Temperature-dependent tensile properties and deformation modes of a novel peak-aged Fe-based superalloy GH2070P

Evolutions in the tensile properties and deformation-fracture mechanisms of a peak-aged Fe-based superalloy GH2070P with temperature are systematically characterized in the temperature range from room temperature to 800 °C. It is found that the alloy exhibits a slight increase in the yield strength from 589±11 MPa to 621±5 MPa with temperature below 700 °C, followed by a dramatic reduction to 450±9 MPa upon raising the temperature up to 800 °C. With regard to the ultimate tensile strength, it exhibits a monotonic decrease across the full temperature range investigated. However, in contrast to these evolving trends, the experimental alloy displays pronounced intermediate-temperature brittleness at 700-750 °C, but the minimum value of the elongation to fracture is still maintained at 18±1%. Microstructural observations on slightly deformed specimens reveal that both anti-phase boundary shearing and Orowan looping operate concurrently during initial plastic deformation below 700 °C, with Orowan looping gradually becoming a key deformation mechanism as temperature increases. However, above the temperature, plastic deformation is accomplished by the latter deformation mode together with dislocation climb/cross-slip for the experimental alloy. Fractographic examination reveals that for the experimental alloy, ductile transgranular fracture is the predominant fracture mechanism below 600 °C, but the mechanism gradually gives way to a mixed mode of transgranular and intergranular fracture with further increasing temperature. Based on these experimental results, it is deemed that the transitions in the deformation and fracture mechanisms are responsible for the changes in the tensile strength and plasticity of the peak-aged superalloy with temperature.