Corrosion Resistance Of Cu-Zn-Al SMA And TAMZ Alloy In Simulated Body Fluids And Preparation Of HAP Coating By Sacrificial Anode Method

The application of biomedical metals exerts huge effect on promoting living quality of human beings. However, when being implanted into body, metals would be corroded inevitably resulting from the influence of body fluid, which will decrease the mechanical properties of metals, even result in implantation failure. And the metal ions dissolved into body fluid have some side effect on the surrounding tissue, even leading to pathological changes or carcinomatous alteration. Hence, studies on corrosion resistance of biomedical metals have important practical sense in guaranteeing their safe application.Owing to good bioactivity and biocompatibility, hydroxyapatite (HAP) has attracted much interest of researchers. The materials that combine advantages of metals and HAP is a promising biomaterial. The preparation method of HAP coating at low temperature attracts many attentions of researchers.In this article, corrosion behavior of Cu-Zn-Al SMA and TAMZ Ti alloy (TAMZ) was investigated. And sacrificial anode method was applied to prepare bioactive HAP coating on TAMZ. The results were as follows:1) Corrosion rates of Cu and Cu-Zn-Al SMA in pH 7.2 simulated uterine fluid were 66.42, 7.21μ g/d, respectively. The electrochemical reaction was mainly controlled by cathodic reduction of oxygen.2) Cu-Zn-Al SMA occurred pitting corrosion in simulated uterine fluid. The critical pitting potential in pH 7.2 simulated uterine fluid was 1.70 V(SCE). And the dynamic equation of pitting development was i₀ = 465.68 t^-0.5 + 1.5.3) The corrosion model of Cu-Zn-Al SMA in simulated body fluids was proposed based on the analysis of Cu-Zn-Al SMA corrosion morphology in saline solution. The outmost layerwas salt of zinc and aluminum. Next was the deposition Cu layer, then was the selective dissolution layer..4) The inhibitive film was formed on the surface of Cu-Zn-Al SMA by Ni-P electroless plating and BTA passivation method, which improved electrochemical stability of Cu-Zn-Al SMA. Ni-P electroless plated method could produce amorphous layer. Complexes of Cu( I )— BTA and Cu(II)—BTA were formed on the surface of Cu-Zn-Al SMA by BTA passivation method.5) The results of corrosion potential and polarization curves showed that TAMZ possessed the best electrochemical stability. TAMZ had the P phase structure, which possessed the best thermal dynamic stability and electrochemical stability.6) HAP coating could be prepared on TAMZ by the single chamber and dual chambers method successfully. The sacrificial method had the characteristic of easy operation, economic and good repetition, with a promising future.7) The mechanism of the dual chambers method was in accordance with electro deposition method. A CaHPO₄ ? 2 H₂O layer was formed on the metallic substrate firstly, than this layer transformed into HAP through a steam treatment. The mechanism of the single chamber method was controlled by temperature. When the temperature for preparation of initial coating was 20℃, 40℃ and 60℃, the mechanism was the same as electro deposition method. At 80℃, a calcium deficient hydroxyapatite (CDHA) was formed firstly, then it transformed into HAP through a hydrothermal treatment.