A modified CALPHAD model for thermal expansion coefficient in Invar Ni-Fe(FCC) alloys

A modified CALPHAD (Calculation of Phase Diagram) model of the coefficients of thermal expansion (CTE) of Invar Ni-Fe FCC (Face Center Cubic) alloys was established, based on previous models of heat capacity. The key to the modification is the addition of the new parameters to describe the complicated phase transition around the Invar alloys composition. The parameters of the CALPHAD model were assessed over the whole composition range and in the temperature range from 200 K to 1200 K according to previous CTE data reported in the literature. Using assessed parameters, the calculated CTE values for the Ni-Fe FCC alloys are in remarkable agreement with the experimental test data, especially around the Invar alloys composition. This work provides an effective CALPHAD model to deal with CTE in Ni-Fe FCC alloys, which will be of benefit for the development of Invar alloys and Ni-Fe-base superalloys.