Determination of the precipitation kinetics of Ni3Al in the Ni–Al system using differential scanning calorimetry

Jackson, M.P., Starink, M.J. and Reed, R.C. (1999) Determination of the precipitation kinetics of Ni3Al in the Ni–Al system using differential scanning calorimetry. Materials Science and Engineering: A, 264 (1-2), 26-38. (doi:10.1016/S0921-5093(98)01120-4).

Abstract

With the aim of establishing the kinetics of ?? precipitation in the Ni–Al system, quantitative differential scanning calorimetry (DSC) has been used to determine the evolution of enthalpy at cooling rates of 5, 10 and 20 K min?1 for alloys of nominal composition 13.0, 14.2, 15.8 and 18.5 at.% Al. A theoretical model for the reaction has been constructed in order to deduce the reaction kinetics from the calorimetric data. It is assumed that the variation of enthalpy is governed by the changes in ?? volume fraction and ?? concentration with time and temperature; any contribution from the coarsening of ?? is neglected. A thermodynamical description of the system is required, and an accurate assessment with respect to the generalised sublattice model has been employed. For modelling purposes a critical undercooling is needed and this has been estimated from the calorimetric data. A single nucleation event is assumed to occur within a spherical transformation volume, the radius of which is chosen to be consistent with experimental measurements made on the microstructures of the DSC samples. It is shown that the approach is able to reproduce the DSC curves with a reasonable degree of accuracy. The method has been used to estimate continuous cooling transformation (CCT) curves for these alloys. It is believed that these are the first reported measurements of the kinetics of the ?? precipitation reaction in this system.

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