The term microstructure is used to describe the structure of metals. A basic visual examination of etched metal surfaces and fractures will reveal some configurations in etched patterns that relate to structure, but magnification of minute details will yield
considerably more information.
Three widely used tools for the examination of structures in metals and their applications are:
(1) The low-power magnifying glass, when applied to etched metal surfaces reveals gross details in microstructure.
(2) The metallograph, an optical microscope, usually fitted with an inverted stage for convenience in scanning the flat face of prepared specimens. Metallographic examination usually requires magnification in the range of 50 to 1500X (X = diameters). Because of the wave length of visible light, there is an upper limit of about 2000X for magnification of an optical microscope.
(3) The electron microscope, capable of magnifying at least 200000X with remarkably good depth of focus and resolution. Images of metal microstructure are obtained either by electron beams transmitted through a specimen or by beams that are reflected and emitted.