Precipitation and dissolution kinetics in metallic alloys with focus on aluminium alloys by calorimetry in a wide scanning rate range

Abstract

The application properties of metallic materials are frequently adjusted by heat treatments utilising controlled microstructural changes-i.e. solid-solid phase transformations like non-diffusional martensitic transformation or diffusional secondary-phase precipitation and/or dissolution. For technical application, knowledge about the characteristic temperatures and times but moreover about their time dependence (kinetics) is required. As the relevant solid-solid phase transformations all show a heat effect (e.g. precipitation → exothermic; dissolution → endothermic), one outstanding measurement technique to follow these phase transformations is calorimetry, particularly differential scanning calorimetry (DSC). Appropriate combinations of DSC methods and devices to cover nine orders of magnitude in heating and cooling rates (10-4-105 K/s) will be introduced, using dissolution and precipitation reactions in aluminium alloys as examples. Basically, these techniques allow one to record time-temperature transformation (or precipitation/dissolution) diagrams for various materials during heating, isothermal annealing and even during continuous cooling, making DSC a very powerful tool for the investigation of solid-solid phase transformations. Nowadays, physically based models verified with DSC results moreover allow one to predict precipitation volume fractions and solute mass fractions.