METALLOGRAPHY: The science dealing with the constitution and structure of metals and alloys as revealed by the
unaided eye or by such tools as low-powered magnification, optical microscope, electron microscope and diffraction or
METALLURGY: The science and technology of metals.
MeV: One million electron volts.
MHz: Abbreviation for megahertz.
MICRO: A prefix that divides a basic unit by one million.
MICROFISSURE: A crack of microscopic proportions.
MICROGRAPH: A graphic reproduction of the surface of a prepared specimen, usually etched, at a magnification
greater than ten diameters. If produced by photographic means it is called a photomicrograph (not a microphotograph).
MICROHARDNESS: The hardness of microscopic areas or of the individual microconstituents in a metal, as measured
by such means as Tukon, Knoop or scratch methods.
MICRO-INSPECTION: Utilizes a mild etch and high magnification (up to 1000 diameters) for examination of
specifically prepared polished samples.
MICRO-SHRINKAGE: Irregular feathery cavities occurring in the grain boundaries. (Occurs predominantly in
MICROPOROSITY: Porosity visible only with the aid of a microscope.
MICROSCOPIC STRESSES: Residual stresses which vary from tension to compression in a distance (presumably
approximating the grain size) which is small compared to the gage length in ordinary strain measurements. Hence not
detectable by dissection methods, they can sometimes be measured by X-ray line shift.
MICROSECOND: Unit of the time equivalent to 10-6 second or 0.000001 second.
MICRORADIOGRAPHY: A technique used to examine very small objects or minute detail through the use of low
voltage X-rays and an ultrafine grain film emulsion which is examined with the aid of optical enlargement.
MICROSHRINKAGE (ON RADIOGRAPH): Cracks that appear as dark feathery streaks, or irregular patches that
indicate cavities in the grain boundaries.
MICROSTRUCTURE: The structure of polished and etched metals as revealed by a microscope at a magnification
greater than ten diameters.
MILLI: A prefix that divides a basic unit by one thousand.
MILLIAMPERAGE (RT): Milliamperage is a measure of the current flowing between the cathode and the anode in an
X-ray tube, and is a measure of the intensity of the emitted radiation.
MILLIAMPERE (RT): A unit of electrical current equal to one thousandth of an ampere.
MILLIAMPERE-SECONDS (RT): A term used to quantify radiographic exposures made with X-rays. It is the product
of tube current in milliamperes and exposure time in seconds. Abbreviation: mAs.