Thermal Processes in the Heating of Powder Compacts of Metals and Their Compositions III. Thermokinetics of Recrystallization Processes in the Heating of Compacts Produced from a Mixture of Aluminum and Iron

Abstract

The thermokinetics of recrystallization processes that occur during the heating of porous compacts, produced by cold pressing a mixture of ultrapure aluminum and iron powders in a 50: 50 ratio in a steel die, was experimentally studied. Over the 130–190°C temperature range, the aluminum component of the mixture undergoes relaxation, exhibiting wave-like behavior with a period of 0.2– 0.3 sec. Complete recrystallization occurs within the 165–235°C range. Subsequently, the relaxation process begins in the iron component of the mixture, with the initial stage characterized by nonlinear oscillations, transitioning to the next stage involving wave propagation of thermal energy. There are several periods of changes in wave propagation. The nonlinear wave-like rise in temperature during relaxation typically ends with another surge of energy release when the temperature rise period shortens, indicating more intense heat release. At its initial stage, the recrystallization process shows stationary linear behavior, which later transitions to the emergence of nonlinear waves. Changes in wave frequency are observed, along with intermittent wave behavior, suggesting the turbulence of thermal flows. Following this regime, the temperature increases up to the melting point of aluminum. However, complete melting does not occur because of crystallization within lower-temperature regions. All transitions marked by changes in thermokinetic paths at both relaxation and recrystallization stages are accompanied by bifurcation changes in the amplitude of the thermal waves.