Effect Of Heat And Citric Acid Treatment On The Formation Of Ca-P Coating On NiTi Alloy Surface

In this work, calcium phosphates coating was successfully induced on NiTi alloysurface through biomimetic modification. Heat treatment was introduced into thepre-treatment process, and citric acid was added into SBF during the calcificationprocess. The focuses were especially on the effect of heat treatment and the content ofcitric acid on the formation mechanism of calcium phosphates in this article. Thefactors of Ca-P coating formation were theoretically illustrated. SEM,XRD,EIS wereemployed to investigate the morphology, composition of the as-received and thetreated NiTi surface. Direct tensile and…… micro-indentation tests were carried outto measure the bonding strength between the Ca-P coating and NiTi substrate.The results showed that hydrogel layer of porous network structures wereformed on the surface of NiTi specimens after acid and alkali treatment. It becamedenser after heat treatment, and the shape was minor rod-like. The chemicalcomposition mostly were sodium titanate, TiO2 (including rutile and anatase). Heattreatment could promote the formation of Ca-P coating. Uniform minor coating couldbeen got through heat treatment.The morphology of the coating became treelike from spherical crystal, includingsome hole with 1μm in it with the addition of citric acid. After calcification 3d in SBFwith 1mM citric acid, the integrity of Ca-P coating formed on the NiTi surface wasbetter than others, and the same to the uniformity. The crystal grain became smaller.The composition of the coating is composed of HA, Ca(H2PO4)2,Ca3(PO4)5,Ca3(PO4)2. The results of EIS, direct tensile and indentation tests revealed the goodproperties of the coating formed under the condition.