Numerical Modelling of Stress and Strain Evolution during Solidification of a Single Crystal Superalloy
During the manufacture of turbine blades from single crystal nickel-based superalloys by investment casting, recrystallisation can occur during solution heat treatment. The introduction of grain boundaries into a single crystal component is potentially detrimental to performance, and therefore manufacturing processes and/or component geometries should be chosen to prevent their occurrence. In this work, numerical models have been designed to enable a predictive capability for the factors influencing recrystallisation to be constructed. The root cause is plasticity on the microscale caused by differential thermal contraction of metal, mould and core; when the plastic deformation is sufficient, recrystallisation can take place subsequently. The models take various forms. First, one-dimensional models based upon static equilibrium have been produced – our calculations indicate that plastic strain is likely to take place in two temperature regimes: by creep between 1150°C and 1000°C and by tensile (time-independent) strain below 650°C. The idea of a strain-based criterion for recrystallisation is then proposed. Second, more sophisticated three-dimensional calculations based upon the finite element method are carried out. Our predictions are compared critically with experimental information.
C. Panwisawas et al., "Numerical Modelling of Stress and Strain Evolution during Solidification of a Single Crystal Superalloy", Advanced Materials Research, Vol. 278, pp. 204-209, 2011