Metallic materials used in extremely cold environments must maintain high strength, ductility and fracture toughness to support applications in aerospace, clean energy, superconducting systems and deep-space exploration. However, traditional alloys often suffer performance degradation at ultralow temperatures because of the long-standing trade-off among strength, ductility and toughness. Although metals may become stronger at lower temperatures, they can also become more brittle and prone to fracture. The sinking of the Titanic is a well-known historical event associated with low-temperature brittle failure. This vulnerability, known as “cold brittleness”, remains a bottleneck in the development of deep-sea and deep-space exploration technologies.
A research team led by Prof. Zibin CHEN, Assistant Professor of the Department of Industrial and Systems Engineering at The Hong Kong Polytechnic University (PolyU), has achieved two breakthroughs in addressing this challenge. Using an innovative nanoscale interface strategy to adjust a metal’s internal microstructure, the team developed novel metallic materials that achieve an unprecedented combination of strength, ductility and toughness at ultralow temperatures of 77 K, equivalent to approximately −196°C. Building on this work, the team also integrated additive manufacturing, commonly known as 3D printing, with tailored post-processing to develop a novel nano-architecture strategy. Published in two successive studies in Nature Communications, these advances provide a high-performance, scalable material foundation for next-generation deep-sea and deep-space exploration equipment.
The “Negative-Curvature Interface” Strategy
To address the long-standing challenge of cold brittleness in alloys, Prof. Chen and his team pioneered a “negative-curvature interface” (NCI) strategy. By changing the surface geometry of nanoscale particles within an alloy, the team enabled the material to withstand high loads while retaining the ability to deform, reducing the likelihood of sudden fracture.
The resulting multi-principal element alloy (MPEA), composed of nickel, cobalt, chromium, aluminum and tantalum (NiCoCr-AlTa), achieves an unprecedented combination of strength, ductility and toughness at liquid-nitrogen temperatures, setting a new benchmark for cryogenic alloys. Additionally, it can be fabricated using conventional smelting, rolling and short-term ageing, without relying on complex new manufacturing methods. This provides a solid foundation for future large-scale production and engineering applications. The team will next validate industrial-scale samples, with the aim of translating the research into commercial applications within the next ten years.
Prof. Chen said, “Our NCI strategy transforms internal precipitates, tiny particles dispersed within the metal, from passive strengtheners into active tunable agents that regulate how the material deforms under load. This concept is applicable across all precipitation-hardened alloy systems, including superalloys, age-hardening steels and aluminum alloys. This work opens up a new dimension in advanced material design, offering a cost-effective and scalable pathway for designing high-performance structural materials for industrial applications.”
The design was inspired by the energetic evolution during nanoparticle coarsening. Working at the nanoscale, the team proposed constructing NCI on coherent nanoprecipitates, creating specially curved interfaces on the surfaces of particles within the alloy to influence its internal structural response. As the material deforms under load, numerous partial dislocations, small-scale defects in the crystal structure, form dynamically, producing hierarchical stacking faults (SFs) within the alloy. These layered structural features enhance the material’s mechanical performance.
PolyU’s advanced aberration-corrected transmission electron microscopy and mechanical property evaluation systems enabled the team to observe and characterise these novel microstructures and assess their mechanical performance.
The dense hierarchical SFs significantly enhance the material’s strain-hardening capacity and damage tolerance. As a result, the NiCoCr-AlTa MPEA delivers a record-setting combination of cryogenic mechanical properties: a yield strength of approximately 1.30 GPa, an ultimate tensile strength of approximately 1.80 GPa, a tensile ductility of 50% and a fracture toughness of approximately 213 MPa·m¹/².
The study, titled “Negative-curvature interfaces enable highly synergistic strength-ductility-toughness at 77K”, has been published in Nature Communications, and marks an important milestone in the development of cryogenic structural materials for extreme exploration environments.
Hybrid 3D Printing and “Hierarchical Nano-Orderings” Strategy
In another breakthrough, also published in Nature Communications, Prof. Chen’s team integrated additive manufacturing with tailored post-processing to construct a “hierarchical nano-orderings” (HNOs) architecture in a NiCoCr-based alloy. The study is titled “Hierarchical nano-orderings enable extraordinary cryogenic strength-ductility synergy in a medium-entropy alloy”.
The team’s strategy sequentially activates dislocation sources to enable cooperative strain-hardening, allowing the material to become stronger as it deforms. At liquid-nitrogen temperatures, the alloy delivers record-setting strength, with a yield strength of approximately 2.0 GPa, an ultimate tensile strength of approximately 2.4 GPa and a uniform tensile ductility of 22%. The team aims to validate industrial-scale components, targeting commercial deployment within the next five years.
Prof. Chen added, “This work provides a foundation for microstructure design strategies and establishes a viable framework for maximising mechanical performance. By integrating novel manufacturing approaches with conventional processing techniques, we demonstrate that material properties can be enhanced beyond the limits of traditional manufacturing methods. Furthermore, this innovative approach expands the application of 3D printing in microstructural design and further demonstrates its value in materials science.”
Prof. Chen, an awardee of the PolyU Young Innovative Researcher Award (YIRA) in 2022, is a core member of the State Key Laboratory of Ultra-precision Machining Technology at PolyU. His research focuses on designing sustainable materials with superior structural, functional and service properties, and addressing practical engineering challenges across different material systems. His work on low-alloy, low-cost and high-performance sustainable metal alloys, as well as record-breaking ferroelectric materials for energy storage and piezoelectric applications, has attracted considerable attention worldwide.
