Effect of gas pressure infiltration on microstructure and bending strength of porous Al2O3/SiC-reinforced aluminium matrix composites

Abstract

High porous ceramic preforms were produced by chemical route, and molten aluminium was infiltrated into these preforms by using gas pressure. Slurry was prepared by mixing aluminium sulphate and ammonium sulphate in the water, and silicon carbide powder was added into the slurry. The slurry was heated up in a ceramic crucible in the open air furnace up to 1200 °C to fabricate dual ceramic preform. At the end of the reaction sequences, 3D honeycomb structure α-alumina grains and uniformly distributed SiC cake were obtained. An apparatus was designed for gas pressure infiltration of Al alloys into the preform. The preforms which contained different amount of porosity were infiltrated with different pressures and temperatures. Not only porosity but also pore size affects infiltration rate. The resulting preforms and metal-matrix composites were characterised by optical and SEM observations. Three point bending tests were applied for the infiltrated metal-matrix composites (MMCs). The highest strength value (558 MPa) was obtained at 800 °C and 3 MPa. By controlling fabrication procedure of Al2 O3/SiC preforms and infiltration conditions, this high strength in the composite is obtained. The networking flaky alumina particles and encapsulated SiC particles within the preform delayed crack propagation and provided crack deflection during the fracture. © 2004 Elsevier Ltd. All rights reserved.