The integrated effect of grain configuration and δ phase on micro-scaled mechanical stability of Nickel-based superalloy foil

The variety and complexity of the size effect make it difficult to predict the plastic deformation behavior of foil. In this study, 0.08 mm foils with different thickness-to-grain size ratios (t/d) and δ phase distribution were obtained by adjusting the rolling and annealing processes, and the microstructure evolution before and after tensile deformation was investigated. The results show that with the decrease of the t/d ratio, the reduced grain layers number in the thickness direction facilitates grain rotation and grain boundary sliding, which accelerates the dislocation annihilation and leads to poor work hardening ability and low flow stress. Meanwhile, the lack of restrictions between adjacent grains leads to the rapid expansion of cracks after void nucleation, mainly manifested as brittle fractures. The diffuse δ phase and fine grain enhance the constraining effect on dislocations and promote dislocation proliferation and interactions. The increased number of grain layers coordinates the deformation and contributes to an increase in the Schmid factor, which supports the sliding system opening and exhibits a superior elongation of 18.1%. The uniform δ phase exhibits good deformation compatibility and alleviates the stress concentration during the deformation process, and the interaction between neighboring grains promotes the development of uniform dimples after void nucleation, exhibiting a dominant ductile fracture. This study provides a new idea for the regulation of foil mechanical properties.