A new study published in the Journal of Materials Science by Ester Kelly Starick Pellegrino and colleagues at the University of São Paulo, together with collaborators at the Federal University of Itajubá and the Federal University of Rio de Janeiro, has now filled that gap. The team constructed a liquidus projection for the cobalt-rich region of the Co-Si-B system, a two-dimensional map that shows which crystalline phases are the first to solidify from the molten alloy across the entire compositional space. This map is far more than an academic exercise. When engineers want to manufacture an amorphous metallic ribbon, they need to know exactly which competing crystalline phases will try to form as the melt cools, because those crystals are the enemies of glass formation and can destroy the delicate amorphous structure that gives the alloy its superior properties.

The logic behind these alloys is elegantly chemical. Amorphous metallic alloys typically contain 70 to 85 atomic percent transition metals, with the remaining 15 to 30 percent made up of metalloids such as silicon and boron. Boron, with its small atomic radius, promotes a denser and more complex liquid structure that hinders the atomic rearrangement needed for boride crystals to nucleate. Silicon works synergistically by increasing the viscosity of the melt and stabilizing the amorphous network against premature devitrification. Together, these metalloids allow molten metal to be rapidly quenched into a homogeneous glassy ribbon rather than a polycrystalline solid. But the glass is metastable, and upon heating it will always try to crystallize into the equilibrium phases. Knowing precisely what those phases are, and at what compositions they dominate, is therefore the foundation of rational alloy design.

To build their map, the researchers first performed a thermodynamic extrapolation using Thermo-Calc software, combining the most recent optimized assessments of the binary Co-Si, Co-B, and Si-B systems and accounting for the known ternary phase. They then synthesized a series of cobalt-rich alloys by arc melting high-purity elements in a water-cooled copper crucible under argon. Each composition was remelted four times to guarantee chemical homogeneity, with total mass losses kept below one percent so that the nominal compositions could be trusted as the true alloy compositions. The as-cast samples were then interrogated with an arsenal of characterization techniques: X-ray diffraction, scanning electron microscopy with backscattered electron imaging, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction, the latter used to definitively identify crystal phases in the microstructures.

The resulting liquidus projection identifies ten primary precipitation fields, meaning ten different crystalline phases that can be the first to appear as the liquid cools, depending on composition. These include the cobalt solid solution in its high-temperature and room-temperature allotropic forms, the silicides Co3Si, alpha Co2Si, beta Co2Si, and CoSi, the borides Co3B, Co2B, and CoB, and the ternary phase Co4.75Si2B. The map also traces the monovariant lines, the boundaries along which two phases crystallize simultaneously from the melt, and proposes nine ternary invariant reactions involving the liquid phase, including three ternary eutectic points where three phases solidify together. Twelve binary invariant reactions inherited from the Co-Si and Co-B edge systems anchor the projection, and the arrows along the monovariant lines point the way toward lower temperatures, tracing the solidification paths that molten alloys of any given composition will follow.

Perhaps the most striking finding concerns the ternary phase Co4.75Si2B, first identified in the literature more than sixty years ago but never before characterized in terms of its melting behavior. By preparing an alloy with exactly the stoichiometric composition of this phase, the researchers discovered that it does not melt congruently. Instead, the microstructure showed crystals of Co4.75Si2B enveloping primary grains of alpha Co2Si, a classic signature of a peritectic reaction. In other words, the ternary phase forms when the liquid reacts with pre-existing alpha Co2Si crystals rather than crystallizing directly from the melt on its own. This single observation, expressed as the reaction L plus alpha Co2Si yielding Co4.75Si2B, resolves a long-standing question about the phase and reshapes the topology of the entire liquidus surface around it.

Equally fascinating is the discovery of three thermal maxima along the monovariant lines, labeled m1, m2, and m3. These points act as thermodynamic watersheds on the liquidus surface. On one side of a maximum, the liquid composition evolves toward one ternary eutectic point during solidification; on the other side, it flows toward a completely different one. The researchers demonstrated this with pairs of alloys whose compositions straddled the maxima: alloy 41, for example, saw its liquid become richer in boron as it solidified toward the EI eutectic, while alloy 5a, on the opposite side of maximum m2, saw its liquid become richer in cobalt and terminate along a different monovariant line. Tiny shifts in the initial composition, therefore, send the solidification process down entirely different trajectories, a fact of enormous practical importance for anyone trying to control the microstructure of a cast or rapidly quenched alloy.

