Absence of Threshold Stress for High-Temperature Creep of Dispersion- and Solution-Hardened Al-3.1 at% Mg-1.3 vol% be Alloy

In order to examine the Srolovitz's theory of attractive interaction between dislocations and dispersed particles, an Al-3.1 at% Mg-1.3 vol% Be alloy having a combined effect of dispersion- and solution-hardenings was subjected to creep tests and transmission electron microscopic observation. The creep test was conducted at temperatures from 623 to 723 K and at stresses from 1.8 to 51.4 MPa which correspond to the range of 0.34-7.64σ_v (σ_v is the void hardening stress). The results show that the dislocation-particle interaction is attractive, but no clear threshold stress is observed under the conditions tested. This suggests that the absence of threshold stress should have no bearing on the climb mechanism. The reason for the absence of threshold stress in this alloy is discussed from viewpoints of solution hardening and grain boundary sliding.