Microstructure evolution and mechanical property of W/Ta bimetal foil produced by a high wave impedance explosive welding technology

Welding of dissimilar metal foils is challenging, especially between high melting temperature and brittle metals. In this study, the direct welding of tungsten foil and tantalum foil was achieved using metal protection plates in an explosive welded configuration. The microstructure, chemical composition, and hardness distribution in the corresponding microscopic regions of the W/Ta interface were characterized by electron backscattered diffraction (EBSD), energy-dispersive spectroscopy (EDS), and nano-indentation. The W/Ta interface formed a wavy bonding interface, and a large number of refined grains smaller than 1 µm were created at the interface. Different melting zones were investigated employed EBSD and nano-indentation to understand the vortex structure’s evolution mechanism. It was found that the formation of holes in the melting zone was mainly due to the cooling shrinkage after intense jet agitation. Besides, the more intense jet promotes recovery and recrystallization. However, the stronger intrusion of the jet causes higher nano-hardness in the melt zone, which is attributed to the effect of the jet on the heterogeneous microstructure. Mechanical tests show that the tensile strength of W/Ta bimetal foil exceeds 850 MPa, and there is no crack propagation on the surface of the metal foil. The analysis of welding parameters and material properties revealed that increasing the material temperature during the explosive welding process and providing high-impedance material confinement are the main ways to solve the problem of explosive welding of brittle materials.