The effect of alumina-based sintering aid on the microstructure, selected mechanical properties, and coefficient of friction of Cf/SiC composite prepared via spark plasma sintering (SPS) method

Abstract

Cf-SiC air brake discs are being developed due to their high-temperature oxidation resistance compared to conventional Cf/C discs. The Cf-SiC air brake discs should have a coefficient of friction (COF) close to 0.4, a low wear rate, a density higher than 95% of the theoretical density, and flexural strength of more than 200 MPa. To reach the properties of Cf-SiC composite to the required characteristics of the air brake disc, different amounts of alumina-based sintering aid were used. For this purpose, first silicon carbide nanoparticles, sintering aids Al2O3–MgO, MgAl2O4, Al2O3–Y2O3, Al2O3–SiO2–MgO, and carbon fiber (20 wt%) with a 5-mm length were prepared. Next, the final composite bulk was created via the SPS method at 1900 °C under a pressure of 50 MPa. The density of the sample sintered with the Al2O3–SiO2–MgO sintering aid was higher than that of other sintering aids. The density value was obtained at 98% and 100% at 8 wt% and 4 wt% respectively. It was also found that the use of 4 wt% of Al2O3–SiO2–MgO offered better mechanical properties compared to 8 wt%, due to the absence of Al8Si4O20 phase at 4 wt%. The examination of mechanical properties showed that the hardness (3564 Vickers) and flexural strength (479 MPa) of the sample with the Al2O3–SiO2–MgO sintering aid were higher than those of other sintering aids. The samples with the Al2O3–SiO2–MgO sintering aid with 4 wt% revealed a COF of 0.41, showing the closest feature to the desired indices of aircraft brake discs.