What does polymorphism in metals refer to?

Polymorphism in metals specifically refers to the ability of a metal to adopt different crystal structures at different temperatures, pressures, or compositions. This characteristic allows metals to transform between forms based on environmental conditions or processing techniques. For example, iron exhibits polymorphism, existing in both body-centered cubic (BCC) and face-centered cubic (FCC) structures at different temperatures. The presence of multiple crystal structures can influence the physical properties of the metal, such as strength, ductility, and melting point.

The other options do not accurately capture the concept of polymorphism. Blending different metals is related to the formation of alloys, which can involve multiple elements but does not pertain to changes in crystal structures within a single metal. The idea that alloys only form at high temperatures refers to certain manufacturing processes but again does not define polymorphism. Lastly, suggesting that polymorphism is characterized by the inability to change crystal structures contradicts the very definition of the term, which emphasizes the ability to adopt different forms.