Microstructure and Mechanical Properties of New AlCo_xCrFeMo_0.5Ni High‐Entropy Alloys

Abstract

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.

On microstructure and mechanical performance of AlCoCrFeMo0.5Nix high-entropy alloys

“…Ni-2.0 alloy has a larger amount of FCC phase and both BCC and s phase are reduced. As compared with the content effect of another FCC stabilizer, Co, which is thought to be the second to Ni in terms of FCC stabilization, the phase partitioning among the three phases is very different [30]. When Co content v is zero (AlCo v CrFeMo 0.5 Ni alloys), there is a large amount of s phase besides B2 phase.…”

“…1. Three phases: FCC, B2 (ordered BCC), and s phase (body-centered tetragonal structure) [29,30,32,34] are identified and listed in Table 1 for comparison. Their lattice constants are listed in Table 2.…”

Data mining accelerated the design strategy of high‐entropy alloys with the largest hardness based on genetic algorithm optimization

“…Owing to the large grain size of the cast alloy, the intensity of the precipitate phase σ peak detected in the XRD analysis is relatively weak, making the diffraction peak challenging to identify. Generally, in HEAs containing Al and transition metals, there is an enrichment of Co and Cr elements in the BCC phase, while the σ phase resembles the binary mesophase CoCr, featuring a body‐centered tetragonal structure [71,72] . Mo possesses a moderately large atomic size suitable for both solid solution and precipitation hardening.…”

A Criterion for Topological Close-Packed Phase Formation in High Entropy Alloys

“…According to the methods reported by Morinaga [47][48][49][50], the value of the parameter Md was calculated for the reported HEA system that contained TCP phases. The values are shown in Table 1 [5,6,34,[36][37][38]39,42,43,[53][54][55][56][57][58][59][60][61][62][63][64][65]. It was found that all the HEAs in Table 1 were synthesized by arc melting and then solidified in a water-cooled copper hearth.…”