Experimental and Computational Studies of Compression and Deformation Behavior of Hafnium Diboride to 208 GPa

The compression behavior of the hexagonal AlB2 phase of Hafnium Diboride (HfB2) was studied in a diamond anvil cell to a pressure of 208 GPa by axial X-ray diffraction employing platinum as an internal pressure standard. The deformation behavior of HfB2 was studied by radial X-ray diffraction technique to 50 GPa, which allows for measurement of maximum differential stress or compressive yield strength at high pressures. The hydrostatic compression curve deduced from radial X-ray diffraction measurements yielded an ambient-pressure volume V-0 = 29.73 angstrom 3/atom and a bulk modulus K-0 = 282 GPa. Density functional theory calculations showed ambient-pressure volume V-0 = 29.84 angstrom 3/atom and bulk modulus K-0 = 262 GPa, which are in good agreement with the hydrostatic experimental values. The measured compressive yield strength approaches 3% of the shear modulus at a pressure of 50 GPa. The theoretical strain-stress calculation shows a maximum shear stress tau(max)similar to 39 GPa along the (1-10) [110] direction of the hexagonal lattice of HfB2, which thereby can be an incompressible high strength material for extreme-environment applications.