L10 Phase Research Articles

Structural changes of TiPt high-temperature shape memory alloys induced by high pressure torsion

The microstructure of a TiPt high temperature shape memory alloy induced by high pressure torsion (HPT) was studied using synchrotron radiation experiments and transmission electron microscopy. Upon the severe plastic deformation, the parent B19 martensite is strongly refined and highly strained. While neither strong chemical disorder nor amorphization are encountered, the occurrence of crystal reflections is observed that can be indexed in terms of the L10 phase and long range ordered stacking structures. The occurrence of the L10 phase might be triggered by the high hydrostatic stress as well as shear stress superimposed during the HPT. The austenite and martensite start and finish temperatures of TiPt are not affected by the HPT since upon heating, recrystallization occurs prior to the onset of the reverse martensite to austenite transformation.

Ejection of boron from L10 phase for sputtered FePt-BN granular films by post-annealing

In this study, post-annealing under NH3 gas atmosphere was conducted in order to promote the two-phase separation of FePt-BN granular films. Magnetic properties and structural analysis for the Fe50Pt50–30 vol% BN granular films revealed that (1) saturation magnetization (M s) of the granular film increased from 500 to 650 emu cm−3 with increasing post-annealing time from 0 to 10 min, (2) the orientation of FePt grains changes from (002) to (111) and fully ordered with increasing post-annealing time up to 30 min, (3) the unit cell volume of FePt grains in the granular film decreased from 55.91 to 55.55 Å3 with increasing post-annealing time from 0 to 10 min, which suggests dissolve and eject of solid solution element. From the above, M s reduction for the FePt-BN granular films is considered to be caused by the solid solution of B in the FePt grains.

Strength and ductility enhancement of high-entropy FeCoNi2Al0.9 alloy by ultrasonically refining eutectic structures

The solidification process of high-entropy FeCoNi2Al0.9 alloy was modulated by 20 kHz power ultrasound with maximum 13 μm amplitude. The statically solidified eutectic structures were composed of L12 and B2 phases growing by K-S synergistic relationship. With the increase of ultrasound amplitude, the eutectic cell width and regular lamellar spacing were significantly refined, the proportion of strictly semi-coherent L12/B2 interfaces increased, and the solute concentration fluctuation in each eutectic phase was obviously suppressed. The steady-state cavitation and acoustic flow displayed remarkable influences on eutectic microstructure evolution. The yield strength, ultimate strength, and total elongation were increased by 23%, 21%, and 19% as compared with statically solidified alloy. This provided an effective approach to promoting the mechanical properties and overcoming the strength-ductility trade-off for those high-entropy alloys with eutectic structures.

Excellent tensile properties and deformation mechanisms in a FeCoNi-based medium entropy alloy with dual-heterogeneous structures

A dual-heterogeneous structure with both heterogeneous grain structure and coherent L12 nano-precipitate was obtained in a (FeCoNi)86Al7Ti7 medium-entropy alloy (MEA) after cold rolling, critical annealing, and aging treatments. The volume fraction of the L12 phase is found to increase from 0% to 34.5% after aging treatment, resulting in severer heterogeneity. The unaged samples of (FeCoNi)86Al7Ti7 MEA are found to have a much better synergy of strength and ductility as compared to the FeCoNi MEA. Moreover, the tensile properties for the aged samples of (FeCoNi)86Al7Ti7 MEA with dual-heterogeneous structures are even better than those for the corresponding unaged samples. The hetero-deformation-induced hardening plays a more important role in the aged samples than in the unaged samples, producing a higher density of geometrically necessary dislocations. High density dislocations are discovered in grain interiors for the aged samples and the deformation is dominated by the planar slip in the unaged samples. Meanwhile, a high density of dislocations are observed inside L12 nano-precipitates; thus, L12 nano-precipitates can be sheared by dislocations, indicating that L12 nano-precipitates are strong but deformable. The strong interactions between dislocations and L12 nano-precipitates should provide additional strain hardening for better tensile properties in the aged samples.

