| Shear band formation during the tension of Al-3wt%Cu single crystals has been studied. A series of uniaxial tensile tests has been carried out for this purpose using the crystals with nominal solid solution and crystals containing θ′ precipitates at room temperature. The slip behavior and the band formation were continuously monitored with a video camera and a recorder. Optical microscopy, SEM, and TEM were then used to document the structure and micro-mechanism of localization processes. The localized shearing modes in single crystals were found to appear in two distinctly distinguishable processes, viz. coarse slip and macroscopic shearing. Coarse slip bands(CSB) were generally developed first on either the primary or conjugate slip planes, often accompanied by a significant load drop. Macroscopic shear band(MSB), on the other hand, occurred on an apparently non-crystallographic plane directly responsible for the final fracture of crystals. No clear indication of prior microfracture was detected Before shear band formation indicating that damage softening is not necessary for the shear localization. Slip planes seemed to strain harden continuously during the localized deformation in shear bands. TEM observation of CSBs in a solid solution crystal showed that the crystal lattice within the slip band was misoriented by less than 1˚ with respect to the matrix lattice. The experiments show that the geometrical softening, caused by non-uniform lattice rotation, has an important micromechanical influence on the localization process in single crystals. |
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