Hardness

Hardness is a material’s resistance to localized indentation, scratching, or wear. Its measured value depends on the test method and the deformation process being assessed.

Plastic deformation: Permanent deformation that remains after a material’s load is removed. Indentation hardness reflects the material’s resistance to permanent deformation beneath an indenter.
Brinell hardness test: A hardness test that measures the indentation made by a hard ball under a specified load. Its broad impression averages hardness across coarse or heterogeneous metal structures.
Strength of materials: The ability of materials to withstand applied forces without failure or excessive deformation. Strength covers broader loading and failure behavior than localized hardness tests.
Crystal structure: The ordered, repeating arrangement of atoms in a crystalline solid. Crystal geometry and available slip systems shape resistance to indentation.
Indentation size effect: The tendency for measured hardness to vary with indentation depth or size, especially at small scales. It complicates comparisons between microhardness measurements and larger-scale tests.
Dislocation: A line defect in a crystal lattice that enables layers of atoms to slip. Dislocations govern much of the plastic flow resisted during indentation.
Rockwell hardness test: A hardness test that derives a value from the depth of an indenter under specified loads. Its direct depth reading makes it useful for rapid production checks.
Yield strength: The stress at which a material begins to deform plastically. Yield strength is related to indentation hardness but is measured under a different loading condition.
Grain boundary: The interface separating crystals with different orientations in a polycrystalline material. Grain boundaries can impede dislocation motion and raise hardness.
Nanoindentation: A method that measures material response as a sharp indenter penetrates at nanometer-to-micrometer scales. It extends hardness measurement to thin films and tiny material volumes.

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