DENSITY CHANGES DURING ISOTHERMAL ANNEALING OF A QUENCHED PB-7.45 AT-PERCENT SN ALLOY

The increase in density of a Pb-7.45 at % Sn alloy annealed at 150, 16 5, 180, and 195 degrees C and quenched at 20, 21.5, 23, 25, and 30 deg rees C is measured isothermally. This increase in density accompanies the formation of the Sn-rich phase precipitating as a function of time at the quenching temperature. The quenching is rapid enough to retain some vacancies at equilibrium at the annealing temperature. These vac ancies accelerate the early stages of precipitation. The change in den sity versus time obeys the kinetic law allowing the determination of t he reaction rate constant for several annealing and quenching conditio ns.