PSI - Issue 30

M.N. Safonova et al. / Procedia Structural Integrity 30 (2020) 136–143 Safonova M.N. et al. / Structural Integrity Procedia 00 (2020) 000–000

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Fig. 3. Gain of yield strength by (4) – UDND content dependence

3. The discussion of the results The calculations show that the samples with the addition of NDP have a smaller grain size compared to the initial ones. This fact can be explained as follows. The diamond particles, settling at the grain boundaries of the material, help to reduce their average size. As a result, the geometry of the boundaries between the grains changes; barriers to dislocations are formed; and thus, the potential capability of the material to resist plastic deformation is enhanced. Diamond particles settling at the grain boundaries of the material cause a decrease in the average grain size, thereby contributing to the development of the geometry of the boundaries between them and increasing the potential ability of the material to resist plastic deformation due to the formation of barriers for dislocations. The yield strength increases by about 12–13 MPa, which correlates with the calculated data obtained using the Orowan theory for dispersion hardening. For a polycrystalline material, in principle, the yield strength increases with decreasing grain size. Diamond particles, when added to the matrix volume change the grain geometry, reducing their average area and size, thereby increasing the yield strength. 4. Conclusions The calculations showed an increase in the hardening of the material in proportion to the number of diamond particles introduced into the volume, which differs from the experimental data. The assumption was made that the Orowan hardening model does not take into account the formation of carbon and the agglomeration of diamonds into larger objects in the matrix volume with an increase in the amount of input diamonds. The decrease in the number of pores when adding particles of UDND in the amount of 1-2% can be explained by the high sorption properties of the filler. During sintering of compacts obtained by powder metallurgy, UDND particles absorb oxygen contained in the powder mixture with the formation of CO and CO 2 gases, which are reducing gases. The resulting gases destroy the oxide film covering the particles of the powder mixture and prevent oxidation during sintering, thereby reducing the total volume of gases in the powder mixture. At the same time, reducing gases accelerate the sintering of the material. The combination of these factors ultimately reduces the residual porosity in the material, which is also confirmed by the calculated data. With an increase in the number of UDND particles to 3%, the carbon content in the material increases, and because of this, the filler particles are not completely oxidized, thereby increasing the number of pores in the material. References Azygaliev, U.Sh., 2012. Structural modification of organopolymer building composites. Vestnik of KSUCTA 10, 29-33. Babichev A.P., Babushkina, A.M., 1991.Physical Values. Reference guide, In: Publishing house “Energoatomizdat”. Moscow, pp.363. Carlton, C.E., Ferreira, P.J., 2007. «What is behind the inverse Hall-Petch effect in nanocrystalline materials?». Acta Materialia 55, 3749-3756. Donald, J.V., Yanbin,W., Michael, T.V., 1994. Strength of Diamond. Science 266, 419-422.