High-Entropy Alloys and Advanced Metals — CityU's Flagship Materials Research Line

CityUHK Comprehensive Information Database · 04 Research Module · Materials Science Deep-Dive Series This article focuses on City University of Hong Kong's flagship frontier in materials science — high-entropy alloys (HEAs) and advanced metallic materials — setting out its representative breakthroughs and disciplinary ranking position. For the overview and other landmark achievements (perovskites, PEN, droplet-based electricity generation), see materials-and-engineering-research.md.

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Conventional alloy design follows a near-instinctive logic: pick one metal as the lead actor — steel, for instance, is built around iron — then stir in small amounts of other elements for flavouring. High-entropy alloys turn this on its head. They mix five or more metallic elements in near-equimolar proportions, deliberately engineering a kind of atomic "chaos". Counter-intuitively, this disorder does not degrade the material; it yields an extraordinary combination of properties — high strength, high toughness, heat resistance, corrosion resistance and radiation tolerance. This is why HEAs are tipped for extreme environments such as aerospace, automotive engineering and nuclear power. CityU has gathered an active cluster of researchers in this frontier field, publishing densely across Nature, Science and top materials journals over the past few years, and gradually developing what is internationally recognisable as a "CityU school" of high-entropy alloy research.

# I. What Are High-Entropy Alloys and Why They Matter

Traditional alloys are built around a single principal element (steel, for example, is iron-based), with small additions of other elements. High-entropy alloys invert this logic: they are made from five or more metallic elements in near-equimolar proportions. The resulting disordered ("high-entropy") atomic arrangement confers an unusual combination of properties — high strength, high toughness, heat resistance, corrosion resistance, radiation tolerance and more. This is why HEAs are earmarked for extreme environments such as aerospace, automotive engineering and nuclear engineering (CityU research story^※).

CityU has built an active community of researchers in this frontier area, publishing densely across Nature, Science and top-tier materials journals over the past several years, and forming what has become internationally recognised as a "CityU school" of HEA research.

# II. Representative Research Outcomes (with Public Sources)

# 2.1 Thermally Stable High-Entropy Alloys: Using Cobalt to "Lock Down" Nanoparticles (2022)

In November 2022^※, CityU materials scientists showed that tuning the concentration of cobalt in a high-entropy alloy can suppress the rapid coarsening of nanoparticles at high temperatures. Nanoparticle coarsening degrades a material's performance under heat, and this finding paves the way toward next-generation high-entropy alloys that can serve in high-temperature extreme environments — with aerospace, automotive and nuclear engineering singled out as target applications.

# 2.2 Strength and Ductility Together: A New Heterogeneous Strain-Strengthening Mechanism (2022)

A material's "strength" and "ductility" usually trade off against each other — the harder, the more brittle. In August 2022^※, a team co-led by CityU's Professor Yang Yong found that heterogeneous strain fields in multi-principal element alloys can, via a new mechanism of heterogeneous strain-induced strengthening, simultaneously improve both mechanical properties — breaking the conventional strength–ductility trade-off.

# 2.3 Multi-Stage Deformation at Ultra-Low Temperatures

An international team (led by CityU scientists) discovered that high-entropy alloys display exceptionally good mechanical properties at ultra-low temperatures, thanks to the coexistence of multiple deformation mechanisms — a so-called multi-stage deformation process (SciTechDaily report^※). This has direct implications for material selection in cryogenic service conditions such as spaceflight, deep-space missions and low-temperature storage and transport.

# 2.4 Fatigue Performance of Additively Manufactured Metals

According to a review in the Advanced Materials special issue marking CityU's 30th anniversary (2024)^※, CityU's Professor Jian Lu and colleagues examined the fatigue performance of additively manufactured (3D-printed) metal alloys, while Professor Yong Yang and colleagues contributed a review on multifunctional high-entropy alloys with severe lattice distortion. The two strands correspond respectively to "advanced manufacturing" and "fundamental mechanisms".

