Microstructure Evolution And Mechanical Properties Of ?-Type Ti-35Nb-2Ta-3Zr Alloys Prepared By 3D-Printing

Additive manufacturing(AM)has a substantial capability to produce superior and divergent properties of titanium alloys for biomedical implants,unlike the existing conventional technologies.With this notion in mind,we investigated the mechanical properties and microstructure evolution of ?-type Ti-35Nb-2Ta-3Zr alloys by using selective laser sintering(SLS).The SLS-produced specimen shows length-wise scan track boundaries along with columnar grain structure.The Zigzag and V-shaped formation of {112}<111>? twins,coexisting with stress-induced ?-formation were observed by the transmission electron microscope.This alloy display Type I twin martensite along with ?-structure,which is attributed to superelastic and elastic recovery during deformation.Furthermore,atomic resolution,HRTEM observations was used to investigate the transition between ??? phases,formed at high concentration stress region due to the collapse of [11-1] atom planes.Thin layers of ?-formation in weak interfacial stress region along with the longitudinal twin boundaries are also analyzed.However,high concentration stress region exhibit twin-induced ?-formation along with both side of ?-matrix boundaries,which is formed by overlapping of ?-phase upon ?-twin.Furthermore,dislocation tangling and dislocation pile-ups were generated along with twin martensite,stress-induced ?-phase,and ?-phase.Recently,the porous structure of ?-type titanium alloys has significantly developed for implants due to their low Young's modulus,excellent superelasticity and shape memory effect.The complex shape porous structure by following the 3D-CAD model successfully prepared,using SLS-process,which is based on different porosity level(0.34%,0.41%,and 0.48% porosity).The maximum elastic recovery of the strain of porous specimens is ~18.1% at 0.48% porosity,acquired from cyclic loading-unloading tensile testing.Furthermore,Young's modulus at 0.48% porosity was ~3.1±0.3 GPa.The mechanical properties of porous-structure including different porosity level,influence in superelastic behavior,compressive strength and microstructure evolution of porous specimens.It is seen that the superelastic properties of the specimen are improved by increasing porosity.In addition,the porous specimen also shows columnar grain boundaries are adjacent along with scan track layers.Compared with Ti-6Al-4V and Ti-24Nb-4Zr-8Sn,?-type Ti-35Nb-2Ta-3Zr porous samples exhibit higher superelastic properties,better plastic deformation ability,and high compressive strength.