Mechanism of α-Cr precipitation and crystallographic relationships between α-Cr and δ phases in Inconel 718 alloy after long-time thermal exposure

Abstract

To study the precipitation mechanism of α-Cr phase in Inconel 718 alloy, the samples after long-time aging at 650 and 677°C were examined by microstructural observations and chemical phase analysis methods. Combining the thermodynamics and kinetics calculation results, α-Cr always precipitates in the vicinity of δ phase, because δ phase rejects Cr into the γ-matrix when growing. The selected area diffraction patterns confirm that the crystallographic relationships of α-Cr with δ phase are (010)δ//(\( \bar 1 \)10)α-Cr and 100δ//111α-Cr. A graphic model is also presented to show the crystallographic relation between α-Cr and δ phases.