MICROSTRUCTURE ENGINEERING OF COMMERCIALLY PURE NI SHEETS TO ENHANCE MICRO-DEEP DRAWING FORMABILITY

摘要

Effects of starting microstructure on deformation behavior of commercially pure Ni blanks during micro-deep drawing was studied utilizing microforming set up that sits inside the chamber of Scanning Electron Microscopy (SEM) enables in situ observation of material flow during deformation. Various microstructure fields were created in Ni blanks using Severe Plastic Deformation (SPD) and heat treatment. SEM based Digital Image correlation (DIC) technique was used to characterize the micromechanics of deformation and its relation to process outcomes/performance. Pre and post-deformation microstructure analysis was carried out by performing Orientation Imaging Microscopy (OIM) to track the microstructure evolution across the micro-formed blanks during deformation in order to identify the process anomalies originated from the characteristics of starting microstructure and its interaction with deformation mechanics. We showed that microstructurally graded sheets consisting of nano-grained/coarse-grained layers significantly improves the formability of micro-blanks and effectively delays strain localization and onset of instability/failure during micro-deep drawing.