Dislocation structure of plastically deformed NaCl polycrystals

Abstract

NaCl polycrystals, produced by press forging of single crystals at 275°C, are deformed in compression at room temperature. The dislocation structure is analysed by transmission electron microscopy as a function of the flow stress. Macroscopic yield of the polycrystals occurs at a stress that is equivalent to the flow stress of single crystals deforming in single glide at a comparable dislocation density. During deformation, a three‐dimensional dislocation structure is observed to form within the grains. This structure bears strong resemblance with that observed in [111]‐ orientated NaCl single crystals. Consistently, the high flow stress of the polycrystals arises due to the activation of considerable glide in subsidiary glide systems. This activation is necessary to accomodate the plastic incompatibilities that occur at the grain boundaries of the polycrystals.

Fractal Dislocation Patterning in Plastically Deformed NaCl Polycrystals

“…f111g or f100g) [6,8]. The dislocation network is characterized by the presence of Burgers vectors of all orientations in approximately equal amounts, and the flow stress is governed by a forest mechanism [6]. All these findings are very similar to the situation in [100] or [111] orientated fcc single crystals or in fcc polycrystals.…”

“…The deformation behaviour of NaCl polycrystals has many similarities with this situation [6]: While alkali halide single crystals usually exhibit macroscopic single glide on f110g glide planes, NaCl crystals deformed in [111] directions and NaCl polycrystals exhibit extensive glide on auxiliary slip planes (e.g. f111g or f100g) [6,8]. The dislocation network is characterized by the presence of Burgers vectors of all orientations in approximately equal amounts, and the flow stress is governed by a forest mechanism [6].…”

“…For a general discussion of different types of dislocation patterns see [5].In the present research note we report results of a fractal dimension analysis performed on dislocation cell patterns developing during severe deformation of polycrystalline NaCl. (For sample preparation and work-hardening behavior see [6].) The samples were deformed in compression at room temperature at a strain rate of 10 À5 s À1 .…”

“…In these materials deformation is characterized by the simultaneous activity of a large number of slip systems. The deformation behaviour of NaCl polycrystals has many similarities with this situation [6]: While alkali halide single crystals usually exhibit macroscopic single glide on f110g glide planes, NaCl crystals deformed in [111] directions and NaCl polycrystals exhibit extensive glide on auxiliary slip planes (e.g. f111g or f100g) [6,8].…”

Near‐surface plastic deformation in polycrystalline SrTiO3 via room‐temperature cyclic Brinell indentation

“…Various studies on the plastic deformation (accompanied by cracking) of polycrystalline rock‐salt ceramics via mechanical deformation at ambient temperature are available in the literature 28–30 . For example, MgO has a cubic structure and was heavily studied in history.…”