Hydroxyapatite coating on 316L stainless steel by dip coating method

Hydroxyapatite (HA) coating on 316L Stainless steel with different amounts of polyvinyl alcohol (PVA) additive and different sintering temperatures were fabricated by using dip coating method. Hydroxyapatite was inosculated with polyvinyl alcohol which was used as surfactant and binder in the composition to obtain adherent, uniform and crack free coatings. The compositions of PVA to deionized water in the mixture are 5 %, 7.5 % and 10 % wt. and the HA amount in the compositions are kept stable at 15 %. The films were subjected to heat treatment at temperatures 500 ºC, 700 ºC and 800 ºC in an atmospheric oven. In the second step, the coated samples were subjected to heat treatment at 800 ºC, 900 ºC and 1000 ºC under vacuum to increase the bonding between the substrate and the HA and to enhance corrosion resistance. The composition of hydroxyapatite slurry and the sintering temperature both affected the morphology of the coatings. Stereo microscope and scanning electron microscopy (SEM) were used to characterize the surface morphology of the coatings. The open porosity and pore connectivity were enhanced with PVA additive in the vacuum furnace. Also, it was observed that at 1000 ºC sintering temperature, films start to peel off from the substrate due to the mismatch of the thermal expansion coefficient of the metal substrates and the HA.