<P> Characterization of microstructures has also been performed using x-ray diffraction (XRD) techniques for many years . XRD can be used to determine the percentages of various phases present in a specimen if they have different crystal structures . For example, the amount of retained austenite in a hardened steel is best measured using XRD (ASTM E 975). If a particular phase can be chemically extracted from a bulk specimen, it can be identified using XRD based on the crystal structure and lattice dimensions . This work can be complemented by EDS and / or WDS analysis where the chemical composition is quantified . But EDS and WDS are difficult to apply to particles less than 2 - 3 micrometers in diameter . For smaller particles, diffraction techniques can be performed using the TEM for identification and EDS can be performed on small particles if they are extracted from the matrix using replication methods to avoid detection of the matrix along with the precipitate . </P> <P> A number of techniques exist to quantitatively analyze metallographic specimens . These techniques are valuable in the research and production of all metals and alloys and non-metallic or composite materials . </P> <P> Microstructural quantification is performed on a prepared, two - dimensional plane through the three - dimensional part or component . Measurements may involve simple metrology techniques, e.g., the measurement of the thickness of a surface coating, or the apparent diameter of a discrete second - phase particle, (for example, spheroidal graphite in ductile iron). Measurement may also require application of stereology to assess matrix and second - phase structures . Stereology is the field of taking 0 -, 1 - or 2 - dimensional measurements on the two - dimensional sectioning plane and estimating the amount, size, shape or distribution of the microstructure in three dimensions . These measurements may be made using manual procedures with the aid of templates overlaying the microstructure, or with automated image analyzers . In all cases, adequate sampling must be made to obtain a proper statistical basis for the measurement . Efforts to eliminate bias are required . </P> <P> Some of the most basic measurements include determination of the volume fraction of a phase or constituent, measurement of the grain size in polycrystalline metals and alloys, measurement of the size and size distribution of particles, assessment of the shape of particles, and spacing between particles . </P>

Why are high speed particles used to examine the internal structure of other particles