Lattice parameters of γ and γ' phases in superalloy SC16 in unconstrained condition

The chemical compositions of γ and γ' phases in the alloy SC16 were determined by means of energy-dispersive X-ray spectroscopy in the transmission electron microscope (TEM/EDS) after heat treatment at different temperatures. According to these measurements, single-phase alloys with compositions identical to those of the γ and γ' phases in SC16 were produced. The temperature dependence of the lattice parameters of these alloys was deduced (i) from the measured values of the lattice parameters at room temperature and (ii) from the measured unidirectional thermal expansion up to 1323 K. These measurements show that the lattice misfit between the γ and γ' phases in unconstrained condition at the different elevated temperatures at which their equilibrium composition in the alloy SC16 was determined, is positive. The results are compared with the misfit values in the alloy SC16 reported in literature for constrained and unconstrained condition and also with the predictions from models on rafting.