BS EN 623-5-2009 pdf download.Advanced technical ceramics Monolithic ceramics General and textural properties Part 5: Determination of phase volume fraction by evaluation of micrographs.
5.2 Cutting
The required section of test-piece shall be cut using the diamond saw (see 4.1).
NOTE For routine inspection of materials, a small area of side no more than 10 mm Is normally adequate as the section to
be polished.
5.3 Mounting
Mount the test piece using an appropriate mounting medium. If the ceramic is suspected to have significant open porosity in some regions (see Clause 1) it is advisable to vacuum impregnate the test piece with liquid mounting resin before encapsulating as this will provide some support during grinding and polishing.
NOTE It is not essential to encapsulate the test piece. For example, It could be affixed to a metal holder. However. encapsulation in a po’ymer-based medium allows easy gripping and handling, especially of small irregularly shaped test pieces and of weak friable test pieces. The method of mounting selected should take into account the etching procedure to be used see Annex B.
5.4 Grinding and polishing
Grind and polish the surface of the test piece. Care should be taken to ensure that grinding produces a planar surface with a minimum of damage. Employ successively smaler grit sizes, at each stage removing the damage from the previous stage until there is no change in appearance when examined by an optical microscope (see 4.4) at high magnification. At least 90 % of the test piece area shall be free from optically visible scratches, or other damage introduced by polishing, which will interfere with the determination. In particular, discrete secondary phases may be plucked out from the surface giving the appearance of pores. This shall be avoided.
NOTE Care should be taken in choosing the sequence of grits and lap types. it is impossible within the scope of this part of EN 623 to make specific recommendations for all types of material. The general principle to be adopted is the minimisation of subsurface damage, and its removal by progressively finer grits whilst retaining a flat surface. Some guidelines on polishing are given in Annex A.
5.5 Etching
When a good quality polished surface has been achieved, the test piece shall be etched if necessary to reveal the individual phases. Any suitable technique shall be used, subject to agreement between parties.
NOTE 1 Some general guidelines recommending etching procedures for various commonly available advanced technical ceramics are given in Annex B.
NOTE 2 For optical evaluation, it is usually necessary to etch oxide materials in such a way that the individual phases are distinguished by having different contrast levels. For evaluation by scanning electron microscopy (SEM), it may not be necessary to etch if a baclcscattered electron detector is used which has adequate resolution of net atomic number difference between the phases such that contrast is generated. if a secondary electron detector is used, it will usually be necessary to etch to produce topographic contrast unless the atomic number difference between the phases Is large.
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 wi 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 Köhler illumination in the microscope.
NOTE Guidance on setting Kóhler 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
ctiaracterised is normal to the electron beam to within 5°.BS EN 623-5-2009 pdf download.