Second-phase-dependent grain refinement in Ti-25Nb-3Mo-3Zr-2Sn alloy and its enhanced osteoblast response

Ti-25Nb-3Mo-3Zr-2Sn (TLM) substrates, which consist of pure beta phase and duplex alpha + beta phases were achieved by different heat treatment. Different substrates with and without alpha phase were subjected to surface mechanical attrition treatment (SMAT) for 5 and 30 min, respectively. Investigated by transmission electron microscopy (TEM), it is found that the content and morphology of alpha phase in the TLM substrates play crucial roles in nanocrystallization of the alloy. During SMAT, the substrates composed of duplex alpha + beta phases are much easier to nanocrystallized than that composed of pure beta phase, and the duplex-phase substrate containing 35 vt% alpha needles is more inclined to grain refinement than those substrates containing 27 vt% alpha cobbles and 31 vt.% alpha needles. Accompanied with the nanocrystallization in the surface layers of the duplex-phase substrates, the stress induced alpha-to-beta phase transition occurs. In addition, employing hFOB1.19 cells, the behaviors of osteoblasts on the unSMATed and as-SMATed surfaces were evaluated by examining the morphology and viability of the cells. It shows that the SMAT-induced grain refinement in the surface layer of the alloy can significantly improve the osteoblast response. Our study lays the foundation for nanostructuring beta titanium alloys to be used as bio-medical implants. (C) 2013 Elsevier B.V. All rights reserved.