Laser nitriding on a low-elastic-modulus refractory high-entropy alloy for improved biomedical properties

Biomedical refractory high-entropy alloys (RHEAs) are attractive implant candidates due to their excellent biocompatibility, but a high elastic modulus with inferior wear resistance constrains their clinical utility. Herein, a novel biomedical [(Sn 0.5 Mo 0.5 )-(Ti 6 Zr 6 Hf 2 )]Nb 3 RHEA with a low E r of 68.60 GPa and a high σ 0.2 of approximately 1 GPa based on the cluster-plus-glue-atom model is designed. Subsequently, a protective high-hardness Ti/Zr/Hf nitride coating with an FCC structure is prepared on the RHEA via laser surface nitriding. The N4 coating exhibits an average thickness of 1.48 μm and is crack-free. The highest nano-hardness (24.23 GPa), H/E, and H 3 / E r 2 in the N4 coating indicate theoretical predictions for improved wear resistance. All the nitride coatings exhibit enhanced corrosion resistance in SBF relative to the untreated RHEA substrate since hard and dense nitride coatings act as an enhanced physical corrosion barrier. The N4 coating shows the best corrosion resistance with the most positive E corr (−1.099 V), lowest i corr (4.871 × 10 -7 A/cm 2 ), highest E b (516.5 mV), lowest I pass (1.41 × 10 -4 A/cm 2 ), and unobserved surface damage after corrosion. In vitro culture confirms the enhanced in vitro biocompatibility of the N4 coating with a higher average cell viability of 96.5% compared to the RHEA substrate. These results can guide laser surface nitriding on RHEAs for biomedical applications.