Transmission electron microscopy study of precipitation behaviors in Cu15 mass%Sn Alloy annealed at 593K

We have investigated precipitation behaviors of Cu15 mass%Sn alloy annealed at 593K by using transmission electron microscopy. Three kinds of precipitates with different morphologies have been observed. Inside grains, plate-like precipitates of approximately ten μm in length were found to display regular configuration. They are the equilibrium ε phase, and the orientation relationship with the matrix α phase can be expressed as (001)ε // (111)α, [100]ε // [110]α, with (001)ε habit planes. At grain boundaries, Sn-rich precipitates of irregular shapes were found to precipitate. They are the δ phase, which is stable above 623 K. Some of them exhibit an incipient stage of growing cellular morphology brought about by diffusion induced grain boundary migration. In addition, there are intragranular particle-like grains of several μm or less, some of them are confirmed to be the δ phase. The observed precipitation behaviors are discussed from the viewpoints of crystallography of these phases.