Surface and mechanical characterization of Ti-Nb-Zr foams for bio-medical application

Abstract

Conventional implant limitations in terms of stress shielding, aseptic loosening and presence of toxic elements is considered as major reason for revision surgery. Stress shielding is considered as primary reason for implant failure and revision surgery. As, the implant is placed in human body, its high modulus hinders the uniform distribution of stress on the bone and subsequently disturbs the bone formation cycle. This phenomenon is known as stress shielding effect. The cortical bone has an elastic modulus of 10-30 GPa, while the metals and its alloys have high elastic modulus than bone (Ti-6Al-4V, 114 GPa). The porous structure not only provide a viable solution to aseptic loosening by anchoring of bone in implant but also lower the elastic modulus, thus reducing the stress shielding effect. Open foam structures were produced in our research by using chemical dealloying method. Dealloying method was used due to its unique advantages such as reduced variables, process at ambient conditions, low cost over other foam producing techniques (powder sintering / micro-wave sintering / additive manufacturing etc.). Ti-13Nb-13Zr foam alloys were prepared by insertion of filler metal (Yttrium) in the base or master alloy using arc melting process, followed by its removal through chemical dealloying. Different characterization techniques such as SEM, XRD and EDS were performed to understand the microstructure, crystal structure and elemental distribution before and after dealloying. SEM results revealed the development of porous structure. XRD results revealed the absence of yttrium phases after dealloying. EDS results revealed the elemental distribution of yttrium and its subsequent removal after dealloying. Mechanical testing was done to evaluate the effect of development of foam structure on the elastic modulus of our foam samples. Micro-Vickers hardness testing was also performed on our foam samples. Corrosion, wear testing and contact angle measurement were also done to understand the effect of introduction of porosity on developed foams behavior.