Surface modification layer and mechanical properties of biomedical beta-type Ti-29Nb-13Ta-4.6Zr subjected to friction stir process

Abstract

This study investigated the effect of the friction stir process (FSP) on the mechanical properties and microstructure of biomedical beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), and Ti-6A1-4V ELI (Ti64), which is one of representative biomedical alpha/beta type titanium alloy used in practical applications. The surface layer of TNTZ subjected to FSP was composed of severely deformed and heat-affected zones with a large amount of precipitated fine alpha phases or relatively coarse beta phases. On the other hand the surface layer of Ti64 was comprises almost entirely of a heat-affected zone with relatively small acicular alpha and beta phases in the prior beta phase. Vickers hardness of TNTZ and Ti64 subjected to FSP showed the highest value at the very edge of the specimen surface and decreased significantly with increasing depth from the surface. The trend in the change of Young's modulus of TNTZ and Ti64 subjected to FSP was approximately the same as the change in the Vickers hardness. The tensile strength of TNTZ subjected to FSP increased bv around 100 MPa when compared to that of as-solutionized TNTZ. The elongation however showed a reverse trend. The change in the tensile properties of Ti64 subjected to FPS was small. ©2013 The Japan Institute of Metals and Materials.