Aging Characteristics of Cu-30%Ni–Al Alloys

Abstract

The precipitation process in Cu-30%Ni-1∼3%Al alloys during aging at 773 or 873 K after water quenching from 1323 K, and the characteristics of the nodule formed by the grain boundary reaction were investigated by means of optical and electron microscopy, hardness measurement and X-ray diffraction analysis.
When the specimens were aged at 873 K, the hardness measured at room temperature increased monotonously with the progress of aging. But hardening occurred in two stages during aging at 773 K . The lines of θ phase and the side-bands were observed in X-ray diffraction patterns from the early stage of aging. In the transmission electron micrographs, the modulated structure was observed at the early stage of aging. The mode of precipitation in the alloys was of the discontinuous type: α super-saturated solid solution→modurated structure→equilibrium α phase+equilibrium θ phase within the composition range from (Ni_0.67Cu_0.33)₃Al to (Ni_0.85Cu_0.15)₃Al.
Fine structure inside the nodule grew gradually during aging, and a granular θ phase was observed at the later stage of aging. The hardness inside the nodule changed with the growth of the fine structure.