L10 Phase Research Articles

Enhancing oxidation resistance via grain boundary engineering in L12-strengthened medium entropy alloys

The concept of grain boundary engineering (GBE) has been successfully applied to L12-strengthened (CoCrNi)94Al3Ti3 medium entropy alloy, with the aim of improving the oxidation resistance by increasing the ratio of special boundaries and suppressing discontinuous precipitation. Surprisingly, our results reveal that GBE treatment not only slows down the oxidation kinetics and but also alters the oxide scale from TiO2 and multi-defect Cr2O3 to continuous and protective Cr2O3 and Al2O3, thereby contributing to an enhanced oxidation and anti-spalling resistance. The GBE treatment reduces the oxidation weight gain of the current alloy from 1.950 mg cm–2 to 1.211 mg cm–2 after 100 h of cyclic oxidation at 800 °C. The findings show that the extensive outward diffusion of Ti accelerates ion transport and promotes microporosity, thus leading to more defects being formed in the oxide film. The GBE treatment suppresses the discontinuous precipitation of the Ti-bearing L12 phase and breaks the random large angular grain boundaries network, inhibiting the diffusion of Ti and ultimately enhancing the oxidation properties of the alloy. The current work provides an idea of oxidation resistance enhancement for Ti-bearing L12-strengthened alloys without changing the alloy composition.

Effect of heat treatment on microstructure and mechanical properties of lightweight high-entropy alloy

High-performance lightweight materials are in demand for a wide range of critical applications in the automotive, aviation, and aerospace industries. However, it remains difficult to enhance the strength of these alloys without significantly reducing their tensile ductility. Here, using different heat treatment routes, we overcome this inherent strength and ductility trade-off dilemma by introducing low lattice misfit precipitates in a lightweight high-entropy alloy (LHEA). In particular, the A700 alloy exhibits a high yield strength of 609 MPa and a tensile ductility of ∼24 % at room temperature, benefitting from the highly dispersed, low lattice misfit L12 and nano-lamellar body-centered cubic (BCC) phases.

First-Principle Study on Tailoring the Martensitic Transformation of B2 Nb50−xTixRu50 Shape-Memory Alloy for Structural Applications

NbRu has a potential as a high-temperature shape-memory alloy (HTSMA) because it has a martensitic transformation temperature above 1000 °C. However, its shape-memory properties could be improved for consideration in the aerospace and automotive industry. The unsatisfactory shape-memory properties could be associated with the presence of a brittle tetragonal L10 martensitic phase. Therefore, in an attempt to modify the transformation path from B2→L10 in preference of either B2→orthorhombic or B2→monoclinic (MCL), an addition of B2 phase stabiliser, titanium (Ti), has been considered in this study to partially substitute niobium (Nb) atoms. The ab initio calculations have been conducted to investigate the effect of Ti addition on the thermodynamic, elastic, and electronic properties of the Nb50−xTixRu50 in B2 and L10 phases. The results showed that the B2 and L10 phases had comparable stability with increasing Ti content. The simulated data presented here was sufficient for the selection of suitable compositions that would allow the L10 phase to be engineered out. The said composition was identified within 15–30 at.% Ti. These compositions have a potential to be considered when designing alloys for structural application at high temperatures above 200 °C.

Data-driven design of high-curie temperature full-heusler alloys for spintronic applications

In this study, we employ density functional theory (DFT) and subgroup discovery (SGD) to explore the structural and magnetic properties of full cubic Heusler compounds, with a particular emphasis on their Curie temperatures (Tc) and magnetic stability. Our comprehensive examination of 2903 structures across both L21 and Xa phases identifies configurations that exhibit both structural stability and superior magnetic properties. Notable among these, compounds such as Co2MnSi, Co2CrGe, and Cr2VGe exhibit remarkable magnetic stability, maintaining their ferromagnetic properties well above room temperature. Co2MnSi displays a substantial magnetic moment of 5.00 μB and maintains its ferromagnetic properties up to a Curie temperature of 937 K, underscoring its suitability for high-temperature applications. Similarly, Co2CrGe, with a magnetic moment of 4.00 μB, transitions to a paramagnetic state at a higher temperature of 952 K, demonstrating enhanced thermal durability. Moreover, Cr2VGe, notable for its robust magnetic moment of 2.81 μB, retains its ferromagnetic characteristics until an exceptional 2412 K, making it extremely valuable for thermally intensive environments. These findings underscore the potential of these materials in developing durable and efficient spintronic devices that operate under extreme thermal conditions. By mapping the interplay between electronic structure and magnetic properties, our study provides a predictive framework for optimizing the performance of spintronic materials.

