PolyU scholar develops novel cryogenic metallic materials, overcoming “cold brittleness” bottleneck to provide key materials for deep-space and deep-sea exploration

A research team led by Prof. CHEN Zibin, Member of Research Institute for Advanced Manufacturing (RIAM) and Research Centre for Resources Engineering towards Carbon Neutrality (RCRE), and Assistant Professor of Department of Industrial and Systems Engineering, has achieved two major breakthroughs in cryogenic structural metallic materials.  The team has overcome the longstanding challenge of simultaneously achieving high strength, ductility and toughness at ultralow temperatures, thereby addressing the problem of “cold brittleness”.  These landmark findings have been published in two separate papers in the prestigious academic journal Nature Communications.

Breakthrough 1: Pioneering “Negative-Curvature Interface” Engineering for Exceptional Cryogenic Strength and Toughness

Conventional alloys often suffer performance degradation and increased brittleness under extreme cryogenic conditions.  To address this, the team pioneered a “negative-curvature interface” design strategy.  By tailoring the geometric curvature of nanoscale precipitates within the alloy, the team created conditions that promote the spontaneous formation of dense “hierarchical stacking faults” under mechanical loading.  This nanoscale mechanism significantly improves the alloy’s strain-hardening capacity and damage tolerance.

The team’s novel alloy, composed of multiple elements including nickel, cobalt, chromium, aluminium and tantalum (NiCoCr-AlTa), demonstrated record-breaking mechanical properties at liquid nitrogen temperature (77 K): a yield strength of approximately 1.30 GPa, an ultimate tensile strength of around 1.80 GPa, a tensile ductility of 50%, and a fracture toughness of roughly 213 MPa·m¹/².  Combining exceptional strength with high damage tolerance, the NiCoCr-AlTa alloy can be fabricated using conventional manufacturing processes without reliance on complex, new manufacturing equipment.  This lays a robust foundation for future large-scale industrial production and engineering applications.  The study is titled “Negative-curvature interfaces confer highly synergistic strength–ductility–toughness in an alloy at 77 K”.

Breakthrough 2: Fabricating Ultra-High-Strength “Hierarchical Nano-Ordered Structures” via Additive Manufacturing

In a separate study, Prof. Chen’s team combined metal additive manufacturing (3D printing) with tailored post-processing to construct a “hierarchical nano-orderings” architecture in a NiCoCr-based medium-entropy alloy.  This strategy works by sequentially activating dislocation sources during plastic deformation, enabling cooperative strain hardening that allows the material to become stronger as it deforms.

Experimental results showed that the alloy achieved record-setting strength at liquid nitrogen temperatures: a yield strength of approximately 2.0 GPa, an ultimate tensile strength of about 2.4 GPa, and a uniform tensile ductility of 22%.  This paper is titled “Hierarchical nano-ordered structure confers exceptional cryogenic strength–ductility synergy in a medium-entropy alloy”.

These two complementary breakthroughs mark a significant milestone in the development of structural materials for extreme environments.  By combining exceptional mechanical performance with industrial scalability, they provide a promising materials foundation for future deep-space exploration and deep-sea exploration technologies.

Online coverage:

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