Effect of the loading ramp length on the evolution of surface and dislocation structures in cyclically deformed polycrystalline copper
- Univ. of Vienna (Austria)
The effect of the start-up procedure on the cyclic stress strain behavior, surface topography and dislocation substructures of polycrystalline copper were studied by SEM and TEM techniques. Two different loading ramps were used with N{sub R} = 1 and 100 cycles, respectively. They result in different magnitudes of unidirectional strain, saturation plastic strain ranges, density of surface slip markings, PSB formation and different dislocation substructures. For specimens with N{sub R} = 1 it was found that the PSB nucleated preferentially at tensile deformation bands. Based on TEM observations a microscopic model can be worked out. The stabilization of the vein structure occurs by secondary dislocations gliding on primary planes; destabilization of the veins and nucleation of PSB can be caused by local internal stresses arising from secondary dislocations gliding on secondary planes. This model yields consistent explanations for: (a) the formation of coarse slip lines for N{sub R}= 1; (b) the correlation between slip lines and PSB: (c) the larger density of PSB and therefore a lower cyclic hardening for N{sub R} = 1; (d) the occurrence of different cyclic hardening for different ramp lengths and its maximum near the PSB nucleation stress.
- OSTI ID:
- 100599
- Journal Information:
- Acta Metallurgica et Materialia, Vol. 43, Issue 8; Other Information: PBD: Aug 1995
- Country of Publication:
- United States
- Language:
- English
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