Study on precipitation in (CoCrFeMnNi)90Al6Ti4 high entropy alloy

(CoCrFeMnNi)90Al6Ti4 high entropy alloy (HEA) was prepared by adding Al and Ti elements into CoCrFeMnNi HEA. The alloy underwent processes including copper mold suction casting, 1473 K homogenization, 30 % cold rolling + 1273 K annealing + 1073 K aging, and water quenching and heating treatment. Microstructure and phase composition of both as-cast and heat-treated (CoCrFeMnNi)90Al6Ti4 HEA were studied using metallographic microscope, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and transmission electron microscope (TEM). The effect of heat treatment processes on the precipitation of second phases in (CoCrFeMnNi)90Al6Ti4 HEA was investigated, and mechanical properties of as-cast and heat-treated (CoCrFeMnNi)90Al6Ti4 HEA were studied via hardness tests. The results show that in as-cast (CoCrFeMnNi)90Al6Ti4 HEA, the second phase precipitated is primarily L21 structured AlTiNi2 phase. After homogenization, cold rolling, annealing, and aging processes, both the quantity and size of the second phase increase, with a small amount of nanoscale L12 phase appearing after aging treatment. With the progression of heat treatment, the hardness of (CoCrFeMnNi)90Al6Ti4 HEA increases, and mechanical properties are improved.

Effect of Al content on microstructure and mechanical properties of the (FeCoNiV)100-xAlx high-entropy alloys

It is well known that face-centered cubic (FCC) high-entropy alloys (HEAs) typically have excellent ductility at room temperature but relatively low strength, which greatly limits their structural applications. To address the strength-ductility trade-off, researchers synthesized a series of (FeCoNiV)100-xAlx (x = 0–20 at. %) HEAs, investigated the effect of alloying Al on microstructure and tensile properties, then analyzed the strengthening mechanism. It was found that the crystalline structure changed from an initial single FCC structure to a duplex FCC plus body-centered cubic (BCC) structure and then to a single BCC structure with increasing Al concentration. After homogenization process, the FCC and BCC phases can be transformed to ordered L12 and B2 phases, respectively. These HEAs with duplex FCC/L12 plus BCC/B2 structure exhibit the potential for excellent mechanical properties, and their properties can be modulated by Al content and heat treatment. The properties can be tuned by both Al content and heat treatment, as the Al content can modulate the BCC phase content and the heat treatment can change the ordered structure. A careful analysis reveals that the solid solubility of Al element in this system was only 3.6 at. %, which has a limited effect on the strength. FCC/L12 bears the main plastic strain and the high tensile strength of the alloy is achieved thanks to the contribution of the BCC/B2 phase to the work-hardening rate of the alloy during the early stages of deformation and the unique work-hardening ability of the L12 phase.

Discontinuous coarsening behavior and kinetics of L12 precipitate in high-entropy alloys

Coarsening is a metallurgical process that is related to solute transmission and system energy decrease. However, for the coarsening behavior of the L12 precipitate in high-entropy alloys, the influence of moving boundary is still an open question. Here, we found the moving boundary accelerates the discontinuous coarsening of L12 phase. The multiple defects-accelerated diffusion and continual particle-capturing ability of the moving boundary provide a high-efficiency solute transport for the fast-coarsening kinetics of L12 phase. In addition, a boundary-encountered assisted precipitate formation mechanism is also validated in the recrystallized area.

