Harder and tougher----three-dimensional interconnected multi-walled carbon nanotube (MWCNT) diamond composite
July15, 2026
3D Carbon Nanotube Network Enables Super-Tough Diamond Composite
Researchers from the Institute of Physics, Chinese Academy of Sciences, together with Beihang University, have reported a groundbreaking diamond composite in Nature Synthesis, demonstrating that diamond can simultaneously achieve near single-crystal hardness and unprecedented fracture toughness. The work introduces a fundamentally new structural design strategy for next-generation superhard materials.
The Long-Standing Challenge of Diamond
Diamond possesses the highest known hardness together with exceptional thermal conductivity, making it indispensable for precision machining, wear-resistant components, semiconductor processing, and advanced manufacturing.
However, despite its outstanding mechanical strength, diamond remains intrinsically brittle. Conventional single-crystal diamond typically exhibits a fracture toughness of only 3.4–5.0 MPa·m<sup>1/2</sup>, making it susceptible to catastrophic cracking under impact loading or complex stress conditions.
For decades, improving diamond toughness has generally required sacrificing hardness, creating the well-known hardness–toughness tradeoff that has limited the development of next-generation superhard materials.
A New Interface-Engineering Strategy
Instead of modifying the diamond itself, the research team developed an extrinsic toughening mechanism by introducing a highly dispersed three-dimensional interconnected multi-walled carbon nanotube (MWCNT) network throughout the polycrystalline diamond microstructure.
The composite was fabricated under 15 GPa and 2000°C using high-pressure high-temperature (HPHT) sintering.
More importantly, atomic-scale sp²–sp³ hybrid covalent interfaces were formed between the carbon nanotubes and diamond grains.
Unlike conventional composites where reinforcement phases interact mainly through weak physical contact, the newly created chemical bonding enables:
efficient stress transfer across interfaces
enhanced load-bearing capability
continuous energy dissipation during crack propagation
superior structural integrity
This represents a transition from physical interfaces to chemically bonded interfaces, significantly improving mechanical reliability.
Exceptional Mechanical Performance
The resulting composite demonstrates an outstanding combination of hardness and toughness rarely observed in superhard materials.
These values represent:
approximately 5× higher toughness than single-crystal diamond
approximately 1.8× higher than conventional polycrystalline diamond (PCD)
fracture toughness exceeding many tungsten-based engineering alloys while maintaining ultrahigh hardness
Under an extremely high 98 N Vickers indentation load, the composite exhibited almost no surface cracking. Instead, damage occurred to the indenter itself, highlighting remarkable impact resistance.
Why Does It Work?
Using in-situ TEM observations together with density functional theory (DFT) simulations, the researchers identified multiple synergistic toughening mechanisms.
When cracks encounter the interconnected CNT network, they undergo:
crack deflection
crack bridging
nanotube pull-out
increased crack propagation path
continuous fracture energy absorption
At the atomic scale, the sp²–sp³ covalent interface dynamically reconstructs under shear loading.
Rather than failing catastrophically, chemical bonds repeatedly break and reform, continuously dissipating strain energy.
Meanwhile, the continuous three-dimensional diamond framework preserves structural rigidity and prevents the hardness degradation commonly associated with introducing secondary phases.
The result is an ideal combination of:
ultrahigh hardness
exceptional fracture toughness
excellent impact resistance
improved structural reliability
Scientific Significance
This work is the first to integrate three critical structural elements into a single superhard composite:
a continuous three-dimensional carbon nanotube network
atomic-scale sp²–sp³ covalent interfaces
a continuous diamond skeleton
Together, these features overcome the traditional conflict between hardness and toughness that has constrained superhard materials for decades.
Beyond developing a superior diamond composite, the study establishes a new theoretical framework demonstrating that atomic-scale interface continuity is the key to efficient stress transfer and energy dissipation.
Potential Industrial Applications
The combination of ultrahigh hardness and exceptional toughness opens new opportunities across multiple industries, including:
Ultra-long-life cutting tools
High-impact machining inserts
Semiconductor wafer processing tools
Precision grinding and polishing components
Aerospace wear-resistant parts
Extreme-environment mechanical systems
High-reliability engineering materials
As demands continue to increase in aerospace, semiconductor manufacturing, precision machining, and advanced manufacturing, this interface-engineered diamond composite represents a promising pathway toward the next generation of industrial superhard materials.
DIASEMI Perspective
While this breakthrough primarily targets structural superhard applications, the underlying concept of atomic-scale interface engineering is equally relevant to advanced thermal management materials.
For companies such as DIASEMI developing diamond–metal composites, diamond heat spreaders, and diamond/copper heat sinks, the study reinforces an important principle: the performance of diamond composites is increasingly governed by interface chemistry rather than the intrinsic properties of the constituent materials alone. Engineering robust covalent or chemically bonded interfaces can simultaneously improve mechanical reliability, thermal stability, and long-term durability—an approach that is expected to influence the future design of high-performance diamond materials for both cutting tools and semiconductor thermal management.
