Dynamic strain ageing in Ni-base superalloy 720Li

Abstract

An experimental investigation into the dynamic strain ageing (DSA) of a wrought Ni-base superalloy 720Li was conducted. Characteristics of jerky flow have been studied at intermediate temperatures of 350, 400 and 450 ° C at strain-rates between 10⁻³ and 10⁻⁵ s⁻¹. Serrations of Type C are predominant within the temperature/strain-rate range explored. The major characteristics of the serrations-i.e. (a) critical plastic strain for onset of serrations, ε _c; (b) average stress decrement, Δ σ _avg; and (c) strain increment between serrations, Δε _BS-have been examined at selected temperatures and strain-rates. Negative strain-rate sensitivity was observed in the DSA regime. However, temperature did not influence tensile properties such as yield strength, ultimate strength, elongation, reduction in area, and work hardening rate or fracture features in DSA regime. Analysis of the results suggests that locking of the mobile dislocations by substitutional alloying elements is responsible for the DSA in alloy 720Li.