The monovariant line separating the alpha Co2Si and Co4.75Si2B primary fields turned out to have a dual personality. Between the thermal maximum m1 and the invariant point UIII, the line behaves as a eutectic valley, with the two phases crystallizing in a coupled fashion. Between m1 and the invariant point UVI, however, the line switches to peritectic behavior, with one phase reacting with the liquid to form the other. This kind of behavioral switch along a single monovariant line is a subtle feature of ternary phase diagrams, and detecting it required the careful microstructural detective work that characterizes the whole study, including the identification of fine-scale eutectic constituents that push the resolution limits of electron backscatter diffraction to roughly one micrometer.

The new projection is in good agreement with the partial liquidus map proposed by Omori and Hashimoto in 1977 for the region above 66.7 atomic percent cobalt, but it extends and refines that pioneering work substantially, adding fields for phases such as CoSi, CoB, Co3Si, and beta Co2Si that the earlier study could not resolve. The authors note that the actual temperatures of the invariant reactions, liquidus, and solidus were not determined in this study, leaving a clear target for future differential thermal analysis and thermodynamic modeling. Even so, the compositional framework alone provides what the field has lacked: an experimentally grounded prediction of solidification behavior across the cobalt-rich ternary space.

For the growing community working on soft magnetic materials, the implications are immediate. Cobalt-based metallic glasses are prized in high-precision applications where magnetic cores must be stable, efficient, and corrosion-resistant, and every improvement in glass-forming ability translates directly into better ribbons and devices. With the liquidus projection now in hand, alloy designers can anticipate which borides and silicides will compete with glass formation for any candidate composition, choose compositions that maximize the distance from troublesome primary phase fields, and understand why small compositional tweaks near the thermal maxima can dramatically alter the outcome of rapid solidification. It is a reminder that even in a field as mature as metallurgy, fundamental maps still hold the power to unlock the next generation of technology, one carefully melted button of alloy at a time.

Subject of Research: Phase equilibria and solidification behavior of the cobalt-rich Co-Si-B ternary alloy system

Article Title: Liquidus projection of the cobalt-rich Co–Si–B system

Article References: Pellegrino, E. K. S., Boas, S. B. V., da Silva, A. A. A. P., Ferreira, L. M., Faria, M. I. S. T., Coelho, G. C., & Nunes, C. A. (2026). Liquidus projection of the cobalt-rich Co–Si–B system. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13756-y

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13756-y

Keywords: metallic glasses, amorphous alloys, cobalt alloys, liquidus projection, phase diagrams, peritectic reaction, ternary system, solidification, magnetic materials, silicides, borides, thermodynamics

The secret of the amorphous advantage begins at the atomic scale. In a crystalline alloy, grain boundaries, dislocations and other lattice defects act as chemically energetic hotspots where corrosion preferentially initiates. An amorphous alloy has no grains and no grain boundaries, presenting a chemically homogeneous surface to the environment. Combined with the right alloying recipe, typically iron blended with chromium, molybdenum, tungsten, boron, carbon and sometimes cobalt, nickel or phosphorus, this structural uniformity allows the coating to form dense, adherent passive films rich in chromium and molybdenum oxides. The review emphasizes that Fe-based AMCs consistently outperform conventional steels in aggressive chloride-rich environments such as seawater, where pitting corrosion normally drills microscopic pinholes through protective layers and eats into the underlying metal.

But chemistry alone does not tell the whole story, and the review is unusually candid about the gap between laboratory promise and field performance. The dominant way to make these coatings is thermal spraying: high-velocity oxy-fuel (HVOF), high-velocity air fuel (HVAF), detonation spraying, atmospheric plasma spraying and laser cladding all propel molten or semi-molten powder particles onto a substrate at extreme speeds. Each splat solidifies within microseconds, locking in the amorphous structure, but the process also stamps the coating with intrinsic defects. Porosity, unmelted particles, oxide inclusions, micro-cracks and splat boundaries thread through the deposit, and these are precisely where corrosion attacks first. Studies cited in the review show that pitting in sprayed Fe-based amorphous coatings frequently nucleates at pores and oxide inclusions rather than on the pristine amorphous matrix, meaning the coating’s Achilles heel is manufactured, not inherent.

