A eutectic high-entropy alloy with good high-temperature strength-plasticity balance

Abstract

We developed a eutectic high-entropy alloy (EHEA) with appreciable high-temperature strengthplasticity balance. Structural characterizations of the as-cast sample revealed a lamellar structure with austenite (face-centered-cubic, FCC) and Laves phases. Upon annealing at 873 K, precipitation of nanoscale (Ni, Al, and Zr)-rich L1 2 phase from the FCC phase took place, which eventually transformed into a martensitic (hexagonal,) phase with rearrangement of atomic species. Compressive properties revealed a brittle behavior at temperatures below 873 K, but changed to a ductile behavior with considerable strain hardening at 973 K, due to the formation of a high density of deformation twins observed by transmission electron microscopy. IMPACT STATEMENT A eutectic high-entropy alloy with attractive high-temperature compressive strength-plasticity balance was realized by tuning the microstructure via heat treatment, during which nanoscale L1 2 phase formed within the FCC matrix phase.

A novel equiaxed eutectic high-entropy alloy with excellent mechanical properties at elevated temperatures

“…Also, it has been demonstrated that a minor addition of Al (1.7 at. %) to the non-equimolar Co 27 Cr 21 Fe 18 Ni 24 Ta 10 EHEA promoted the formation of a high-density L1 2 ordered nano-precipitates [16]. The coherently ordered L1 2 precipitates were found to be thermodynamically stable against high-temperature annealing, which offered an effective strain hardening source to counteract against softening at elevated temperatures [16].…”

“…%) to the non-equimolar Co 27 Cr 21 Fe 18 Ni 24 Ta 10 EHEA promoted the formation of a high-density L1 2 ordered nano-precipitates [16]. The coherently ordered L1 2 precipitates were found to be thermodynamically stable against high-temperature annealing, which offered an effective strain hardening source to counteract against softening at elevated temperatures [16]. However, the Co 27 Cr 21 Fe 18 Ni 24 Ta 10 EHEA with a minor addition of Al exhibited typical Laves + FCC eutectic structure formed during the conventional solidification process, and the long-striped Laves phase was found to cause early crack initiation during compression, leading to a prevailing brittle fracture at high temperatures [16].…”

“…The HEAs were initially defined as equal-atomic solid solution alloys with more than five elemental species [2], but later were expanded to include multicomponent alloys locating near the middle of phase diagrams. Although several key hypotheses proposed for HEAs, such as the 'high-entropy', 'sluggish diffusion', 'lattice distortion' and 'cocktail effect' are still under debate [3][4][5], the research of HEAs stimulates the exploration (hard) is one promising candidate for engineering applications at elevated temperatures [13][14][15][16], where the Laves phase and the FCC phase are the products of an eutectic reaction [17]. Although the FCC phase can provide a large room for dislocation accumulation during deformation, and therefore contribute enormously to the ductility [13][14][15].…”

“…The coherently ordered L1 2 precipitates were found to be thermodynamically stable against high-temperature annealing, which offered an effective strain hardening source to counteract against softening at elevated temperatures [16]. However, the Co 27 Cr 21 Fe 18 Ni 24 Ta 10 EHEA with a minor addition of Al exhibited typical Laves + FCC eutectic structure formed during the conventional solidification process, and the long-striped Laves phase was found to cause early crack initiation during compression, leading to a prevailing brittle fracture at high temperatures [16]. In this regard, the Laves phase is believed to be detrimental to the high-temperature mechanical properties of EHEAs when its size, morphology and distribution are not properly controlled.…”

“…In this regard, the Laves phase is believed to be detrimental to the high-temperature mechanical properties of EHEAs when its size, morphology and distribution are not properly controlled. On the other hand, it was found that equiaxed Laves phase is more resistant against the crack initiation and propagation during compression tests [16,20]. Hence, in order to further improve the high-temperature mechanical properties of the Laves phase-containing EHEAs, it is desired to tune the morphology of Laves phase so that an early crack formation and propagation can be prevented.…”