Misfit in Inconel-Type Superalloy

Abstract EN

An important parameter for the characterization of microstructural changes in nickel base superalloys is the misfit - the relative difference between lattice parameters of γ matrix and γ′ precipitates.

The misfit in IN738LC superalloy was examined at POLDI time-of-flight (TOF) neutron diffractometer both at room temperature and in situ at elevated temperatures using a high-temperature furnace.

A careful out-of-furnace measurement yielded the lattice parameters of both γ and γ′ phase at room temperature (aγ=3.58611(10) Å, aγ′=3.58857(17) Å) as well as the misfit (equal to 6.9(6)×10-4).

The in situ measurement at elevated temperatures provided the temperature dependence of the lattice parameters of γ (up to 1120°C) and γ′ (up to 1000°C).

Using these data, the evolution of the misfit with temperature was calculated.

The misfit decreases with increasing temperature until it reaches zero value at a temperature around 800°C.

Above 800°C, it becomes negative.