Plasticity without dislocations in a polycrystalline intermetallic

Abstract

Dislocation activity is critical to ductility and the mechanical strength of metals. Dislocations are the primary drivers of plastic deformation, and their interactions with each other and with other microstructural features such as grain boundaries (GBs) lead to strengthening of metals. In general, suppressing dislocation activity leads to brittleness of polycrystalline materials. Here, we find an intermetallic that can accommodate large plastic strain without the help of dislocations. For small grain sizes, the primary deformation mechanism is GB sliding, whereas for larger grain sizes the material deforms by direct amorphization along shear planes. The unusual deformation mechanisms lead to the absence of traditional Hall-Petch (HP) relation commonly observed in metals and to an extended regime of strength weakening with grain refinement, referred to as the inverse HP relation. The results are first predicted in simulations and then confirmed experimentally.

Friction of Metals: A Review of Microstructural Evolution and Nanoscale Phenomena in Shearing Contacts

“…This effect has recently been seen for alloys (Fig. 8B) and ceramics in experiments and simulations [169,170]. Van Swygenhoven and Caro [171], however, assumed that no new boundaries are created and used a slip-dashpot model with a strain rate dependence of d −1 .…”

“…where ̇ is the strain rate, ̇0 is a fundamental strain rate, ΔF is the activation energy, is the applied shear stress, V * is the activation volume, T is temperature and k is Boltzmann's constant. When the grain size is small, the grain boundaries should be able to form a connected shear layer, as in Yang and Ghosh [178], and when the grain size increases, stresses will be transferred to the core region of the grains, where amorphization will be required to continue shear, similarly to the model of Padmanabhan et al [163,164], and the effects seen in Guo et al [170] and Luo et al [169]. The activation energy, then, is that required for amorphization of a crystal.…”

“…11 a Comparison of aggregate experimental (crosses) [81,82,161,189] and computational (circles) [101] strengths, best fits for Hall-Petch strengthening from Cordero et al [81] (blue or black lines), and (red lines) predictions from the amorphization model for quasi-static and dynamic cases, from Chandross and Argibay [182]. b Overlay of model prediction (red lines) [182], molecular dynamics simulation results (circles) showing inverse Hall-Petch behavior with nanocrystalline Au, from Liu et al in 2020 [89], experimental strengths (crosses) with best fit (blue line) Hall-Petch strengthening from Cordero et al [81] and nanocrystalline strength prediction (green line) from Asaro et al [45] for Au and SmCo 5 ; the SmCo 5 plot shows an overlay of model predictions (red lines) using a rule of mixtures based on atomic fractions and grain size-dependent strength data from simulations and experiments from Luo et al [169]. In all cases, dashed lines correspond to extrapolations, for visualization purposes, where the respective prediction model fits are not applicable or relevant (color figure online)…”

Enhancing the phase stability of ceramics under radiation via multilayer engineering

“…To protect the sample surface from damage during FIB preparation, a 3.0-μm Pt protective layer was deposited on the surface by two steps: (i) A 2 kV electron beam (low energy) was used to deposit a 1.0-μm Pt layer to avoid damage from high-energy ion deposition, and (ii) a 12 kV ion beam was used for the deposition of another 2.0 μm Pt layer. The thinning process was sped up by a high-energy ion beam (30 kV) at the beginning and ended with a low-energy ion beam (2 kV) to carefully remove the amorphous area generated in the former stage ( 41 ).…”

Full-Field Temperature Measurement of Stainless Steel Specimens Subjected to Uniaxial Tensile Loading at Various Strain Rates

“…Grain boundaries have a much greater influence on the mechanical properties of metals than dislocations [4,5]. The high energy level of grain boundaries determines Materials 2021, 14, 5259 2 of 15 the occurrence of many phenomena, such as continuous mobility of boundaries leading to grain growth and lower corrosion resistance [6][7][8]. Grain boundaries also have a strong influence on the ductility of metals.…”