# 2.5 Intermetallics That Are Strong Without Being Brittle: An Unconventional Use of Lattice Distortion (2024)

Intermetallic compounds have long been the textbook case of "strength bought with brittleness" — their atoms are arranged in a highly ordered fashion, their bonding approaches that of ceramics, and they are hard but snap rather than bend; engineers seldom use them alone. Professor Yang's team carried the "chaos" logic of high-entropy alloys into this family of materials, which had always prized orderliness. They designed a single-phase B2 high-entropy intermetallic whose lattice is highly distorted by the coexistence of multiple principal elements — chemically ordered but not perfectly so — thereby activating multiple slip systems and a dynamic hardening mechanism: dislocation slip does not soften the material but keeps strengthening it, so that the alloy never exhibits the "thermal softening cliff" common in conventional alloys across a wide temperature range, and its plasticity outperforms a variety of body-centred cubic (BCC) and B2 alloys (per the Nature Communications paper (08/2024)^※). This result extends the high-entropy-alloy idea of "trading chaos for performance" from conventional alloy structures all the way into the intermetallic family, long known for brittleness.

# 2.6 Eutectic High-Entropy Alloys, Refined: Taming Strength and Toughness Through Heterogeneity (2024)

The heterogeneous strain-induced strengthening mechanism covered in Section 2.2 received a more finely wrought sequel two years later, this time in eutectic high-entropy alloys — a dual-phase system in which two phases alternate in a lamellar arrangement. The Communications Materials paper (02/2024)^※ shows that, by simultaneously optimising chemical and microstructural heterogeneity, the team pushed the strength–toughness balance further in a eutectic high-entropy alloy. Compared with the 2022 finding, this work advances "heterogeneity engineering" from single-phase alloys into the more complex dual-phase eutectic family — evidence that the approach is generic across structural types rather than an accidental property of one particular alloy.

# 2.7 A "Hidden Strain Order": Turning Superelasticity into a Dial (2026)

Superelastic materials — which can deform substantially under load and spring back when the load is removed — are widely used in medical devices and precision instruments. But the elastic behaviour of conventional superelastic alloys is typically a "factory setting", fixed and not adjustable on demand. The Nature Communications paper (2026)^※ reports that Professor Yang's team, through compositional tuning, made a high-entropy alloy's elastic behaviour continuously and reversibly switchable between "Hookean superelasticity" and "non-Hookean superelasticity" — the latter achieving an ultrahigh recoverable strain of about 8%. The team attributes this tunability to a previously unrecognised "hidden strain order" — local lattice distortions arising from the "frustrated crystallisation" of two competing phases, forming an inhomogeneous strain field that modulates the material's phase stability, transformation tendency and elastic response. The mechanism was verified by combining atomic-scale strain imaging with first-principles calculations. This work extends the "tunable design" philosophy of high-entropy alloys from strength and ductility to elastic behaviour itself.

# 2.8 From "Stronger and Tougher" to "More Versatile": Energy-Absorbing Materials, Flexible Oxide Membranes and Hydrogen-Embrittlement Resistance (2025–2026)

Over the past two years, CityU's high-entropy-alloy research line has visibly branched out from structural strengthening into a wider range of functional applications:

• Macroscale architected energy-absorbing alloys. The Nature Communications paper (2026)^※ reports that the team used machine learning to screen multi-principal element alloy compositions capable of spinodal decomposition, then applied electrochemical dealloying to produce bulk-scale architected alloys. The resulting structure spans seven orders of magnitude — from atomic-scale lattice distortion, nanoscale precipitates and amorphous oxide layers, to micron-scale ligaments and macroscale network dimensions — enabling cooperative deformation mechanisms. The energy absorption capacity reaches about 106 MJ/m³ in bulk samples and up to about 305 MJ/m³ at the micron scale, overcoming the long-standing problems of 3D-printed micro/nano-lattices ("hard to scale up") and conventional foams (the "strength–ductility dilemma").
• Two-dimensional high-entropy oxide membranes for flexible electronics. The Nature Communications paper (2025)^※ reports that the team constructed nano-oxide scaffolds in situ within a hydrogel, producing fracture-resistant self-supporting high-entropy oxide (HEO) nanomembranes with an elongation of nearly 90%, toughness exceeding 300 MJ/m³ — better than traditional metal/metal-oxide films and various advanced 2D materials — visible-light transmittance of 83.2%, and strong adhesion to a range of substrates. This targets the chronic weakness of metal-oxide films in flexible electronics: brittleness.
• A long-standing problem for medical and nuclear applications: resistance to hydrogen embrittlement. According to CityUHK Scholars^※, the CrCoNi medium-entropy alloy suffers pronounced gaseous hydrogen embrittlement. The team found that triggering co-segregation of carbon, boron and chromium substantially suppresses this phenomenon, reducing the loss of ductility from 71% to about 16%. Hydrogen-embrittlement-resistant alloys of this kind are of direct relevance to service in hydrogen environments, such as hydrogen energy storage and transport equipment and nuclear power pipelines.

