Fabrication of Al 2O 3–Al composites by infiltration method and their characteristic

Abstract

The present paper is focused on Al 2O 3–Al composites obtained via infiltration of porous ceramics by liquid Al. Infiltration of porous ceramics by liquid metal leads to produce microstructure with percolation of metal phase in ceramic matrix. However, the process of Al released caused by pressing is observed. This effect should be taken into consideration in designing of composites (in calculation of the amount of Al which is needed for full infiltration). To improve wettability between Al 2O 3 and Al the ceramic preforms were coated by the Ni–P. Ni–P deposited in form of a thin, tight film encapsulated ceramic grains and as a consequence, the liquid Al contacts first with Ni and then penetrates inside porous preform. The size of metal phase in this case depends on the size of pores. The size of pores influences also the kinetics and extent of infiltration. This method is useful for fabrication composites with metal phase size in the range of micrometers. During the process of infiltration, the new phases appeared. Among them there are spinel phase and aluminides. These phases are an evidence of diffusion reaction between liquid aluminium and alumina. As a consequence, they can influence the fracture toughness of the composites. Filling up pores by the metal provide a microstructure with interpenetrating network. Such composites are design for their strength and toughness. Moreover, such a microstructure can be an important in applications in which electrical properties of material are relevant.