Microhardness

Microhardness is not a separate material property but a test regime in which Vickers or Knoop indenters apply forces small enough that impression diagonals remain on the order of tens of micrometres. It answers questions that macro tests cannot: hardness of electroplated layers, laser-clad tracks, decarburized skin, or individual phases in multiphase alloys.

Knoop uses an elongated pyramid to produce an asymmetric impression; the long diagonal is measured to compute HK. Knoop can be advantageous on brittle materials or very thin films because it drives less subsurface plastic zone along the short axis, though interpretation still requires validated procedures.

Sample preparation is critical: 1 µm or finer final polish is common, and etching may be required to locate microstructural targets. Thermal drift during long dwells can falsify results; modern instruments correct using reference materials or environmental enclosures.

Because impressions are small, elastic springback and edge effects inflate scatter. Operators should report force, dwell, indenter type, and imaging method. Compliance to ASTM E384 or ISO 6507 annexes for low-force testing ensures comparability across laboratories.