Superhard material – Harry & Co Jewellery

Definition and Properties of Superhard Materials

Superhard materials have a hardness value exceeding 40 GPa when measured by the Vickers hardness test.
They are virtually incompressible solids with high electron density and high bond covalency.
Diamond is the hardest known material with a Vickers hardness in the range of 70-150 GPa.
Recent research focuses on finding compounds that are thermally and chemically more stable than pure diamond.
Superhard materials have high shear modulus, high bulk modulus, and do not deform plastically.
Defects can actually strengthen some covalent structures.
Short covalent bonds in a material make it less likely to undergo plastic deformation.
Fracture toughness, the ability to resist breakage from forceful impact, is related to hardness but distinct from toughness.
Diamond has high fracture toughness compared to other gemstones and ceramics, but lower compared to many metals and alloys.

Superhard materials have traditionally been synthesized under high-pressure and high-temperature conditions.
Recent synthesis methods aim to use less energy and lower cost materials.
Two approaches have been taken in the search for new superhard materials: emulating the short, directional covalent carbon bonds of diamond and incorporating light elements with transition metals.
Tungsten carbide is an example of a material synthesized using the second approach.
Borides combined with transition metals have also been a rich area of superhard research.

Superhard materials can be classified into two categories: intrinsic compounds and extrinsic compounds.
Intrinsic compounds include diamond, cubic boron nitride, carbon nitrides, and ternary compounds.
Extrinsic materials have superhardness and other mechanical properties determined by their microstructure.
Nanocrystalline diamond, known as aggregated diamond nanorods, is an example of an extrinsic superhard material.
The classification of superhard materials takes into account bulk moduli, shear moduli, and elasticity.

Historically, hardness was defined as the ability of one material to scratch another.
Hardness is now measured using a nanoindenter and evaluated on scales such as Vickers, Brinell, Rockwell, and Knoop.
Vickers hardness values are load-dependent, and the indentation size effect must be considered.
Bulk modulus is used as a preliminary measure of a material's hardness, but other properties must also be taken into account.
Shear modulus measures a material's resistance to shape change and is related to bulk modulus and Poisson's ratio.

Diamond is an allotrope of carbon with a modified face-centered cubic structure.
Synthetic diamond is a major focus of research due to the wide variation in properties of natural diamonds.
Dense amorphous carbon has a Vickers hardness of 113 GPa and is currently the hardest amorphous material.
Cubic boron nitride (c-BN) was first synthesized in 1957 and has high thermal conductivity and low X-ray absorptivity.
Beta carbon nitride (β-C) was proposed to be harder than diamond, but synthetic samples have not validated the hardness predictions.
Boron carbon nitride compounds and metal borides are also studied for their superhard properties.
Rhenium diboride, tungsten borides, and aluminium magnesium boride (BAM) are examples of specific superhard materials.

Reference	URL
Glossary	https://harryandcojewellery.com.au/blogs/glossary/superhard-material
Wikipedia	http://en.wikipedia.org/wiki/Superhard_material
Wikidata	https://www.wikidata.org/wiki/Q2557782
Knowledge Graph	https://www.google.com/search?kgmid=/m/04gflf