Effects of Co content on microstructures and hot hardness of a new high‐entropy alloy system, AlCoxCrFeMo0.5Ni (x = 0.5 to 2.0) were investigated. As cobalt content increases, the microstructure changes from dendrite to polygrain type and the constituent phases change from BCC + σ at x = 0.5 to BCC + FCC + σ at x = 2.0. The alloy hardness varies from Hv 788 at x = 0.5 to Hv 596 at x = 2.0. This can be explained with the relative amount of hard σ phase, medium hard BCC phase and soft FCC phase. All the AlCoxCrFeMo0.5Ni alloys possess higher hardness level than that of Ni‐based superalloys In 718/In 718 H from room temperature to 1273 K. They obey the Westbrook equation presenting the normal heating behavior. Both alloys of x = 0.5 and 1.0 exhibit a transition temperature higher than that of Co‐based alloy T‐800 by about 200 K. They also have a high hot hardness of Hv 347 at 1273 K, which is higher than those of In 718 and In718 H by Hv 220. The strengthening mechanism for their superiority is proposed. The AlCoxCrFeMo0.5Ni alloy system has great potential in high‐temperature applications.
High-entropy alloys (HEAs) Al x CoCrCuFeNi with different aluminum contents (x = 0 to 1.8) were plasma nitrided at 525°C for 45 hours with an aim to develop wear-resistant structural parts. The nitrided layer comprises a well-nitrided dendrite phase and an un-nitrided Cu-rich interdendrite phase. Surface hardening is a result of the formation of various nitrides in the nitrided dendrite: CrN, Fe 4 N, and AlN. With increasing aluminum content, the hardness of the nitrided layer increases due to the increased amount of hard AlN phase and the increased volume fraction of bcc phase being harder than the fcc one. The nitrided layer thickness shows an apparent decrease with the increasing aluminum content of the alloy. The present alloy system provides a wide range of substrate hardness from Hv 170 to 560 before nitriding, which even becomes harder by around Hv 30 after nitriding. For Al 0.5 CoCrCuFeNi alloy having the highest surface hardness of Hv 1300, a layer thickness of 23 lm, and a substrate hardness of Hv 300, an adhesive wear test confirms its superior wear resistance as being 17 times that of the un-nitrided samples.
The microstructure, hardening behavior, and adhesive wear behavior of Al0.3CrFe1.5MnNi0.5 high‐entropy alloys were investigated. All alloys exhibit superior adhesive wear resistance to cast iron FC‐300, bearing steel SUJ‐2, and hot‐mold steel SKD‐61. The superior wear resistance of the alloys is attributable to the formation of ρ phase during the furnace cooling from the homogenization at 1100 °C or the in situ formation of the ρphase induced by the high interface temperature and severe plastic deformation during wear sliding.
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