Ductility is when a solid material stretches under tensile stress. If ductile, a material may be stretched into a wire. Malleability, a similar property, is a material's ability to deform under pressure (compressive stress). If malleable, a material may be flattened by hammering or rolling.
Both of these properties are aspects of plasticity. Plasticity is how far a solid material can be plastically deformed without fracture. Also, these material properties are dependent on temperature and pressure. This was investigated by Percy Williams Bridgman as part of his Nobel Prize–winning work on high pressures.
Ductility and malleability do not always go together. Gold has high ductility and malleability, but lead has low ductility and high malleability. The word ductility is sometimes used to embrace both types of plasticity.
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