Deformation Behavior of a High-Entropy Al–Co–Cr–Fe–Ni Alloy Fabricated by Means of Wire-Arc Additive Manufacturing

A nonequiatomic high-entropy alloy (HEA) of the Al–Co–Cr–Fe–Ni system has been obtained using a wire-arc additive manufacturing (WAAM) technique in an atmosphere of pure argon. The initial wire consists of three cores having different chemical composition: pure aluminum wire (99.95% of Al), chromium-nickel wire (20% of Cr, 80% of Ni), and a cobalt-alloy wire (17% of Co, 54% of Fe, and 29% of Ni). The obtained sample of the high-entropy alloy represents a parallelepiped consisting of 20 deposited layers in height and 4 layers in thickness. The alloy has the following elemental composition revealed by energy-dispersive X-ray spectroscopy: aluminum (35.67 ± 1.34 at %), nickel (33.79 ± 0.46 at %), iron (17.28 ± 1.83 at %), chromium (8.28 ± 0.15 at %) and cobalt (4.99 ± 0.09 at %). By using scanning electron microscopy, it has been revealed that the initial material has a dendritic structure and contains second-phase particles at the grain boundaries. The element distribution maps obtained by a mapping technique demonstrate that the grain bulk is enriched in aluminum and nickel, whereas the grain boundaries contain chromium and iron. Cobalt is distributed in the crystal lattice of the obtained HEA in a quasiuniform manner. It is shown that during tensile testing, the material destruction occurs according to an intragrain cleavage mechanism. It is revealed that brittle cracks are formed along the boundaries and at the junctions of grain boundaries, i.e., within the zones containing second-phase inclusions. It is suggested that the reasons for the increased fragility of HEA produced by wire-arc additive manufacturing consists in the uneven distribution of elements revealed in the microstructure of the alloy, and there are discontinuities having different shape and size in the bulk of the material.