TEST METHODS AND PROPERTIES OF POWDERED MATERIALS COMPARISON OF THE RESULTS OF MEASUREMENTS OF POROSITY BY DIFFERENT METHODS V. M. Kaptsevich, V. K. Sheleg, V. V. Savich, A. N. Sorokina, V. V. Mazyuk, and T. A. Anishchik UDC 621.762 Measurement of porosity is one of the principal methods of quality control of finished products obtained by the method of powder metallurgy. Porous powderedmaterials (PPM) and products made of them cannot be investigated or devised without an accurate notion concern- ing this characteristic. A number of methods of determining porosity is known: the hydrostatic method [i], the method of mercury porometry [2], the metallographic method [3], by permeability [4], etc. An attempt was made in [5] to evaluate the results of measurements by the most widespread methods. However, since there were no quantitative values of porosity obtained by different methods, it was impossible to draw conclusions as to the absolute and relative error of each method involved. The object of the present work is to compare the results of measurements of porosity by the most widespread methods. For our research we" used the following equipment: a balance VLR-100 (error of measure- ment • g); a micrometer MK (accuracy of measurement • mm); a mercury porosimeter model "autopore-9200" made by Micromeritix (US); a TVmicroscope "Quantimet-720" made by Metal Research (Great Britain); a laboratory stand for determining the coefficient of per- meability and the pore size, made according to GOST 25.283-82 and GOST 26849-86 (accuracy of measuring permeability is 5%, of measuring pore size 10%). The object of investigation were PPM made by sintering freely poured powders of bronze marque BrOFI0-1 and of titanium marque VT9, and also obtained by compaction under different pressures and by sintering powder of steel marque PKhI8NI5. The specimens of PPM had the shape shape of disks with 30 mm diameter, 3-4 mm thick. The particle size of the initial powder was -0.i + 0.063 mm; with the given thickness this ensured a regular structure [6-8]. To make sure that the obtained results were reliable, we measured the porosity of each specimen by all the five methods. First we determined the coefficient of permeability and the size of the pores, then we determined porosity by calculation and by the hydrostatic method, after that the dried specimen was split into two parts, to one of them the method of mercury poro- simetry was applied while a metallographic section was made from the second part for metallo- graphic investigations. Table 1 presents the results of the investigations and Fig. I shows photographs of metallographic sections of specimens of PPM. It is known from the literature sources that the hydrostatic method is the most accurate method of determining open porosity (if the lquid is correctly chosen and the apparatus is accurate), whereas the calculation method makes it possible to determine total porosity only [5]. The porosity of PPM determined by calculation is therefore greater than the one esta- blished hydrostatically. However, for PPM made from spherical powders the values of total and open porosity are close to each other, practically the same (the difference does not exceed 0.3-2%), because there is no closed porosity in them (except for possible pores with- in the particles); on the other hand, for PPM made from spongy powder the difference between these characteristics is substantial (24-38%) because the proportion of interparticular and intraparticular closed porosity is larger (Fig. i). It should also be noted that the results of determining porosity by the calculation method are affected by the surface roughness of the object, too. For instance, with PPM made by sintering freely poured powder, the surface roughness of the specimen is proportional to the particle size. Therefore, even when there is no closed porosity, we find a difference Bryansk Scientific and Production Asociation of Powder Metallurgy. Translated from Poroshkovaya Metallurgiya, No. 2(314), pp. 48-52, February, 1989. Original article submitted August 18, 1987. 0038-5735/89/2802-0117512.50 @ 1989 Plenum Publishing Corporation I17