Microstructure And Properties Of Biocompatible Titanium Alloys By Powder-bed Electron Beam Additive Manufacturing

In order to solve the main problems of biomedical titanium alloy orthopedic implants by additive manufacturing technology,this study focused on the compressive behaviors of the porous titanium alloys with different pore structure and microstructure firstly.Meanwhile,to fabricate the low modulus,high strength(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)100_-xSi_x alloy implants by SEBM technology is proposed for orthopedic application.The fabrication of spherical titanium alloy powders,SEBM process parameters and the characteristics of ? titanium alloys were studied systematically,which provided a new method for the preparation of personalized orthopedic implants.For the first time,?-annealing was introduced to improve the compressive ductility of Ti-6A1-4V lattice structure fabricated by powder-bed additive manufacture technology.The results indicated that when the compressive strain exceeds 50%,no local fracture is found in the sample after heat treatment at 1050? for 2h.The reason for the transformation in the compression deformation behavior of Ti-6A1-4V lattice structure,were mainly due to the Widmanstatten structure and bamboo-like grains,with superior the fracture toughness compared with the as-built samplesThe spherical(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)100_-xSi_x alloy powders were fabricated by plasma rotating electrode atomization process on the basis of fully understanding the atomization mechanism.And then,the bulk samples of the(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)100_-xSi_x alloys were fabricated by SEBM system with high relative density,and the SEBM processing windows were identified.The microstructure of the?T169.71Nb23.72Zr4.83Ta1.74?100_-xSi_x alloy were sensitive to the fabricated methods.In the as-built condition,the microstructure of TNZT is composed of columnar? grains with a width of about 35 ?m and a small amount of nano-scale ? phase,and its microstructure evolution law is L????+?.And a small amount of nano-scale?Ti,Zr?2Si particles?S2 phase?are precipitated at the grain boundary of(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)99Si alloy.The size of columnar ? grains is about 13 ?m,and the microstructure evolution law is L?L+???+S1+???+S2+?.A titanium matrix composite reinforced with S2 phase particles is formed during the SEBM processing for the(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)95Si5 alloy.The volume fraction of the reinforced S2 phase was 8.38%,the average size was about 270 nm,and it was continuously distributed at the grain boundaries.In addition,the increase of silicon content significantly reduces the preferred orientation of ? grains in?T169.71Nb23.72Zr4.83Ta1.74?100_-xSi_x alloyThen,it was found that the Ti_69.71Nb_23.72Zr_4.83Ta_1.74 alloy was strengthen by the addition of Si on the condition of low elastic modulus.Specifically,(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)95Si5 alloy shows the highest compressive strength?908MPa?and higher compressive strain?29.63%?,closed to the Ti-6A1-4V alloy.The elastic modulus of the Ti_69.71Nb_23.72Zr_4.83Ta_1.74 and(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)99S1 alloys was 63.59±2.35GPa and 65.93±3.18 GPa,and they also show excellent plastic deformation ability.It was concluded that the strengthening effect of silicon on(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)100_-xSi_x mainly comes from the improvement of the yield strength of the material due to the alloy graining.For(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)95S15 alloy,the mechanical properties are depending on the size and distribution of the reinforced S2 phase.After annealing at 1100? for 2h,the(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)95Si5 alloy shows the best combination of strength?853.94MPa?,elastic modulus?81.28GPa?and ductility?51.44%?.Forth,the SEBM-ed(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)100_-xSi_x represent excellent corrosion resistance compared to Ti-6A1-4V alloy in 37 ? SBF solution.Specifically,the(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)95Si5 alloy has the lowest corrosion tendency,its self-corrosion potential is-0.22 V,the corrosion current density is 1.32 ?A/cm2.It was also found that the suitable addition of Si is beneficial for the wear resistance of(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)100_-xSi_x alloys.The wear rate reached the lowest value with 1 at%Si addition,and the wear rate is 2.24 mm3·N-1·mm-1.The order of wear resistance of these biomedical titanium alloys is:(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)99Si>(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)95Si5>Ti_69.71Nb_23.72Zr_4.83Ta_1.74>Ti-6A1-4V,when paired with the GCr15 steel ball in the SBF solution.Finally,the(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)100_-xSi_x lattice structures were fabricated by SEBM technology.The results indicated that Ti_69.71Nb_23.72Zr_4.83Ta_1.74 lattice structures show the highest compressive ductility,and no local fracture was found when the compressive strain exceeds 50%.The strength and modulus of(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)100_-xSi_x lattice structure increased with the increased of the Si content,and the mechanical properties of(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)₉₅Si₅ lattice were comparable to Ti-6A1-4V lattice structures.Different from the bulk(Ti_69.71Nb_23.72Zr_4.83Ta_1.74)₉₅Si₅ alloy,the changes in the morphology and distribution of the silicide particles by substrate heat treatment have little influence on the compressive strain due to the small volume fraction of the reinforcing phase particles.