Enhancing strength-ductility combination of Fe–Ni–Cr–Al–Ti high-entropy alloys via co-precipitation of sigma and L21 phases

The sigma phase is a well-known harmful phase in transition metal alloys, leading to severe embrittlement due to its inherent brittleness. However, in this work, we develop a new strategy to obtain enhanced strength-ductility combination via the synergistic effects of interlocking co-precipitation of the sigma and L21 phases in Fe40Ni30Cr20Al5Ti5 (at. %) high-entropy alloy (HEA). This HEA exhibits a good strength-ductility combination after aging treatment (800 °C for 4h), with a yield strength (YS) of about 920 MPa and an ultimate tensile strength (UTS) of about 1300 MPa while maintaining a total elongation (TE) of 24 %. It is attributed to the interlocking co-precipitation of the sigma and L21 phases with equal volume fractions into the face-centered cubic (FCC) matrix through thermomechanical treatment. During the tensile deformation, the softer L21 phase coordinates the deformation around the sigma phase, suppresses the local stress concentration, and achieves a stable high work hardening capability, as well as stacking faults (SFs) networks and density Lomer-Cottrell (L-C) locks, contributes to the excellent strain hardening capacity and thus obtains the enhanced strength-ductility combination in the HEA. This study will provide a new strategy to obtain enhanced strength-ductility combination for alloys containing brittle and hard topologically close-packed (TCP) phases, such as the sigma phases.

Tailored precipitation assisted by laser-induced cellular dislocation network structures in Al0.3CoCrFeNi high entropy alloy

Cellular dislocation network structures play a critical role in strengthening metals, while their ability to tailor the precipitation of second-phase particles has long been overlooked. Herein, a novel strategy combining laser surface treatment and two-steps annealing is proposed to produce B2 network structures in the as-cast Al0.3CoCrFeNi high-entropy alloy. Cellular dislocation network structures are first introduced in the plates by the laser surface treatment on both sides, then the L12 phase is precipitated on the wall of the dislocation networks by annealing at 700 °C. During second annealing at 800 °C, previously precipitated L12 precursors provide kinetically preferred sites and element segregation for the precipitation of the B2 phase, finally forming dense B2 network structures within the defect-scarce matrix. Dislocations can easily move inside the network structures, and they are blocked by the B2 particles in the wall areas, thus presenting a superior strength-ductility synergy.

High Magnetic Performance in MnGa Nanocomposite Magnets.

In view of their potential applicability in technology fields where magnets are required to operate at higher temperatures, the class of nanocomposite magnets with little or no rare earth (RE) content has been widely researched in the last two decades. Among these nanocomposite magnets, the subclass of magnetic binary systems exhibiting the formation of L10 tetragonal phases is the most illustrious. Some of the most interesting systems are represented by the Mn-based alloys, with addition of Al, Bi, Ga, Ge. Such alloys are interesting as they are less costly than RE magnets and they show promising magnetic properties. The paper tackles the case of MnGa binary alloys with various compositions around the Mn3Ga stoichiometry. Four MnGa magnetic alloys, with Mn content ranging from 70 at% to 75 at% were produced using rapid solidification to form the melt. By combining structural information arising from X-ray diffractometry and transmission electron microscopy with magnetic properties determined by vibrating sample magnetometry, we are able to document the nature and properties of the structural phases formed in the alloys in their as-cast state and upon annealing, the evolution of the phase structure after annealing and its influence on the magnetic behavior of the MnGa alloys. After annealing at 400 °C and 500 °C, MnGa alloys are showing a multiple-phase microstructure, consisting of co-existing crystallites of L10 and D022 tetragonal phase. As a consequence of these structurally and magnetically different phases, co-existing within the microstructure, promising magnetic features are obtained, with both coercive fields and saturation magnetization exceeding values previously reported for both alloys and layers of MnGa.

