What does hardness refer to in materials science?

Hardness in materials science specifically refers to a material's resistance to indentation or scratching. This property is significant because it determines how a material will perform under mechanical stress and wear conditions. Hardness is usually evaluated by measuring how well a material can resist surface deformation when subjected to a hard object or an indenter.

High hardness indicates that the material can withstand significant pressure without deforming, making it suitable for applications that require durability and toughness, such as tools and structural components. Various scales, such as the Mohs hardness scale or Vickers hardness test, are used to quantify the hardness of different materials.

In contrast, hardness does not pertain to a material’s ability to resist bending, corrosion, or thermal expansion; these are measured by different properties. For instance, resistance to bending is related to a material's tensile or flexural strength, while resistance to corrosion reflects chemical stability and is tied closely to material composition and surface treatment. Similarly, resistance to thermal expansion is related to how a material reacts to temperature changes, which involves its coefficient of thermal expansion.