Complex SRO isothermal kinetics in quenched Cu-12 at.% Mn assessed by microhardness measurements

Abstract

The isothermal kinetics of the return of short-range-order (SRO) in quenched Cu-12 at.% Mn alloy samples subsequently annealed at various temperatures was analyzed by means of microhardness measurements. An apparent first-order kinetic function is suitable for describing the overall kinetics. Deviations from the straight line in the Arrhenius plot were unequivocally detected. Apparent activation energy values, which lie between those for defect migration of unbound and bound vacancies, approach to that of the unbound ones as annealing temperature is raised. An apparent compensation effect CE was also confirmed. By using an isoconversional equation can be concluded that the degree of conversion is independent of activation energy. The deviation of the isotherms from a formal first-order kinetic mechanistic equation is interpreted in terms of entangled parallel reactions contributed by bound and unbound vacancies. The use of an overall single step rate reaction equation as an operative one, as it was done here, instead of the true rate equation describing a complex process involving multistep reactions is often applied in kinetic analysis.