Impedance Studies of Thermochemically Activated 316L Stainless Steel
This study proposed a novel thermochemical activation (TCA) method to modify the surface of 316L stainless steel (SS). At the first stage, phosphate ions were introduced to 316L SS surface by a heat-diffusion process. After rapid quenching into calcium citrate solution, calcium and hydroxide ions were sealed in the TCA compound layer. The TCA and original 316L SS were immersed in Hanks’ solution to evaluate their biocompatibility. Electrochemical impedance spectroscopy analysis showed that the surface active compound layer affected the TCA 316L SS, and its total impedances of Bode and Nyquist plots were higher than that of the original ones during immersed in Hank’s from 1 to 14 days. After TCA treatment, the corrosion resistance increased greatly, and thus reducing the release of ions from stainless steel, such as Fe, Cr, Ni and Mo. In the Ca- and P-rich areas, the ions were guided to deposit in the Hanks’ solution, forming bone-like hydroxyl apatite. The treatment has been proven to reduce the ionic release from 316L SS, which is considered to be a great improvement for implanted alloys.