• Schleifer, F.
• Glatzel, U.
• Fleck, Michael
• Lin, Y.-Y.

Abstract

The precipitation behavior of the metastable γ'' phase was studied in the single crystalline modified IN718 (Alloy 718M), which contains only the FCC solid solution matrix and the BCT γ'' phase within our processing parameters.Single crystal specimens were prepared in order that the precipitation behavior of the γ'' phase was not affected by the grain boundaries, and the δ phase or carbides that can heterogeneously precipitate along them.Solution heat-treatment at 1423K for 24 h was applied after single crystal casting, following by the isothermal aging treatment at 1033K for 2 h. γ'' phase precipitated rapidly in the matrix according to two abnormal patterns. The particles were all in the shape of oblate spheroid and the normals of the plates pointing towards any of the <100> directions with the equatorial length of 50-150 nm. The patterns formed by the γ'' precipitates were found to be highly related to the distribution of the dislocations before aging treatment, which were generated between the dendritic and interdendrtic regions after casting. As for the FCC single crystal matrix, the dislocations showed as slip bands lying on the {111} planes toward <011> directions, or dislocations distributed densely along the dendritic boundary. After aging treatments, γ'' phase preferentially precipitated on the dislocation sites. As a result, the particles piled up with each other in <011> directions with respect to the view in (001) plane, or they precipitated along the polygonized curves formed by the dislocations along the dendritic boundary during the aging treatment.

Topics

• single crystal
• grain
• nickel
• phase
• carbide
• dislocation
• precipitate
• precipitation
• casting
• aging
• aging