DIFFUSION OF NI INTO AL2O3-FIBERS DURING HOT-PRESSING OF AL2O3 NI3AL LONG-FIBER COMPOSITES/

Intermetallic matrix composite specimens of Ni3Al-matrix reinforced wi th continuous Al2O3 fibres (FP-fibres) were investigated by means of T EM, SEM, EDS and EPMA with regard to chemical stability during diffusi on bonding. The specimens were hot pressed at 1280 degrees C and 20 MP a for 2 h in vacuum and air. The experimental results revealed a notic eable diffusion of Ni into the fibres during hot pressing. The diffusi on 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 di ffusion. Based on these results it is proposed that Ni-diffusion in th e fibres involves both volume and grain boundary diffusion. In additio n, oxygen diffusion in the fibres during hot pressing in air is concei ved to proceed by diffusion along grain boundaries as well as through the bulk. The influence of Ni-and oxygen-diffusion in the fibres on th e formation and growth of Ni-reaction products during hot pressing in air is discussed. (C) 1997 Acta Metallurgica Inc.