Kinetics of the eutectoid transformation in the Cu-In system

The present study concerns a detailed investigation of the kinetics of the eutectoid transformation in the Cu-In system based on both the isothermal g rowth rate of the eutectoid colony (monitored by microstructural change) an d enthalpy changes during non-isothermal heating (determined by differentia l scanning calorimetry) of solution-treated and quenched samples. The maxim um growth distance of the eutectoid cells and the equilibrium interlamellar spacing have been determined by optical and scanning electron microscopy i n the temperature range 600-825 K. The reaction front velocity was observed to increase with the isothermal ageing temperature in the temperature rang e studied. A detailed analysis of the isothermal growth kinetics through th e models available in the literature has yielded an activation energy of 12 5-127 kJ mol(-1) the operating diffusion process, which is comparable with that for discontinuous precipitation in Cu-ln or for grain boundary tracer diffusion of In-115 in Cu, but significantly lower than that for volume dif fusion of In in the beta Cu-ln alloy. A subsequent differential scanning ca lorimetric study has indicated a similar activation energy of 133 kJ mol(-1 ) for the concerned eutectoid transformation. It is thus concluded that the eutectoid transformation in the Cu-In system is a boundary-diffusion-contr olled process. (C) 1999 Kluwer Academic Publishers.