Grain size effect on plastic microformation behavior for Inconel 718 foils: Experiment and modeling

With the rapid development of the aerospace industry, there is an increasing demand for miniaturized parts made of Inconel 718 foils. However, the grain size effect on the plastic deformation behavior of thin sheets is significant, which considerably limits the fabrication and application of micro-components from Inconel 718. In this study, a series of uniaxial tensile tests and scanning electron microscopy experiments were conducted on Inconel 718 foils with different grain sizes to investigate the grain size effect on plastic deformation behavior. The grain size, orientation, and kernel average misorientation were characterized via electron backscatter diffraction to elucidate the deformation mechanism associated with the grain size effect. The results demonstrate that as the grain size increased, the number of grain orientations transforming into \(< 2\bar 32 >\) gradually decreased owing to weakened grain rotation and coordination under tensile stress, leading to a significant reduction in yield strength and maximum tensile strength. Additionally, the plastic deformation within the grain interior diminished significantly, while grain boundary sliding became a prominent deformation mechanism during tension as grain size increased, resulting in decreased fracture strain and ductile fracture characteristics. Finally, a mixed material constitutive model incorporating grain size and strain was developed for microforming research on Inconel 718 foils.