Abstract
In order to understand the mechanism of strain bursts previously observed in polycrystalline metal tested in cyclic creep, studies have been carried out on single crystals, variously oriented. Regular stage I and stage II creep were observed under pulsating tension and a saturated hysteresis loop developed during stage II creep. For stresses above a threshold of 35 MPa in maximum stress, strain bursts occurred frequently in the single crystals. The bursts proceeded through the crystals in the manner of Luders bands. Studies of the dislocation structure by TEM showed the bursts to be accompanied by very large increases in secondary dislocation densities and by the formation of cell structures. The strain bursts are interpreted by cyclic latent softening and dislocation avalanches originating from secondary-rich dislocation clusters. Cyclic creep acceleration is interpreted as a gentler and more widely-pervading form of strain bursts.
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