Microstructure, Phase Transformation, Mechanical Behavior, Bio-corrosion and Antibacterial Properties of Ti-Nb-xSn (x = 0, 0.25, 0.5 and 1.5) SMAs Mustafa K. Ibrahim, E. Hamzah, and Safaa N. Saud (Submitted January 20, 2018; in revised form August 26, 2018) Porous Ti-Nb-xSn shape memory alloys (SMAs) are fabricated by microwave sintering technology. The microstructures exhibit needle-like morphologies, b (N) (normal straight and crossed needles along with needle-like morphology that resembles spaghetti or irregular lines with a-phases in between) as well as plate-like morphologies [normal straight plate-like morphology, a¢¢ and dendritic plate-like morphology, b (D) ]. Increases in Sn addition significantly induce an increase in the density of the a-phase. XRD patterns exhibited three phases, namely the b-main phase with smaller intensities of a¢¢ and a. Further, the addition of 0.25% Sn led to more effective improvement in the intensity of the a¢¢-phase compared with 0.5% and 1.5% Sn addition. Additions of Sn also enhanced the fracture strength and its corresponding strain along with the shape memory effect (SME), where the best enhancement was achieved at 0.25% Sn. The corrosion rate (Ri) was reduced by rising Sn content, while both corrosion resistance and antibacterial zones were increased. The lower elastic modulus, as well as the robust mechanical properties and bioactivity, made these SMAs rather suitable for biomedical application purposes, where the low elastic modulus had value in terms of avoiding the problem of ‘‘stress shielding.’’ Keywords antibacterial effect, mechanical and corrosion behav- iors, microstructure, microwave sintering, porous Ti- Nb-xSn, shape memory alloys (SMAs) 1. Introduction Pure Ti and Ti alloys have been widely used as implanting materials and for clinical repair based on their excellent mechanical properties, superb corrosion resistance and bio- compatibility (Ref 1-6). At present, the elastic modulus of Co- Cr and Ti-6Al-4V is leveraged for orthopedic implant applica- tions, with greater than 100 GPa (Ref 7), while the elastic modulus of the bone is between 4 and 30 GPa depending on measurement direction and bone type (Ref 8, 9). This large difference between bone tissues and implant devices causes stress-shielding problems because of bone resorption (Ref 10), and as such, total hip arthroplasty is necessary based on the loosening of devices. To overcome the critical issue of stress shielding, Ti-Nb-based alloys for biomedical applications have recently attracted much attention, and many alloys with low elastic modulus as well as robust biocompatibility and high strength have been developed, e.g., Ti-33.6Nb-4Sn (Ref 11), Ti-29Nb-13Ta-4.6Zr (Ref 12), Ti-35Nb-5Ta-7Zr (Ref 13), and Ti-13Nb-13Zr (Ref 14). The existence of pores in titanium alloys reduces the elastic modulus (Ref 15-17) as well as allows for the implant cells to grow into the pores and integrate with the host tissue (Ref 17-19). It was reported by Yang et al. (Ref 16) that porous Ti-(10-35) wt.% Nb alloys were produced by powder metallurgy (PM) technology and featured low elastic modulus (YoungÕs modulus) of 6-15 GPa. Matsumoto et al. (Ref 20) reported that adding Sn to Ti-Nb alloys can enhance the strength of these alloys. It is evident the corrosion rate was reduced after adding Sn, Khalifa et al. (Ref 21) described the presence of Sn with the oxide layer of TiO 2 that improved the effect of this layer in an aggressive environment, enhanced corrosion resistance and diminished the Ri, while Ghoranneviss et al. (Ref 22) noted that pure Sn exhibits antibacterial properties. Ti-Nb-based alloys can be fabricated by PM through several methods, including conventional sintering (Ref 23, 24), metal-injection molding (Ref 25-27), self-propagating high- temperature synthesis (Ref 28), hot-isostatic pressing (Ref 29), spark-plasma sintering (Ref 23, 30, 31) and microwave sintering (MWS). The MWS technique is a relatively new method for preparing Ti-Nb alloys, and it is considered a novel sintering method for metals, composites, ceramics and semi- conductors (Ref 32-34). Overall, MWS has several advantages, such as an enhanced diffusion process, reduced energy and sintering-process time, rapid heating rates and improved mechanical and physical properties (Ref 32, 33). Therefore, the purpose of this study was to evaluate the impact of the amount of Sn on the microstructure characteristics, martensitic transformation, mechanical properties, bio-corrosion and antibacterial effects of Ti-Nb-xSn SMAs. The results are beneficial for the development of Ti-Nb-xSn SMAs for biomedical applications. Mustafa K. Ibrahim and E. Hamzah, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia (UTM), 81310 Johor Bahru, Johor, Malaysia; Safaa N. Saud, Faculty of Information Sciences and Engineering, Management and Science University, Shah Alam, Selangor, Malaysia. Contact e-mails: mustafakhaleel4@gmail.com and esah@fkm.utm.my. JMEPEG ÓASM International https://doi.org/10.1007/s11665-018-3776-x 1059-9495/$19.00 Journal of Materials Engineering and Performance