Why are alloys harder than pure metals?

Alloys are harder than pure metals because they disrupt the regular arrangement of atoms, preventing layers from sliding easily.

In pure metals, atoms are arranged in a regular, repeating pattern. This regularity allows layers of atoms to slide over each other easily when a force is applied, making the metal malleable and ductile. However, this also means that pure metals are relatively soft and can be easily scratched or dented.

Alloys, on the other hand, are mixtures of two or more elements, at least one of which is a metal. The atoms of the different elements in an alloy are different sizes. When these different-sized atoms are mixed together, they disrupt the regular arrangement of atoms in the metal. This makes it more difficult for layers of atoms to slide over each other when a force is applied. As a result, alloys are generally harder and stronger than pure metals.

The hardness of an alloy can also be increased by a process called work hardening or strain hardening. This involves deforming the alloy, for example by bending or hammering it. The deformation causes dislocations in the arrangement of atoms, which impede the movement of other dislocations. This makes the alloy harder and stronger.

In addition, the properties of an alloy, including its hardness, can be tailored by changing the proportions of the different elements. This allows alloys to be designed for specific applications, such as aircraft components, car parts, or dental fillings.

In summary, the hardness of alloys compared to pure metals is due to the disruption of the regular arrangement of atoms, which prevents layers from sliding easily. This is further enhanced by work hardening and can be tailored by changing the proportions of the different elements.