Sunflower-like eutectic solidification in gas atomized Al0.3CrFeNiTi0.3 medium-entropy alloy powders: A comprehensive microstructural study

The addition of larger atomic size elements, such as Al and Ti, to CrFeNi medium-entropy alloys (MEAs) offers a strategic approach to overcome the strength-ductility trade-off. This study focuses on examining the morphological, solidification, phase, and elemental characteristics of Al0.3CrFeNiTi0.3 feedstock powders produced through gas atomization (GA). The rapid cooling rate inherent in GA results in sunflower-like eutectic solidification. This structure exhibits firstly solidified Cr-rich BCC phases filled with cuboidal-shaped L21-type precipitates, each measuring up to ∼20 nm. Their peripheral regions display outward and radial growth of L21 and Fe-rich BCC eutectic phases, while FCC phase develops at the remaining sites. Intermediate B2 layers between BCC and L21 phases are considered as kinetic buffers, which enhance the interfacial stability. The size and shapes of powders determine their cooling rates, leading to a transition from comparably large sunflower-like eutectic structures to finer equiaxed grains alongside reduced elemental segregation with decreasing powder size. Nano-hardness measurements demonstrate superior mechanical strength in the peripheral regions due to the higher volume fraction of the L21 phase and its optimal interfacial coherency with the Fe-rich BCC phase. Furthermore, the slightly higher concentrations of Al and Ti in Fe-rich BCC phase (compared to the Cr-rich BCC phase) induce a better lattice distortion effect.

Formation of lamellar eutectic structure and improved mechanical properties of directional solidified Al0.9CoCrNi2.1 high-entropy alloy

In this study, Al0.9CoCrNi2.1 EHEA was prepared by directional solidification at various withdrawal rates from 6 to 120 μm/s. The lamellar eutectic structure is formed containing FCC (L12) and BCC (B2) at different withdrawal rates during directional solidification. The solid-liquid interface of the alloy transfers from nearly-planer to cellular eutectic interface and the lamellar spacing decreases from 7.17 μm to 1.65 μm as the withdrawal rate increases. The lamellar spacing is negatively correlated with withdrawal rates which was identified by the Jackson-Hunt model and its growth rate index (0.484) is closely related to the theoretical value (0.5). The tensile experiment demonstrates that the structure of Al0.9CoCrNi2.1 EHEA is finer and the ultimate tensile strength and elongation increase as the withdrawal rate increases. The elongation of Al0.9CoCrNi2.1 EHEA is two times higher than that of the as-cast alloy at the withdrawal rate of 120 μm/s. It is concluded that the formation of the L12 phase and Cr-rich precipitated phases in the directional solidified eutectic structure are associated with the enhancement of mechanical properties due to grain refinement at high withdrawal rates.

Corrosion Behavior of Al-Containing CoNiV Medium Entropy Alloy Coating Fabricated by Laser Cladding.

CoNiV medium entropy alloys (MEAs) have been widely recognized for their superior corrosion resistance. Nonetheless, their extensive application has been hindered by high production costs and complex fabrication processes. In this study, CoNiVAlx MEA coatings were synthesized on AISI 304 stainless steel substrates via laser cladding technology. The microstructure, phase composition, corrosion resistance, and corrosion mechanisms of the coatings were systematically investigated by using advanced characterization techniques, including optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and electrochemical workstation analysis. The ratio of O2-/OH- in the passivation film of the coated surface exhibited a gradual increase with the addition of Al. The formation of the Al-containing precipitated phase L21 was observed at x = 0.3 and 0.4. The results demonstrated that moderate Al doping (x ≤ 0.2) enhanced corrosion resistance by improving the stability of the passivation film and reducing the thermodynamic tendency toward corrosion. In contrast, excessive Al doping (x > 0.2) led to the formation of the L21 phase, which increased the susceptibility to localized corrosion, thus compromising the overall corrosion resistance.

Effect of Ti on the corrosion resistance of Al-Cr-Fe-Mn-Mo-Ni single and multi-phase CCAs

Five Al0.3Cr0.5Fe2Mn0.25Mo0.15Ni1.5Tix compositionally concentrated alloys were synthesized, forming alloys with an FCC matrix. At Ti concentrations of 5 at% and above, an L21 phase enriched in Al, Ti and Ni was present within the FCC matrix. At Ti concentrations of 9.6 at% Ti and above, a three-phase microstructure containing FCC+L21+Laves phases was formed, with the Laves third phases enriched in Cr and Mo. Ti(IV) was a prominent constituent in the passive film. Resistance to localized corrosion improved with Ti concentration before reaching an optimal concentration and beginning to decrease, likely due to the formation of new phases.

