Cleavage Fracture and Dislocation Structures of Ductile L1₂ Type Ni₃Ge Single Crystals

<jats:title>ABSTRACT</jats:title><jats:p>Fracture and dislocation structures of single crystals of the L1<jats:sup>2</jats:sup>-type compound Ni<jats:sub>3</jats:sub>Ge deformed in tension-compression at room temperature are investigated by optical and electron microscopy. After considerable plastic deformation, cracks nucleate along primary (111) planes of [<jats:overline>2</jats:overline>45]-oriented single crystals and grow in zigzag manner by connecting one octahedral plane to another. Fracture occurs by brittle cleavage. Similar cleavage fracture also occurs when thin films (whose plane is (111)) prepared from cyclically deformed specimens are further deformed at room temperature. These observations are different from those reported in a previous study where the cleavage plane is claimed to be {001} for single crystals deformed in tensio at room temperature. A number of piled-up dislocations are emitted due to stress concentration at and ahead of crack tips, evidencing that this compound is intrinsically ductile. Superlattice intrinsic stacking faults are observed in front of crack tips along with a moire structure. Although there is argument that such moire structures are formed in persistent slip bands during cyclic deformation of Ni<jats:sup>3</jats:sup>Al, this is unlikely in the present case. The moire structure observed is believed to be formed by deformation of the thin (111) film.</jats:p>