The onset of serrated yielding in Au(Cu) alloys

Abstract

The onset of serrated yielding in Au(Cu) alloys has been investigated as a function of strain rate, temperature, Cu concentration and initial state of order both in prequenched and furnace cooled specimens. The results have been analyzed in terms of a model proposed by Sleeswijk and McCormick. The parameters m, γ and β describe the increase with strain of vacancy concentration (C c), total dislocation density ( ρ t ) and mobile dislocation density ( ρ m ) resp. Under certain assumptions m and γ can be determined from the stress-strain curve. The main findings are: 1. 1. The value of m found from the onset of serrated yielding and from the stress-strain curve using Saada's theory of vacancy production are the same. 2. 2. The observed concentration dependence of the onset of serrated yielding points to solute atoms as the main obstacles to dislocation motion in the alloys studied. 3. 3. Using conclusion 2 it is found that β = 0.9 ± 0.1. Comparison with γ = 0.86 found from the stress-strain curve points to a proportionality of mobile and total dislocation density. 4. 4. The influence of a change of the initial state of short range order on the onset of separations can be ascribed to changes of the vacancy migration energy by a few hundredths of an eV.