This site contains articles by and an obituary on Professor F.R.N. Nabarro, Fellow of the Royal Society (FRS), who passed away on 20 July 2006 at the age of 90. At the time of his death he was Honorary Research Professorial Fellow in the School of Physics, University of the Witwatersrand, Johannesburg.
A general review is given of recent work on diffusion and precipitation in alloys, with special emphasis on the theoretical mechanism of diffusion, and on the factors governing the shape and size of the precipitate. The effects of internal stresses on diffusion and precipitation, and of precipitation on the mechanical properties, are discussed.
The purpose of this paper is to put forward certain advances in the theory of dislocations, and in particular to discuss their application to the theory of transient creep, in the sense in which the term is used by Andrade (1911, 1914, 1932) and by Orowan (1947).
Snoek has shown that when carbon atoms move from one possible set of interstitial sites in the lattice of a-iron to another set they cause shear strains. Cottrell has shown that the stress around a dislocation may be relieved by the migration of solute atoms in its neighbourhood, and that the dislocation is then bound to its present position. By combining these theories with the usual theory of age-hardening it is possible to explain the existence of a yeield point, quench aging, strain aging, delayed yield and blue brittleness as consequences of the presence of carbon in iron. A rough quantitative theory of the time-aging effects is given, and shown to agree with experiment. The need for further experiment is emphasized.
It is shown that at sufficiently low temperatures metals become ferromagnetic owing to an orientation of the nuclear spins. The domain structure of such ferromagnetics is analogous to that of ordinary ferromagnetics.