Structure and mechanical properties of near-eutectic refractory Al-Cr-Nb-Ti-Zr high entropy alloys

Abstract In this study, the structure and mechanical properties of the near-eutectic refractory Al 24 Cr 11 Nb 11 Ti 37 Zr 17 , Al 20 Cr 20 Nb 25 Ti 25 Zr 10 , and Al 28 Cr 15 Nb 15 Ti 20 Zr 22 (at.%) high entropy alloys were investigated. Both the Al 24 Cr 11 Nb 11 Ti 37 Zr 17 and Al 20 Cr 20 Nb 25 Ti 25 Zr 10 alloys had a hypoeutectic structure, while the Al 28 Cr 15 Nb 15 Ti 20 Zr 22 alloy had a hypereutectic one. The proeutectic phase in the Al 24 Cr 11 Nb 11 Ti 37 Zr 17 and Al 20 Cr 20 Nb 25 Ti 25 Zr 10 alloys was the ordered B2 phase and in the Al 28 Cr 15 Nb 15 Ti 20 Zr 22 alloy – the C14 Laves phase. In all three alloys, the eutectic regions possessed a fine lamellar structure composed of a mixture of the C14 Laves and B2 phases. The densities of the alloys were 5.20-5.89 g/cm 3 . The Al 24 Cr 11 Nb 11 Ti 37 Zr 17 and Al 28 Cr 15 Nb 15 Ti 20 Zr 22 alloys were extremely brittle at 22°C, while the Al 20 Cr 20 Nb 25 Ti 25 Zr 10 alloy showed some ductility (ε = 0.7%) and high yield strength of 1830 MPa. At 800°C, all alloys became ductile. The highest yield strength (1010 MPa) was demonstrated by the Al 20 Cr 20 Nb 25 Ti 25 Zr 10 alloy and the lowest one (235 MPa) – by the Al 24 Cr 11 Nb 11 Ti 37 Zr 17 alloy. The comparison between the experimental as-solidified structures and the CALPHAD predictions was made.