Alloy composition remains the most powerful lever designers can pull. Chromium is the workhorse: it enriches the passive film and dramatically improves resistance in chloride solutions, with its benefit depending on having enough of it uniformly distributed. The review highlights work showing that eliminating chromium-depleted zones, which can form during spraying when oxidation selectively consumes elements, substantially enhances localized corrosion resistance. Molybdenum and tungsten act synergistically with chromium, improving the stability and repassivation behavior of the passive film, while boron and carbon promote glass formation, which is essential because a coating that crystallizes during deposition loses much of its corrosion advantage. Minor additions of nickel, cobalt, niobium or phosphorus tune glass-forming ability and electrochemical behavior, though the review notes that trade-offs exist, since elements that improve corrosion resistance can degrade the amorphous-forming capacity or mechanical properties if pushed too far.

Crystallization itself emerges as a nuanced theme. The amorphous structure is metastable, and thermal exposure during spraying or in service can trigger partial crystallization. The reviewed literature shows that the effect on corrosion is not uniformly negative: small amounts of nanoscale crystals can sometimes refine passivation, but solute-lean nanocrystals tend to deplete the surrounding amorphous matrix of chromium, creating galvanic couples that accelerate pitting. Structural relaxation, the subtle atomic rearrangement that occurs below the crystallization temperature, also shifts corrosion behavior. Recent work on thermal regulation of coatings demonstrates that carefully controlling the thermal history can actually be used as a strategy to enhance corrosion resistance, turning what was once seen purely as a degradation mechanism into a processing tool.

Environment matters as much as the material. The review surveys how temperature, hydrostatic pressure, applied electrochemical potential, and the identity of aggressive ions all reshape corrosion behavior. Elevated temperatures accelerate passive film dissolution and alter its semiconducting properties, while high hydrostatic pressure, relevant to deep-sea applications, changes both the thermodynamics and kinetics of pit initiation and growth. Chloride ions remain the primary villain, breaking down passive films and stabilizing pit growth, and sulfur-bearing species can compound the damage by interacting with oxide inclusions. The authors also point to tribo-corrosion, the coupled action of wear and corrosion, as a critical consideration for real components, since mechanical removal of passive films forces the surface into a continuous cycle of repassivation that not every coating chemistry can sustain.

Fortunately, the toolbox of enhancement strategies has grown impressively. Post-spray laser remelting re-fuses the coating surface, healing pores and splat boundaries and restoring a fully dense amorphous or amorphous-nanocrystalline layer. Sealing treatments, from traditional inorganic sealants to novel waterborne silicone-modified acrylics and eco-friendly rosin-based hybrid sealants loaded with functionalized silica and graphene oxide, plug the through-thickness porosity that would otherwise let electrolytes reach the steel substrate. Perhaps the most eye-catching strategy is superhydrophobicity: by combining micro-scale laser texturing or spray texturing with low-surface-energy chemistry, researchers have produced Fe-based amorphous coatings that repel water entirely, achieving self-cleaning, anti-fouling and dramatically enhanced anti-corrosion performance in a single surface.

Composite approaches push the concept further. Reinforcing the amorphous matrix with stainless steel powders, titanium nitride, aluminum oxide, titanium diboride or carbon nanotubes, sometimes delivered as core-shell structured powders or molybdenum-clad feedstock, simultaneously boosts wear resistance, impact toughness and corrosion performance. Reactive plasma spraying that forms titanium nitride phases in situ has produced coatings with improved multi-scale mechanical behavior and corrosion-abrasion resistance. These developments matter because in applications such as engine pistons, hydraulic rods, marine hardware and biomass-fired boiler tubes, coatings rarely face corrosion alone; they face corrosion combined with sliding, erosion, impact and heat, and the review argues that this coupled degradation, rather than pure electrochemical corrosion, defines the true service envelope of Fe-based AMCs.

