Static displacements and the electrical resistivity of interstitial alloys

Abstract

It appears that the predominant mechanism by which interstitial solute atoms influence the electrical resistivity of alloys, unlike substitutional solutes, is through the associated static displacements of the host atoms. A quantitative test of this hypothesis is possible in the case of tetragonal iron-carbon martensites, where the magnitude of the static displacements is experimentally known. The resistivity component arising from the static displacements is estimated by analogy to the mean-square thermal displacements and corresponding electrical resistivity of pure iron. The result agrees fairly well with various measurements on the effect of dissolved carbon on the resistivity of martensitic alloys. The displacement hypothesis also provides a logical explanation for the anomalous resistivity increase observed during the aging of iron-carbon and iron-nickel-carbon martensites. Spontaneous rearrangements of the interstitial atoms during aging tend to occur in such a manner as to increase the static displacements, as illustrated by theoretical treatment of the formation of carbon-atom pairs. The normal aging behavior can be altered, however, by the prior introduction of a dense dislocation substructure through thermomechanical treatment, as in ausformed martensites.