A material's microstructure must often be observed rather than inferred only from bulk properties. Microscopy converts spatial variations in composition, crystal orientation, topography or phase into images that can be measured.

Optical microscopy

Visible-light microscopy can reveal grains, phases, pores and cracks when features are large enough and the surface has appropriate contrast. Metallographic samples are commonly sectioned, polished and selectively etched so that different grains or phases interact with light differently.

Scanning electron microscopy

A scanning electron microscope (SEM) sweeps a focused electron beam across a surface. Signals emitted from the interaction region can provide high-resolution topographic contrast or composition-sensitive contrast over a useful depth of field.

Transmission electron microscopy

A transmission electron microscope (TEM) sends electrons through an electron-transparent specimen. It can resolve much smaller structures and can reveal defects, nanoscale precipitates and crystallographic information, but requires demanding sample preparation and examines a very small volume.

An image is a measurement

Magnification alone does not guarantee useful resolution. Pixel size, interaction volume, sample preparation, detector response and field of view all limit what can be concluded. A micrograph should therefore include a calibrated length scale, and quantitative claims such as grain size or pore fraction should be based on a sampling procedure rather than one visually attractive field.

Microscopy links processing to observed structure; other techniques, such as diffraction, provide complementary information averaged over a larger volume.