Study Of Fabrication And Properties Of HA Of The Ti Alloyed Layer On The Surface Of NiTi Alloy

NiTi alloys have been widely used in biomedical fields,such as hard tissue substitutes,orthopedic materials and cardiovascular scaffolds,due to their unique shape memory effect,super-elasticity and high damping capacity.However,concern should be raised in the implantation of nickel-containing materials,as the presence of nickel element and nickel-rich compounds on the surface of NiTi alloys provides a source of potential release of Ni ions,leading to the risk of allergic and adverse reactions to the human system.In addition,excessive corrosion on the surface of the implant enhanced the release of nickel ions.Moreover,as a bone substitute material,NiTi alloy cannot be directly combined with human bone and has poor biological activity.Therefore,it is very important to improve the corrosion resistance and biological activity of NiTi alloy.Hydroxyapatite(HA)is the main inorganic component of human bones,which has good biocompatibility and osteogenesis.NiTi alloy coated with a layer of hydroxyapatite does not change the excellent mechanical properties of titanium and nickel,and has excellent bioactivity and biocompatibility of HA.In this paper,the effects of the electrical parameters of micro-arc oxidation(voltage,frequency,time)and the concentration of Al₂O₃additive on the corrosion resistance of micro-arc oxidation ceramic coating were studied,and the optimal micro-arc oxidation experiment scheme was determined.Oxidation coatings containing HA were prepared on NiTi alloy surface by the combination of double glow plasma surface alloying technology,micro-arc oxidation and hydrothermal synthesis,then using the double glow plasma surface alloying technology and micro-arc oxidation,hydrothermal synthesis technology in the combination of NiTi alloy surface preparation of the oxide film containing HA,the microstructure,composition and morphology of alloyed layers were studied by means of SEM,EDS and XRD.And the electrochemical workstation was used to study the corrosion resistance of the oxide coating,the contact Angle measuring instrument was used to study the wettability of the oxide coating,and the oxide film immersion experiment was carried out to study the surface morphology,phase structure and quality changes of the sample after immersion.The main research results are as follows:(1)When the micro-arc oxidation voltage is 260 V,the frequency is 500 Hz,the time is 30min,and the concentration of Al₂O₃additive is 6 g/L,the corrosion resistance of the ceramic coating was the best.After hydrothermal treatment(180?,8 h),the surface of the oxide film changed from rough and porous to relatively smooth and low porosity,and the corrosion resistance was also improved.(2)The Ti permeated alloy layer was uniform and dense,and the composition wass gradient distribution.After Ti infiltration,the surface hardness was increased from 380 HV_0.1to 1033 HV_0.1.Using the alloy layer Ti as the precursor,the samples of PSA-MAO,PSA-MAO-HS,PSA-MAO-Al-HS,and PSA-MAO-Al-HS were prepared.The surface of PSA-MAO sample is rough and porous,and the surface of PSA-MAO-HS sample and PSA-MAO-Al-HS sample was very flat and had no pores.Among them,smaller HA aggregates were generated on the surface of PSA-MAO-HS sample,and the surface of PSA-MAO-Al-MAO sample was covered by a large amount of needle-like and columnar HA.XRD results showed that HA was not generated in PSA-MAO samples,and HA was generated on the surface of both PSA-MAO-HS and PSA-MAO-Al-HS samples.(3)The results of electrochemical corrosion measurement show that the corrosion resistance of the treated samples is improved to different degrees than that of the substrate,and the corrosion resistance of the PSA-MAO-Al-HS sample is the best.The contact angle measurement results show that the wettability of PSA-MAO-Al-HS sample is the best.(4)The results showed that the morphology of different samples was different after soaking.Through comparison,it was found that the surface of PSA-MAO-Al-HS samples was completely covered by HA after soaking,and the bioactivity was the best.XRD results showed that the diffraction peak of HA in PSA-MAO-Al-HS samples increased after soaking,indicating that the crystallinity of HA increased,which was conducive to long-term implantation.With the prolonging of soaking time,the quality of the samples increased firstly and then decreased.