Strength and electronic structure

Abstract

The main attribute of a solid is its resistance to deformation, or its ‘strength’. We discuss first the interpretation of the strength parameter. The current situation with regard to the central problem of providing a microscopic description of the strength parameter is briefly reviewed. Electrons in metals provide the cohesion, so that an understanding of the role played by electronic structure in the strength attribute should lead to practical hints for building stronger materials. The useful ‘aircraft alloy’ (Ti + Al + V) illustrates one such important relationship,viz., that the addition of a nond-character metal to ad-electron host strengthens the latter. Again, metals are distinguished from non-metals by the Fermi surface they possess, and it is interesting to examine any possible relationship between the anisotropy of the Fermi surface with the observed anisotropy in hardness (or yield strength). Next, we turn to cleavage, and point out that the assumption that it is the exact opposite of cohesion faces objections. Cohesion is an average property, whereas cleavage is a crack-tip phenomenon. Finally, among the processes familiar to the metallurgist wherein a metal is hardened, electron-moderated mechanisms have been identified in at least two cases, and we conclude with a brief account of these.