Definition - What does Ductility mean?
Ductility is the measure of a material's ability to plastically deform without fracturing when placed under a tensile stress that exceeds its yield strength. High ductility indicates that a material will be more apt to deform and not break whereas low ductility indicates that a material is brittle and will fracture before deforming much under a tensile load. Ductility depends largely on a material's chemical composition, a material's crystalline structure, and the temperature at which the ductility is being measured.
Corrosionpedia explains Ductility
Ductility is not the same as malleability. Ductility is a measure of material deformation under a tensile stress, whereas malleability is a measure of material deformation under compressive stress. A material does not necessarily have to have both high ductility and high malleability. It could have high malleability and low ductility.
Metals that have high ductility include gold, platinum, silver and iron. Low ductility metals include tungsten and steels with high amounts of carbon. Polymers are usually ductile; however there are brittle polymers available. Ceramics are typically brittle.
The ductility of a material will change as its temperature is changed. Metals have a ductile to brittle transition temperature. For polymers this is called a glass transition temperature. The exact temperature is different for different materials, but once it is reached, ductility is vastly reduced and the material becomes brittle. The ductile to brittle transition temperature or glass transition temperature of a material is an important consideration for materials subject to extreme cold.