Multifunctional Non‐Equiatomic High Entropy Alloys with Superelastic, High Damping, and Excellent Cryogenic Properties

Abstract

A new class of non-equiatomic FeNiCoAlTaB (NCATB) high entropy alloy (HEA) is introduced, which exhibits tunable properties from cryogenic/ambient superelasticity to ultra-high strength through controlling the nature or type of martensite. In the current NCATB-HEA alloy system, depending on the size of γ'-Ni 3 Al (L1 2 ) precipitates, thin-plate, lenticular, butterfly, and lath-like martensite can form. When thin-plate thermoelastic martensite is favored, a superelastic strain of about 0.025 (ambient) and %0.01 (cryogenic) is achieved with a high yield stress of %800 MPa and a high-damping effect (10 times higher than Cu-Al-Ni superelastic alloy). While for butterfly and lath-like martensite dominated NCATB-HEA, an ultra-high yield stress of around 1.1 GPa is achieved while no superelasticity is demonstrated. This current alloy system helps to expand the application domain of HEAs, for example, into high-damping applications, robust actuators, space exploration, and other structural material applications.

On the Impact of Texture and Grain Size on the Pseudoelastic Properties of Polycrystalline Fe–Ni–Co–Al–Ti Alloy

“…For the specimen being characterized by a reduction ratio of 92%, the texture main component is Goss-{110}h001i c , whereas for both 85 and 90 specimens the main component is close to {230}h001i. This texture evolution is in good agreement with previous results observed by various authors [12][13][14]18]. However, texture intensities reported in this paper are higher than the ones obtained in previous works when looking at similar reduction ratios.…”

“…Samples treated according to TT-1250°C and TT-1300°C were aged at 600°C for 4 h to induce c 0 -phase precipitates. Besides the influence of texture, the size and the volume fraction of the c 0 -phase play an important role in phase transformation as both affect the morphology of the martensite and eventually the amount of irreversible deformation following pseudoelastic testing [9,13]. Figure 9 shows the pseudoelastic response at room temperature for the specimens treated according to TT-1250°C and TT-1300°C (RD is parallel to load direction).…”

“…Obtaining a thermoelastic character of the MT in FNCAX is strongly related to the presence of coherent, ordered c 0 -(L1 2 ) precipitates of Ni 3 Al-type [9]. Due to the formation of coherency stress fields, these fine dispersed precipitates mechanically strengthen the matrix of the parent phase [7,13]. However, the formation of the b-NiAl (B2) phase, particularly along grain boundaries, evokes pronounced brittleness deteriorating the mechanical properties [14,15].…”

“…grain size, orientation distribution and texture, respectively, have a significant impact on the functional and structural properties of FNCAX SMAs [14,15]. The relationship between crystal orientation, crystallographic texture and PE is well understood for Fe-Ni-Co-Al-Ta(-B) [6,9], Fe-Ni-Co-Al-Nb(-B) [16] and other alloys belonging to the FNCAX family [13,14,17]. For the polycrystalline FNCAX SMAs, all of them containing Boron as an element suppressing the evolution of the bphase, cold rolling followed by recrystallization is a wellestablished approach to obtain an excellent PE response in the polycrystalline condition [7].…”

Effect of Stacking Fault Energy on Microstructure and Texture Evolution during the Rolling of Non-Equiatomic CrMnFeCoNi High-Entropy Alloys

“…Although there is some controversy around this definition, it is sure that such combinations provide a larger composition space to design new alloys in simple solid solution form. From that point of view, many non-equiatomic HEAs are identified with unique microstructures and desirable properties [17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The most commonly referred to and well-investigated HEA has the equiatomic composition CrMnFeCoNi and is a single-phase solid solution with a face-centered cubic (FCC) structure.…”