Influences of Al metal and Al–Si alloys on in-situ synthesis of SiC nanowhiskers in porous Al2O3–SiC composites obtained by carbothermal reduction

Abstract

SiC nanowhiskers are good reinforcing phases for enhancing the strength and thermal shock resistance of porous Al2O3–SiC composites. In this work, Al metal and Al–Si alloys were used as reducing agents to assist the in-situ synthesis of SiC nanowhiskers in the porous Al2O3–SiC composites prepared by carbothermal reduction method. The influences of Al metal and Al–Si alloys on the phase composition, microstructure, porosity and strength of the porous Al2O3–SiC composites were studied by XRD, SEM, TEM, etc. The results indicate that the use of Al metal and Al–Si alloys effectively promoted the carbothermal reduction and decreased the synthesis temperature of β-SiC phase from the original 1500 °C–1400 °C. SiC nanowhiskers were in-situ synthesized at a relatively low temperature of 1500 °C with the use of Al metal and Al–Si alloys. Al metal and Al–Si alloys effectively enhanced the strength of the porous composites by reducing the amount of pores and increasing the yield of SiC nanowhiskers. The samples that were added with Al–20Si alloy obtained the highest β-SiC yield of 23.2% and the highest flexural strength of 5 MPa. The thermal shock resistance of the porous composites was effectively enhanced by the in-situ synthesis of SiC nanowhiskers. The oxidation of SiC nanowhiskers during the thermal shock tests (room temperature to 1100 °C) could improve the flexural strength of the porous composites to 6.3 MPa by densifying the microstructure and increasing mullite content.