Modeling Precipitation Kinetics with Calphad-Based Tools and Application to Ni-Based Superalloys

Sophisticated precipitation reaction models, in conjunction with well-developed and critically assessed CALPHAD databases, provides an efficient and cost-effective way to simulate precipitate microstructures that maximize strengthening effects via the optimization of alloy chemistries and heat treatment schedules. TC-PRISMA, is a new user friendly computational tool that integrates the reliable Thermo-Calc and DICTRA system with additional interface property data and simulates the kinetics of the precipitation process.

New developments in TC-PRISMA to incorporate models refined especially for non-isothermal conditions are presented here with focus on the simulations of precipitate microstructure evolutions in Nickel-base superalloys under arbitrary heat treatment conditions. The effect of different cooling profiles on the formation of multimodal microstructures has been examined in order to understand the underlying thermodynamics and kinetics. Meanwhile, validations against several experimental results have been carried out. Practical issues that are critical to the accuracy and applicability of the current simulations, such as modifications that overcome mean-field approximations, compatibility between CALPHAD databases, selection of key parameters (particularly interfacial energy and nucleation site densities) are also addressed.