Looking ahead, the authors identify clear development trends. Better control of feedstock oxidation and particle in-flight behavior during spraying should shrink the defect population at its source. Machine-assisted alloy design promises compositions that balance glass formation, passivation and cost more effectively. Standardized long-term testing under realistic conditions, including hydrostatic pressure, thermal cycling and tribocorrosion, is needed to close the credibility gap between electrochemical laboratory data and decades-long service life. And hybrid strategies that combine dense amorphous matrices, sealing layers and superhydrophobic topcoats point toward multi-functional surfaces that resist corrosion, wear and fouling at once. For a civilization whose infrastructure is steadily dissolving, these glassy iron coatings, born from a refusal of atoms to line up, may prove to be one of the most quietly consequential materials stories of the coming decade.

Subject of Research: Corrosion behavior and enhancement strategies of Fe-based amorphous metallic coatings

Article Title: Review: the factors influencing and the development trends of the corrosion behavior of Fe-based amorphous coatings

Article References: Cui, S., Zhang, X., Zhai, H., Kong, L., Zhang, J., Wang, B., Deng, L., Sun, W., Li, W., Liu, T., Zhao, X., & Liu, J. (2026). Review: the factors influencing and the development trends of the corrosion behavior of Fe-based amorphous coatings. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13750-4

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13750-4

Keywords: Fe-based amorphous coatings, metallic glass, corrosion resistance, thermal spraying, passive film, pitting corrosion, laser remelting, sealing treatment, superhydrophobic coating, tribocorrosion, alloying elements, crystallization

The launch of the Journal of Materials Science: Metallurgy, a sister title to the long-established Journal of Materials Science, marks a deliberate return of focus to metals after decades in which the broader field of materials science absorbed and expanded upon metallurgical principles. The inaugural editorial, written by Sophie Primig of UNSW Sydney and Megumi Kawasaki of Oregon State University and published in November 2025 as the first article of the journal’s first volume, sets out why the editors believe metallurgy is once again at the frontier of science rather than a mature discipline resting on its laurels. Their argument rests on simultaneous breakthroughs in four areas: alloy design, processing, characterisation, and performance in extreme environments.

To understand why this moment matters, it helps to trace the intellectual lineage of the field. Metallurgy is often described as one of the oldest sciences, with origins stretching back more than 6,500 years, yet its modern scientific form crystallised in the twentieth century. By the mid-1900s, researchers had begun applying metallurgical principles, particularly those governing phase transformations, thermodynamics and the structure of crystalline solids, to ceramics, polymers and semiconductors. That expansion gave birth to materials science and engineering as an inherently interdisciplinary field, one that integrates physics, chemistry and engineering within a unifying framework known as the processing-structure-property-performance relationship, frequently visualised as the materials science tetrahedron. Each corner of that tetrahedron constrains and enables the others: change how a material is processed and you alter its internal structure, which in turn dictates its properties and ultimately its real-world performance.

The Journal of Materials Science itself was founded in 1966 by Robert W. Cahn, a distinguished physical metallurgist celebrated for his work on the thermodynamics and kinetics of phase transformations in solids. Under his influence the journal quickly became a leading platform for the rapidly growing materials community, and like metallurgy itself it has continued to thrive while broadening its scope to encompass every class of material. The new sister journal reverses that expansion, narrowing the aperture deliberately to metals and alloys at precisely the moment when the field’s rate of discovery is accelerating. The editors describe their aim as capturing a new era of discoveries in one of humanity’s most foundational and continually evolving sciences.

The first engine of that new era is a revolution in alloy design. For most of history, metallurgists worked with alloys built around a single dominant element, with smaller additions of other elements tuned to refine properties: iron with carbon and chromium to make stainless steel, aluminium with copper or lithium to make aerospace alloys, nickel with cobalt and refractory metals to make superalloys. That paradigm is now being challenged by multiple principal element alloys, often called high-entropy alloys, in which four, five or more elements are mixed in near-equal proportions. Because these compositions occupy vast, previously unexplored regions of chemical space, they access property combinations that conventional alloys cannot reach, from exceptional strength at cryogenic temperatures to remarkable resistance to softening at high temperature. Alongside them sit metallic glasses, amorphous metals whose disordered atomic structure confers extraordinary elasticity and corrosion resistance, and, most strikingly, alloy compositions generated by artificial intelligence algorithms that no human designer would have proposed.

