Laser surface modification of 316 L stainless steel with bioactive hydroxyapatite

Laser-engineered net shaping (LENS™), a commercial additive manufacturing process, was used to modify the surfaces of 316 L stainless steel with bioactive hydroxyapatite (HAP). The modified surfaces were characterized in terms of their microstructure, hardness and apatite forming ability. The results showed that with increase in laser energy input from 32 J/mm2 to 59 J/mm2 the thickness of the modified surface increased from 222 ± 12 μm to 355 ± 6 μm, while the average surface hardness decreased marginally from 403 ± 18 HV0.3 to 372 ± 8 HV0.3. Microstructural studies showed that the modified surface consisted of austenite dendrites with HAP and some reaction products primarily occurring in the inter-dendritic regions. Finally, the surface-modified 316 L samples immersed in simulated body fluids showed significantly higher apatite precipitation compared to unmodified 316 L samples.