Image forces on screw dislocations in multilayer structures

High resolution transmission electron microscopy studies of metal/ceramics interfaces

“…9). Note that most of these stand-off dislocations (Kamat et al, 1987(Kamat et al, , 1988Mader and Knauss, 1992) come in pairs with opposite characters, i.e., each pair forms a dipole. Figure 10 shows a Burgers circuit around one of the dislocations, which indicates that the projection of the Burgers vector is a/270118 where a is the lattice parameter of vanadium.…”

Single-dislocation-based strengthening mechanisms in nanoscale metallic multilayers

“…If X remains constant with h, then the strength of the multilayers will not depend on h. Finally, the mismatch in shear modulus between the two layers produces an image force (Koehler 1978) that repels the glide dislocation crossing the interface from the lower shear modulus layer to the elastically stiffer layer (figure 2(d)). To a first approximation, if the elastic constants do not change with layer thickness, the strengthening contribution from this process will also be independent of h. For a nanoscale multilayer system, multiple image effects (Kamat et al 1987) and changes in elastic constants induced by the large coherency stress (Hoagland et ul. 2002) may change the simplified view depicted in figure 2 ( 4 .…”

Mechanical properties of sputtered Cu/V and Al/Nb multilayer films

“…The yield strength of certain metallic multilayers, estimated as 1/3 of nanoindentation hardness [5], can approach 1/2 to 1/3 of the lower-bound estimate of theoretical strength limit of G/30 (where G is the shear modulus) [6]. The evolution of film hardness as a function of layer thickness has been studied, and various strengthening mechanisms have been proposed [7][8][9][10][11][12][13][14][15]. At micron to submicron length scale, the yield strength of multilayers is proportional to h −0.5 , where h is the layer thickness, a phenomenon that can be explained by Hall-Petch model of dislocation pile-ups at layer interfaces.…”