Exothermic Reaction of Cu-Al Binary Mixed Powder Compacts During Vacuum Sintering

Abstract

One of the authers⁽¹⁾ has already reported that the Cu-Al binary mixed powder compacts with different Al-contents were always expanded considerably by the exothermic reaction just above the eutectic temperature of 548°C on heating in the atmosphere of hydrogen.
However, exact measurement of the abnormal expansion and the heat of evolution could not be carried out in the above experiment by the gas-flow of hydrogen.
From this point of view we studied especially the vacuum sintering process of Cu-Al binary mixed powder compacts with different contents between 4 and 46.5 wt%Al in the present experiment, and the following results were obtained.
(1) The abnormal expansion and the heat of evolution increased with increasing Al content up to 17 wt%, beyond which they decreased. The mixed powder compact with 17 wt%Al corresponded to the composition of γ₂(Cu₉Al₄)-phase.
(2) The calculated heat of evolution which was obtained on the assumption that the exothermic reaction just above the eutectic temperature of 548°C resulted from the heat of γ₂-formation, was in good agreement with the measured one which was obtained from the thermal analysis and X-ray diffraction data.
Accordingly, it was confirmed from the above results that the abnormal expansion accompanied by the exothermic reaction just above the eutectic temperature of 548°C originated in the formation of γ₂-phase.