Effect of Si addition on the magnetic properties of FeNi-based alloys with L10 phase through annealing amorphous precursor

As a promising candidate of rare-earth free hard magnetic materials, L1 0 -FeNi has been paid much attention in the last decades. However, it is difficult to be artificially fabricated due to its low thermal stability and sluggish diffusion ability of atoms below the crucial temperature of 320 °C. In this study, a promising method of annealing amorphous precursor was extensively developed through (Fe 50 Ni 50 ) 84−x Si x P 16 (x = 0, 4 at%) and (Fe 50 Ni 50 ) 86−x Si x P 14 (x = 2, 4, 8 at%) alloys. Especially, the effect of Si on the formation of L1 0 phase in annealed FeNi-based alloys was investigated and clarified. It is found Fe 42 Ni 42 P 16 with a much low crystallization temperature could be an appropriate basic amorphous alloy for the formation of L1 0 phase. The addition of Si enhanced the thermal stability of Fe-Ni-P amorphous alloys. Interestingly, Si could stabilize the L1 0 phase in annealed samples and increase its disordering temperature above which L1 0 -FeNi phase could deteriorate into soft magnetic phase. As expected, appropriate Si addition indeed improved the hard magnetic properties of the annealed alloys and samples with high coercivity above 900 Oe was obtained. Further Si addition would deteriorate the magnetic-crystalline anisotropy of L1 0 phase and decrease the coercivity of annealed Fe-Ni-Si-P alloys. Nevertheless, the results indicate that increasing the order-disorder transition temperature through element doping in L1 0 lattice would be a promising strategy for the massive formation of L1 0 -FeNi like other ordered phases (i.e. L1 2 -FeNi, L1 0 -CoPt), and could substantively contribute to the artificial fabrication of FeNi-based rare-earth free magnets in future. • Sample with the high coercivity above 900 Oe is obtained by annealing Fe-Ni-Si-P amorphous alloy. • The addition of Si increases the crystallization temperatures and thermal stability of Fe-Ni-P amorphous alloys. • Si could enhance the thermal stability and the disordering temperature of L1 0 phase. • Excessive Si addition would deteriorate the intrinsic magnetic hardness of L1 0 phase.

Microstructure, magnetic properties, corrosion resistance and catalytic activity of dual-phase AlCoNiFeTi and AlCoNiFeTiSi high entropy alloys

The high entropy AlCoFeNiTi and AlCoFeNiTiSi alloys were prepared by two methods to determine the influence of the cooling rate on the structure and properties. The Mössbauer spectra of AlCoFeNiTi alloys showed the coexistence of a nonmagnetic part with a magnetic hyperfine portion. The spectra for AlCoFeNiTiSi alloy in an as-cast and plate states contain only nonmagnetic components. The X-ray diffraction analysis confirmed that the silicon addition drastically changes the phase composition of AlCoFeNiTi alloy. Whereas alloy without Si was characterised by the coexistence of L21 and BCC phases, the addition of silicon resulted in the formation of Ti-rich HCP and Al-rich B2 phases. AlCoFeNiTi plate exhibits a high saturation magnetisation value of 29.83 emu/g and the best corrosion resistance (polarisation resistance of about 38.6 kΩcm2 and corrosion current density of 0.77 μA/cm2). The highest hardness (1096 HV) was achieved for AlCoFeNiTiSi plate, which is related to the phase composition changes generated by Si addition. The influence of the Si addition on the properties of studied alloys was also confirmed in the decolourisation of Rhodamine B using a modified photo-Fenton process. The decolourisation efficiency within 60 min was 92% for AlCoFeNiTiSi alloy, and 95.5% for the AlCoFeNiTi alloy.

Investigations on the Phase Transformations, Equilibria and Athermal ω in Ni-Ga-Cr Ternary System.

In the present work, the phase equilibria of the Ni-Ga-Cr ternary system at 850, 1000 and 1150 °C were experimentally investigated to provide the essential data for developing the high-entropy shape memory alloys (HESMAs) containing Ni, Ga and Cr. At 850 °C, in the Ni-rich portion, the B2 phase shows equilibrium with the L12 phase when the Cr content is less than 10.49 at. %, while displaying the equilibrium with L12 and BCC phases when the Cr content increases. The B2 + L12 + BCC changes into B2 + FCC + BCC three-phase equilibria from 850 to 1150 °C, as the L12 phase region becomes narrow with rising temperature. The two-phase equilibrium, B2 + BCC, was found at all the isothermal sections investigated. Other three-phase equilibria were also discovered: B2 + α-Cr3Ga + BCC and Ni2Ga3 + α-Cr3Ga + L at 850 °C, and B2 + α-Cr3Ga + L at 1000 °C. Significantly, an athermal ω intermetallic compound with the space group of P3¯m1 was observed distributing at the B2 phase in the quenched Ni45.98-Ga25.50-Cr28.52, Ni42.23-Ga15.70-Cr42.07 and Ni16.54-Ga13.63-Cr69.83 (at. %) alloys after being annealed at 1150 °C for 10 days. The high-resolution transmission electron microscopy (HRTEM) results reveal that the ω shows a crystallographic orientation of [11¯0]B2//[112¯0]ω; (111)B2//(0001)ω with the B2 parent phase.

