材料期刊网

The characteristics of the deformation bands (DBs), formed in cyclically deformed copper single crystals with various orientations, were summarized systematically. The Formation mechanism of DBs was also explored. It was shown that the apperance of DBs seems to be a general phenomenon in cyclically deformed copper single crystals with various slip orientations, especially with double- or multiple-slip orientations, for which the critical plastic strain amplitude needed for the formation of DBs is rather low (about 10(-3)). The DB denoted by DBI develops roughly along the primary slip plane {111}, and the habit piano of DBII is close to the conventional kink plane {101}. The habit planes of DBI and DBII are strictly perpendicular to each other. An analysis based on the crystallographic deformation geometry showed that the local irreversible rotation of crystal which exists during symmetrical push-pull loading may be responsible for the Formation of DBI and DBII. When a certain crystallographic geometrical condition is satisfied, DBI and DBII are very hard to form coincidentally. In addition, a favourable macroscopic state of stress might also be responsible for the occurrence of other types of DB, such as (001) DB in the [011] crystal. Finally, the dislocation structure relevant to DBs was observed tentatively by electron channelling contrast in scanning electron microscopy. It was revealed that the DBs formed in copper single crystals during cyclic straining may exhibit quite different microstructures, depending upon the crystallographic orientation.