metallographic

Metallography is the science and practice of characterizing the microstructure of metals and alloys. It involves preparing thin, polished sections and examining them under light or electron microscopes to reveal features such as grains, phase distribution, inclusions, and defects. The microstructure influences properties like strength, hardness, toughness, and corrosion resistance.

Preparation: Specimens are cut and mounted in resin; surfaces are ground with abrasive papers of increasing fineness, then polished to a mirror finish. Etchants or chemical reagents are applied to reveal microstructural features by preferentially corroding different phases or grain boundaries. The choice of etchant depends on alloy system (steel, aluminum, copper alloys, ceramics).

Imaging and analysis: Optical microscopy is common for qualitative assessment and grain size measurement. Scanning electron microscopy provides higher resolution and can reveal morphology of second phases. Electron backscatter diffraction maps crystallographic orientations and grain boundaries. Microhardness tests and image analysis quantify grain size, phase fractions, and inclusion content.

Applications: Metallography supports quality control, failure analysis, heat-treatment development, and material selection. It is used in failure investigations to identify improper heat treatment, corrosion mechanisms, or mechanical damage. It is foundational to standards and certification in many manufacturing sectors.

Standards and practice: Laboratories follow standards for specimen preparation, etching, imaging, and data interpretation, including defined procedures and calibration protocols. The field integrates with other materials characterization methods such as X-ray diffraction, spectroscopy, and mechanical testing.