High strain-rate spallation and fracture of tungsten by laser-induced stress waves

This paper presents a study on the high strain-rate spallation and fracture behavior of bulk tungsten and tungsten/tungsten interfaces using laser-induced stress waves. The behavior of bulk polycrystalline tungsten was studied using both Gaussian and shock waves. In-plane cracking and spallations were observed at sufficiently high amplitude stress waves. The in-plane cracks propagated along relatively straight paths and extended to distances two to three times of the loading diameter. Microstructural study of the fracture mechanism show that bulk tungsten spallation was mainly due to grain boundary decohesion resulted from the growth, interconnection and coalescence of micro-voids on grain boundaries. The spallation behavior of tungsten/tungsten interface produced by a tungsten film magnetron sputtered on a tungsten substrate was studied using shock waves. The spallation occurred right at the interfacial region. The spall strength of bulk tungsten was estimated to be between 2.7 ± 0.2 and 3.1 ± 0.3 GPa, and the interfacial strength of tungsten/tungsten interface was estimated to be 875 ± 161 MPa.