Analysis on the amplitude of serrated flow associated with the Portevin-LeChatelier effect of substitutional fee alloys

Abstract

The serration of flow curve is a common feature of the Portevin-LeChatelier effect of substitutional fcc alloys. Under the condition that the onset strain of serration decreases with increasing temperature, previous experimental results have shown that the serration stress amplitude, Δσ, increases with increasing strain (ε) and temperature (T); it decreases with increasing grain size (d) and strain rate (ε). A conventional rationalization assumes that Δσ is proportional to the number of solute atoms, N, in dislocation atmospheres, where N is a function of the diffusion coefficient, aging time, and temperature. By adopting this approach and taking into account the effects of strain rate, strain, and grain size, the relation Δ α[ε⁻¹ ε^β(1/2 + γ) d⁻ⁿ(1/2 + γ) T^-1 exp (-Q/kT)]^2/3 is proposed, where Q is the activation energy associated with substitutional diffusion. The proposed model fits well with the experimental data of an Al-3.7 wt pct Mg alloy.