A new study published in the Journal of Materials Science by Xintong Zhang, Wei Sun, and colleagues at the University of Science and Technology Beijing, working with Ling Cheng of the China Electric Power Research Institute, has now traced exactly how the way a Fe50Co50 alloy is quenched before hot rolling determines whether the finished sheet emerges strong and ductile or weak and fracture-prone. The work combines microstructural characterization, first-principles calculations, uniaxial tensile testing, and actual rolling deformation into a single multiscale picture, connecting what happens at the level of individual atomic planes to the macroscopic behavior of a rolled plate.

The team prepared specimens using two different quenching routes, labeled HOQ and HWQ, and then examined the room temperature lattice and microstructural states of each before any hot rolling took place. The differences were subtle but consequential. Compared with the HOQ condition, the HWQ specimens showed an apparent relative lattice contraction of approximately 0.46 percent, a tiny squeeze of the crystal lattice that turned out to ripple through every subsequent stage of processing. Beyond the lattice itself, the two conditions also differed in grain structure, crystallographic orientation, the density of geometrically necessary dislocations, and the character of their grain boundaries.

To understand why such a small lattice change could matter, the researchers turned to density functional theory calculations, a quantum mechanical method that models the behavior of electrons in a crystal from first principles. They focused on the generalized stacking fault energy, or GSFE, a quantity that describes the energetic cost of sliding one block of atoms past another along a specific crystallographic plane. Stacking fault energies govern how easily dislocations, the line defects that carry plastic deformation, can move through a metal, and they therefore sit at the heart of any theory of ductility.

The calculations revealed a clear trend. In the undistorted model of the B2 FeCo lattice, the maximum GSFE along the selected slip pathway was 0.898 joules per square meter. When the experimentally measured 0.46 percent lattice contraction was applied to the computational cell, the maximum GSFE rose to 0.926 joules per square meter. Pushing the contraction to an exaggerated 10 percent drove the value up to 1.067 joules per square meter. In other words, squeezing the lattice makes it energetically harder for slip to proceed, which is precisely the kind of change that would be expected to embrittle the material. The authors are careful to note, however, that these DFT results illuminate slip energetics at the atomic scale and are not intended to directly represent dislocation behavior during the high temperature, high strain environment of hot rolling.

With the starting microstructures characterized and the atomic scale energetics mapped, the team subjected both quenched conditions to hot rolling and compared what came out the other side. The differences were striking. The HOQ-HR condition, meaning the HOQ-quenched alloy after hot rolling, exhibited a weaker deformation texture, meaning its grains were less strongly aligned into preferred orientations by the rolling process. It also retained a higher fraction of high angle grain boundaries, showed less pronounced local dislocation entanglement, and, critically, demonstrated better resistance to the cracking that rolling deformation tends to induce. The HWQ-HR condition told the opposite story, with a stronger deformation texture and far more extensive dislocation entanglement woven through its microstructure.

Deformation texture and dislocation entanglement are not merely cosmetic features. A strong texture means that most grains share a common crystallographic alignment, which can concentrate deformation along specific planes and directions and create paths for crack propagation. Dense dislocation entanglement, meanwhile, locks up the mobile dislocations that a metal needs in order to flow plastically, raising the local stress required for further deformation and encouraging cracks to nucleate instead. The microstructural evidence therefore painted a consistent picture: the HOQ route left the alloy in a state that could accommodate rolling deformation gracefully, while the HWQ route left it primed to accumulate damage.

Room temperature tensile tests confirmed the story quantitatively. The HWQ-HR specimens achieved an average ultimate tensile strength of 500.1 megapascals, with a standard deviation of 24.41 megapascals, but managed an elongation after fracture of only 4.6 percent, plus or minus 1.1 percent. The HOQ-HR specimens were in a different league altogether, reaching an average ultimate tensile strength of 725.4 megapascals with a remarkably tight standard deviation of 5.62 megapascals, while still stretching 19.3 percent, plus or minus 1.21 percent, before breaking. That combination of roughly 45 percent higher strength and more than four times the ductility represents a decisively more favorable strength-ductility balance for the HOQ-HR condition.

For a material class whose brittleness has historically limited its adoption, these numbers carry real industrial weight. Equiatomic FeCo and related Fe-Co-V alloys are prized for soft magnetic applications ranging from high performance electric motors to aerospace power systems, and prior research has explored routes as varied as heat treatment optimization and additive manufacturing to coax ductility out of them. The new work adds a deceptively simple lever to that toolkit: the quenching route chosen before hot deformation, which sets the lattice parameter, the dislocation density, and the grain boundary character that the alloy carries into the rolling mill.

