Zero-thermal-expansion (ZTE) materials are widely used in precision optics, cryogenic equipment, sensors, where even small temperature changes can cause performance problems. Yet creating ZTE materials that also conduct heat efficiently and remain mechanically robust has long been a challenge. Most conventional ZTE materials transfer heat poorly, while ZTE metal matrix composites often sacrifice strength and toughness due to the large amount of brittle negative-thermal-expansion particles they contain.
Recently, inspired by hierarchical structures found in nature, a research team from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences developed a novel bio-inspired laminated ZTE metal matrix composite that overcomes these limitations. The design draws inspiration from the “brick-and-mortar” laminated structure of abalone nacre, which is known for its exceptional strength and toughness, as well as the thin inner membranes of bamboo stems that enable efficient transport of water and nutrients.
Guided by this bio-inspired concept, the researchers designed a laminated composite composed of alternating pure copper foil layers and copper layers reinforced with Zn₀.₅Sn₀.₃Mn₀.₂NMn₃ (ZSM) NTE particles showing negative thermal expansion.. In this architecture, the copper foil layers serve as continuous heat-transfer pathways, effectively preserving the high intrinsic thermal conductivity of copper. As a result, a laminated composite incorporating 100 μm-thick copper foils exhibits a thermal conductivity about three times higher than that of conventional homogeneous ZTE metal matrix composites, ranking among the highest values reported for ZTE materials.
“The key innovation lies in separating the functions of heat conduction and thermal expansion compensation into different layers,” said Prof. TONG Peng, who led the team, “By allowing copper to act as a ‘thermal highway’ while the NTE-reinforced layers regulate dimensional stability, we successfully avoid the performance compromise seen in traditional ZTE composites.”
The laminated structure also significantly improves mechanical performance. The copper foil layers reduce stress concentration and suppress crack propagation, causing multiple cracks to form and deflect instead of a single catastrophic failure. This mechanism allows the composite to absorb much more fracture energy, with the flexural fracture energy reaching 53 kJ·m⁻²—four times higher than that of the monolithic composite.
Meanwhile, thermal stresses at the semi-coherent interfaces between adjacent layers offset each layer’s intrinsic expansion and contraction. This stress-coupling effect results in zero thermal expansion perpendicular to the lamination direction and ultimately produces isotropic ZTE behavior.
“This design provides a new paradigm for developing ZTE materials with both high thermal conductivity and high toughness,” Prof. TONG added. “It expands the application potential of ZTE composites, especially in environments involving repeated thermal shocks and mechanical impacts.”
A bioinspired laminated copper composite exhibiting zero thermal expansion, high directional thermal conductivity and superior toughness. (Image by TONG Peng)
Nacre-Inspired Copper Composite Achieving Zero Thermal Expansion (Image by TONG Peng)