By David Kennedy, Updated Mar 24, 2022
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When we talk about hardness, we’re referring to a material’s ability to resist scratching, deformation, and high‑temperature wear. While many metals can be hardened through alloying, a handful of elements and compounds truly stand out as the toughest known materials.
Hardness isn’t a single, absolute measurement. Scientists use several scales to evaluate how a material compares to others:
Steel, an alloy of iron, carbon, and other elements, can be engineered for exceptional hardness. Adding chromium—an element with a Mohs rating of 8.5—creates “chrome” or “chromium” steel, which is harder than the pure metal itself. Even minimal chromium content dramatically boosts strength, corrosion resistance, and hardness. Chrome plating, a thin protective layer, further enhances surface durability.
Wolframite‑based tungsten carbide 857 (85.7% WC, 9.5% Ni, 1.8% Ta, 1.5% Ti, 1% Nb, 0.3% Cr) ranks 8–9 on the Mohs scale—four times harder than titanium. This composite material is prized for cutting tools and wear‑resistant components.
When metals are combined with other elements, the resulting “metalloids” or “ceramic” structures—known as covalent‑bonded solids—can surpass even diamond’s natural hardness. Rhenium and osmium, for instance, form borides that are harder than steel. Remarkably, osmium diboride can scratch natural diamond, the toughest naturally occurring substance.
