Selective Laser Melting In-situ Fabrication Of Medical Ti-Nb Alloys: Process, Microstructure And Properties

Selective laser melting(SLM)is one of the most important additive manufacturing technologies.By melting fine metal powder through high-energy laser beam layer by layer,SLM can be utilized to directly manufacture near-dense complex parts.It is particularly suitable for the manufacture of human bone implants with a personalized shape and internal microporous structure.Titanium-niobium(Ti-Nb)alloy,a near-? titanium alloy,is considered to be ideal replacement material for human bone implant due to its high specific strength,low modulus,good corrosion resistance and excellent biocompatibility.In this paper,Ti-Nb mixed powders with different proportion were prepared by ball milling method from pure Ti and pure Nb powder.Ti-x Nb alloys(x = 0,15,25,45 at.%)were in-situ fabricated by SLM.The effect of Nb content on the phase transformation,microstructure evolution,mechanical properties,in vitro apatite-forming capability and corrosion resistance was systematically studied.The main conclusions are as follows:(1)The SLM process parameters of Ti-15 Nb alloy were optimized.The optimized process parameters are: laser power of 330 W,scan speed of 1000 m/s,layer thickness of 0.03 mm,hatch space of 0.10 mm.The microstructure of Ti-15 Nb alloy is composed of acicular ?' martensite and ? grains,and contains a few microcracks,micropores and unmelted Nb particles.High density and refined ? ' grain were obtained at optimized laser energy density(110 J/mm3),which effectively increase the microhardness to 261 ± 7 HV0.1.The microhardness of the SLM-processed Ti-15 Nb alloy is 11.83% higher than the cast one.(2)Based on the optimized laser process parameters,the influence of composition ratio on micro-macro performance was studied.The increase of Nb content results in the increase of ? phase amount but decrease of ? grain dimension.The former effect is due to the suppression of martensitic transformation and strengthening of solid solution behavior,while the latter phenomenon can be attributed to the increase of heterogeneous nucleation sites.Especially,the ? grain size of Ti-45 Nb alloy is lower than 1 ?m.Due to the comprehensive effect of grain strengthening and solid solution strengthening,Ti-45 Nb alloy exhibits superior strength of 1030 ± 40 MPa and microhardness of 356 ± 7 HV0.1,which is 97.32% and 52.53% higher than cast one,respectively.Simulated body fluid(SBF)immersion experiment and electrochemical corrosion experiment showed that Ti-Nb alloys exhibit better in vitro apatite-forming capability and corrosion resistance than pure Ti due to the existence of Nb element.The former is due to the fact that ?-phase have the ability to induce the formation of apatite,while the latter is caused by the increase of Nb2O5 content in passivation film.The above results indicate that under the appropriate process conditions and the ratio of material,SLM technology can be used to fabricate Ti-Nb alloy with excellent mechanical properties,in vitro biological activity and corrosion resistance to meet the basic performance requirements of bone implants.It lays a preliminary theoretical basis for the preparation of Ti-Nb alloys for human bone implants.