Abstract: Vacuum plasma sprayed Ti coatings were chemically treated with 5.0mol/L NaOH at 40℃ for 24h and immersed into two kinds of simulated physiological
solutions containing Ca²⁺, HPO^2-₄ ions. The surface morphologies and compositions of Ti coating before and after alkali treatment were examined by SEM
and AES respectively. The formation layers on the Ti coating after immersion in FCS and SBF were characterized by SEM, EDS, XRD and FT-IR. The changes of ion
concentration and pH value of FCS after immersion were measured by ICP-AES and pH meter. The results obtained indicate that the fibrous and net-like surface
structure forms on the surface of porous Ti coating by treatment of NaOH solution which consists of Na，Ti and O element with the atom ratio nearly equal to that
of Na₂TiO₃. After immersion in simulated physiological solutions, the treated Ti coating shows apatite-forming ability and the apatite formed in FCS is oriented crystallized,
plate-like HA with trace of OCP whereas the apatite precipitated in SBF is needle-like carbonate-containing hydroxyapatite. The bioactivity of the alkali treated Ti coatings
can be explained in terms of the formation of hydrated titanate which can induced apatite nucleation and growth in FCS and SBF.

Key words: plasma sprayed Ti coating, hydroxyaptite, bioactivity, NaOH treatment