The genesis of cellular precipitation in copper rich copper-indium alloys

The morphology of cellular precipitation in a Cu-9.5at.%In alloy has been investigated by light and electron microscopy and x-ray and electron diffraction. Both cellular and general precipitation were observed to occur simultaneously in quenched and aged alloys while only cellular precipitation was observed to occur in isothermally aged alloys. Because of the presence of wide, vacancy depleted precipitate free zones in the vicinity of grain boundaries, general precipitation was observed to have no effect on the early development of cellular precipitation. Hence, the early development of cellular precipitation was found to be identical for both types of heat treatment. By light and electron microscopy of the early stages of precipitation a mechanism for the development of cells from an initially unoccupied grain boundary was developed. According to this mechanism the grain boundary allotriomorphs begin to form, the boundary interacts with them by bowing out between them and trailing precipitate behind to eventually develop a steady state cellular structure. Assuming that the critical step in the development of a cell is the ability of the boundary to bow between initial allotriomorphs, a criterion for the occurrence of cellular precipitation was developed --Abstract, page ii