Investigation of casted and annealed Ti6Al4V, Ti25Nb10Zr and Ti10Nb10Zr5Ta alloys as materials for orthopedic implants

M. AVALOS; A. VLADESCU; R. BOLMARO

La Falda, Córdoba

Congreso; 5to Congreso Argentino de Microscopía SAMIC; 2018

samic

Titanium-basedalloys offer a wide variety of properties required for materials used formedical applications, such as good corrosion resistance and biocompatibilityinside of human body and a good ductility for processing complex geometries asthose those required for medical replacements. In orthopedic applications,Ti6Al4V is commonly used. In last years, it was reported that this alloyconducted to cytotoxic reaction due to the Al and V elements, which are in theway of being replaced by other biocompatible alloys. Other problem of Ti6Al4Valloy is ?stress shielding? due to the difference between its elastic modules (~114 GPa) and that of human bone (max 30 GPa).Based on this conclusion, many efforts were directed to replace Ti6Al4V alloyby others with improved mechanical, anticorrosive, tribological and biologicalperformance such as Ti-Nb, Ti-Ta, Ti-Nb-Zr, etc..  The challenge is huge, because the mainconcern is to develop a novel biocompatible alloy with low elastic modulus (E) close to thatof human bone (E = 2?30 GPa). A survey on the literature showed that thealloys of system Ti-Nb-Zr are the right choice due to its E values, which canrange from 70 to 14 GPa (i.e. 14 GPa for Ti19NbZr; 54 GPa for Ti10Nb9Zr; 62 GPafor Ti13Nb13Zr or Ti34Nb25Zr or Ti5Nb9Zr; 50 GPa for Ti(18-20)Nb(5-6)Zr; 70 GPafor Ti16Nb10Zr). Consequently, the elastic modulus is sensitive to thecomposition and can be decreased by alloying with additional elements. In thismanner, the system of Ti-Nb-Zr-X, where X could be Ta, Mo, etc., has beeninvestigated. It was revealed that the reduction of E could be achieved bysuppressing the transformation of β phase into α¢ one at high temperatures. It is true thatadditional elements will decrease the E value, but the production cost willincrease the final cost of the implants. Thus, the best solution is to keep thenumber of alloying elements at a minimum and to find the best composition forthe proposed applications at a decent price. In the case of alloy, the conditionsof heat treatment such as type of treatment, aging temperatures, and coolingrate also play an important role in the final properties. Thus, our study aimsto investigate a few alloys as possible candidates for orthopedic implants. Inthe current presentation we show an initial characterization by EBSD of threealloys in two heat treatment states for understanding the complexity of the initialtasks. As cast materials show a large volume fraction of Alpha phase with aminor contribution of beta phase that tends to grow in a wave basket structureafter heat treatment.