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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hardened matrix materials. Also, for the wear resistance of composites, an important factor is the strength of the interface of the components. A strong adhesive bond at the interface provides a composite with high rigidity and higher static strength as pointed by Kallip et al. (2017), Jiang et al. (2017), Liu et al. (2017), Saba et al. (2019), Loktyushin et al. (2004). The ultrafine particles of diamond distributed in the volume of the bundle, according to the Orowan mechanism, affect the strain hardening of the composite material. Particles of dispersed filler introduced into the matrix inhibit the movement of dislocations in the metal, increasing its strength at normal and elevated temperatures, and also represent a mechanical obstacle to the propagation of cracks that can appear in the matrix and increase the fracture resistance of the composite material. Another characteristic determining the relationship between the reinforcer and the matrix is the temperature coefficient of linear expansion. For solids, the criterion of thermodynamic equilibrium at constant pressure and temperature is the minimum of Gibbs energy - a value that shows the change in energy during a chemical reaction and shows the possibility of chemical reactions between material components, as found by Liu et al. (2017). Thus, the minimum change of the Gibbs energy corresponds to a stable equilibrium between the components of the system (Table 1). Table 1. Physical Characteristics of Fillers [Donald et al. (1994), Mishchenko and Ravdel (1974), Babichev et al. (1991)] Substance Δ G o , 298,15 kJ/mol Microhardness, х 10 2 MPa Temperature stability, °C

С

2.377

1000

650-700

W

0

258

3300-3400 1500-1700 1100-1300 1200-1300

Al 2 O 3

-1582,3

180-220 800-900 300-320

BN SiC

-226,8

-60

BeO Be 2 C

-579,9

152 780

2500 2150

-948

The Table 1 shows that the optimal filler is diamond. It has a fairly low value of Gibbs energy change, the highest microhardness value, but the lowest temperature stability. Diamond has a high adsorption capacity, as found by Parkaeva et al. (2010) and is the least chemically active compared to other forms of carbon. These properties are important advantages when using diamond as a hardener. The work objective is to study features of the mechanisms of forming the metal-matrix composition structure. Based on the foregoing, the choice of filler in a post of composite material in favor of diamond particles is justified, for use as a dispersed reinforcer. Objects of study We used M2-01 tin bronze (20 wt. % tin, 80% copper) as a basic binder. Ultradisperse natural diamond (UDND, 0.5–4 wt. %) was added to it, as well as powders of natural diamond (3/2 μ m fraction, 7/5 μ m, – 40 μ m). 2. Research Methodology Natural diamond powders (NDP, 3/2 μ m fractions, 7/5 μ m, –40 μ m) and the UDND submicropowder were obtained during the processing of diamonds at the enterprise of “Sakha Diamond” JSC. The powders were made on the crushing and screening equipment and shaking tables under the optimum conditions. Fig. 1 shows the stages of obtaining the powders. The images were taken using the scanning electron microscopy (SEM).