An in-depth look at the stability, electronic structure, mechanical properties, and thermodynamics characteristic of Ir3TM (TM: Sc, Ti, V) compounds

In this paper, the structural, mechanical, electronic, and thermodynamic properties of Ir3TM (TM = Sc, Ti, and V) intermetallic compounds in the cubic (L12) and hexagonal (D019 and D024) phases are presented. The outcomes of the simulation rely on density functional theory (DFT) within the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) based on the full-potential linearized augmented plane wave (FP-LAPW) approach. The existing study was performed on the L12 cubic phase. in addition to hexagonal D024 and D019 phases, which may be relative but differ in the way that the atomic layers are stacked. The calculated total, cohesive energy, and heat formation suggest that the Ir3Sc compound can be stable in the D024 phase because of an overlap between the L12 and D024 phases with a total energy difference of around 0.026 eV/atom. Ir3Ti and Ir3V are more stable in L12 and D019, respectively. From elastic constants calculations, it reveals that the studied compounds are mechanically stable and harder in the cubic phase than hexagonal phase. However, Ir3Sc has the lowest hardness due to its relative ductility. Inversely, Ir3V has the maximum hardness with a lack of ductility. It was observed that these compounds have an elastic anisotropy based on the three-dimensional Young's modulus surface, and Ir3Sc has the strongest anisotropy, while Ir3V has the weakest in the L12 phase. The total density of state (TDOS) calculations shows that Ir3Ti and Ir3V are stable in the L12 and D019 phases, respectively, except for the Ir3Sc compound which might undergo a martensitic transition. Also, the pseudogap for Ir3V moves quite close to the Fermi level, indicating that the covalent bonding in this compound is sharper than the other compounds. Moreover, via the quasi-harmonic Debye model within the Gibbs computational code, thermodynamic properties are calculated and analyzed with temperature and pressure.

The p-type (Mn1.5Co0.5)VAl Heusler alloy with high Curie temperature for spintronics device applications

The solid-state method was employed to synthesize (Mn1·5Co0.5)VAl Heusler alloy particles it exhibits soft magnetic property with semiconducting nature. The X-ray diffraction technique was used to study the structural investigation, it revealed a pure L21 phase with a lattice parameter of a = 5.83 Å. It was thermally stable up to 900 °C, confirmed through thermogravimetric and differential thermal analysis with no observed weight loss, underscoring the alloys impressive thermal resilience. A positive carrier concentration was detected through the Hall measurements, its affirming the p-type semiconducting nature of the alloy. The magnetic property analysis revealed its soft magnetic nature with low coercivity. Remarkably, the Curie temperature was found at 799 K, surpassing both experimental and theoretical predictions. The magnetic characteristics of multicomponent alloys are significantly influenced by the degree of atomic order on the various crystallographic sites. Since, this type of material consuming little energy, it may be utilize magnetic switching for spintronic devices applications due to its high Curie temperature and low coercivity.

Microstructure and mechanical properties of CoCrNiVAlx multi-principal component alloy

Multi-principal component alloy has been proved to form disordered solid solution in most cases. However, multi-principal component alloy with single phase solid solution has a few disadvantages in mechanical properties, such as low strength or poor plasticity. Aiming at CoCrNi-based multi-principal component alloy with low strength, this paper proposed a method to enhance the multi-principal component alloy through composition design. CoCrNiVAlx multi-principal component alloy was melted by non-consumable vacuum arc melting, and the content of σ phase in the multi-principal component alloy was changed by adjusting the content of Al element. With the addition of Al element, the fcc disordered phase in the multi-principal component alloy gradually went to the ordered L12 phase with the same structure. When the amount of Al was 1.5 wt%, the compressive strength reached 2347 MPa and the hardness reached 760.8HV, which were 30% and 20% higher than the compressive strength (1828 MPa) and hardness (619.3HV) of CoCrNiV multi-principal component alloy, respectively. With the further increase of Al element to 2.0 wt%, the σ phase in the multi-principal component alloy increased further, resulting in the simultaneous decrease of strength and plasticity. The strengthening mechanism of multi-principal component alloy was analyzed, and the strengthening action of L12 phase was confirmed. The results showed that the strengthening of multi-principal component alloy was mainly provided by L12 phase strengthening (1229.55 MPa, 52.39%) and grain boundary strengthening (376 MPa, 16.02%). This paper provided a probable strategy to increase the strength of the multi-principal component alloy, which opened up a new idea for the composition design of multi-principal component alloy.

