Structure And Properties Of TiTaZrMoNbx High Entropy Alloys For Biomedical Applications

There is a great demand for biomedical metal materials with excellent biological properties in medical health and related fields.However,some biomaterials like Ti-based alloys are facing great challenges caused by their own characteristic limits.Novel metallic biomaterials need to be developed to meet the urgent needs.Traditional alloys are mainly designed based on one or two main elements.As a class of new materials,the highentropy alloys(HEAs)have attracted great attentions in recent decades.Based on five or more metal elements in equal or near-equal atomic ratio,numerous HEAs with unique properties have been developed.If this novel composition design concept is applied to research and design HEAs with excellent biocompatibility,it will be of great benefit to the development of biomedical metallic materials.Based on the "cocktail effect" of HEAs,t this dissertation firstly focused on the study of the effect of the Nb addition on the structure of TiTaZrMoNbx HEAs.Following this line,the mechanical properties,corrosion resistance and wear resistance of Nb-doping HEAs were explored.The contents of this dissertation are listed as follows:(1)TiTaZrMoNbx HEAs consist of dual phases with BCC structures corresponding to the ZrTiNb phase and the NbTi phase.As the Nb content increases from x=0.25 to x=1.5,the structure of TiTaZrMoNbx HEAs changes from BCC1 phase to BCC2 phase,whereas the lattice constant of the NbTi phase decrease firstly and then increase slightly.SEM observations show that the TiTaZrMoNbx HEAs are typical dendrite structures.With increasing the atomic ratio of Nb,the interdendritic structures decrease gradually,while the grain size of the dendrite regions decrease first and then increases slightly.The mechanical test results indicate that,as the atomic ratio of Nb increases from 0.25 to 1.5,the hardness and compressive yield strength of the HEAs increase firstly and then decrease,whereas their plasticity decreases gradually.(2)The corrosion performances of TiTaZrMoNbx HEAs in 0.9%Na Cl are studied.As the Nb content increased,the corrosion resistance of the alloy increased firstly and then decreased slightly.The corrosion types of HEAs are pitting and intergranular corrosion.The alloy with x=0.50 possesses the highest corrosion potential and the smallest corrosion current density,suggesting the best corrosion resistance among the alloy system,together with pure Ti and Ti-6Al-4V.(3)The wear resistance of TiTaZrMoNbx HEAs is studied.TiTaZrMoNbx HEAs containing low-Nb content show better wear resistance.The HEA with x=0.50 has the lowest coefficient of friction and the lowest relative mass loss.Three-dimensional morphological observations show that the worn surface of x=0.5 alloy is the smoothest,implying the most excellent wear resistance.The above results suggest that the explored HEAs demonstrate promising biomedical applications.