Interpretation of the Habit Plane of δ Precipitates in Superalloy Inconel 718

Abstract

A calculation method based on a combination of ∆ g parallelism rule, good matching site (GMS) analysis, CSL/DSCL (coincidence site lattice/displacement shift complete lattice) and the O-lattice theory has been applied to interpret the observation of the habit plane (HP) of the δ precipitates and the linear defects in the HP in an Inconel 718 superalloy. The small scattering in the HP orientation around an ideal rational plane is interpreted by the existence of a mixture of two types of steps with different heights and inclinations. These steps play a significant role to enhance the degree of matching in the HP. They are associated with secondary dislocations, with Burgers vectors of \(1/6\left[ {1\;1\;\bar{2}} \right]_{\gamma } / 1/3[0\;0\;1]_{\delta }\), and with a direction parallel to a near-invariant line along \([1\;\bar{1}\;0]_{\gamma }\). The spacing of the secondary dislocations projected on the terrace plane is around 6.3 nm. The calculated dislocation structure is in good agreement with the observation.