Transmission Electron Microscopy Study of Precipitation Behaviors in Cu-15 mass%Sn Alloy Annealed at 593 K

We have investigated precipitation behaviors of Cu-15 mass%Sn alloy annealed at 593 K by using transmission electron microscopy. Three kinds of precipitates with different morphologies have been observed. Inside grains, plate-like precipitates of approximately ten mu m in length were found to display regular configuration. They are the equilibrium epsilon phase, and the orientation relationship with the matrix alpha phase can be expressed as (001)(epsilon) // (111)(alpha), [100](epsilon) // [1 (1) over bar0](alpha), with (001)(epsilon) habit planes. At grain boundaries. Sn-rich precipitates of irregular shapes were found to precipitate. They are the delta 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 mu m or less, some of them are confirmed to be the delta phase. The observed precipitation behaviors are discussed from the viewpoints of crystallography of these phases. [doi :10.2320/matertrans.MAW201206]