Design and characterization of eutectic refractory high entropy alloys

Eutectic alloys are natural in-situ composites with near-equilibrium structures, impressive strength-ductility trade-off, and perfect castability. In the current study, novel eutectic Al-Cr-Nb-Ti-Zr refractory high entropy (RHEAs) were designed using a CALPHAD (CALculation of PHAse Diagrams) approach. A starting Nb30Ti40Zr30 (at.%) alloy was based on single-phase bcc solid solution. Alloying Cr Al induced formation hypoeutectic (Cr20Nb30Ti40Zr10, Al15Cr20Nb15Ti40Zr10, Al23Cr20Nb15Ti32Zr10), (Al28Cr20Nb15Ti27Zr10), hypereutectic (Al33Cr20Nb15Ti22Zr10) structures due to Laves phase precipitation. additions also resulted in B2 ordering changing polytype from C15 (fcc) C14 (hcp). transfer microstructure, connected amount's growth, increased alloys' compressive strength brittle-to-ductile transition temperature pronouncedly. Quantitative relationships between phase's volume fraction yield at different temperatures established. Detailed analysis after plastic deformation 800 °C demonstrated stability lamellar B2/C14 microstructure saving an initial orientation relationship (OR) (011)B2||(101¯3)C14, [11¯1]B2||[33¯01¯]C14 ensuring small lattice mismatch. The precipitation new D019 structure having (011)B2||(101¯3)C14||(02¯21)D019 OR revealed. obtained findings demonstrate approaches design RHEAs (nearly) promising balance mechanical characteristics.