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We show that polycrystalline samples of Ti3SiC2 loaded cyclically at room temperature, in compression, to stresses up to 1 GPa, fully recover on the removal of the load, while dissipating about 25% of the mechanical energy

Fully reversible, dislocation-based compressive deformation of Ti3SiC2 to 1 GPa

NATURE MATERIALS, no. 2 (2003): 107-111

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摘要

Dislocation-based deformation in crystalline solids is almost always plastic. Here we show that polycrystalline samples of Ti3SiC2 loaded cyclically at room temperature, in compression, to stresses up to 1 GPa, fully recover on the removal of the load, while dissipating about 25% (0.7 MJ m(-3)) of the mechanical energy. The stress-strain ...更多

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简介
  • Slip by dislocation motion is the prevalent micromechanism of plastic deformation in almost all crystalline materials.
  • The authors report stress–strain curves measured in simple compression on polycrystalline samples of Ti3SiC2 with two different grain sizes at both room and higher temperatures and at varying strain rates.
重点内容
  • Slip by dislocation motion is the prevalent micromechanism of plastic deformation in almost all crystalline materials
  • The kink bands mentioned above were first observed[17] in Zn single crystals loaded parallel to their basal planes.Kinking is distinct from slip
  • The term incipient kink band (IKB) is used in this paper to denote a kink band for which the dislocation walls remain attached at its ends, that is, one that remains lenticular in shape (Fig. 1a);once the walls separate we will refer to them as kink bands.This distinction is important because the production and annihilationof IKBsisbelievedtobeareversibleprocess,whereasthatof the kink bands is an irreversible one
  • The stress–strain curves at room temperature (Fig. 2) depict fully reversible, reproducible, rate-independent, closed loops whose size and shape depend on the grain size
  • We have shown that IKBs can be transformed to KBs at room temperature, if the stresses are high enough such as under the tip of a 13.5 μm spherical indenter(A
结果
  • It is seen that fine-grained Ti3SiC2 can be compressed to a stress of about 1 GPa and a strain of about 0.6%.
  • The stress–strain curves at room temperature (Fig. 2) depict fully reversible, reproducible, rate-independent, closed loops whose size and shape depend on the grain size.
  • The area enclosed by the hysteresis loop reflects the energy dissipated per unit volume per cycle, Wd. Generally speaking, in crystalline solids, three processes could possibly explain the results[20,21]: point defect, dislocation and/or grain-boundary relaxations.
  • The hysteresis loss in room-temperature tests (Fig. 2) must be related to the reversible motion of dislocations, a well-established phenomenon in the metallurgical literature[20,21,22,23], it has only been documented far at much lower stress and strain levels.
  • T2024 (Al alloy) E = 66 GPa sources will result in kink bands with regions of lattice reoriented to facilitate basal slip in continued loading (Fig. 1d).
  • The energy dissipated, Wd, results from the friction associated with the to and fro motion of the dislocations comprising the IKBs and pile-ups.Because the dislocations are confined to the basal planes and cannot readily interact, the distances over which they glide reversibly are of the order of the grain size; which explains the significantly high values of Wd. Second,the stress needed for the formation of IKBs can be extracted from plots of Wd against stress (Fig. 4b).It is seen that the IKB initiation stress is about 38 MPa for the CG material and about 70 MPa for the FG material.
  • The observed reductions in Wd after high-temperature cycling of the CG material and general stiffening are consistent with the physical models presented above.
结论
  • In high-temperature cycling, IKBs open up and produce kink bands, in essence producing a material having a finer grain size, which in turn exhibits a lower Wd and a higher stiffness.
  • These polycrystalline nanolaminates are almost ideal model materials for the study of dislocation dynamics and interactions of walls or pile-ups with grain boundaries, and other obstacles.
基金
  • This work was funded by the Army Research Office (DAAD19-00-1-0435) and the Division of Materials Research of the National Science Foundation (DMR-0072067)
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