Starink, M.J. and Thomson, R.C.,
Modelling microstructural evolution in conventionally cast Ni-based superalloys during high temperature service
Strang, A. and McLean, M. (eds.)
In Modelling of Microstructural Evolution in Creep Resistant Materials.
Full text not available from this repository.
Modern conventionally cast (CC) Ni-based superalloys are highly alloyed metals that undergo a number of complex microstructural changes during in-service exposure to high temperatures. This paper focuses on modelling the kinetics of reactions involving carbides.
An important element in various approaches for modelling of kinetics of reactions in Ni-based superalloys is so-called thermodynamic modelling (CALPHAD method). A detailed comparison of CALPHAD predictions made by one database with extensive long term experimental data for the MarM002 Ni-based superalloy for all phases is presented.
A comparison of CALPHAD predictions made by the Thermotech database for Ni-based superalloys with long term experimental data shows that for the MarM002 Ni-based superalloy the volume fractions and compositions of the FCC gamma ?matrix, the L12 ordered gamma' and the M23C6 carbide phase are predicted well. Thermodynamic modelling is currently unable to predict the presence of M6C in this alloy. The reason for this is primarily due to the large number of carbides of different types and compositions within MarM002. There must be a balance of stability for all of the carbides and therefore slight perturbations to the Gibbs free energy polynomials describing each phase can limit the accuracy of the prediction for minor carbides. It is also shown that it is necessary to allow for a miscibility gap in the MC carbide phase to enable a more accurate prediction of its chemical composition in such a complex alloy system.
A method for modelling the kinetics of reactions using an approximation of the diffusion fields around particles (i.e. akin to the well-known Johnson-Mehl-Avrami-Kolmogorov approach) is described. With this method the carbide reactions in during high temperature exposure of CC Ni-based superalloy can be accurately described.
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