Microstructure and mechanical properties of bimodal Ti-Bi alloys fabricated by mechanical alloying and spark plasma sintering for biomedical applications

In this study, the bimodal Ti-xBi (x = 0, 0.5, 1, 3 and 5 at.%) alloys were fabricated using mechanical alloying (MA) and spark plasma sintering (SPS) from elemental powders. The microstructure evolution of mechanical alloyed (MAed) powders as well as the effect of Bi content on microstructure and mechanical properties of Ti-Bi alloys are investigated. The Ti-Bi alloys showed bimodal structure consisting coarse grains (CG) region in "core" and ultrafine grains (UFG) region in "shell". The Ti-Bi matrix was alpha-Ti with hexagonal close-packed (HCP) structure while Bi-riched phase was identified as beta-Ti with body-centered cubic (BCC) structure. The mechanical properties showed that the as-built bimodal alloys had high strength and large plastic deformation. The Ti-Bi alloys showed similar to 22%-44% higher compressive yield strength compared with commercially pure Ti (CP-Ti) alloy for same the ball-milling time, and strengthening mechanisms are mainly ascribed to grain boundary strengthening and solid solution strengthening. When Bi content was 0.5%, the alloy exhibited excellent comprehensive mechanical properties with high compressive strength (compressive yield strength of -1080 MPa, ultimate compressive strength of similar to 2226 MPa) and excellent ductility (fracture strain of similar to 34.3%).