The influence of laser energy density on the low cycle fatigue behavior for laser powder bed fused tantalum

Abstract

Laser powder bed fused tantalum (LPBF-Ta) holds significant potential for applications in orthopedic implants and aerospace industries. However, the risk of low-cycle fatigue (LCF) failure remains a critical challenge that has yet to be adequately addressed. This study is the first to elucidate the effects of varying laser energy densities on the microstructure and defects of LPBF-Ta, as well as their crucial influence on its fatigue life response and failure mechanisms. Specifically, the findings demonstrate that optimizing laser energy density can effectively control microstructure and defect morphology, significantly enhancing the LCF life of LPBF-Ta. High initial dislocation densities at low-angle grain boundaries and lack-of-fusion (LOF) pores preferentially drive crack nucleation and propagation under cyclic loading, representing potential factors for fatigue performance degradation. In contrast to randomly distributed LOF pores formed under insufficient low laser energy density, LOF pores, induced by spatter under high laser energy density, are linearly distributed along the building direction, forming vertically aligned pore chains. Additionally, the spatter enriched with carbon and oxygen elements destabilizes interlayer bonding, causing localized embrittlement and detrimentally reducing the fatigue life. These findings and insights provide critical references for understanding the LCF behavior of LPBF-Ta and ensuring its safe engineering application design.