High-throughput Characterization of Spall Strength of Niobium

Metallic alloys with superior mechanical properties at elevated temperatures remain in high demand for a variety of applications in aerospace, space, and energy industries. With a high melting temperature (>2400 degree Celsius) and desirable ductility, niobium is a potential candidate for extreme environments that involve concurrent high operating temperatures and high strain rate deformations. Despite this potential, our understanding of the dynamic and shock-induced mechanical response of niobium remains limited both experimentally and theoretically. In this work, laser-driven micro-flyer impact experiments were performed on thin niobium foils (300 micron) in a high-throughput manner to investigate the shock-induced mechanical response of this bcc metal. Photonic doppler velocimetry (PDV) was used to measure the particle velocity of the target back free surface, with automated analysis of the obtained PDV signals. Spallation of niobium was observed above a critical impact velocity. The obtained spall strength values are greater than those previously reported from plate impact experiments, possibly because of the higher tensile strain rates (105 – 106 1/s) achieved in our experiments. Increasing the shock stress from 6 to 11 GPa resulted in an increase of the spall strength, and efforts are currently underway to examine this trend at higher shock stress values. Post-mortem characterization of the impact sites using white-light interferometry, scanning electron microscopy, and X-ray micro computed tomography are underway to understand the underlying mechanisms of spall failure.