T.O. 33B-1-1Glossary 55METALLOGRAPHY: The science dealing with the constitution and structure of metals and alloys as revealed by theunaided eye or by such tools as low-powered magnification, optical microscope, electron microscope and diffraction orX-ray techniques.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 magnificationgreater 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 measuredby such means as Tukon, Knoop or scratch methods.MICRO-INSPECTION: Utilizes a mild etch and high magnification (up to 1000 diameters) for examination ofspecifically prepared polished samples.MICRO-SHRINKAGE: Irregular feathery cavities occurring in the grain boundaries. (Occurs predominantly inmagnesium alloys.)MICROPOROSITY: Porosity visible only with the aid of a microscope.MICROSCOPIC STRESSES: Residual stresses which vary from tension to compression in a distance (presumablyapproximating the grain size) which is small compared to the gage length in ordinary strain measurements. Hence notdetectable 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 lowvoltage 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 thatindicate cavities in the grain boundaries.MICROSTRUCTURE: The structure of polished and etched metals as revealed by a microscope at a magnificationgreater 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 anX-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 productof tube current in milliamperes and exposure time in seconds. Abbreviation: mAs.
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