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Wybrane właściwości mechaniczne kompozytów ziarnistych Al2O3/Mo

Matysiak H., Konopka K., Kuźniak M., Olszyna A.

Kompozyty

2001

R. 1, nr 2

215-218

Wytworzono kompozyty Al2O3/Mo o udziale wagowym molibdenu 10,15, 20, 35, 50%. Przeprowadzono badania mechaniczne: twardości, wytrzymałości na zginanie i odporności na pękanie. Dokonano oceny wpływu naprężeń resztkowych na uzyskane wyniki doświadczalne.

The study is concerned with the effect of the Mo particles introduced into the Al2O3 composites on their mechanical properties. The Al2O3 composite with Mo content of 10, 15, 20, 35 and 50 wt.% was fabricated using the sintering technique at a temperature of 1700°C in vacuum. The properties examined included: the density and porosity (by the Archimedes method), elastic constants (ultrasonic method), hardness (Vickers method), bending strength (three-point bending of beams - Fig. 1) and the fracture toughness (three-point bending of notched beams). An attempt was also made at estimating how the residual stresses (determined from the Eshelby formulas - eqs. 5-9) affect the results obtained experimentally. It has been found that the Mo particulates introduced into the corundum matrix increase the relative density of the sintered material to 96:99% (Table 1, F"ig. 3). They also increase the bending strength (Table 2, Fig. 5), KJC and the fracture energy (Table 2, Fig. 6) with the relatively high hardness of the composites being maintained almost unchanged (Table 2, Fig. 5). The introduction of Mo particles also affects the Young and Kirchoff moduli: they slightly decrease in a linear way with increasing Mo content of the composite (Table 2, Fig. 4). In the composite containing 15% Mo, the bending strength increased by ca. 30%, the stress intensity factor by ca. 12% (Table 2, Fig. 6), the cracking energy by ca. 53% (Table 2, Fig. 6) with a minute decrease of the hardness by ca. 5% (Table 2, Fig. 5). In the composites with 50% Mo, the increase in the KJC coefficient and the cracking energy was considerable (ca. 66% and ca. 230%, respectively - see Table 2, Fig. 6), but it was accompanied by a remarkable decrease of hardness (more than threefold) and a minute increase (ca. 3%) of the bending strength (Table 2, Fig. 5). An analysis of the residual stresses has shown that the stresses induced in the Al2O3 matrix are tensile, whereas those in the Mo particles - compressive. As the Mo content increases, the tensile stresses in the matrix increase from 9 MPa with 10% Mo to 62 MPa with 50% Mo, and the compressive stresses in the Mo particles decrease from -206 MPa with 10% Mo to -149 MPa with 50% Mo (Table 3, Fig. 8).