Diffusion of Ni into Al2O3-fibres during hot pressing of Al2O3/Ni3Al long fibre composites

Intermetallic matrix composite specimens of Ni3Al-matrix reinforced with continuous Al2O3 fibres (FP-fibres) were investigated by means of TEM, SEM, EDS and EPMA with regard to chemical stability during diffusion bonding. The specimens were hot pressed at 1280 degrees C and 20 MPa for 2 h in vacuum and air. The experimental results revealed a noticeable diffusion of Ni into the fibres during hot pressing. The diffusion coefficients of Ni in the fibres were estimated from the analytical results of EPMA-analysis. The estimated values for T = 1280 degrees C were D-Ni(v) = (5 +/- 2) x 10(-14) cm(2) . s(-1) for volume diffusion and D-Ni(gb) = (6 +/- 2) x 10(-9) cm(2) . s(-1) for grain boundary diffusion. Based on these results it is proposed that Ni-diffusion in the fibres involves both volume and grain boundary diffusion. In addition, oxygen diffusion in the fibres during hot pressing in air is conceived to proceed by diffusion along grain boundaries as well as through the bulk. The influence of Ni-and oxygen-diffusion in the fibres on the formation and growth of Ni-reaction products during hot pressing in air is discussed. (C) 1997 Acta Metallurgica Inc.