Mechanism of serrated flow in a cast nickel base superalloy

•Serrated flow is observed during hot tensile deformation of alloy CM 247 EA LC.•In the investigated range 300–650°C, serrations were most prominent at 300°C.•In the serrated flow region strain rate sensitivity is observed to be negative.•Serrated flow and negative SRS is attributed to shearing of γ′ by superpartials. Mechanism of serrated plastic flow in a cast nickel base superalloy was investigated in the temperature range of 25–850°C by conducting tensile tests employing strain rates of 1×10−3, 1×10−4 and 1×10−5s−1 and subsequent TEM studies. Shearing of γ′ precipitates by superpartials a/2[110] bounded by anti- phase boundaries are found to be responsible for the serrated yielding.