Precipitation at faceting grain boundaries of Cu–Ni–Sn alloys

The effect of recrystallisation heat treatment on the microstructure of copper–nickel–tin alloys Cu–9Ni–6Sn and Cu–6Ni–7Sn was studied. Cold deformed wire material was recrystallised by a short term anneal at 850°C, close to the solidus of the alloy. Non-cold deformed material was heat treated for up to 1 h at the same temperature range (T=800–900°C). Slow cooling of the alloys resulted in faceted grain boundaries. Planar precipitates of (Cu,Ni)3Sn were detected at the facets. The present observations are discussed based on two possible explanations: the non-equilibrium segregation of alloying elements during cooling and the grain boundary shape modifications due to the precipitate growth.