New lightweight high-entropy alloy coatings: Design concept, experimental characterization, and high-temperature oxidation behaviors

Lightweight high-entropy alloy (HEA) coatings by laser cladding (LC), which combines the advantages of high-entropy alloys and laser cladding, are potential materials for high-temperature applications. Al20Cr5Fe50Mn20Ti5 and Al25Cr20Fe20Mn15Ti20 HEAs were designed, and the calculated thermal parameters were close to the Ni-based alloy substrate (Inconel 718). Based on this, Al20Cr5Fe50Mn20Ti5 and Al25Cr20Fe20Mn15Ti20 HEA coatings were fabricated by LC on the substrates. The main phase structures of the two designed HEAs are the BCC + L21 phase, as revealed by the CALculation of PHAse Diagrams (CALPHAD). The high-temperature oxidation properties of the coatings were systematically investigated using isothermal oxidation tests. The oxidation activation energies of both coatings were 154.8 and 133.4 kJ/mol. Combined with molecular dynamics (MD) simulation, the clustering mechanism of Al and Ti elements was revealed in the formation of the L21 phase, whereas the high proportion of Ti elements increased the vacancy concentration, which was not conducive to oxidation resistance. Through this study, lightweight HEA coatings with excellent high-temperature performance can be designed and developed in the Al-Cr-Fe-Mn-Ti HEA system.

An excellent combination of strength and ductility via hierarchical precipitation structures in Co-free medium-entropy alloys

A Co-free non-equiatomic Ni2·5CrFeAl0·25Ti0.25 medium-entropy alloy (MEA) with an excellent strength-ductility synergy was fabricated, which shows a multiphase structure composed of face-centered cubic (FCC), L12 (ordered FCC), and Cr-rich body-centered cubic (BCC) phase by thermomechanical processing. Specifically, the aged sample displays the outstanding yield tensile strength (YTS, ∼1188 MPa), ultimate tensile strength (UTS, ∼1560 MPa) and work-hardening rate (WHR, ∼4.5 GPa) values as well as an acceptable plasticity of ∼16.6%. Theoretical calculations suggest that precipitation strengthening significantly contributes to achieving the fascinating tensile strength among various strengthening contributors. Further analyses reveal that multiple nanoscale stacking-fault (SF) networks are activated during plastic deformation in the aged alloy. Accordingly, the dual effects consisting of the hierarchical precipitation structure and SF networks lead to the combination of excellent tensile strength and strain-hardening capacity.

In situ study of phase transformations in the metastable Fe-42Ga alloy

The evolution of the structural phases of the Fe-42.4 at% Ga alloy was studied using neutron diffraction performed with high-intensity continuous scanning in a wide temperature range. The sequence of occurrence of structural states both during heating and subsequent cooling is reported. The structural phases Fe13Ga13, Fe13Ga9, α-Fe6Ga5, D03, L12, A2 are present in the alloy and they disappear upon heating above 800 °C into the partially ordered B2/A2 phase. The high-temperature Fe13Ga13 intermetallic compound exists in two temperature ranges: 25–580 °С and 770–800 °С during heating and precipitates again during cooling. The persistence of the phase upon cooling down to room temperature is inconsistent with the phase diagram, indicating that the alloy remains in a metastable state after the heating and subsequent cooling. The D03, α-Fe6Ga5 and L12 phases are formed during cooling.