Nanomaterials with record hardness

Could there be any material with excellent hardness like diamond?

Researchers have successfully created a new non-carbon material that is as hard as diamond.

Natalia Dubrovinskaia (University of Heidelberg, Germany) together with colleagues in Bayreuth (Germany), Paris and Grenoble (France) successfully synthesized a super hard nanocomposite material from Boron Nitride (BN) with hardness Vickers around 85 GPa. The surprisingly high anti-fracture properties and abrasion resistance of the materials show that they can be used as super abrasive abrasives in industry as well as in the mining and drilling industries .

Succeeded for the first time in 1950, Bo-Nitride cube crystals were used in many different technical applications similar to diamond. This material has a thermal stability of up to 1650 K compared to only 950 K of diamond. Moreover, it is used as a super abrasive material for machining hard steels. However, the patient cannot completely replace the diamond because the hardness is only half that of diamond (50 GPa compared to 100 GPa of diamond).

Recently, the group of Dubrovinskaia (University of Heidelberg) has once made the first time to create patients with thermodynamic stability with the hardness of diamond. The team obtained this result by reducing the particle size from micrometer size to nanometer scale.

Photo of some members of the research team: Leonid Dubrovinsky (BGI, University of Bayreuth), Natalia Dubrovinskaia (Mineral Physics and Structural Research, Mineralogical Institute, University of Heidelberg), and Nobuyoshi Miyajima (BGI, University of Bayreuth).

The collaborative research team between France and Germany used a 5000 ton press machine at the Bavarian Institute (University of Bayreuth, Germany) to synthesize patients at high pressure and temperature conditions. A series of BN materials with different particle sizes were successfully built, and nanostructures were observed on high-resolution electron microscopes. The team also used different techniques to analyze the mechanical properties and structure of materials including Vickers hardness measurement. The reliability of the results is even higher when measurements are carried out independently in two laboratories in Bayreuth and Paris.

The team found that when the particle size of the material dropped to a size of 14 nm, it led to the simultaneous formation of two solidified phases with hexagonal structure and cube structure. This composite property produces materials with maximum Vickers hardness of up to 85 GPa, 2 times higher than that of single crystal crystals. And this hardness decreases as the particle size increases (see figure). At the same time, the bearing capacity (fracture) and abrasion resistance are also abnormally high (15 MPa.m1 / 2 and 11). This characteristic is much better than polycrystalline diamond (only limit fault of 5.3-7.0 MPa.m1 / 2 and abrasion resistance only 3-4).

Dependence of Vickers hardness on particle size.

Also according to the results of the group's release, this property is stable at temperatures as high as 1600 K in the air, meaning it is a rare super-abrasive material. Materials can be used in exploration, mining, or machining applications for steel, super-hard ceramics. Moreover, it could be a way to open up many materials with rigidity, toughness and other thermal stability - still a great goal for material science.

The researchers say that increased hardness is due to two factors : firstly due to the nanoscale effect, which limits the spread of network deviations in the material (making the material weaken. ); and quantum imprisonment effect increases the specific hardness of crystalline particles.

These results have just been published in Applied Physics Letters (Appl. Phys. Lett. 90 (2007) 101912).

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