Superplastic Deformation Behavior and Microstructural Evolution of Electroformed Nickel Foils Determined by Thermomechanical Analysis

Superplastic deformation, which occurs when fine-grained metals exhibit high ductility (often exceeding 300%) under specific conditions at approximately half of their melting temperature, allows the creation of complex shapes required by the aerospace and electronic material industries. Typically, superplastic characteristics are evaluated using universal testing machines (UTMs). However, nickel (Ni) and its alloys, which are applied as electrodeposits in the fabrication of electronic materials, are nanocrystalline in nature and exhibit superplasticity under specific temperatures and deformation conditions. Electrodeposited foils are very thin, making traditional UTM testing challenging; therefore, a new approach is required. In this study, we used a thermomechanical analyzer (TMA) to analyze the superplastic properties of electrodeposited nickel foils simply and precisely. TMAs are particularly appropriate when evaluating thin foils because they yield detailed thermal deformation data, whereas UTMs do not. A TMA reveals thermal deformation of electrodeposited nickel foils across various temperatures, as well as microstructures and grain growth. We performed superplastic analysis at 400 °C, 500 °C, and 600 °C at a strain rate of 1 × 10^-3 s^-1, and microstructural data were obtained through X-ray diffraction and electron backscatter diffraction. Superplastic deformation was apparent at 400 °C. The data obtained through our systematic analysis using a TMA will guide future studies on the application of superplastic properties of electrodeposited nanocrystalline nickel foils.