Morphology and Orientation Relationships of Ge Precipitates in Ag-Ge Alloys

Abstract

Ag-Ge forms a simple binary eutectic with only two solid phases - a Ag-rich fee phase and a Ge-rich diamond-cubic phase, both with very limited solid solubility for the other element. Because both phases are cubic and there are no intermediate compounds, precipitation of Ge in an Al matrix might be expected to be crystallographically and morphologically simple. However, previous investigations of similar alloys (Al-Ge and Al-Si) have shown that precipitation in such apparently simple eutectic systems can be surprisingly complex [1,2]. For example, it was found that Ge precipitation in Al-Ge alloys depends sensitively on the availability of lattice vacancies and that at least five different orientation relationships and even more types of morphologies can form during aging after a quench. In the course of that work it was discovered that twinning is a key factor in the development of precipitate morphologies. To understand the role of twinning in precipitation this study investigates the characteristics of precipitation in Al-Ge alloys.