Quench Sensitivity and Continuous Cooling Precipitation Diagrams

Abstract

The application properties of metallic materials are frequently adjusted by heat treatments utilizing controlled microstructural changes—i.e., solid–solid phase transformations like nondiffusional 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 aluminum 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.