Phase formation and crystallographic relationships in Cu–30 at%Zn//Cu–80 at%Zn diffusion couples

The phase formation in binary Cu–30 at.%Zn//Cu–80 at.%Zn diffusion couples annealed at 565°C is investigated by means of electron backscatter diffraction and energy-dispersive x-ray spectroscopy. Growth kinetics and crystallographic relationships of the forming intermetallic compound phases are characterized in detail. The growth rates of all forming phases follow a parabolic growth law even down to annealing times of only 27 s, verifying diffusion-controlled growth for the early stages. About 37% of the analyzed α/β interfaces were found to display near Kurdjumov-Sachs orientation relationships (misorientations > 5°), which predominantly corresponded more accurately to Bain or Nishiyama-Wassermann relationships (misorientations < 5°). Almost 60% of the investigated β/γ phase boundaries exhibit a cube-on-cube relationship. The δ phase, which is only stable above 560°C, undergoes an eutectoid decomposition during quenching, forming a lamellar structure of γ and ε phase. Almost all eutectoid ε has the same orientations as the initial adjoining ε grains. A considerable fraction of the eutectoid γ phase is oriented to the eutectoid ε phase according to the Potter and Burgers relationships. The solubilities of the Zn-rich phases δ and ε at 565°C and 580°C were found to exhibit systematically lower Zn concentrations than predicted by thermodynamic descriptions from literature and assessed Cu–Zn phase diagrams available in literature.