The second engine is a rethinking of processing itself. Traditional thermomechanical routes, the carefully choreographed sequences of heating, deformation and heat treatment that metallurgists have refined over generations, are being joined by radically new techniques, most prominently additive manufacturing. When a metal component is built layer by layer from a melt pool measured in fractions of a millimetre, the solidification behaviour, the welding metallurgy and the non-equilibrium solid-state phase transformations all depart from textbook expectations, forcing researchers to reassess fundamental assumptions about how microstructures form. At the same time, sustainable metallurgy is emerging as a design philosophy rather than an afterthought: circular processing routes that recycle alloys with lower environmental footprints, and more ethical stewardship of limited natural resources, are becoming central criteria for how new materials and processes are judged.

The third engine lies in how scientists see and measure metals. Advanced multiscale characterisation now spans from in-situ methods that watch components deform or transform under realistic loads at the laboratory scale, down to atomic-resolution imaging and diffraction that reveal individual dislocations, solute clusters and grain-boundary chemistry. Crucially, this experimental knowledge is increasingly coupled with multiscale modelling and simulation, allowing researchers to connect what happens at the scale of a nano-sized precipitate to the behaviour of an entire turbine disc. The prediction of processing-microstructure-property relationships using machine learning, validated against targeted experiments, is described in the editorial as an emerging and rapidly growing field, one that promises to compress development cycles that once took decades into years or even months.

The fourth engine is the relentless push into extreme environments. Alloys are now engineered to combine superior high-temperature strength with ductility, a combination that has historically involved difficult trade-offs because the microstructural features that resist deformation at high temperature often embrittle the material. Add exceptional corrosion and degradation resistance, and the resulting materials are redefining what the editors call extreme materials can achieve in demanding applications, from hypersonic flight and next-generation nuclear reactors to hydrogen infrastructure and deep-earth energy extraction. Each of these applications demands metals that survive conditions, temperatures, stresses and chemistries, that would destroy conventional alloys within hours.

Against this backdrop, the new journal positions itself as a dedicated platform for high-quality, original research that advances fundamental understanding of metals and alloys. The editors state a particular preference for interdisciplinary studies that integrate modelling, novel experimental approaches and advanced analytical techniques, and they explicitly welcome both work that extends current fundamental understanding and breakthroughs arising from collaboration between industry and academia. That dual emphasis reflects a practical reality of modern metallurgy: the distance between a laboratory discovery and an engineered product remains long, and closing it requires simultaneous progress in theory, experiment and manufacturing practice.

What emerges from the editorial is a portrait of a discipline that is neither nostalgic about its ancient roots nor complacent about its achievements. The materials science tetrahedron that unified the field in the twentieth century still holds, but every corner of it is being redrawn at once. Compositions once dismissed as thermodynamic curiosities are being screened by algorithms and confirmed in the laboratory; components are being solidified under conditions that classical theories never anticipated; microscopes and simulations are converging on the same atoms from opposite directions; and the alloys that result are expected to work where no metal has reliably worked before. For a science older than the pyramids, metallurgy appears to be entering its most dynamic chapter yet, and the research community now has a venue built specifically to document it.

Subject of Research: The launch of a new metallurgy journal and the advances in alloy design, processing, characterisation and extreme-environment performance driving a new era in metallurgical science

Article Title: Editorial: Journal of Materials Science: Metallurgy

Article References: Primig, S., & Kawasaki, M. (2025). Editorial: Journal of Materials Science: Metallurgy. Journal of Materials Science: Metallurgy, 1(1), Article 1. https://doi.org/10.1007/s44492-025-00001-x

Image Credits: AI Generated

DOI: 10.1007/s44492-025-00001-x

Keywords: metallurgy, materials science, high-entropy alloys, alloy design, additive manufacturing, machine learning, sustainable metallurgy, microstructure, phase transformations, extreme environments, metallic glasses, Journal of Materials Science