Silicon carbide fiber-reinforced alumina extrusion

Abstract

Silicon carbide fiber-reinforced alumina bodies have been produced by ram extrusion. The Al2O3 powder and SiC fiber were milled together to give a dry dispersion of up to 30 vol % fiber which was subsequently mixed to a paste by high shear kneading using hydroxypropylmethylcellulose solutions as the binder phase. Extruded bodies with green densities ranging between 56 and 63% full theoretical density were achieved. The paste flow behavior was characterized using physically based equations which show that for any given moisture content the pressure drop and the constituent paste parameters are all systematically reduced as the fiber loading is increased. This observation can be explained almost completely by combining packing theory with the paste rheology data. Fiber interactions within the paste and the die system appear not to greatly influence the rheological character of the material. It is shown statistically that the fibers are homogeneously dispersed throughout the paste mass after extrusion. Image analysis has been used to aid in macrodefect analysis, and it is shown that the optimum concentration of fiber was 20 vol % with a quantity of binder sufficient to give an initial yield stress of 2 MPa.