Effect of Cr on Microstructure and Properties of a Series of AlTiCr x FeCoNiCu High-Entropy Alloys

A series of AlTiCr (x) FeCoNiCu (x: molar ratio, x = 0.5, 1.0, 1.5, 2.0, 2.5) high-entropy alloys (HEAs) were prepared by vacuum arc furnace. These alloys consist of alpha-phase, beta-phase, and gamma-phase. These phases are solid solutions. The structure of alpha-phase and gamma-phase is face-centered cubic structure and that of beta-phase is body-centered cubic (BCC) structure. There are four typical cast organizations in these alloys such as petal organization (alpha-phase), chrysanthemum organization (alpha-phase + beta-phase), dendrite (beta-phase), and inter-dendrite (gamma-phase). The solidification mode of these alloys is affected by Chromium. If gamma-phase is not considered, AlTiCr0.5FeCoNiCu and AlTiCrFeCoNiCu belong to hypoeutectic alloys; AlTiCr1.5FeCoNiCu, AlTiCr2.0FeCoNiCu, and AlTiCr2.5FeCoNiCu belong to hypereutectic alloys. The cast organizations of these alloys consist of pro-eutectic phase and eutectic structure (alpha + beta). Compact eutectic structure and a certain amount of fine beta-phase with uniform distribution are useful to improve the microhardness of the HEAs. More gamma-phase and the microstructure with similar volume ratio values of alpha-phase and beta-phase improve the compressive strength and toughness of these alloys. The compressive fracture of the series of AlTiCr (x) FeCoNiCu HEAs shows brittle characteristics, suggesting that these HEAs are brittle materials.