Selective laser melting of NiTi cardiovascular stents: Processibility, surface quality and mechanical properties

Selective laser melting (SLM) is regarded as a promising alternative technology for manufacturing customized cardiovascular stents with complex geometries. In this study, a systematic study on the printability, densification and surface roughness regarding SLM of NiTi alloy were explored. It was revealed that macro cracks were mainly formed at volume energy density (VED) of 25-86 J/mm³ due to insufficient energy input with un-melted powders. However, even with the same VED, the different combinations of processing parameters exhibited unique surface characteristics. After optimization, the samples with laser power of 90 W, and scanning speed of 600 mm/s exhibit a superior relative density of 99.96 % and the minimal surface roughness Sq of 5.992 μm. Subsequently, The SLM capability for intricate structures was demonstrated by fabricating cardiovascular stents with varying radial thicknesses. The results indicated that the surface morphologies of SLMed stents exhibit varying degrees of powder adhesion phenomenon. However, the dimensional deviation for the radial thickness of 0.2 mm exhibits a higher percentage of 72 %, whereas the deviation reaches 104 % for that of 0.6 mm. For the compression test, the thinner radial thickness stent has better recovery ability.