Effect of Phase Composition on Microstructure and Mechanical Properties of Biomedical Ti-15Nb-5Sn Alloy Prepared by Material Extrusion Additive Manufacturing

Abstract

In this study, a Ti-15Nb-5Sn (at.%) alloy was prepared by material extrusion additive manufacturing (MEAM) process for biomedical application. Elemental Ti, Nb, and Sn powders were blended with a thermoplastic polyurethane (TPU) binder in a ratio from 40 to 50 vol.%. The filament preparation and printing process parameters were then investigated and optimized. Considering the surface roughness and extrusion speed, the optimal extrusion temperature and printing temperature of the filament were selected to be 150 degrees C and 225 degrees C, respectively. After thermal debinding, microstructures of Ti-15Nb-5Sn specimens were characterized by the coexistence of alpha phase, beta phase, alpha '' martensite, and TiC. alpha phase remained even after solution treatment (ST) due to the high oxygen levels ranging from 1.17 wt.% to 1.66 wt.%. An elastic modulus of 0.2 and 0.4 GPa was achieved at room temperature in solution-treated 45 vol.% (ST45) and 50 vol.% (ST50) metal content specimens, respectively. These elastic moduli in ST45 and ST50 specimens were similar to that of cancellous bone, helping to avoid the stress shielding effect. The compressive strength and elongation of ST45 and ST50 specimens were 7.9 MPa and 16.6 MPa, 6.9% and 9.0%, respectively. The maximum recoverable strains in ST45 and ST50 specimens were measured to be 0.3% and 0.8%, respectively. A noticeable decrease in the XRD intensity of (110)beta peak and the appearance of (020)alpha '' XRD peak indicated that the mechanism of the recoverable strain is attributed to superelastic behavior. This study was the very first attempt to fabricate a superelastic Ti-based alloy using elemental powder by the MEAM process for biomedical applications.