Mobility of dislocations in Aluminum: Faceting and asymmetry during nanoscale dislocation shear loop expansion

A Comprehensive Report on Ultrasonic Attenuation of Engineering Materials, Including Metals, Ceramics, Polymers, Fiber-Reinforced Composites, Wood, and Rocks

“…At 20 to 25 kHz, ∆ was found to vary on the low side, ranging from 0.001 [58] to 0.0037 [57] and as high as 0.08 [59], with a median value of 0.007. This ∆ range agreed with the prediction of the KGL model using the dislocation drag factor obtained from theory, experiments and atomistic simulations [60][61][62]. Low-frequency internal friction studies used a strain amplitude range of 10 −7 to 10 −5 [58][59][60], but one study used an amplitude of up to 3 × 10 −4 [58].…”

“…Such dislocation velocities were well below the velocities limited by the dislocation damping coefficient, B. Hikata et al [60] experimentally obtained B = 5.0 × 10 −6 Pa•s at 300 K, while Olmsted et al [61] found B = 1.4 × 10 −5 Pa•s at 342 K via a molecular dynamics (MD) approach. Another MD result [62] gives B = 2.8 × 10 −5 Pa•s at 100 K (averaging screw and edge values). At 260 kPa, these B values predict dislocation velocities of 5.5 to 156 m/s, all exceeding the maximum dislocation velocities needed in the proposed bow-out mechanism of dislocation damping; that is, the bow-out damping mechanism operates in the quasi-static regime.…”

Temperature and composition dependent screw dislocation mobility in austenitic stainless steels from large-scale molecular dynamics

“…Continued advancements in the implementation of such rules has equipped DDD with the ability to describe mechanisms such as dislocation glide, climb, and cross slip, which contribute to development of threedimensional dislocation structures 9,10 . A fundamental driver in all such extensions is the mapping of the local resolved shear stress to the dislocation glide velocity on specific slip systems, described by the mobility law [11][12][13][14][15] . While difficult to ascertain experimentally, mobilities have been readily computed via molecular dynamics (MD) simulations for pure metals and binary alloys for both face-centered-cubic (fcc) and body-centered-cubic (bcc) crystals [12][13][14][15][16][17][18] .…”

“…A fundamental driver in all such extensions is the mapping of the local resolved shear stress to the dislocation glide velocity on specific slip systems, described by the mobility law [11][12][13][14][15] . While difficult to ascertain experimentally, mobilities have been readily computed via molecular dynamics (MD) simulations for pure metals and binary alloys for both face-centered-cubic (fcc) and body-centered-cubic (bcc) crystals [12][13][14][15][16][17][18] . To date, the lack of mobility data for more complex alloys has limited the application of DDD simulations to the SLM austenitic stainless steels of interest, with some authors 19,20 opting to take single bulk handbook values for the mobility despite clear evidence of temperature and composition dependence 12,16,21 .…”

A comparison of different continuum approaches in modeling mixed-type dislocations in Al

“…Mixed-type dislocations are prevalent in metals because for a given b in the lattice, θ can have any value between the two extremes if l is infinitesimally varied. To date descriptions of dislocation cores have been best provided by atomic-scale simulations, which find that key characteristics of mixed-type dislocations cannot simply be extrapolated from those of pure-type ones [3][4][5][6][7][8][9]. Moreover, atomistic simulations are limited to nano/submicron length scale even with dedicated high-performance computing resources [10].…”