Constrained lattice misfit measurement in bulk inconel 718 using high resolution neutron diffraction

Abstract

Lattice misfit is important in Inconel 718 (IN718) as coherency strain strengthening from y" precipitates is the principal source of strengthening in this alloy. The value of lattice misfit is defined by the difference in lattice parameter between each phase. In this study, high resolution time-of-flight (TOF) neutron diffraction has been used to measure the constrained lattice parameters and lattice misfits of a bulk IN718 sample. Thanks to the high resolution of the diffractometer, overlapped diffraction peaks are successfully deconvolved, and the lattice parameters of different phases and lattice misfits are determined. The measured constrained lattice parameters of γ″ phase are much less than the reported unconstrained lattice parameters measured from extracted γ″ precipitates. The lattice misfit between γ″/γ phases along c-axis of γ″ phase is -0.015% indicating the γ″ precipitates are largely constrained and highly coherent with y matrix in bulk IN718.