Continuous cooling transformation (CCT) diagrams of β Ti-40Nb and TMZF alloys and influence of cooling rate on microstructure and elastic modulus

Abstract

Considering an increase in the interaction time between a patient and a metallic implant, new problems can emerge, such as stress shielding and fracture due to mechanical failure. Thus, metallic biomaterials that are used as implants need to be improved decreasing their elastic modulus as the mechanical biocompatibility between a bone and an implant can be improved and prevent the stress shielding phenomena. Therefore, β Ti alloys have gained ground over the last decades as both the β phase and the martensitic α″ phase can lead to a decrease in the elastic modulus. This research aimed to obtain experimental continuous cooling transformation (CCT) diagrams for metastable β Ti-12Mo-6Zr-2Fe (TMZF) and stable β Ti-40Nb (wt. %) alloys through dilatometry tests and differential scanning calorimetry (DSC) analysis. The microstructure characterization by optical (OM) and scanning electron microscopy (SEM), the elastic modulus, E (GPa) and the Vickers microhardness (HV) were analyzed under varied cooling rates from the β field, as well as rapidly solidified by copper mold casting. The results showed that the higher the cooling rate imposed, the lower the Vickers microhardness and elastic modulus values for both alloys, which were 56 GPa and 144 HV for Ti-40Nb and 74 GPa and 333 HV for the best condition (rapid solidified).