Microstructure and Electrochemical Behaviors of Equiatomic TiMoVCrZr and Ti-rich TiMoVCrZr High-Entropy Alloys for Metallic Biomaterials

The present study investigated various thermodynamic parameters, microstructures and electrochemical behaviors of TiMoVCrZr and Ti-rich TiMoVCrZr high-entropy alloys (HEAs) prepared by vacuum arc remelting. The microstructures of the alloys were analyzed using X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM), and potentiodynamic polarization tests. The determined thermodynamic values of the Ω-parameter and the atomic size difference (δ) for the HEAs were determined to be in the range of Ω ≥ 1.1, and δ ≤ 6.6% with valance electron configuration (VEC) ≤ 5.0, suggesting the HEAs were effective at forming solid solutions. XRD patterns of the equiatomic Ti20 Mo20 V20 Cr20 Zr20 HEA revealed four phases consisting of the body centered cubic1 (BCC1 ), BCC2 , hexagonal close-packed (HCP), and intermetallic compound Cr2 Zr phases. Three phases were observed in the XRD patterns of Ti-rich Ti40 Mo15 V15 Cr15 Zr15 (BCC, HCP, and Cr2 Zr) and a single BCC phase was observed in Ti-rich Ti60 Mo10 V10 Cr10 Zr10 HEAs. The backscattered-electron (BSE) images on the equiatomic Ti20 Mo20 V20 Cr20 Zr20 HEA revealed BCC and HCP phases with Cr2 Zr precipitates, suggesting precipitation from the HCP solid solution during the cooling. The micro-segregation of Ti-rich Ti60 Mo10 V10 Cr10 Zr10 HEAs appeared to decrease remarkably. The alloying elements in the HEAs were locally present and no phase changes occurred even after additional HIP treatment. The lowest current density obtained in the polarization potential test of Ti-rich Ti40 Mo15 V15 Cr15 Zr15 HEA was 7.12×10-4 mA/cm2 was obtained. The studied TiMoVCrZr HEAs showed improved corrosion characteristics as compared to currently available joint replacement material such as ASTM F75 alloy