Abstract:  Directionally solidified microstructures of Cu-75%Sn peritectic alloy were investigated at the growth rate ranging from 1 to 300μm/s. With the growth rate increasing, directionally solidified plate-like microstructures in Cu-75%Sn peritectic alloy are refined by the increase of nucleation quantities of primary ε phases and cooling rate. Peritectic η phase can grow by the peritectic transformation and direct solidification from the liquid. At the low growth rate varying from 5 to 10μm/s, the width of ε phase increases due to the effect of the peritectic transformation; however, at higher growth rate, the deviation between the width of ε phase and the whole platelike microstructure increases resulting from direct solidification of η phase from the undercooled melt. The regressed data show that the relationship between the width of the whole plate-like microstructure(W) and the growth rate(v) satisfies as Wv^0.27=117μm^1.27•s^-0.27 and the primary dendritic arm spacing(λ) with the growth rate has a relation of λv^0.208=153.8μm^1.208•s^-0.208 as the growth rate increases from 3 to 300μm/s.

Key words: Cu-75%Sn alloy; peritectic alloy; directional solidification; primary dendritic arm spacing