What makes the study conceptually interesting beyond metallurgy is its multiscale architecture. Rather than treating the alloy as a black box, the researchers linked an experimentally measured lattice distortion to a computationally predicted change in slip energetics, and then connected both to observable microstructural evolution during rolling and finally to macroscopic tensile performance. Each link in that chain is independently verifiable, and together they demonstrate that a sub-percent lattice contraction, invisible to the naked eye, can cascade into a fourfold difference in ductility. As electrification drives demand for better soft magnetic alloys, understanding how processing history echoes from the atomic scale to the finished component may prove to be the difference between a material that cracks on the production line and one that rolls cleanly into the next generation of electric machines.

Subject of Research: Microstructural and atomic-scale effects of quenching conditions on the hot deformation behavior of equiatomic FeCo alloy

Article Title: Multiscale microstructural characteristics of quenched Fe50Co50 alloy and their effects on hot deformation behavior

Article References: Zhang, X., Sun, W., Xiao, X., Zhang, H., Zu, C., Li, X., Zhang, Z., Cheng, L., & Wang, Z. (2026). Multiscale microstructural characteristics of quenched Fe50Co50 alloy and their effects on hot deformation behavior. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13832-3

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13832-3

Keywords: FeCo alloy, quenching, hot rolling, lattice contraction, stacking fault energy, density functional theory, dislocation density, deformation texture, ductility, soft magnetic materials, grain boundaries, tensile strength

The two contenders are known as A2 and B2. The A2 phase is a disordered body-centered cubic solid solution, in which iron and chromium atoms occupy crystallographic sites in essentially random fashion. The B2 phase is its ordered sibling, an arrangement in which aluminum and nickel segregate to distinct sublattices, producing an ordered lattice enriched in aluminum, nickel, and cobalt. The distinction matters enormously in practice. The relative amounts of A2 and B2 influence how strongly the alloy strengthens, and the ordered B2 phase has been repeatedly linked to reduced corrosion resistance in these materials. Engineers designing turbines, marine hardware, or any component exposed to aggressive environments therefore need to know exactly how much B2 lurks in the microstructure, and whether that amount can be predicted or controlled.

Here is the problem that has frustrated the field for years: the lattice parameters of A2 and B2 differ by less than about 0.4 percent. X-ray diffraction, the workhorse technique for phase quantification in metals, simply cannot reliably separate the two across most of the composition range. Worse, published thermodynamic phase diagrams of the Al-Co-Cr-Fe-Ni system disagree substantially with one another about where the A2, B2, and mixed A2-plus-B2 fields begin and end. Different thermodynamic databases yield different widths for the two-phase field and even different conclusions about whether a nominally single-B2 region exists at high temperature. That disagreement leaves a deceptively simple question dangling: even if theory predicts a single B2 phase at elevated temperature, can that state actually be trapped at room temperature by practical quenching?

To answer it, the team led by Michael Aizenshtein and Shmuel Hayun prepared a series of AlxCoCrFeNi alloys spanning aluminum contents from one to four atoms per formula unit. Each alloy was arc melted under ultra-high-purity argon with a titanium getter to scavenge oxygen, remelted and flipped five times to homogenize the chemistry, and cast into six-millimeter rods. Samples were then held in a vertical tube furnace at 1593 to 1623 kelvin for thirty minutes under flowing argon before being quenched into room-temperature water. The aluminum-leanest composition received the slightly hotter treatment, a deliberate choice to suppress the formation of unwanted face-centered cubic and brittle sigma phases during cooling. Thirty minutes was a pragmatic compromise: long enough to approach the high-temperature state, short enough to avoid excessive coarsening of the phases.

The analytical strategy had to be as layered as the microstructure itself. High-resolution scanning electron microscopy was tried first, but the A2 precipitates turned out to be nanoscale, far below what scanning electron microscopy can quantify reliably. X-ray diffraction with whole-pattern fitting could resolve the B2 superlattice reflections only at higher aluminum contents, roughly x greater than or equal to 2.75. For everything leaner in aluminum, the burden fell to transmission electron microscopy. Thin foils were extracted by focused ion beam milling and examined with a field-emission TEM equipped for energy-dispersive X-ray spectroscopy. Electron diffraction identified the phases; elemental maps revealed their chemistry. The A2 fraction was estimated from the areal fraction of the chromium- and iron-rich precipitates within the B2 matrix, a reasonable approximation of local volume fraction because the precipitates are nanoscale and approximately equiaxed. Where both methods were feasible, their estimates agreed in trend and were averaged.

