Planar dislocation bands formed in Ti-5at.% Al single crystals deforming by double prism slips

摘要

It is well known that cyclic plastic deformation may result in a variety of dislocation configurations. In Cu, Ni and Al single crystals, some fatigue dislocation patterns such as PSB-ladders, cells and labyrinths are formed, depending on the cyclic straining histories and the shear strain amplitudes [1-5]. Further, the dislocation arrangement is strongly affected by the character of slip. The planarity of the slip in the pure metals is believed to depend on the stacking fault energy (SPE). Whereas, in alloys short range ordering (SRO) and short range clustering (SRC) often play a decisive role [6-10]. Most work has concentrated on metals and alloys which possess a cubic crystal structures [1-8]. In contrast, studies of cyclic deformation in hexagonal close-packed (h.c.p.) metals and alloys are relatively rare. Umakoshi and co-workers investigated the cyclic deformation behavior of Ti_3Al single crystals with the DO_(19) structure [11, 12]. A peculiar structure called the "saturation bundle structure" (SBS) was reported to be responsible for cyclic slip localization in Ti_3Al single crystals at the saturation stage under activation of double prism slip [11, 12]. The stability of SBS plays an important role in producing strain concentration regions and controlling fatigue life in Ti_3Al single crystals as PSB does in fatigued f.c.c. metals. To data, it has not yet been found which structure is responsible for the plastic strain localization and cyclic saturation behavior in h.c.p. Ti single crystal, which is the purpose of this work.