Heat Treatment and Composition Optimization of Nanoprecipitation Hardened Alloys

Abstract

A modeling strategy for designing nanoprecipitation strengthened alloys is presented here. This work summarises the application of a new thermokinetics approach wherein multiple design criteria are enforced: corrosion resistance and high strength combined with affordable thermomechanical processing schedules. The methodology presented here iteratively performs thermodynamic and kinetic calculations, which are aimed at determining the best precipitate nanostructures following multiple design objectives. A genetic algorithm is employed to more rapidly find optimal alloy compositions and processing parameters consistent with the design objectives. The strength was maximized, while conditions on the microstructure were imposed: corrosion resistance, fine martensite formation, and the prevention of primary and undesirable precipitate particles. It is possible to computationally design new alloys strengthened by Ni-based nanoprecipitates and carbides with yield strengths exceeding 1.6 GPa and good corrosion resistance. A major limitation in the methodology is the determination of optimum processing times, which require the computation of the formation energies of non-equilibrium precipitates employing other techniques. A method to circumvent this limitation is discussed.

Keywords:

• Alloy design
• Genetic algorithms
• Kinetics
• Thermodynamics