Local Structure Insight into Hydrogen Evolution Reaction with Bimetal Nanocatalysts.

The revelation of the atomic 3D structure of sub-5 nm bimetal nanocatalysts challenges the limitations of conventional methods. Notably, the identification of the cooperative relationship between the active sites and nearby coordination environment during catalytic reactions depends on the stereo distribution of local phases and chemical composition within a short range. As a model nanocatalyst in our investigation, we studied the ordered PtFe bimetals in hydrogen evolution reactions (HER). By combining pair distribution functions with reverse Monte Carlo, local-range phase symmetry, chemical composition, and atom distribution were determined. The segregation of local phase segments as disordered Pt-rich A1 and Pt3Fe L12 phases can be attributed to the marked improvement of HER activity and stability in Pt56Fe44. Following the etching of the outermost-surface Fe, the remaining disordered segregation offered a large number of active Pt sites for discharge and electrochemical desorption reactions. It resulted in local-bonding Pt pairs that made it easier for adsorbed hydrogen atoms to recombine. The current research will provide structural insight into the local range for bimetal nanocatalysts and be valuable for the creation of new, low-cost nanocatalysts.

Effective combination of solid solution strengthening and precipitation hardening in NiCrFeWTiAl multi-principal element alloys

Face-centered-cubic (FCC) Multi-principal element alloys (MPEAs) have attracted intensive scientific research interest due to their excellent fracture toughness and ductility. Still, the strengths of single-phase MPEAs are unsatisfactory. Although great progress has been made by utilizing multiple strengthening mechanisms, it remains challenging to take advantage of large-atom solutes and nano-precipitates simultaneously because solutes always partition into the precipitates. In the present work, we successfully achieved an effective combination of solid solution strengthening and precipitation hardening in the NiCrFeWTiAl multi-principal element alloys. Our experimental results showed that W is partitioned into the FCC matrix, while Ti and Al tend to exist in the L12 phase. This controlled elemental partitioning leads to a good combination of solid solution strengthening and precipitation hardening effects and results in good tensile properties at temperatures from 25 ℃ to 760 ℃. The strengthening mechanisms were revealed based on the quantified microstructure analysis. The solid solution hardening of all the solute atoms contributes ∼140 MPa in total, but W mainly contributes to solid solution hardening, and L12 precipitates enhance the yield strength by ∼330 MPa through ordering strengthening.

Mechanical, electronic, thermodynamic and vibrational properties of X2MgAl (X = Sc, Ti and Y) from first principles calculations.

Due to growing interest to predict and design new potential Heusler alloys by using theoretical calculations and highly functional software, research on Heusler alloys has taken great attention. From this point of view, this study considers investigation of X2MgAl (X = Sc, Ti and Y) alloys by adopting first principles calculations for the first time. A thorough investigation has been carried out to reveal these alloys' mechanical, electronic, vibrational and thermodynamic properties. It is seen that all alloys have negative formation energies as - 0.278eV/atom for Sc2MgAl, - 0.058eV/atom for Ti2MgAl and - 0.304eV/atom for Y2MgAl which indicates synthesisability and thermodynamic stability. Mechanical stability investigations based on the elastic constants of alloys have revealed that all alloys are mechanically stable. The electronic band structures of alloys demonstrate that X2MgAl (X = Sc, Ti and Y) alloys are metallic since there is no energy gap near the Fermi level. Cauchy's pressures of alloys are found as - 17.791 GPa for Sc2MgAl, 31.404 GPa for Ti2MgAl and - 11.759 GPa for Y2MgAl which displays that Sc2MgAl and Y2MgAl are brittle and Ti2MgAl is ductile. The phonon dispersion curves are calculated along the lines of high symmetry within the first Brillouin region. Phonon frequencies are completely positive in the full Brillouin region, which proves the dynamic stability of the L21 phases of these alloys. Several thermodynamic properties such as Debye entropy, temperature and vibrational free energy are also computed and analysed. Debye entropies of alloys follow Ti2MgAl > Y2MgAl > Sc2MgAl relationship.

