Influence of Hafnium Addition on the Microstructure, Microhardness and Corrosion Resistance of Ti(20)Ta(20)Nb(20)(ZrMo)(20−x)Hf(x) (where x = 0, 5, 10, 15 and 20 at.%) High Entropy Alloys

The presented work aimed to investigate the influence of the hafnium/(zirconium and molybdenum) ratio on the microstructure, microhardness and corrosion resistance of Ti(20)Ta(20)Nb(20)(ZrMo)(20−x)Hf(x) (where x = 0, 5, 10, 15 and 20 at.%) high entropy alloys in an as-cast state produced from elemental powder and obtained via the vacuum arc melting technique. All studied alloys contained only biocompatible elements and were chosen based on the thermodynamical calculations of phase formation predictions after solidification. Thermodynamical calculations predicted the presence of multi-phase, body-centered cubic phases, which were confirmed using X-ray diffraction and scanning electron microscopy. Segregation of alloying elements was recorded using elemental distribution maps. A decrease in microhardness with an increase in hafnium content in the studied alloys was revealed (512–482 HV1). The electrochemical measurements showed that the studied alloys exhibited a high corrosion resistance in a simulated body fluid environment (breakdown potential 4.60–5.50 V vs. SCE).