Static and Dynamic Compression and Deformation Behavior of High-Entropy Transition Metal Borides

High-entropy transition metal boride (HEB) sample (Hf, Mo, Nb, Ta, Zr)B₂ with unit cell volume V₀ = 28.2 ų was synthesized under high-pressure and high-temperature in a large-volume Paris-Edinburgh cell at HPCAT, Argonne National Laboratory and the sample was recovered for subsequent static and dynamic compression studies. The hexagonal AlB₂ structure of HEB sample was found to be stable up to 240 GPa in a diamond anvil cell study employing platinum as a pressure marker. The average nanoindentation hardness of the recovered sample is 20 GPa. The compressive yield strength or maximum differential stress of the HEB sample was measured by radial x-ray diffraction technique in a Panoramic diamond anvil cell at HPCAT to 60 GPa. The measured compressive yield strength approached 8% of the shear modulus at the highest pressure of 60 GPa. Future shock compression experiments are planned on THOR at Sandia.