| Titanium and titanium alloys have been widely used in biomedical implant materials due to their excellent properties.Selective laser melting(SLM)is a near-net-shape stereo printing technology,which can significantly improve the production efficiency and reduce the cost of biomedical implant parts.The directional solidification characteristics of SLM technology will make the material form obvious anisotropy,and there are few studies on the causes of biological performance differences and their effects on service.In this paper,Ti6Al4 VE medical metal material prepared by SLM is taken as the object(SLM-Ti6Al4VE).The effects of building direction and heat treatment on the mechanical properties,corrosion resistance,friction properties and biological coating were studied.The results show that the SLM-Ti6Al4 VE alloy is mainly composed of α/α’ phase and a small amount of β phase.The diffraction peak intensity and distribution of the constituent phases are significantly different due to the different building directions.Heat treatment significantly reduces the mechanical properties of the alloy,but improves its plastic deformation ability.The strength of the same heat-treated alloy perpendicular to the forming direction(X direction)is higher than that parallel to the forming direction(Z direction),while the plasticity is opposite.Through the Schmidt factor(SF)analysis of the α phase texture and each slip system of the alloy,it is determined that the prismatic <α> is the main way of tensile deformation of the alloy,and the activation of the basal <α> slip system is the main reason for the mechanical anisotropy of the alloy.The number of basal <α> slip systems that can be activated is lower than that in the Z direction when the tensile force is loaded along the X direction.The deformation resistance of the alloy increases and exhibits higher strength.The rise in heat-treated temperature reduces the corrosion resistance of the SLM-Ti6Al4 VE alloy in Hanks solution,which is primarily brought on by the growth in grain size.The corrosion resistance of the alloy with lower heat-treated temperature perpendicular to the building direction(XY plane)is slightly lower than that parallel to the building direction(XZ plane),and the corrosion anisotropy of the alloy with higher heat-treated temperature becomes not obvious.The dynamic corrosion resistance of the alloy also decreases with the increase of heat-treated temperature,showing obvious isotropy.With an increase in annealing temperature,The alloy’s friction characteristics initially decrease and then increase with an increase in heat-treated temperature.The wear resistance of the alloy heat treated at 900°C is the worst with the largest wear loss.The wear mechanism is mainly adhesion wear and oxidation wear,whereas the other samples exhibit both abrasive wear and adhesive wear.The micro-arc oxidation(MAO)coatings of SLM-Ti6Al4 VE alloy(pore size,film thickness,roughness and Ca,P content,etc.)are significantly affected by the heat-treated temperature,while the building direction has no regular effect on the MAO coatings.It is found that the microstructure of different heat-treated alloys is the main reason for the difference of MAO coating properties.The passive film with lots of flaws was apt to form at the initial MAO stage due to the fine acicular α’ and lamellar αphases in the SLM-formed Ti6Al4 VE alloy.These flaws would be beneficial to the formation and growth of the MAO coating.The formation process of MAO coating composed of lath α phase in the microstructure of matrix alloy is more stable.MAO-HT coatings exhibit outstanding ability of apatite induction capability,and the best alloy is heat treated by 800°C.The building direction has no obvious regular effect on the apatite induction ability of the coating. |
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