Alloying and magnetic disordering effects on the thermodynamic properties and phase stability of Co2Cr(Ga, Si) and Co2Cr(Al, Si) Heusler alloys

Using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, the alloying and magnetic disordering effects on the thermodynamic properties and phase stability of the ferromagnetic L21- and D022-CoxCr78−xZ11Si11 (Z=Ga and Al, 46≤x≤62) alloys are systematically investigated. It is shown that at 0 K, with increasing x the D022 structure gets relatively more and more stable in the energy and stabilized instead in the two groups of alloys with x≥56 and 60, respectively. There, upon the martensitic transformation (MT) the bulk modulus gets a little larger than that of the austenite, and both significant magnetocaloric and magnetovolume effects could be also expected. The tetragonal shear elastic constant (C′=(C11−C12)/2) of the L21 phase decreases whereas that (Cs=C11+C12+2C33−4C13) of the D022 phase increases with the Co addition, mechanically favoring the relative stability of the more ductile D022 martensite as well. The magnetic excitations decrease the electronic total energy but increase the phonon vibrational free energy of the D022 phase relative to the L21 one. The two effects nevertheless almost offset each other at their Curie temperature. The reentrant MT (RMT) is then predicted without the magnetic excitations effect in the Z=Ga and Al alloys with 50≤x≤54 and 54≤x≤58, respectively, and their critical temperatures (TM) for the RMT decrease with increasing x, in line with the measured data of the Z=Ga alloys. With the Co addition, the increase of the relative stability of their D022 phase is finally confirmed maybe originating from the increase of the Co 3d minority DOS around the Fermi level in their L21 phase.

A novel L12-strengthened AlCoCuFeNi high-entropy alloy with both high hardness and good corrosion resistance

In this work, a high hardness, crack-free AlCoCuFeNi high-entropy alloy with good corrosion resistance was successfully produced by spark plasma sintering at 1000℃ and 30 MPa for 10 min, followed by hot rolling to a thickness reduction of 10 % after holding at 600℃ for 30 min. The microstructure of the alloy was composed of fine equiaxed grains of (Fe, Co, Ni, Al)-enriched BCC, Cu-enriched FCC, nano-sized L12, and Al2O3 phases. The maximum texture index of the material is only 1.53, indicating a low anisotropy. The alloy possessed a high hardness (599 HV), a low friction coefficient (0.1), and a low corrosion current density (1.13 μA/cm2), implying both good wear and corrosion resistance. In addition, the creep mechanism was found to be grain boundary sliding.

Electrodeposition of Equiatomic FePt Permanent Magnets from Non-Aqueous Electrolytes Based on Ethylene Glycol

The highly ordered L10 hard-magnetic phase of the equiatomic FePt alloy is of significant interest for a great number of magnetic applications, ranging from the realization of micromagnets for integrated sensors to the deposition of thin layers for vertical recording media [1]. In this context, the development of wet deposition processes able to yield high-quality layers of FePt represents a topic of considerable industrial relevance. Even though several aqueous-based electrodeposition approaches have been developed for the manufacturing of FePt, most formulations evidenced substantial technological limitations, specifically connected to the use of water as solvent (hydrogen evolution, oxygen contamination of the deposit...).From this point of view, non-aqueous electrolytes represent a promising alternative for the electrosynthesis of metallic layers. These alternative solvents are characterized by attractive applicative properties: they present wide electrochemical windows, are simple to prepare, formulated from relatively cheap components, almost unreactive with water and, in most cases, biodegradable. Thanks to these properties, they have been widely employed for the electrodeposition of metals [2], alloys [3] or composites [4].The present work describes the deposition of FePt from a non-aqueous electrolyte based on ethylene glycol, which presents potential advantages over water-based baths in terms of gas evolution reduction and purity improvement of the obtained coatings. Deposition is carried out using Fe(III) and Pt(IV) as precursors and ammonium chloride as additive to enhance the quality of the coatings and their compositional uniformity. In this way, equiatomic FePt thin films characterized by a good morphology are easily obtained. These layers are subsequently characterized to assess their morphology, phase composition and magnetic properties. After annealing at 600 °C, the microstructure changes and the disordered face centered cubic phase present in the as-plated alloy evolves into the highly magneto-crystalline anisotropic L10 phase. As a consequence, the coercivity of the layers reaches values in excess of 10 kOe.[1] Lodder et al.; Encyclopedia of Materials: Science and Technology, pp. 1-10 (2005)[2] Abbott et al.; Phys. Chem. Chem. Phys. 8, 4265-4279 (2006)[3] Bernasconi et al.; J. Phys. Chem. B 124(47), 10739-10751 (2020)[4] Rosoiu et al.; Metals 10(11), 1455 (2020)

