Scaling Anomaly in the Mechanical Response in Microscale Reverse Extrusion of Copper

Abstract

The continuing trend of device miniaturization brings increasing demand for small metal parts and, consequently, significant interest in microscale metal forming technologies. In this work, the influence of grain size on mechanical response in microscale axisymmetric reverse extrusion of Cu 110 alloy was investigated in detail. A characteristic plastic strain associated with material deformation in the extrusion process was, for the first time to the best of our knowledge, defined, measured, and used to evaluate the material's bulk flow stress at this corresponding strain. This flow stress was then used to scale measured mechanical response in reverse extrusion and help identify deviations from scaling behavior expected in continuum plasticity. A scaling anomaly was indeed observed, indicating a dependence of mechanical response on both the initial grain size and the characteristic dimension of microforming operations. Detailed microstructural examination of grains in extruded Cu parts was conducted, and points to directions for future study to better understand mechanisms behind the observed scaling anomaly.