Microstructure analysis of hydroxyapatite coating on stainless steel 316L using investment casting technique for implant application

Abstract

Osteoporosis and traffic accidents are a significant factor that causes a bone fracture in Indonesia. One solution for the bones fracture treatment is by using fixation implant that has similar characteristics with the human bones. Stainless Steel (SS) 316L is one of biomaterial that has been used as an implant material due to its corrosion resistance, excellent biocompatibility, and excellent mechanical properties. However, the bioactivity properties of the material are needed to improve by coating it with hydroxyapatite (HA). In this research, HA was coated to the surface of 316L SS by using investment casting technique. A slurry of HA was poured into the casting cavity surface prior to the metal casting process and then followed by sintering at temperatures of 850°C, 900°C, and 950°C. Characterization of HA coating layer on specimen surface was conducted by Optical Microscope, Scanning Electron Microscope (SEM), and Energy Dispersive X-Ray (EDX). The hardness of the samples was measured by Vickers Hardness Tester. The result of the experiment shows that the investment casting is successfully to coat the HA on the SS 316L surface. Pouring method produces HA layer with thickness (spongy and porous surface) in the range of 60 μm - 110 μm. The increasing of sintering temperature increases the hardness number of the surfaces, and affect the purity of HA, but it is not related to coating thickness. The optimum sintering temperature is obtained at 900°C which produces the best calcium and phosphate ratio. The investment casting method is found as a simple and non-expensive technique that can be used to coat HA powder to SS 316L that produces good properties and optimum crystallinity of HA that suitable for orthopaedic implant application.