Metallurgical and Materials Transactions A

, Volume 33, Issue 2, pp 213–218

Creep at very low rates

  • F. R. N. Nabarro

DOI: 10.1007/s11661-002-0083-8

Cite this article as:
Nabarro, F.R.N. Metall and Mat Trans A (2002) 33: 213. doi:10.1007/s11661-002-0083-8


The creep rate in a land-based power station must be less than 10−11 s−1. At these low rates of deformation the transport of matter occurs by the migration of vacancies rather than by the glide of dislocations. A quantitative understanding of these diffusional processes is, therefore, important. First type of diffusional creep (Nabarro-Herring (N-H)): the sources and sinks of vacancies are grain boundaries. The vacancies may diffuse through the bulk of the grain or along the grain boundaries (Coble (C)). Second type (Harper-Dorn (H-D)): the vacancies diffuse from edge dislocations with their Burgers vectors parallel to the major tensile axis to those with Burgers vectors perpendicular to this axis. The coherence of the polycrystalline aggregate is maintained by sliding along the grain boundaries. The three mechanisms of vacancy migration, grain boundary sliding, and dislocation glide may all interact. The theories of N-H and C creep in pure metals are established and confirmed, but H-D creep and grain boundary sliding are less well understood.

Practical engineering materials are usually strengthened by precipitates that accumulate on grain boundaries and slow down creep in complicated ways.

Copyright information

© ASM International & TMS-The Minerals, Metals and Materials Society 2002

Authors and Affiliations

  • F. R. N. Nabarro
    • 1
    • 2
  1. 1.Materials Physics InstituteUniversity of the WitwatersrandJohannesburgSouth Africa
  2. 2.the Division of Manufacturing and Materials TechnologyCSIRPretoriaSouth Africa