Scanning transmission electron microscope observations of defects in as-grown and pre-strained Mo alloy fibers

Influence of pre-existing dislocations on the pop-in phenomenon during nanoindentation in MgO

“…2 clearly shows an increase in the pop-in load while the density of pre-existing dislocations decreases, as has been qualitatively reported in the literature for other materials [11,18,19]. As the dislocation density decreases, the scatter in the pop-in load increases, this observation being consistent with those of Bei et al [5] and Phani et al [23]. The scattering is likely to be linked to the statistical probability of encountering a pre-existing dislocation in the deformed volume.…”

“…They concluded that the theoretical shear stress must be reached in order to observe homogeneous dislocation nucleation. This result has also been reported by Bei et al [5] and Phani et al [23], on pre-strained Mo alloy micropillars and fibers, respectively. They studied the mechanical response of different samples ranging from 0 to 11% pre-strain.…”

Influence of bulk pre-straining on the size effect in nickel compression pillars

“…The dislocations are hindered from leaving the pillars by the impenetrable interface enhancing dislocation storage in the material and by this the probability for dislocation multiplication and interactions. In fact, while their initial material is close to defect free, Phani et al [63] observed an increase from approximately 10 12 m À 2 at 4% pre-strain to approximately 10 13 m À 2 for 16% pre-strain, which is more pronounced than in the present case (Table 2). Further, this embedded pre-straining creates surface steps on the pillars that facilitate dislocation nucleation [64].…”

“…As a consequence, new dislocations need to be nucleated from dislocation sources to maintain plastic deformation, explaining the jerky stress-strain behavior of the Ni pillars. Conversely, for the Mo pillars the dislocations were less entangled and only loosely organized [63]. As a consequence, the mobile dislocation density in these pillars is higher relative to the pre-strained Ni pillars.…”

One‐dimensional simulation of the creep behavior of directionally solidified NiAl‐9Mo

“…1). The physical reason for this behavior is based on the dislocation density in the fibers, which increases with increasing creep strain [2].…”