The Influence of Substructure and Dislocation Mobility on the Creep Properties of Some Single Phase Metals

Abstract

<p>Single phase pure metals and alloys deformed at high temperatures show large variations in the form of their strain-time curves and in the stress dependence of the strain rate. At present, it is not possible to predict theoretically the mechanical responses of a given alloy.</p> <p>This thesis is concerned with the deformation of pure copper, copper-5 wt.% tin and iron-3¼ wt.% silicon at temperatures above half the melting point. Mechanical experiments involving both constant load and constant strain rate teats have established that these three materials exhibit a spectrum of behaviour as wide as wide as any previously reported. Detailed microstructural examination has revealed corresponding variations in dislocation arrangements and in the extent of grain boundary distortion in crept specimens.</p> <p>It is argued that the form of the primary creep curve and strain transients following a change in stress, obtained in a given metal, is closely related to the mobility of mobile dislocations, rather than to an internal resistance arising from the substructure. To explain the observed mechanical responses, a model has been proposed which provides some semi-quantitative predictions of material behaviour. Both the mechanical and microstructural results suggest that the recovery theories of creep, in which hardening and recovery are considered as separately definable parameters, do not deal realistically with the creep process.</p>