High-Entropy Alloys with a Hexagonal Close-Packed Structure Designed by Equi-Atomic Alloy Strategy and Binary Phase Diagrams

Abstract

High-entropy alloys (HEAs) with an atomic arrangement of a hexagonal closepacked (hcp) structure were found in YGdTbDyLu and GdTbDyTmLu alloys as a nearly single hcp phase. The equi-atomic alloy design for HEAs assisted by binary phase diagrams started with selecting constituent elements with the hcp structure at room temperature by permitting allotropic transformation at a high temperature. The binary phase diagrams comprising the elements thus selected were carefully examined for the characteristics of miscibility in both liquid and solid phases as well as in both solids due to allotropic transformation. The miscibility in interest was considerably narrow enough to prevent segregation from taking place during casting around the equi-atomic composition. The alloy design eventually gave candidates of quinary equi-atomic alloys comprising heavy lanthanides principally. The XRD analysis revealed that YGdTbDyLu and GdTbDyTmLu alloys thus designed are formed into the hcp structure in a nearly single phase. It was found that these YGdTbDyLu and GdTbDyTmLu HEAs with an hcp structure have delta parameter (d) values of 1.4 and 1.6, respectively, and mixing enthalpy (DH mix ) = 0 kJ/mol for both alloys. These alloys were consistently plotted in zone S for disordered HEAs in a d-DH mix diagram reported by Zhang et al. (Adv Eng Mater 10:534, 2008). The value of valence electron concentration of the alloys was evaluated to be 3 as the first report for HEAs with an hcp structure. The finding of HEAs with the hcp structure is significant in that HEAs have been extended to covering all three simple metallic crystalline structures ultimately followed by the body-and facecentered cubic (bcc and fcc) phases and to all four simple solid solutions that contain the glassy phase from high-entropy bulk metallic glasses.

MoNbTaV Medium-Entropy Alloy

“…Thus, HEA design has opened up a door to explore new alloy families with unique compositions [3][4][5]. The HEAs reported in the literature generally form with face-centered cubic (FCC) [6], body-centered cubic (BCC) [7], or hexagonal close-packed (HCP) structures [8][9][10]. Reference [11] provides a list of single-phase HEAs in these structures that have been experimentally verified or computationally predicted.…”

Design of Light-Weight High-Entropy Alloys

“…These parameters are listed in Table 2. For a comprehensive list of single-phase HEAs in face-centered cubic (FCC) [1, 3,6], body-centered cubic (BCC) [3,6,39], or hexagonal close-packed (HCP) [3,6,7,[40][41][42] structures that are experimentally verified or computationally predicted, the reader is referred to a recent publication [26]. It should be noted that the listed alloys in Table 2 were in the as-cast state, except for Al 20 Li 20 Mg 10 Sc 20 Ti 30 and AlFeMgTiZn, which were produced by mechanical alloying.…”

Effect of starting grain size on the evolution of microstructure and texture during thermo-mechanical processing of CoCrFeMnNi high entropy alloy

“…equiatomic CoCrFeMnNi [1]), BCC and FCC+BCC [2] and HCP [3]. The formation of rather simple crystal structures in these alloys is explained by the increased configurational entropy due to the mixing of a large number of elements.…”