POST-COATING TREATMENT EFFECTS ON THE PHYSICOMECHANICAL AND CORROSION RESISTANCE OF PLASMA-SPRAYED HYDROXYAPATITE (FSHA) ON TI-13NB-13ZR ALLOY FOR BIOMEDICAL APPLICATIONS
β titanium alloys are widely used in orthopaedic applications as an alternative to the high modulus α + β titanium alloys which leads to aseptic loosening of implants as a result of the mismatch of the modulus to that of human bone. Hydroxyapatite (HA) coating has been used to enhance the biological properties of Ti alloys. The present study determined the effect of heat treatment on the properties of plasma-sprayed low modulus Ti-13Nb-13Zr alloy using a natural and economical HA derived from fish scales (FsHA) and FsHA-doped yttria stabilized zirconia (YSZ). The microstructure was examined by SEM-EDS and the hardness was determined using Vickers hardness tester whereas the corrosion resistance was studied using potentiodynamic polarization method. The SEM micrograph of the as-coated FsHA revealed micro pores and cracks with partially melted and unmelted FsHA particles while the as-coated FsHA/YSZ samples developed denser coatings, lesser number of pores with increased number of melted FsHA particles, fine micro cracks and evenly dispersed ZrO2 particles. On the other hand, the post-coating treatment led to a much denser and finer lamellar morphology with more cracks as well as a significant increase in the microhardness as the heat-treated FsHA and FsHA/YSZ coatings had 514.7 and 566.9 Hv respectively, compared to their non-heat-treated values of 467.8 and 492.5 Hv. However, heat treatment recorded a slight increase in corrosion rate as the as-coated FsHA and FsHA/YSZ samples had 44.54 and 22.72 mmpy while their heat-treated counterparts recorded 83.7 and 73.88 mmpy respectively.