Taken together, these efforts sketch a clear shift in CityU's HEA research line: from the early structural-materials narrative centred on "strength–ductility–thermal stability", it has progressively expanded into a far broader functional spectrum covering energy absorption, flexible electronics and tolerance of hydrogen environments.

# 2.9 Back to Basics: Biomedical Implants and Refractory Alloys, Testing Both Ends of "Extreme Environments"

The opening of this article noted that high-entropy alloys are earmarked for extreme environments such as aerospace, automotive engineering and nuclear power. Two concrete touchpoints for that claim can be found in CityU's research output — conveniently corresponding to the two poles of "extreme": inside the human body and ultra-high temperature.

• Orthopaedic implants. The team systematically mapped the fundamental relationships between composition, microstructure and properties in the biomedical TiZrTaNbMo high-entropy alloy (per the Materials Science and Engineering: A paper (2024)^※). This system is built from five biocompatible metals — titanium, zirconium, tantalum, niobium and molybdenum — and combines a low Young's modulus (closer to human bone, reducing "stress shielding"), high strength and good wear and corrosion resistance. Published data on comparable TiZrNbTaMo systems indicate a Young's modulus of about 153 GPa, compressive yield strength of about 1390 MPa and plastic strain of about 6% — making it, after the dual-phase nanoscale magnesium alloy covered in this site's Materials and Engineering Research overview, another product line in CityU's implantable medical metals portfolio.
• Ultra-high-temperature structures. A separate team contributed a systematic review of design routes for refractory complex concentrated alloys (RCCAs) (per the Current Opinion in Solid State & Materials Science review (2026)^※), covering everything from empirical rules to machine-learning-driven composition discovery, strategies for suppressing room-temperature brittleness, oxidation resistance and additive-manufacturing feasibility — aimed squarely at the performance ceiling of conventional nickel-based superalloys above 1200°C, in service for aero-engines, energy and defence applications.

From "37°C inside the body" to "above 1200°C in an engine bay", CityU's high-entropy-alloy research covers essentially both ends of the material service-temperature spectrum — confirming that the "aerospace, automotive, nuclear" application list cited at the top of this article is no empty slogan.

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# III. Application Frontiers: From Structural Materials to Energy Conversion

The early narrative of high-entropy alloys was almost entirely about structural performance — "stronger, tougher, more heat-resistant". But over the past two or three years, a clear trend in CityU's research line has been an extension toward energy and catalysis: high-entropy alloys are now being designed as a class of "multi-principal-element synergistic" functional materials, not merely structural ones.

Hydrogen production by water electrolysis: trading "disorder" for low cost and high activity. A team at CityU's Centre for Advanced Structural Materials (CASM) combined the multi-principal-element synergy of high-entropy alloys with the "structural site separation" advantage of intermetallic compounds. By tuning the alloy's ordered/disordered structure, they designed periodically arranged high-entropy intermetallic catalysts for water electrolysis: at a current density of 10 mA/cm², the hydrogen evolution overpotential is as low as about 88.2 mV — activity comparable to precious-metal catalysts such as platinum, at a fraction of the cost (per the CASM research-highlights page^※). The Centre also appears in the platform list at institutes-and-labs.md; it is an important shared facility underpinning several of CityU's frontier directions in materials and engineering.

