contacthardheid

Contact hardness, or contacthardheid in Dutch, refers to the resistance of a material’s surface to plastic deformation under the load applied by a mating body in contact. It is a practical expression of how hard the surface behaves under real contact stresses, and it can differ from the bulk hardness due to surface treatments, coatings, residual stresses, and finite coating thickness.

Measurement and interpretation: Hardness values are usually obtained from standard indentation tests such as Vickers, Rockwell, or Brinell on the contact surface. For thin films and coatings, micro- or nanoindentation provides localized hardness values. In tribology, contact hardness is often used in wear and contact-stress analyses, for example in Archard’s wear law, where wear resistance increases with higher hardness (up to a limit where toughness becomes critical).

Influencing factors: Surface hardness depends on material composition, heat treatment, and microstructure, as well as surface finish, residual stress, and the presence of coatings (e.g., hard coatings like ceramic or carbon-based films). Condition at the contact, such as temperature and lubrication, as well as contact geometry, influence the actual stress distribution and effective hardness during sliding or rolling.

Relation to performance: Higher surface hardness typically improves wear resistance and reduces plastic deformation under contact. However, if hardness is too high relative to toughness, cracking, spalling, or coating delamination can occur. Therefore, designers seek an optimal balance between hardness and toughness in the near-surface region.

Applications: Contact hardness is a key parameter in the design of gears, bearings, piston rings, and cutting tools, and it is used to evaluate surface treatments and coatings intended to improve wear resistance and fatigue life.