Metallografia

Metallography is the study of the microstructure of metals and alloys through the preparation and examination of specimens. It aims to reveal features such as grain size and morphology, phase distribution, inclusions, and porosity, which influence mechanical properties, performance, and failure mechanisms. The field combines materials science, microscopy, and surface engineering, and uses optical or electron-based methods to interpret the microstructure.

Specimen preparation is critical. Typical steps include sectioning a representative sample, mounting in a resin, grinding with progressively finer abrasives to remove deformation, and polishing to a mirror finish. Etching with chemical reagents or electrolytes selectively reveals grain boundaries and phases. The prepared sample is then examined by optical metallography, scanning electron microscopy, or transmission electron microscopy.

Analysis commonly assesses grain size and shape, grain-boundary character, phase constitution, precipitation, inclusions, and defect structures such as dislocations. Image analysis software may quantify features, and microhardness tests can be integrated to relate structure to hardness. Advanced techniques include electron backscatter diffraction for crystallographic orientation mapping and TEM for nanoscale features.

Applications span materials development, quality control, failure analysis, and failure prediction in industries such as automotive, aerospace, energy, and manufacturing. The field traces its origins to 19th-century pioneers such as Henry Clifton Sorby and has since evolved with advances in optical and electron microscopy. Standardization exists through organizations such as ASTM, ISO, and JIS, which provide guidelines for specimen preparation, imaging, and interpretation.