ASTM B933:16 pdf download

ASTM B933:16 pdf download.Standard Test Method for Microindentation Hardness of Powder Metallurgy (PM)Materials.
X2.1 The methods described in this appendix are proven practices for metallographic preparation of porous PM materials for microindentation hardness testing. It is recognized that other procedures or materials used in preparation of a sample may be equally as good and can be used on the basis of availability and preference of individual laboratories.
X2.2 Method 1:
X2.2.1 The porous samples should be free of oil or coolant. Remove any oil using Soxhiet extraction. Mount and vacuum impregnate samples with epoxy resin, to fill porosity and to prevent the pickup of etchants. Use a sample cup or holder to form the mount. Pour epoxy resin over the sample in the cup to a total depth of about 0.75 in. (19 mm). Evacuate the cup to minus 26 in. of mercury (88 kPa) and hold at that pressure for 10 mm. Then restore ambient air pressure to force the resin into most of the sample. Cure at room temperature or at 122 °F
(50 °C).
X2.2.2 Grind on 240, 400. and 600 grit wet SiC paper, on a rotating wheel, and change the polishing direction 90° after each paper. Etch samples for 1 mm in their normal etchant, for example, 2 % nital, to begin to open the porosity. Rough polishing for 8 to 12 mm total on 1 pm alumina (Al,03), long napped cloth (for example, Struers felt cloth), at 250 rpm, and 300 gf load, using an automated polisher opens smeared pores. This rough polishing opens and exaggerates the pores. To return the pores to their true area fraction, polish for 4 mm at 125 rpm on a shorter nap cloth (for example. Struers MOL cloth), with 1 pm diamond paste. Final polishing is done for 20 to 30 s using 0.05 pm deagglomerated alumina, and a long napped cloth (for example, Buehler Microcloth), at 125 rpm, and 75 gf load, on an automated polisher. Polishing may also be done by hand for the times indicated. The first two polishings require moderate pressure and the final polish requires light pressure.
X2.2.3 The metallographic structure should be free of smeared porosity. Generally at 800 to l000x, the edge of a smeared over pore will appear as a thin gray line outlining one side of the pore, and occasionally outlining most of the pore.
X2.2.4 The specimen should be etched prior to microindentation hardness testing. Careful etching is necessary because heavy etching obscures features and may interfere with the measurement of the diagonals. For heat-treated steels, swabbing with or immersion in 2 % nital for 4 to 7 s gives an appropriate structure. Martensite will be very light and the darker etching non-martensitic transformation products.