hårdhed

Hårdhed, or hardness in materials science, is a measure of a material's resistance to permanent deformation under load, especially from indentation or scratching. It reflects how difficult it is to permanently deform the surface through mechanical contact and wear.

The concept is defined and measured in several ways. The Mohs scale provides qualitative scratch resistance for minerals. Modern engineering uses indentation-based tests that yield numeric values under defined loads and geometries: Brinell (HB), Vickers (HV), and Rockwell (HRC, HRB, HRA). Microhardness tests (Knoop, HV under small loads) are used for thin films and coatings or small features.

Hardness is influenced by composition, crystal structure, grain size, phase distribution, work hardening, and heat treatment. Generally, harder materials resist plastic deformation better and often exhibit higher yield strength, but they can be more brittle and less tough.

Limitations: hardness is a surface property and depends on surface finish, indenter geometry, and load. It does not directly measure wear resistance, toughness, or fatigue resistance, and conversion between scales is not universal.

In practice, hardness is used as an indicator of material performance and as a control parameter in processing, such as heat treating steel, applying hard coatings, and ceramic manufacturing.