Composites, which consisted of a Ni3Al matrix that was reinforced with continuous Al2O3 fibers, were investigated by means of transmission electron microscopy, scanning electron microscopy, X-ray energy-dispersive spectroscopy and electron-probe micro-analysis. The specimens were hot-pressed (1280C, 20MPa, 2h, vacuum and air), and the experimental results revealed a noticeable diffusion of Ni into the fibers during pressing. The diffusion coefficient of Ni in the fibers was estimated from electron-probe micro-analyses. The estimated coefficients at 1280C were equal to 5 x 10-14cm2/s for volume diffusion and to 6 x 10-9cm2/s for grain-boundary diffusion. On the basis of the results, it was proposed that Ni diffusion in the fibers involved both volume and grain boundary diffusion. The diffusion of O in the fibers during hot pressing in air was suggested to occur via diffusion along grain boundaries as well as through the bulk.

W.Hu, P.Karduck, G.Gottstein: Acta Materialia, 1997, 45[11], 4535-45