titanium alloy within TO structures highlights the complex relationship between porous structure design, microstructure, compressive strength, and fatigue performance.

Keywords

• Selective laser melting
• Beta titanium alloy
• Laser powder bed fusion
• Fatigue
• Topological porous structures
• Phase transformation