BS ISO 18550:2016 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Testing method for macro-heterogeneity in microstructure
5.4 Polishing machine, suitable machine capable of polishing the ceramics. 5.5 Micrometer, capable of measuring the thickness of the polished ceramic section with an accuracy of 2 μm. 5.6 Microscope slide, suitable transparent microscope slide for mounting the test-piece in the microscope.
5.7 Transparent film with circles of various diameter, to determine the equivalent circle diameter of defects.
6 Test specimen
The specimen shall be thin enough for observation in the transmission mode of the microscope. The typical thickness depends on the material and its porosity, and is between 30 μm and 200 μm. The specimen shall be prepared as follows.
a) Cut a thin slab from the ceramic using a cutting machine. A thickness of the slab of more than 1 mm plus the final thickness is recommended. For a ceramic with thickness of less than 2 mm, this process can be omitted.
b) One face of the slab shall be ground using a grinding machine and polished with a polishing machine by using polishing grains of a sequence of decreasing sizes with the finishing grit size of less than 1 μm.
c) The other face of the slab shall be ground to adjust the thickness of the slab appropriately. Finally, the ground face shall be polished with the polishing machine by using polishing grains of a sequence of decreasing sizes as mentioned above to prepare a thin specimen for observation.
d) Finally, mount the thin specimen on the microscope slide for observation. Transparent thermoplastic resin is recommended for mounting.
e) The thickness of the specimen must be adjusted for adequate transparency before examination. With a specimen of adequate transparency, defects located at any depth in the specimen can be well focused. Scratches on both front and back surfaces are conveniently used to examine the applicability of this International Standard. If they are clearly seen from the opposite side, this International Standard can be applied.
7.1 Measurement of specimen thickness
The thickness of the specimen shall be measured at the centre of the specimen with a micrometer to the nearest 0,002 mm.
Adjust the microscope as follows; set the numerical aperture of the condenser lens in the illumination system 0,1 or less. The objective lens used for observation should have the magnification under ×10.
The minimum sizes of defects subjected for examination is 10 μm equivalent circle diameter. With the numerical aperture of the lens of 0,1, the maximum thicknesses of specimens which can be examined in one micrograph will be 48 μm and 28 μm multiplied by the refractive index of the specimen, for the objective lenses of magnifications ×4 and ×10, respectively.
The position of focus should be at half of the specimen thickness from the top surface. The refractive index of major phase shall be used for a specimen with multiple phases. If the specimen is highly transparent, a thicker specimen can be used. A series of micrographs shall be taken by changing the position of focus through the depth direction of specimen. The interval in the position of focus shall be less than 48 μm and 28 μm multiplied by the refractive index of the specimen, for the objective lenses of magnifications ×4 and ×10, respectively. The photographed areas shall not overlap and micrographs should cover at least 100 macro- heterogeneities which shall be analysed.
8 Measurement of macro-heterogeneities
8.1 Determination of specimen volume under examination The volume, V, under examination is given by the image area, A i , the thickness, t, of the slab, and the number, n L , of locations under examination.
V = A i × t × n L
8.2 Measurement of the size of macro-heterogeneities
The net magnification shall be adjusted to make the defect of the minimum size appear to be over 5 mm equivalent circle diameter on the micrograph. A transparent film with circles of various diameters shall be used to determine the equivalent circle diameter. Determine the size for at least 100 macro- heterogeneities.