Abstract
Effects of Co content on microstructures and hot hardness of a new high-entropy alloy system, AlCo x CrFeMo 0.5 Ni (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 AlCo x CrFeMo 0.5 Ni alloys possess higher hardness level than that of Ni-based superalloys In 718/In 718Hfrom 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 AlCo x CrFeMo 0.5 Ni alloy system has great potential in high-temperature applications. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.