Abstract
The Immm-Ni2(Cr,Mo,W) body centered orthorhombic (BCO) intermetallic phase, denoted as γ´´´, is the primary strengthening phase in commercial Ni-base HAYNES® 242® and 244® alloys. Due to the relatively low symmetry and six crystallographic variants precipitating in the face-centered cubic solid solution γ matrix, the deformation mechanisms are expected to be complex, and a myriad of planar defects are predicted to be observed on the close-packed {013} and {110} planes, which are nearly co-planar to the matrix {111} plane. We find that these defects include those analogous to the γ´-Ni3Al phase: superlattice intrinsic stacking faults, antiphase boundaries, and complex stacking faults. We determined these planar defect energies and generalized stacking fault energy surfaces utilizing ab-initio density functional theory calculations. The γ´´´ {013} and {110} planes exhibited comparable planar defect energies but showed drastically different dislocation shear pathways due to the lower symmetry of the orthorhombic phase. We observed that the addition of W increased the fault energies significantly, which could correspond to the observed increase in yield strength of 244 alloy over that of 242 alloy.
Published Version
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