Laser-Induced High-Strain-Rate Superplastic 3-D Microforming of Metallic Thin Films

Abstract

Microforming of metals has always been a challenge because of the limited formability of metals at the microscale. This paper investigates an innovative microforming technique: microscale laser dynamic forming (¿LDF), which induces 3-D superplastic forming in metallic thin films. This forming process proceeds in a sequence of laser irradiation and ionization of ablative coating, shockwave generation and propagation in metallic thin films, and conformation of metallic thin films to the shape of microscale molds. Because the deformation proceeds at ultrahigh strain rates, it is found that materials experience superplastic deformation at the microscale. In this paper, experiments are systematically carried out to understand the deformation characteristics of ¿LDF. The topologies and dimensions of the deformed samples are characterized by scanning electron microscopy and optical profilometry. The thickness variations are characterized by slicing the cross section of the deformed material using the focused ion beam. The magnitude of deformation depth in ¿LDF is determined primarily by three critical factors: film thickness, mold geometry, and laser intensity. The relationships between these factors are explored in process maps to find suitable processing conditions for ¿LDF. Nanoindentation tests are conducted to show that the strength of the thin films is increased significantly after ¿LDF.