Developments in Microcoining Rippled Metal Foils

Rippled metal foils are currently sought for high-strain-rate material strength studies at laser facilities. Because these metals typically cannot be diamond turned, we employ a microcoining process to imprint the [approximately]5-m-deep by [approximately]50-m-long ripples into the metal surface. This work details recent process developments to fabricate these rippled metal targets, specifically for iron and tantalum. The process consists of nitriding a steel die, diamond turning the die, and then pressing the die into a polished metal foil of choice. We show: advantages of deeper-nitrided dies, improved foil thickness uniformity and characterization, variation in coining stress over different materials, pattern quality characterization, bowing reduction, and patterning of multimode ripples.