FORMATION AND APPLICATION OF GRAIN-BOUNDARY SERRATIONS

Serrations develop in the grain boundaries (GB) of many metals and all oys as a result of local migrations to absorb dislocation walls. The s errations form only under deformation conditions where the subgrains r each about 2-10 mu m in diameter; the conditions of temperature and st rain rate depend on the metal and the effects of alloying on dynamic r ecovery. The small serrations evidently diminish GB sliding, making la ttice deformation rate controlling. If the conditions are changed to p roduce lower strain rates, then initial serrations increase the creep life. In alloys with limited dynamic recovery, the serrations are also related to initiation of dynamic recrystallization, which is very imp ortant in preventing progression of GB cracking, and thus increasing t he ductility in hot-forming operations. The formation of serrations or of a necklace of fine recrystallized grains along the GB of large gra ins (with good creep resistance) are noted for improving fatigue resis tance.