The examination of corrosion behaviors of hap coated Ti implant materials and 316L SS by sol-gel method

In this research, hydroxyapatite (HAP) coatings have been produced on Ti, Ti6Al4V alloy and 316L stainless steel substrates by sol-gel method. (NH₄) · H₂PO₄ is taken as P precursor and Ca(NO₃)₂ · 4H₂O is taken as Ca precursor to obtain HAP coating. Additionally, three different pretreatment processes (HNO₃, anodic polarization, base-acide (BA)) have been applied to Ti, Ti6Al4V alloy and 316L stainless steel substrates. The corrosion behaviors of bare and HAP coated samples are examined in Ringer and 0.9% NaCl. HAP coated Ti have showed over 87.85% inhibition. HAP coated Ti6Al4V alloys have showed over 87.33% inhibition. In Ringer solution, 99.24% inhibition has been showed in HAP coated anodic pretreatment for 316L stainless steel. All pretreatment processes are effective on clinging of HAP coating to the surface. It is seen that impedance values have increased in HAP coatings (Ti and Ti6Al4V). HAP coatings have raised the corrosion resistance of Ti and Ti6Al4V. The values of polarization resistance in HAP coated samples have increased for 316L stainless steel in 0.9% NaCl and Ringer solutions. It is seen in SEM images that open pores and attachments among pores have been observed in the coating, which increases osteointegration. It is noted in EDX analyses of the surfaces of the HAP coated samples that there is only Ca, O, and P on the surface. Ca/P ratio varies in 1.84–2.00 ranges. As Ca/P ratio increases, the inhibition increases too. It is seen in XRD images of HAP powder that there are HA ate structures. Additionally, it is seen in FTIR analysis, characteristic HA absorption bands have occurred in sintered powders.