Microindentations

Microindentations are small-scale permanent impressions produced on a material surface by a hardness-testing indenter under a controlled load. They are used to assess hardness and related mechanical properties at the microstructural level, enabling characterization of coatings, thin films, and heterogeneous materials where macro-scale tests are unsuitable.

Common microindentation geometries include the Vickers pyramid (square-based), Knoop pyramid (elongated), and Berkovich pyramid. In traditional microhardness testing, hardness is derived from the impression size and applied load. In instrumented indentation (often called nano- or microindentation), the indenter is pressed into the surface while the load and displacement are recorded, and properties such as hardness and elastic modulus are extracted from the load-displacement curve by methods such as Oliver-Pharr.

Typical tested loads span from roughly 0.1 to several hundred gram-force for microhardness, expanding into the milli- to tens of newtons range for some micro/macro hybrids. The method is widely used for coatings and thin films, microelectromechanical systems, diffusion zones, ceramics, polymers, and metal alloys.

Procedure notes include careful surface preparation, control of dwell time, and precise measurement of the imprint dimensions with optical or electron microscopy, or analysis of the load-displacement data. Substrate effects, indentation size effects, creep, anisotropy, and surface roughness must be considered in interpretation.

Standards exist under ISO and ASTM for microhardness and instrumented indentation methods, providing test geometries, loading protocols, and data interpretation guidelines. Microindentation remains a versatile tool for localized mechanical characterization, complementing bulk hardness tests.