High-strength Al0.2Co1.5CrFeNi1.5Ti high-entropy alloy produced by powder metallurgy and casting: A comparison of microstructures, mechanical and tribological properties
Abstract
This work presents an in-depth comparison of the microstructural origins of high strength and high wear resistance in the Al0.2Co1.5CrFeNi1.5Ti high-entropy alloy produced by powder metallurgy (PM) and casting. The PM alloy microstructure is composed almost exclusively of fine-grained FCC phase with minor, in-situ formed TiC particles.
The latter is responsible for a grain-boundary pinning effect and, consequently, the high-hardness of 712 HV was achieved allied with excellent flexural strength (2018 MPa) and elastic modulus of 258 GPa. Its wear properties surpass those of the wear-resistant AISI 52100 steel under 1.2 N load.
Despite the high strength properties of PM alloy, a ductile fracture behaviour was retained. In contrast, the cast alloy is composed of a coarse-grained dendritic microstructure of FCC matrix containing a complex of intermetallic phases.
Its tribological properties are superior to traditional AISI 52100 steel under all sliding conditions, exhibiting the best results among all tested materials. However, its elastic modulus (210 GPa) and flexural strength (1101 MPa), at a comparable hardness level (682 HV), were significantly lower when compared to the PM counterpart.
This stems from the intrinsic brittleness of the cast material, a consequence of its complex microstructure, exhibiting pure cleavage-type fracture in several areas of the fracture surface.