Evolution of geometrically necessary dislocation at the γ-γ′ interface and its effect on tensile deformation behaviour of disk super alloy

Abstract

Abstract The evolution of geometrically necessary dislocation density (GND) at the γ and primary γ′ interface during tensile deformation of turbine disk alloy was studied. Extensive electron microscopy analysis (i.e. EBSD and TEM) was carried out to explore the structure and GND evolution at the γ-γ′ interfaces. It is found that GND value is highest for tensile test specimens at 800 °C, whereas the lowest for tensile specimen tested at 350 °C, and this is attributed to γ/γ′ misfit (δ) value. At high-temperature tensile deformation (i.e. at 720 and 800 °C) specimen starts necking just after the yield point, compared to RT, 350 and 650 °C tensile tested specimens. It is evidenced from GND values and grain interior distortion that localized plastic deformation in γ-matrix near to γ-γ′ interfaces is the primary reason for necking just after yielding of material. Higher GND values and grain interior distortion are caused by the greater value of δ at high test temperature due to difference in thermal expansion between γ and γ′.