The rate of viscous flow of metals: Part 1, tin

Abstract

A description is given of a new method of determining the dependence of the rate of viscous flow of metals on the deforming force and its variation with temperature. The measurements were made by means of an optical lever system, and the effect of changes in length produced by possible temperature fluctuations in the furnace were eliminated by the use of a second wire as a support for the lever. It has been found that, for tin, for very small extensions the velocity of viscous flow v can be considered independent of time, but is connected with the stretching load P by an exponential relation for any given temperature and with the absolute temperature T by an exponential relation for any given load. Different relationships of the form v = δeβPT-αP+γT, where α, β, γ and δ are constants, have been obtained, from the {flow, load} curves, for the rates of flow of tin for glide in one and two directions respectively, and the relations are probably of the type v = K{eβ (P+P0) (T-T0) - 1}, where K, β, P0 and T0 are constants. Evidence has been obtained in support of the view that the temperature of the allotropic modification from β to γ tin takes place at 203° C. and not at 161° C. The loads for transition from single to double glide and the breaking loads have been shown to be connected with the corresponding temperatures by a hyperbolic expression. Finally, the behaviour of the tin wire has been shown to be in general agreement with the results obtained from single crystals.