On defects at nanoscale formed in Al–Cu matrix composites fabricated by pressure infiltration

To study the defects structure at nanometric scale in the composites obtained, positron annihilation lifetime spectroscopy was used. Specifically, in the materials studied preforms of Saffil alumina short fibers with a fiber content of 12 vol.% were infiltrated by gas pressure with liquid alloys containing Al–5Cu, Al–15Cu and Al–33Cu (wt.%). From the experimental results, information on the nanoporosities remaining in the different samples after the fabrication process was obtained. Furthermore, the presence of an important amount of microvoid-like defects or small vacancy-clusters in the composites was also revealed. Specifically, it was found that these microvoids have almost the same size, within the experimental scatter, but their volume fraction depends on the solute content of the matrix.