Metallographic specimens are typically mounted using a hot compression

Metallographic specimens are typically mounted using

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Metallographic specimens are typically "mounted" using a hot compression thermosetting resin. In the past, phenolic thermosetting resins have been used, but modern epoxy is becoming more popular because reduced shrinkage during curing results in a better mount with superior edge retention. A typical mounting cycle will compress the specimen and mounting media to 4,000 psi (28 MPa) and heat to a temperature of 350 °F (177 °C). When specimens are very sensitive to temperature, "cold mounts" may be made with a two-part epoxy resin. Mounting a specimen provides a safe, standardized, and ergonomic way by which to hold a sample during the grinding and polishing operations. After polishing, certain microstructural constituents can be seen with the microscope, e.g., inclusions and nitrides. If the crystal structure is non-cubic (e.g., a metal with a hexagonal-closed packed crystal structure, such as Ti or Zr) the microstructure can be revealed without etching using crossed polarized light (light microscopy). Otherwise, the microstructural constituents of the specimen are revealed by using a suitable chemical or electrolytic etchant. Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical, electron, and scanning probe microscopy, along with the emerging field of X-ray microscopy.
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Optical microscopy and electron microscopy involve the diffraction, reflection, or refraction of electromagnetic radiation/electron beams interacting with the specimen, and the collection of the scattered radiation or another signal to create an image. This process may be carried out by wide- field irradiation of the sample (for example standard light microscopy and transmission electron microscopy) or by scanning a fine beam over the sample (for example confocal laser scanning microscopy and scanning electron microscopy). 2.2.2 Sampling The location from which a specimen is taken depends on whether the investigation is aimed (1) to give data for a specific area (systematic sampling), e.g., if the origin of a failure is clearly visible, (2) to characterize a larger piece (e.g., a laboratory sample) or (3) to characterize the quality of a large amount of material (as in quality control). In the last two cases the statistical fluctuations due to unavoidable inhomogeneities must be considered, and usually more than one specimen is necessary to get a reliable result (statistical sampling). Since usually nothing is known as to the degree of homogeneity, statistical parameters (usually taking the arithmetic mean and the relative standard error). Furthermore, damaging the specimen during cutting it from a larger piece gives rise to erroneous results: Electro erosive cutting (“spark-machining”), for example, changes the composition near the cut faces to an appreciable depth: e.g., 0.9 and 0.3 wt% carbon (stemming from the electrolyte) and 0.8 and 0.2 wt% copper (from the electrode) were found in pure iron at 50 and 150 pm depth, respectively, below the electro-eroded surface.
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  • Electron, Scanning Tunneling Microscope, Scanning electron microscope, Scanning probe microscopy, Atomic force microscopy

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