STRUCTURE EVOLUTION OF NI_3GE SINGLE CRYSTALS DURING CREEP

摘要

The paper presents the study of the macroscopic localization of plastic deformation observed in the Ni_3Ge single crystals in creep oriented along the [001] and [139] axes at high temperatures (higher than the temperature of the anomaly peak). The dislocation structure and deformation relief has been studied by both TEM (transmission electron microscopy) and SEM (scanning electron microscopy) methods. The study of the polished faces of the deformed samples points to a very thin slip. The slip traces are not practically observed. The lines of octahedral slip are not frequently observed; as a rule they are located near the stress concentrator close to the ends and in the angles of crystals. Plastic deformation is heterogeneous at high temperatures and stresses (923, 973 K; a = 1020 MPa). The stability loss of the uniform strain is realized by the formation of the superlocalization band appeared on the crystal surface crossing it. The structure of the superlocalization band is complex. Fragmentation of the single crystal is observed here. Then, the local polycrystalline band is created with the plastic deformation reaching hundreds of percent.