A lightweight intermetallic Al-Cr-Ti medium-entropy alloy with good mechanical properties and oxidation resistance

Structure, mechanical properties, and oxidation behaviour of a Al55Cr23Ti22 (in at%) lightweight (ρ = 3.92 g/cm3) medium-entropy intermetallic alloy were studied. The initial as-cast structure consisted of an (Al, Ti)-rich L12 matrix and Cr-rich C11b lamellae with semi-coherent interfaces due to a (111)L12 || (110)C11b, [11̅0]L12 || [33̅1̅]C11b orientation relationship. The alloy demonstrated a combination of good plasticity (17–19%) and strength (600–610 MPa) both at 22 and 600 ℃; the latter gradually decreased to 155 MPa at 1000 ℃, while plastic strain exceeded 40%. Deformation at 600 and 800 ℃ led to the precipitation of (semi-) coherent C11b_1 and Al2Ti particles inside the L12 matrix and C11b phase, respectively, due to elemental redistributions within the initial phases and low lattice mismatch with a matrix. The alloy gained only 0.27 mg/cm2 after oxidation in the air at 1000 ℃ for 100 h thanks to an early formation of a protective Al2O3 layer. Compared to the current state-of-art lightweight and Al/Cr-containing refractory high/medium-entropy alloys, the Al55Cr23Ti22 alloy had a higher 1000 ℃-specific strength, room-temperature plastic strain, and demonstrated the best oxidation resistance. The obtained results suggest that the multicomponent L12-based trialuminides can be used as structural materials for potential high-temperature applications.