BS EN 623-5:2009 pdf free download – Advanced technical ceramics – Monolithic ceramics – General and textural properties Part 5: Determination of phase volume fraction by evaluation of micrographs.
6 Photomicrography
6.1 General aspects
If it suspected that the average grain size of each phase or the widths of continuous glassy phases between grains is less than 2 pm, it will be necessary to prepare the test piece for SEM. Between 2 pm and 4 pm either SEM or optical microscopy may be used. Otherwise, optical microscopy will normally be adequate.
It is important to achieve sufficient contrast between phases in order to identify individual grains clearly and unambiguously.
6.2 Inspection
Inspect the sampled cross-section in the microscope. If the microstructure appears homogeneous, prepare micrographs from randomly selected areas. If inhomogeneity of microstructure is suspected, select representative areas of relevance for measurement.
6.3 Number of micrographs
At least three micrographs shall be prepared at a magnification sufficient to identify clearly all the phases to be counted. In addition, at least 100 features in total of any given type shall be present to be counted in the set of micrographs.
NOTE For a nominally homogeneous material, it may be sufficient to use a small number of micrographs analysed with a small grid spacing, but for an inhomogeneous material, results representative of the average for the sampled section can be prepared reliably only by selecting a large number of micrographs of different areas, with less intensive counting from a larger grid.
6.4 Optical microscopy
Set up Kähler illumination in the microscope.
NOTE Guidance on setting Köhler illumination conditions is given in Annex D.
Examine the test piece at a magnification sufficient to resolve the individual grains clearly. If the contrast obtained is insufficient, e.g. in white or translucent materials, apply a suitable thin metallic coating by evaporation or sputtering. Prepare micrographs of at least three different randomly selected areas of the test-piece surface, taking into account the apparent homogeneity of the microstructure (see 6.2). As a guideline, the average size of discrete phase area to be counted should appear typically at least 3 mm across. If the total number of individual grains of any one phase to be counted in any one set of micrographs is less than one hundred, prepare more micrographs. Micrographs should be typically of a size (100 x 75) mm, but may with advantage be enlarged later to aid evaluation.
6.5 Scanning electron microscopy (SEM)
Mount the test piece on the test piece holder of the microscope. If the test piece is not electrically conducting, apply a
thin evaporated or sputtered conductive coating. Insert the test-piece in the microscope, ensuring that the surface to be
characterised is normal to the electron beam to within 5°.
NOTE I This ensures that the image does not suffer from excessive distortion or loss of focus due to the angle of viewing.
Prepare micrographs at a suitable magnification (see 6.4) from at least three different randomly selected areas of the test piece, using either secondary electron imaging or backscattered electron imaging.
NOTE 2 Although the contrast between phases can be enhanced using backscattered electron imaging, a noisier image than in secondary electron imaging may result and may render the boundaries between contrasting phases indistinct. It can be helpful to use secondary electron images for counting the phase proportions, but backscattered images to aid identification of each phase.