The influence of vanadium element on the microstructure and mechanical properties of (FeCoNi)100-xVx high-entropy alloys

Despite their unique thermodynamic and kinetic features, Face-centered cubic (FCC) high-entropy alloys (HEAs) are well known to usually possess superior ductility at room temperature but relatively low strength, which greatly limits their structural application. To address this issue of strength-ductility tradeoff, we have systematically investigated in the present work the crystallographic structure, microstructural evolution, and tensile properties of (FeCoNi)100-xVx (x = 10, 15, 20, 25, and 30) HEAs in both as-quenched and annealed conditions. A single-phase solid solution was still obtained by quenching from high temperature when the V concentration was up to 25%. It is interesting to find in that the microstructure of this family of HEA alloys varies with the content of V element and pre-annealing, showing an unusual single phase with L12 chemically ordered structure for (FeCoNi)75V25, but otherwise a composite consisting of a L12 phase coherent with disordered FCC phase matrix for the other V doped FeCoNi alloys such as (FeCoNi)80V20. Owing to the presence of the ordered phase, both (FeCoNi)80V20 and (FeCoNi)75V25 display a remarkable work hardening capability, leading to the enhanced ultimate tensile strengths up to 1.1 and 1.4 GPa, respectively, and the resultant excellent deformability with uniform plastic strain of >30%.

Synergism between coherent precipitation strengthening and FCC-HCP type transformation-induced plasticity

It is becoming a trend that many strengthening methods are applied at the same time to overcome the strength-ductility trade-off. However, the combination of precipitation strengthening and transformation-induced plasticity (TRIP) is rarely used effectively because precipitates will hinder phase transformation. In this work, the coherent precipitation strengthening of L12 phase and Face-Centered Cubic (FCC) - Hexagonal Close-Packed (HCP) type martensitic transformation are combined in a single alloy. With the synergistic effect of both sides, the yield strength of aged Co52Cr30Ni12Al3Ti3 alloy is increased from 437 MPa (annealed alloy with TRIP effect only) to 715 MPa, while retaining a uniform elongation of more than 50% at room temperature. Further research shows that whether L12 phase exist will directly affect its deformation mode. In the tensile process of aged Co52Cr30Ni12Al3Ti3 alloy, the deformation mode of grains without L12 phase will change from previous stacking fault-predominant deformation to the final transformation-induced plasticity. For the regions where L12 phase exists, martensitic transformation is difficult to occur due to the blocking effect of L12 on stacking fault.

Relating the magnetic coercivity to the L10 ordered FePd phase in annealed FexPd100-x nanoparticles

Rare-earth-free or iron-based permanent nanomagnets are emerging as promising candidates for energy-conversion and information technologies. In this interest, FexPd100-x nanoparticles (x = 50, 55, 60, and 63) were prepared from iron acetate and palladium acetate by sonoelectrodeposition. After annealing the nanoparticles at various temperatures from 450 to 700 °C for 1 h, structural changes were observed, and the samples exhibit hard magnetic properties that depend strongly on chemical composition and annealing temperature. The major phase in the as-prepared nanoparticles has a disordered face-centered cubic structure, which, upon annealing, transforms into a multi-phase material containing a L10 ordered FePd phase. The fractions of different phases present in the annealed samples, including that of the L10 phase as functions of chemical composition and annealing temperature, are quantified by means of X-ray diffraction and scanning transmission electron microscopy. Magnetic measurements show the desirable hard magnetic properties for the samples annealed at 550–600 °C. A correlation between the magnetic coercivity and the L10 ordered FePd phase fraction is established for the first time in the FexPd100-x nanoparticles.

A low-density high-entropy dual-phase alloy with hierarchical structure and exceptional specific yield strength

A high-entropy dual-phase AlTiVCoNi alloy with a low density of ∼6.24 g cm−3 is developed, and it consists of a hierarchical structure, including an ordered L21 phase, a disordered body-centered-cubic (BCC) solid-solution phase, and nano-sized L21 precipitates embedded in the BCC phase. It is found that this new alloy shows phase stability after the heat treatment at 1200°C for 24 h, and the compressive yield strength of this annealed alloy is approximately equal to that of the as-cast condition, ∼1.6 GPa. This alloy displays an exceptional compressive strength at room temperature and at 600°C, with the specific yield strengths of ∼261 and ∼210 MPa g−1 cm3, respectively. The semi-coherent interface of the L21 and the BCC phases makes the alloy phase stable and regulates the work-hardening mechanism. Local dynamic-recrystallization behavior and grain evolution are observed in the as-prepared alloy during compression at 800 and 1000°C, which results in the high-temperature softening. This alloy with a muti-phase hierarchical structure would provide a new paradigm for the development of next-generation low-density, high-entropy structural materials for high-temperature applications.

