EBSD Study of Microstructural Evolution in a Nickel‐Base Superalloy during Two‐Pass Hot Compressive Deformation. Issue 7 (4th April 2018) - He, Dao‐Guang
Abstract : Generally, the high‐temperature deformation characteristics and microstructural evolution of alloys are studied by isothermal compressive experiments at stable strain rates. But, the strain rate is variant during the practice industrial production of components. In this work, isothermal two‐pass hot compression experiments with stepped strain rates are performed to analyze the microstructural evolution of a nickel‐base superalloy with δ phase. Results reveal that the mean grain size decreases, but the percentage of undissolved δ phases increases, as the strain rate of the first pass (SROFP) is increased. However, the mean grain size and the percentage of undissolved δ phases decreases with the increase of inter‐pass time (IPT) or the true strain of the first pass (TSOFP). Meanwhile, the increased deformation temperature easily enlarges the mean grain size, but obviously decreases the percentage of undissolved δ phases. In addition, the evolution of Σ3 n boundaries not only results from the "new twinning mechanism", but also "Σ3 n regeneration mechanism". "Σ3 n regeneration mechanism" becomes predominant with decreasing SROFP or increasing IPT/TSOFP. Besides, "new twinning mechanism" plays a major role on Σ3 n boundaries evolution as the temperature is increased from 950 to 980 °C, and then become weaken with further increasing the deformation temperature. Abstract : Microstructural changes of a nickel‐base superalloy with δ phases are investigated during two‐pass hot deformation with stepped strain rates. The mean grain size and the percentage of undissolved δ phases are sensitive to the strain rate/true strain of the first pass, the inter‐pass time, and the deformation temperature. The evolution of Σ3 n boundaries not only results from the "new twinning mechanism", but also "Σ3 n regeneration mechanism".