| Selective laser melting(SLM)has been developed rapidly in recent years as a kind of additive manufacturing technology.Compared with the traditional molding technology,SLM molding technology shows tremendous advantages especially in the field of medical applications.It can realize the personalized customization of medical titanium alloy implants and the control of their mechanical properties.However,the biocompatibility of titanium alloy formed by SLM is similar to that of ordinary titanium alloy,which can not be used directly in biological implant materials,and must be modified on the surface.Therefore,the micro-arc oxidation technology is applied to the titanium alloy formed by SLM,which provides the necessary theoretical support for the further application of SLM molding personalized titanium alloy implants in the medical field.The main research contents and conclusions of this thesis are as follows:(1)The TC4 alloy was formed by reciprocating process scanning technology and its forming characteristics were investigated.Through the reciprocating scanning in the small area,the energy loss of the molten pool can be reduced,and the maintenance ability of the molten pool is strong.The quality and efficiency of the molding specimen can be effectively improved.TC4 alloy formed by SLM was mainly made up of acicular ?' martensite and epitaxial growth of ? columnar crystals.It showed that the TC4 alloy formed by SLM is slightly better than the ordinary forging TC4 alloy after testing of the corrosion resistance and bioactivity.(2)The effects of different electrolyte,pulse current density,pulse frequency,pulse duty ratio and oxidation time on micro-arc oxidation of TC4 alloy formed by SLM were systematically investigated.And the current density of 9-11 A/dm2,pulse frequency of 500-750 Hz,pulse duty ratio of 20%-30%and oxidation time of 10-15 min were found to be the optimum parameters.(3)The difference of micro-arc oxidation film between TC4 alloy formed by SLM and general forging was studied in terms of voltage time change,surface morphology,element,thickness and phase structure.It showed that acicular ?' martensite produced in the forming process of SLM could produce more discharge channels as well as accelerating the chemical reaction and element diffusion during the micro-arc oxidation process.So the surface voids of the film increased in number but decreased in size.Simultaneously,the active elements entering the film would slightly increased.(4)The corrosion resistance and bioactivity of TC4 alloy formed by SLM after micro-arc oxidation were studied systeamatically.With the increase of oxidation time,the corrosion resistance of the sample first rised and then fell under the bionic environment.Compared with the original SLM TC4 alloy,the corrosion potential of the sample was higher,and the corrosion current density decreased by almost one order of magnitude after micro-arc oxidation.It showed that the corrosion resistance of the sample could be enhanced by micro-arc oxidation effectively.The surface of micro-arc oxidation coating on TC4 alloy formed by SLM showed smaller voids,which could effectively inhibit and prevent the penetration of biomimetic solution into the matrix with better corrosion resistance.After the immersed for 10 days,the amount of hydroxyapatite deposited by micro arc oxidation of TC4 alloy formed by SLM was higher than that of untreated sample and conventional forging TC4 alloy,and the Ca/P ratio of the deposited layer was close to the theoretical ratio of hydroxyapatite(1.67). |
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