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Dislocation Structures in Creep‐Deformed Polycrystalline MgO
Author(s) -
BILDESÖRENSEN J. B.
Publication year - 1972
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1972.tb13453.x
Subject(s) - creep , materials science , dislocation , crystallite , annealing (glass) , climb , dislocation creep , slip (aerodynamics) , grain size , composite material , transmission electron microscopy , activation energy , crystallography , condensed matter physics , metallurgy , thermodynamics , chemistry , nanotechnology , physics
Secondary creep of polycrystalline MgO with grain sizes of 100 and 190 μm was investigated at 1300° to 1460°C under compressive loads of 2.5 to 5.5 kgf/mm 2 . The dependence of creep rate on load follows a power law with an exponent of 3.2±0.3. The process is thermally activated, with an activation energy of 76 ± 12 kcal/mol. The creep rate is independent of grain size. The dislocation structure was investigated by transmission electron microscopy. The total dislocation density follows the relation, σ= bG √ρ, commonly found for metals. The dislocations form a 3‐dimensional network in which many dislocation segments lie in their slip or climb planes. On the basis of this structure, a model is proposed in which glide is the principal cause of deformation but the rate‐limiting process, i.e. annealing of the network, is diffusion‐controlled. Theoretical estimates and experimental results agree within 1 order of magnitude.