An investigation on high-temperature properties of a lightweight AlNbTiV2 refractory high-entropy alloy reinforced by Si

Abstract

A series of novel AlNbTiV₂Si_x (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) refractory high-entropy alloys were fabricated by vacuum arc melting. The effects of Si content on the crystal structure, microstructure and high-temperature mechanical properties of the alloys were systematically investigated, and the mechanism of properties enhancement was analyzed in depth. The results showed that the addition of Si resulted in the formation of a hexagonal close-packed M₅Si₃-type silicide phase (M = Al, Nb, Ti, and V), transforming the alloy from a single BCC structure to a dual-phase structure of BCC + M₅Si₃, and increasing the volume fraction of M₅Si₃ phase to 23.1 %. Furthermore, an increase in Si content is beneficial to reduce the density of the alloy. When the Si content reaches 0.5, the alloy density decreases by about 7.0 %. The results of high-temperature compression tests show that the yield strength of AlNbTiV₂Si_x alloys has increased by nearly 70 % at 873 K, and AlNbTiV₂Si_0.5 alloy has the highest yield strength at 1073 K, reaching 1154 MPa. The mechanism of properties enhancement is attributed to the second phase strengthening. When the temperature continues to increase to 1273 K, the strengthening effect of silicides becomes weaker, and the yield strength of AlNbTiV₂Si_x alloys is not significantly different, all around 200 MPa, indicating the dominant role of solid solution strengthening. In addition, the solidification path of AlNbTiV₂Si_x alloys was analyzed and discussed. Our current work contributes to the design of new high-performance lightweight alloys with controllable structure, and provides a reference for future research, development, and production utilization.