Abstract
The characteristics of the grain boundary reaction in Cu-30%Ni-2∼3%Al alloys aged isothermally at temperatures of 623 to 973 K after water quenching from 1323 K were investigated by optical and electron microscopy, hardness measurement and the X-ray diffraction method. The results obtained are as follows:
(1) The nodule began to grow prior to the beginning of hardening of the matrix, and almost stopped to grow under the influence of a rapid increase of the wavelength of the modulated structure in the matrix and did not engulf the matrix entirely.
(2) At the early stage of aging, a light and shade structure with fiber-shaped θ phases which waved periodically was observed in the nodule, and at the later stage of aging, this structure changed to the structure with granuler θ phases. Also the lattice parameter of α phase in the nodule changed with the progress of aging.
(3) The amount of the nodule, X, could be represented by Johnson-Mehl’s equation: X=1−exp(−btn), where t is the aging time and b and n are constants, n’s value being about 0.6 at each aging temperature.
(4) The apparent activation energy for nodule growth was about 130 kJ/mol (31 kcal/mol).
