Abstract
It has been often observed that the mixed powder compacts of multi-components begin to expand from a definite temperature during heating process, and one of the authors has explained these phenomena mainly due to the phase transformation mechanism. However, we observed that the Cu-Ni binary mixed powder compacts expanded from about 600°C during heating process, where the solid Cu and Ni are soluble each other in all range, while any explanation has not yet been established about the meaning of this temperature. In order to investigate this problem, the authors carried out the present work by means of the dilatometric methods by using the Cu-Ni mixed powder compats with different contents, where the pure Cu and Ni powders, the electroless Ni plated Cu powder, the Cu-Ni prealloyed powder, and the electroplated specimen of Cu and Ni in alternate layers were used. The results obtained are summarized as follows.
(1) The Cu-Ni binary mixed powder compacts expanded from about 600°C independently of the heating rate, the compacting pressure, and the particle size.
(2) The multi-layers specimen made by the alternative electroplate of Cu and Ni expanded gradually from 500°C followed by abrupt expansion from about 600°C.
(3) The specimen consisted of the Cu-Ni prealloyed powders and the carbonyl Ni powders showed a higher temperature expansion with the increase of Ni content in the Cu-Ni prealloyed powder, i.e. 650°C for Cu-5%Ni alloy powder, and 680°C for the Cu-10%Ni alloy powder.
(4) In the model experiment by using the synthetic Cu and Ni wire compacts sintered at 600°C for 48 hours, some pores were found on the Cu side. Judging from the Kuczynski's interpretation, it may be considered that the pore formation originates from the Kirkendall diffusion.
