Alloy design for ultra-high temperature steam turbine application: Phase-field simulation of the remelting process
B. Böttger, I. Steinbach, S. G. Fries, Q. Chen, B. Sundman.
Materials for Advanced Power Engineering, Forschungszentrum Jülich, 1333-1342, (2002)
A multiphase-field model coupled to thermodynamic databases is presented which is able to handle multicomponent and multiphase structural evolution on microscopic scale. Databases assessed according to the CALPHAD approach are connected online to the phasefield code using the thermodynamic software package Thermo-Calc and fortran interface. Multi-binary expolation is used to make simulations of realistic systems viable. A unit cell approach is used to apply this model to the remelting process, which locally is simulated as a directional solidification under high thermal gradients. The model is applied to remelting of the three Ni-base superalloys IN706, IN617 and Waspaloy, respectively, which are used as a starting point for the development of new alloys for ultra-high temperature steam turbine applications. From the results secondary phase formation, incipent melting as well as homogenisation times and temperatures can be predicted. Aditionally an alloy-specific freckle criterion is calculated from the simulation results, which allows the estimation of the freckle risk under typical remelting conditions.