High-entropy alloy nanoparticles: from ten elements to "electrocatalytic ammonia synthesis". The Journal of the American Chemical Society (JACS, 2026) paper^※ reports that a team counting CityU Chemistry's Professor Johnny C. Ho among its co-authors developed a nanofluid-assisted synthesis method: using zinc as a "propellant" to build interconnected nanochannels, guiding multi-metal nanofluid flow and triggering alloying, to synthesise — in one step — ten mutually immiscible elements into strained high-entropy alloy nanoparticles. Deployed for the electrocatalytic conversion of nitrate to ammonia, these achieve a Faradaic efficiency as high as 94.8% ± 4.34% and run stably for more than 720 hours — pointing both to the resource-oriented treatment of nitrate pollution in industrial wastewater and to "green ammonia synthesis", a frontier topic in fertiliser and energy storage.

Connecting the dots: structural and functional, on two legs. If we include the hydrogen-embrittlement-resistant CrCoNi medium-entropy alloy from Section 2.8, CityU's high-entropy-alloy research in fact now spans both ends of the hydrogen-energy value chain — the upstream electrolysis catalysts for hydrogen production and the downstream structural materials resisting hydrogen embrittlement in storage and transport equipment — plus electrocatalytic ammonia synthesis, an application niche linking agriculture and energy. This strategy of "one material family, deployed at multiple points" chimes with CityU materials science's broader "doing some things and not others" approach (see the next section).

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# IV. Disciplinary Standing: Ranked First in Hong Kong

The density of CityU's materials research is directly reflected in disciplinary rankings:

A note on metrics: subject rankings fluctuate from year to year; "first in Hong Kong / top 50 worldwide" applies to a specific year and a specific ranking. The figures cited here are from QS by Subject 2026 and CityU's official summaries. For cross-year comparisons, please return to 03-rankings/subject-rankings.md.

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# V. Why Materials Science Became CityU's "Trump Card"

Drawing on public sources, several structural reasons explain how CityU's materials science grew into a concentrated strength:

1. A clear disciplinary focus. CityU is among the smaller of Hong Kong's eight UGC-funded universities, and has long pursued a strategy of "doing some things well rather than everything at all", channelling resources into a few highly productive fields — materials, engineering, computing — rather than aiming for comprehensive coverage.
2. A patent-and-commercialisation orientation. CityU has long touted itself as a "global top-100 university for US patents held" (for the "first in Hong Kong, among the best in Asia" claim, see the overview module's CityU research story^※); materials and engineering are the main patent-producing disciplines.
3. An internationalised faculty. Roughly seven in ten of CityU's academic staff are international (see 00-overview/facts-and-figures.md), and the materials teams boast dense international collaboration networks — several of the achievements above were led by multinational teams.
4. Three decades of accumulation. The fact that Advanced Materials devoted a special issue in 2024 to CityU's materials research on its 30th anniversary^※ is telling: this research line has real historical depth rather than being a flash in the pan.

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# VI. Summary

CityU's flagship status in materials science rests on sustained breakthroughs in the frontier field of high-entropy alloys / multi-principal element alloys: from the thermal-stability strategy of "cobalt tuning to suppress nanoparticle coarsening" and "heterogeneous strain-induced strengthening" to break the strength–ductility trade-off, to the multi-stage deformation mechanism at ultra-low temperatures and fatigue research on additively manufactured metals — and then, in the past two years, the dense run of lattice-distorted intermetallics, the heterogeneity breakthrough in eutectic alloys, tunable superelasticity via a hidden strain order, and functional extensions into energy-absorbing architected alloys, flexible oxide membranes and hydrogen-embrittlement-resistant alloys. Across this field CityU has built a complete chain from fundamental mechanisms to engineering applications, from structural materials to energy catalysis. This research line is both the bedrock of CityU materials science's long-running lead within Hong Kong and its standing among the world's best — and the most fitting footnote to its "small but focused, conversion-oriented" institutional strategy.

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