Bridgman type directional solidification and isothermal peritectic transformation experiments were carried out for Cu-75 Sn alloy in which the peritectic phase has trace solid solubility.Microstructure and composition analysis were characterized by scanning electron microscopy（SEM）

energy dispersive spectrum analysis（EDS）and electron probe micro-analyser（EPMA）.The results reveal that the directional solidification process of Cu-75 Sn hyperperitectic alloy presents a typical non-equilibrium solidification and there exist a large number of primaryεphase in microstructures.EDS and EPMA analysis of the solute profile shows that the tin concentration in theεandηphases is uniform closing to the equilibrium values in the phase diagram

whereas solute concentration in theε/ηand L/ηphase interfaces is changed abruptly during the peritectic transformation.The phase transition will occur when the solute concentration reaches a certain value.Using peritectic transformation mechanism

the primary phase can be eliminated effectively by static heating preservation.With increasing in holding time and decreasing in initial lath structure size

disappear velocity of primary phase is increased with the high peritectic transformation degree.In this case

the relationship between the volumetric fraction of the peritectic phase and the time t fitsφ（η）=0.597×t

0.492

in accord with square root law of solidification.Hence

the peritectic transformation process of Cu-75 Sn is controlled by solute diffusion mechanism.