Interfacial chemical stability during diffusion bonding of Al 2O 3 fibres with Ni 3Al and NiAl matrices

Abstract

MMC with intermetallic matrices (Ni 3Al, NiAl) reinforced with continuous Al 2O 3 fibres were investigated with regard to interfacial reactions during diffusion bonding, by means of TEM, EDS and HRTEM. The specimens were fabricated by hot pressing for 2 h. at 1200–1280°C for the Ni 3Al matrix and at 1300–1450°C for the NiAl matrix. Experimental results revealed a diffusion of Ni from the Ni 3Al matrix into the fibres during diffusion bonding. As a consequence of the diffusion process a chemical reaction took place at the interfacial area: thin films of about 5–20 nm thickness appeared in some sections of the interface, in which the lattice planes were disordered and porous compared with matrix and fibre; in other sections spinels with compound oxides of Al and Ni or (Ni, Mg)Al 2O 4 were formed as interfacial reaction products. In contrast to the results on Ni 3Al, specimens with NiAl matrix showed good stability during hot pressing: no obvious diffusion of Ni from the matrix into the fibre could be detected, and no interaction products were apparent in the interface. The potential influence of these interfacial behaviours on the properties of the composites will be discussed.