Size effect on the forming limit of a nickel-based superalloy thin sheet at the mesoscopic scale

Abstract

With the development of product miniaturization in aerospace and other fields, nickel-based superalloy thin sheets with excellent comprehensive properties have become crucial materials for micro-components in these fields. Due to the complexity of the initial microstructure and strengthening mechanism, there is a lack of in-depth research on the mesoscale formability of nickel-based superalloys under the coupled effects of multiple factors such as feature size (i.e., the ratio of specimen thickness to grain size, t/d), particle size and volume content of the precipitated phase. In this paper, a test platform was constructed for the application of high-precision strain measurements to the analysis of the mesoscale forming limit, and the mechanisms for the influences of feature size and precipitation on the mesoscale forming limit of a nickel-based superalloy were studied. The results showed that feature size influenced the forming limit of the nickel-based superalloy thin sheet at the mesoscopic scale, and the formability decreased with decreasing t/d and increasing γ′′/γ′ particle size and volume content. Based on surface layer theory and ductile fracture theory, the influences of t/d and γ′′/γ′ phases on the forming limit of nickel-based superalloy thin sheets at the mesoscopic scale were revealed. The coupled effects of surface roughening caused by free surface grains and hindered dislocation movement induced by precipitated phases resulted in strain localization and reduced the forming properties of nickel-based superalloy thin sheets at the mesoscopic scale.