Laser surface modification of 316 L stainless steel with bioactive hydroxyapatite

• A high power laser has been used to modify 316 L stainless steel with hydroxyapatite.
• Modified surfaces up to 355 μm thick have been achieved with highest hardness of 434 HV.
• Low laser power and energy input resulted in fine microstructures with high hardness.
• All modified surfaces showed early apatite formation and are non-toxic.

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.