Microstructure of equiatomic and non-equiatomic Ti-Nb-Ta-Zr-Mo high-entropy alloys for metallic biomaterials

The microstructures of equiatomic TiNbTaZrMo (Ti20Nb20Ta20Zr20Mo20—subscript numerals denote at.%) and non-equiatomic Ti2.6NbTaZrMo (Ti39.4Nb15.2Ta15.2Zr15.2Mo15.2) high-entropy alloys (HEAs) were investigated for use in metallic biomaterials, and discussed based on their thermodynamics. Equiaxial dendrite structures were observed in the as-cast specimens. Ta, Nb, and Mo were abundant in the main dendrite phase with a body centered cubic (bcc) structure, while Ti and Zr showed a tendency to be abundant in the inter-dendrite region with a bcc structure. The distribution of the constituent elements can be explained through the distribution coefficients during solidification estimated using thermodynamic calculations. The thermodynamic calculations focusing on the solidification process were effective not only for the evaluation of the solidification microstructure, but also for the design of Ti-Nb-Ta-Zr-Mo-based HEAs. The non-equiatomic Ti2.6NbTaZrMo HEA (Ti39.4Nb15.2Ta15.2Zr15.2Mo15.2) was designed based on thermodynamic calculations and the solidification microstructure was studied. [Display omitted] •Microstructures of Ti-Nb-Ta-Zr-Mo biometallic high-entropy alloys were examined.•Equiaxial dendrite structures were observed in the as-cast specimens.•Ta, Nb, and Mo were abundant in the dendrite phase with a bcc structure.•The elemental distribution was in agreement with thermodynamic calculations.•Ti2.6NbTaZrMo high-entropy alloy was designed based on thermodynamic calculations.