The elemental maps tell a vivid story of chemical self-organization. In Al2CoCrFeNi, the B2 matrix glows with aluminum and nickel, while the embedded A2 precipitates concentrate chromium and iron. The same partitioning appears at the extreme aluminum-rich end, where selected-area electron diffraction using the forbidden (100) reflection, a fingerprint of B2 ordering, confirmed the ordered phase exists but does not fill the field of view. Dark-field imaging revealed that even Al4CoCrFeNi, a composition that thermodynamics says should be overwhelmingly B2, retains nanoscale A2 precipitates after quenching. A single-B2 state was not experimentally retained anywhere in the composition range studied. The retained A2 fraction decreases steadily with increasing aluminum content, and a linear extrapolation suggests it would approach zero only near 57 atomic percent aluminum, close to the ideal 60 percent needed to perfectly fill the body-center sites of the B2 lattice. Yet the experimental curve flattens above roughly 40 atomic percent aluminum, hinting at a stubborn residual A2 fraction that refuses to disappear.

Comparison with thermodynamic calculations sharpens the mystery. The team ran CALPHAD calculations in Thermo-Calc with the TCHEA7 database, stepping through compositions and temperatures in fine increments. The calculations reproduce the qualitative trends beautifully: more aluminum stabilizes B2, higher temperature stabilizes B2, and a single-B2 field should emerge above roughly x equals 3 near 1550 kelvin. Quantitatively, however, the measured A2 fractions are consistently higher than the equilibrium predictions. The authors are careful not to read this as a failure of thermodynamics. Instead, the discrepancy points to kinetics: during the quench, atoms have just enough mobility to redistribute over short distances and re-form nanoscale A2 precipitates inside the B2 matrix before diffusion freezes out.

A simple back-of-the-envelope estimate makes that argument compelling. At a cooling rate of about 50 kelvin per second, cooling from 1473 to 1273 kelvin takes roughly four seconds. That window allows a characteristic diffusion length of only several tens of nanometers, which is precisely the scale of the precipitates observed in TEM. In other words, the microstructure that survives the quench is not a frozen snapshot of the high-temperature equilibrium state; it is the product of a brief, frantic burst of short-range diffusion during cooling. Rapid cooling suppresses long-range coarsening but cannot eliminate short-range precipitation. This insight has a sobering corollary for the field: conventional heat treatment followed by water quenching is fundamentally inadequate for validating the equilibrium high-temperature A2/B2 boundaries in this alloy system. Any phase diagram built on quenched microstructures is really a map of quench retention, not equilibrium.

The practical implications ripple outward. For designers of high-temperature components, the work shows that the corrosion-relevant B2 fraction can be tuned by aluminum content and processing temperature, but that a purely B2 microstructure remains out of reach below 57 atomic percent aluminum, well beyond the composition range of structural interest. For computational metallurgists, it provides a valuable benchmark: the trends of CALPHAD are trustworthy, but experiments must account for kinetic retention when validating high-temperature phase fields. The authors suggest the path forward lies in combining direct high-temperature characterization, which observes phases in situ without quenching, with longer equilibration treatments and refined thermodynamic modeling. Until then, the hidden nanoscale architecture of these five-element alloys will keep reminding materials scientists that what you measure at room temperature is not always what existed at 1600 kelvin.

Subject of Research: Phase fraction determination of disordered A2 and ordered B2 body-centered cubic phases in AlxCoCrFeNi high-entropy alloys after elevated-temperature heat treatment and quenching

Article Title: Determination of the A2/B2 BCC phase fraction in AlxCoCrFeNi (1 ≤ x ≤ 4) at elevated temperatures

Article References: Aizenshtein, M., Salhov, S., Strumza, E., Fadel, D., & Hayun, S. (2026). Determination of the A2/B2 BCC phase fraction in AlxCoCrFeNi (1 ≤ x ≤ 4) at elevated temperatures. Journal of Materials Science: Metallurgy, 1(1), Article 22. https://doi.org/10.1007/s44492-026-00023-z

Image Credits: AI Generated

DOI: 10.1007/s44492-026-00023-z

Keywords: high-entropy alloys, AlxCoCrFeNi, A2 phase, B2 phase, BCC, X-ray diffraction, transmission electron microscopy, CALPHAD, quenching, phase boundaries, corrosion resistance, thermodynamics