Effects of Fe on L12 phase precipitation and mechanical properties in Al0.3CrFeCoNi high-entropy alloy

The newly developed L12-strengthened high-entropy alloy shows great potential to possess superior combinations of physical and mechanical properties. It has been extensively studied how to control the L12 phase by adjusting L12-phase forming elements such as Al, Ti, Ta and Nb. However, the effect of transition-metal elements on L12 precipitation is still unclear. This work investigated the effect of Fe on the stability and distribution of the L12 phase by reducing the level of Fe in a well-studied high-entropy alloy Al0.3CrFeCoNi. A close examination of the precipitation behaviour in the Al0.3CrFeCoNi and Al0.3CrFe0.6CoNi1.4 alloys was conducted using transmission electron microscopes. When the aging temperature reaches 700 °C in the Al0.3CrFeCoNi alloy, nanosized L12 particles would transition to the B2 phase. By reducing the amount of Fe, the stability and density of the L12 phase were both enhanced. After 700 °C annealing, L12 nanoparticles are still stable in the Al0.3CrFe0.6CoNi1.4 alloy and there is no evidence of B2 phase precipitation. Less Fe can lower the concentration of Al in both the fcc and L12 phases during aging at a lower temperature of 620 °C when the L12 phase in both alloys is stable. A lower Fe concentration can also lead to more Cr and Fe atoms occupying Al sites in the L12 phase, which can result in the formation of more L12 particles. Since more L12 particles were precipitated when the amount of Fe was reduced, the Al0.3CrFe0.6CoNi1.4 alloy exhibits better strength and higher hardness than the Al0.3CrFeCoNi alloy. These findings give us insight into how transition metals affect the behaviour of L12 precipitation and suggest ways to develop and improve L12-strengthened HEAs.

Role of structural defects on the magnetic properties of annealed Fe56Pd44 thin films upon development of the ordered L10 phase

Fe56Pd44 thin films grown on a silicon substrate by thermal evaporation were submitted to annealing in furnace in vacuum at 550 °C for increasing time in order to transform the initial disordered fcc phase into an ordered L10 one. Starting from a detailed understanding of the time evolution of the microstructure, the complex resulting magnetic properties have been interpreted. Besides the expected increase of the coercive field due to the development of a magnetically hard phase, a non-monotonous behaviour of the remanence-to-saturation ratio has been attributed to the effects of the ordering of the developing L10 phase first, and of the progressive ordering of the alloy as a whole thereafter, once the L10 phase was already fully developed. The process of ordering of the alloy is characterised by the appearance of microstructure defects (twinned domains, twin boundaries, antiphase boundaries, polytwins), that promote a further increase of the coercive field by pinning domain walls, but also affect the remanence-to-saturation ratio and the arrangement of the magnetic domains by locally tilting and reducing the magnetic anisotropy.

The Observation of Cellular Precipitation in an Ni36Co18Cr20Fe19Al7 High-Entropy Alloy after Quenching and Annealing.

High-entropy alloys (HEAs) comprise a minimum of five major elements. These alloys show some special characteristics, such as excellent mechanical and high temperature properties. The development of the HEAs requires a knowledge of phase transformations during alloy making procedures. The phase transformations of an Ni36Co18Cr20Fe19Al7 HEA were studied in this research. The alloy underwent hot forging, cold rolling, annealing at and quenching from 1323 K, and isothermal holding at 873 K. The alloy is a single face-centered cubic (FCC) phase in the as-quenched condition. After annealing at 873 K, not only fine coherent L12 particles precipitated homogeneously in the FCC matrix, but lamellae of FCC and L12 phases also developed from the grain boundaries. Both lamellar FCC and L12 grains have a cubic-on-cubic orientation relationship (OR). The composition of the lamellar L12 phase is Ni60Co8Cr6Fe6Al20, and that of the lamellar FCC phase is Ni31Co15Cr28Fe21Al4. Cellular precipitation occurs in the HEA, and the high-temperature FCC (γ) transforms to a lamella of low-temperature FCC (γ1), and an L12 phase, i.e., γ → γ1+L12.