Low-cycle fatigue performance of remelted laser powder bed fusion (L-PBF) biomedical Ti25Ta

Abstract

In this study, the fatigue performance of additively manufactured Ti25Ta, produced by laser powder bed fusion (L-PBF) using pre-mixed powder is investigated. Ti25Ta shows promise as a biomedical implant alloy, due to its high strength to elastic modulus ratio. However, the fatigue response of L-PBF Ti25Ta is yet unknown and understanding fatigue behaviour is crucial for cyclically loaded implants.The Ti25Ta alloy was produced employing single melt and remelt scanning strategies. It was shown that the remelt strategy had a positive effect on reducing the amount of remaining partially melted Ta particles from 2.07 ± 0.01 vol % to 0.22 ± 0.01 vol % while only slightly increasing the porosity from 0.15 ± 0.01 vol % to 0.37 ± 0.01 vol %. Furthermore, it was found that the remelt strategy resulted in alloy strengthening and a randomised orientation of the α′ lath microstructure.Machined fatigue samples were tested in the low-cycle fatigue regime under strain-controlled conditions. The alloy demonstrated a superior yield stress normalised fatigue performance compared with commercially pure (CP) Ti, and Ti–6Al–4V ELI, and was second only to pure Ta. However, the Ti25Ta L-PBF material retains less than half the elastic modulus of all the compared materials. The remelt samples showed an increased stress response due to their higher strength and an increased elastic modulus, however a reduced number of cycles to failure. This was attributed to reduced ductility and increased crack propagation rate. It is believed that remelt scan parameter optimisation can further enhance the performance of this alloy.