Microstructure and mechanical properties of lightweight AlCrTiV_0.5Cu_x high-entropy alloys

High-entropy alloys (HEAs) are an emerging and rapidly developing family of alloys with appealing properties such as lightweight HEAs with excellent mechanical properties. In this study, to obtain lightweight HEAs with exceptional hardness, we prepared AlCrTiV_0.5Cu_x ( x =  0, 0.2, 0.4, 0.6, 0.8 and 1.0, denoted as Cu₀, Cu_0.2, Cu_0.4, Cu_0.6, Cu_0.8 and Cu_1.0 alloys, respectively) HEAs and analyzed their microstructure and hardness. The prepared HEAs demonstrated a body-centered cubic (BCC) phase with no Cu addition and BCC + face-centered cubic (FCC) + hexagonal close-packed (HCP) phases in the Cu_0.2 and Cu_0.4 alloys and FCC + HCP phases with continuous Cu addition. All HEAs exhibited a clear dendrite microstructure, and the dendrites were refined with Cu addition. The hardness significantly increased with the addition of small amounts of Cu (Cu_0.2), but gradually decreased with continuous Cu addition. Cu_0.2 HEA was the hardest with a specific hardness (hardness/density) of 0.1628 HV·m³·kg⁻¹, which is significantly higher than those of conventional metallic materials. AlCrTiV_0.5Cu_x HEAs have similar wear resistance properties with H₁₃ die steel; therefore, they can be employed as promising lightweight high hardness materials.