Grain boundary peak in macroscopic graphite particulates reinforced Zn-Al metal matrix composite

In the present paper, temperature spectra of internal friction (IF) are studied in a macroscopic graphite (Gr) particulate reinforced Zn-Al metal matrix composite (MMC). The ZnAl/Gr MMC specimens with up to 51 vol% macroscopic Gr particulates (0.8 mm in diameter) were prepared by air pressure infiltration process. IF and relative dynamic modulus measurements in the ZnAl/Gr MMCs at maximum surface shear strain of 20 x 10(-6) have been performed using a multifunctional internal friction apparatus (MFIFA) at frequencies of 0.5, 1.0, 2.0, and 3.0 Hz over a wide temperature range from room temperature to equilibrium eutectoid isotherm of 277degreesC, during continuously-changing-temperature measurement. At low frequency and low temperature, a distinct IF peak is found in the IF-temperature curve. Corresponding to the IF peak, the relative dynamic modulus decreases rapidly. The IF peak is a grain boundary peak, which is associated with the diffusive grain boundary of Al/Al. Its activation energy has been calculated to be (1.13 +/- 0.03) eV and the pre-exponential factor tau(0) = 10(-14) s in IF measurements. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.