Microstructure And Bioloigical /Mechanical Properties Of Microarcal Ti6AL4V Alloy Coated By Microarc Oxidation

In this research, the surface nanocrystallization (N), shot-peening (S) and supersonic bombardment (SP) methods were used to prefabricate the micro-crater structure at different scales on the surface of Ti6Al4V alloy, then on the top layer of the pretreated alloy, microarc oxidation was adopted to fabricate the micro-pit setting porous bioceramic coatings (N-MAO, S-MAO, SP-MAO coating). The apatite induction ability of the various bioceramic coatings was evaluated by simulated body fluid (SBF) immersion test. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) and other methods were used to determine the microstructure of coatings before and after immersion in SBF, the coating samples after fatigue fracture and worn surface of the coatings, and further revealing the possible influencing mechanisms on biological activity, fatigue and tribological properties.The results show that the M-MAO, N-MAO, S-MAO, SP-MAO coatings prepared in Ca (H2PO4)2 + Ca (CH3COO)2 solution mainly consist of rutile and anatase TiO₂ phases, and a small amount of amorphous compounds containing Ca and P elements. The different system coatings with 10μm thickness have a slight increase content of rutile compared with the corresponding 5μm thick coating. In addition, with the coating thickness increasing from 5 to 10μm, M-MAO and N-MAO coatings surface roughness increase, and S-MAO and SP-MAO surface roughness decrease respectively.After immersed in SBF for 8 weeks, the obvious apatite crystal products deposit on the coatings surface, and by the observation of apatite deposition, ranking the apatite induction ability as SP-MAO>N-MAO>S-MAO>M-MAO. In addition, 5μm thick coatings exhibit a better induced ability than 10μm thick coatings, which is attributed to the poor activity with slightly higher rutile phase content in 10μm thick coatings. After NaOH alkali heat treatment, the different types coatings show an significant improvement of apatite induction capacity , which is attributed to the introduced Ti-OH functional groups by the alkali heat treatment, to significantly promote the nucleation and growth of apatite. Comparatively, the rougher S-MAO and SP-MAO coatings with larger surface area have the more strong induction ability. The microarc oxidation coatings reduce the fatigue life of Ti6Al4V alloy, the coated Ti6Al4V specimens with 5μm and 10μm thick coating decrease the corresponding fatigue life by about 12% and 30% compared with the uncoated substrate, respectively. The pretreatments of surface nanocrystallization (N), shotpeening (S) and supersonic bombardment (SP) can improve the fatigue life of coated specimens.The wear resistance of coatings with 10μm thick is better than 5μm thick coating. SP-MAO5, SP-MAO10 and N-MAO10 coatings performance the best wear resistance. Applications of various coatings enable the corrosion potential of Ti6Al4V to shift positive direction, thus improving the chemical stability and having good corrosion resistance in SBF.