Evaluating the microstructure of U.S. circulating coinage through electron backscatter diffraction (EBSD)

The United States Mint produces circulating coinage for the public in various denominations and material compositions. Since 1965, dimes and quarters have been comprised of a cupronickel clad construction with a copper core. Coins are subjected to a manufacturing process that includes blanking, annealing, washing, upsetting, and striking. In the striking step, the proper force must be selected to not only form the design but also comply with legislative specifications for diameter and thickness. High striking forces can negatively affect die life. Struck dimes and quarters were examined for microstructural evaluation with metallurgical cross-sections. Electron backscatter diffraction (EBSD) was utilized to visualize and quantify grain size, distribution, and orientation across various steps of the coining processes and when using various striking force. Both the cupronickel and copper layers were investigated. Understanding the clad material’s response to striking on the microscale allows for the best optimization of force used, ultimately extending die life.