The world’s most scratch-resistant material is still diamond, but it may soon be out of fashion for industrial drillers.
Scientists have for years been looking for new, superhard materials that can withstand high temperatures, as diamond becomes unstable at 800 degC and begins to chemically react with iron. It is also important to find a thermally stable material that can be used in space exploration and microelectronics applications.
Some of the strongest known superhard materials are diamond, cubic boron nitride (c-BN), carbon nitrides, and ternary compounds like B-N-C. But c-BN and diamond are prone to breaking and disintegrating at the pressures that industrial drillers use, making them unsuitable for cutting steel or other hard metals.
Now, scientists have discovered that a rare natural substance could outdo diamond and become the world’s hardest material. It’s called lonsdaleite and it has a lattice structure similar to diamond but with hexagonal atoms, rather than the more common cubic boron nitride.
It has an indentation strength of 152 GPa, 58% stronger than diamond’s 97 GPa under the same conditions. It’s achieved this through a mechanism known as bond-flipping, which occurs when wurtzite boron nitride (w-BN) is compressed.
The researchers found that under the same compressive conditions, w-BN’s indentation strength increased by 78 percent compared with its value before the bond-flipping occurred. Lonsdaleite’s indentation strength increased by 58 percent compared with the value before the bond-flipping occurred. This new discovery could help researchers find the next generation of superhard materials that can withstand high temperatures and resist wear, fatigue, and corrosion in a range of applications.